Mixing lithium (LiFePO4) Batteries
ฝัง
- เผยแพร่เมื่อ 1 ก.ย. 2023
- So you got a great deal on another LiFePO4 battery for your boat. Or maybe you're thinking of adding one more to your old bank. Or you're just starting out, and you want to know if you can buy some batteries now, and save up to buy more later. Is it safe to mix different ages, brands, or builds of lithium LiFePO4 batteries? That's what today's video is about.
IN THIS EPISODE:
[00:29] Why this Video?
[01:27] What Battery Companies Say
[01:55] General Rules
[02:20] Mixing Lead
[05:40] Mixing LiFePO4
[09:02] A Closer Look: Lab Example
[14:12] Results
[15:29] The Workaround
[18:56] Why You Should Buy Batteries First
[22:42] Upcoming Videos
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You can mix different capacity cells in parallel safely. In series this is a huge problem if you dont have an actibe balancer. All that matters fot parallel is that they are the same chemistry and have their own BMS. I personally have systems like this running with no issue. There are other videos on youtube done by engineers who take deep dives and measure what happens when you do this, some even going to extremes to mix 300ah batteries with 5ah in parallel to prove the point that it is fine to do so. A load will draw more from the higher capacity cells and less from the lower and they will charge in the same manner. This is all self regulating due to the way current reacts to the voltage and resistance changes in each baterry as they charge and discharge. You dont need to buy anything extra or throw good batteries away.
You are exactly right and you don't need any extra hardware. Just make sure your charger doesn't go above 3.55 volts per cell.
Yes it works as in you can charge the batteries. No it doesn't necessarily work as in you can expect 4000 cycles.
This mismatch exposes some batteries to overcharge in getting others up to full. It's likely the difference between a 6 year life span and a 14 year lifespan.
But we all make our own choices.
If you set your charger output voltage to a maximum of 14.2 volts you won't overcharge any of the batteries. @@EmilyAndClark
@@EmilyAndClark ??? but the BMS will prevent over charging. I feel that your video is misinforming your audience. 3.2 vs 3.3 volts can be a HUGE difference in capacity. It is normal that they will charge at different rates. Bring your voltage up to 14 volts and float for about 1-2 hours... both batteries will be fully charged and balanced at that point.
That seems to be the common "knowledge" but it's so very wrong. Sorry.
If you read the procedure describing how the cycle life testing labs work or the research papers on "over charging" you will find they charge at a fixed current until a (surprisingly low) voltage is reached. Charging at a fixed current is impossible in an actively running system with loads and solar. The BankManager has a very complex algorithm that achieves the same effect.
The name for the damage that occurs with the methods you guys suggest is " low current overcharge". If you would like to learn more I suggest you start with Conrad's article linked at the bottom of www.emilyandclarksadventure.com/bbms
This is real science and has been proven again and again.
It's great to see our product in Clark's video again (FEENCE battery), Clark invented the BBMS which is very practical for mixing between different batteries, which is a huge cost saving. The point is, this mixing is very effective. Thank you!
Clark, I want to thank you for taking the time to share your knowledge with us. You and Emily are a great source of knowledge and I look forward to your videos every week.
Thanks for all your work on this series Clark. My go to channel for designing my system.
Hey Clark - thank you so much for this well researched and simple to follow explanation. I've done a lot of electronics work in highschool and college, but LiFePO4 batteries and associated differences for use in RVs, boats, and solar installations have so much more to think about. You've got a new sub! Looking forward to your new content!
Clark, love your explanations.. Thank you
Clark, So glad you explained how to connect the external cables to a bank of parallel batteries, I noticed that the cables go to the first battery and then additional cables to the extra L-A batteries in parallel on my boat.
I was going to simply swap one bank of L-A for Lithium., adding your BBMS between the new Lithium.batteries and the second bank of L-A. I will now follow your advice when installing the Lithium.
As usual you provide some great information I cannot find elsewhere.
Keep up the good work.
Always great information, thank you very much
Clark you just helped me solve my problem. Exactly the information I needed. Thank you so much.
Great.
You might like binging through my other videos. If you liked this I'll suggest you try our capable cruiser playlist
Always great information! Cheers!
Great video again! Thank you for the education!
Good info and video thanks.
Thank you so much!
Great info
Great information. I am in the process of upgrading my system on a 46’ sailboat from Lead Acid to LifPO4 and many questions are answered in your videos. I am fortunate to have an ace ABYS certified electrician to do the job. No amount of time on TH-cam could have prepared me for what he knows. He’s also upgrading me to 50amp shore power. Soon I hope I will be casting off and need to be more self-sufficient and I know your videos will be a help.
Thank for the video!!
Yes, Mr Clarke, thank you very much for this excellent infomercial! 😂
Cool you advised to purchase a 2nd battery bank manager - I like it.
Clark, you are both informative and fun to watch. I would like to upgrade the batteries in my RV to some amount of lithium. Right now I have 200 AH of 12 AGM which I'm pretty sure won't be enough, but I have to convince my wife of this. Fortunately I have an auto start generator so I'll probably never run completely dead and probably the second time the genny wakes her up in the middle of the night my job will become much easier. Thanks for all of the good info for selling a couple of grand worth of lithium to her. Keep the good stuff coming buddy I thoroughly enjoy your videos.
LOL Lit up a few 100watts bulb lights, hidden from your wife... It's goona help draining the batteries faster ... :)
Youve been doing this for a loooooong time..
I don't understand? Are you getting bored with electrical videos??
@EmilyAndClarkeLLC: If you don’t mind me asking,what gauge wiring are you using if you don’t mind me asking? This videos is very informative and I really appreciate your knowledge and advise.
This was just a demonstration with low current flow. Don't go by this video for wire size.
You might like this playlist ELECTRICITY ON BOATS - Clark's Full Masterclass: th-cam.com/play/PLsT7_jPsZM5ogT6or244F49-Gy7pYFV7V.html
The first two videos go into sizing wire.
I learned something new from you today. In the RV the installer connected my batteries in parallel but the solar controller is connected to only 1 battery. Instead the ground should be connected 1 battery and the positive charge cable should be connected to the other 3.
Yes it should. I imagine you will make that small fix to keep your bank happier.
Glad I could help.
I was just wondering about some variables. I actually bought 6 used lithium batteries in 3 different purchases. They are all Valence 12xp-u27 and they all checked out in my less than perfect capacity checker at about 110-115 amp hours. Each is hooked to main buss ar with 3 feet of #4 cable, then into each inverter and off to the boat systems. Each is capable of of delivering 150 amps continuous, and up to 300 amps for 30 seconds. This is great because I use them to start a large diesel engine. When I charge them, my alternators can produce about 200 amps and the solar 80-90 amps, although I have never seen more than 200 amps combined. The alternators will only charge them to 14.1 volts and I have set the solar charge controllers to shut off at 14 volts. When I am out cruising, I rarely see 14 volts at the batteries except after long crossings more than 5 hours. Most of the time, the battery monitor shows 13.6-13.8 volt maximum. Using the batteries, I run the watermaker at 150 amps for a couple of hours every few days. At night there is some cooking using about the same 150 amps for 30 minutes or so. Then through the night I use 10-20 amps just doing led lighting and running 2 refrigeration units. The inverter stays on 24/7 for the 120 volt refrigerator. I have never really had a problem, but am adding more solar and want more capacity. I was going to add 3-4 100 amp Redo batteries and couple them into the same bus as the other batteries with the same 3 feet of #4 wire. Keeping the full charge voltage lower should keep any battery from overcharging, and if I only get 90% on a few of them, that would not really be a problem. I have never let my batteries drop below 12.5 bolts except if I am cooking and making water, that 300+ amps will drop them into that range. I also when I am on the boat hook up the 3 group 24 lead batteries in parallel with the lithium. This allows both alternators to charge both battery banks. I just don't think this system is doing any harm to anything, and currently when the boat is in storage, all lead and lithium is separated and disconnected from all loads.
Any thoughts I may like to consider?
My thoughts are in my videos and here.
www.emilyandclarksadventure.com/bbms
In particular I suggest you read Conrad's article linked to the bottom of that page.
Did you know Li can be damaged slowly but permanently at any voltage over 13.48v
There is no "safe" voltage to charge LiFePO4 to and it should never be floated to those high voltages.
But we are all captains of our own ships.
How do you buy the BBMS+? How to connect it to an charger/inverter when using Lead starting batteries and LiFePO4 house batteries?
Start here www.emilyandclarksadventure.com/bbms
You can find links to the manuals and lots of other information
Hi Clark, thanks for that great video!
After watching trillions videos of electrical systems of boats or RVs, you were the first who answered questions like mixing different batteries, which to buy first, better 2x100Ah or 1x200Ah. Thanks a lot.
One more question, Clark:
If I would:
a) only buy batteries with a Bluetooth BMS
b) and I would limit the charge- and discharge voltage to a certain number near to 10-85% of the newer batteries' capacity to that all the batteries have the same cut-off voltage
c) and I would use a balancer to charge the batteries
could I then use different older/newer or bigger /smaller Ah batteries with the same voltage?
Advantages:
o more control and knowledge about every battery
o treat the newer batteries well to prolong their lifetime
o make use of older batteries which are not so efficient/ Healthy etc.
o Be able to enlarge the battery bank over time
Disadvantages:
o Extra cost for Bluetooth Batteries
o Extra cost for Balancer cables
o Not the maximum available Ah used -> more $/Ah
Thanks, Tom
I hope you find our other videos as interesting, please subscribe if you haven't already.
If you are thinking seriously about Li I bet this will prove useful.
www.emilyandclarksadventure.com/bbms
@@EmilyAndClark Thank You! What do you think about my question with Bluetooth BMS batteries?
First I don't think there is any reason to set an upper limit of 85% charge. That would make sense if you had no way of stopping the charge at 100% accurately since overcharging is very bad for Li and knowing when you reach 100% was a tricky problem to solve.
After the charge issue is properly taken care of I personally think the life of a li bank is simply a function of how many watts are removed. Discharge to 10% and say you see 4000 cycles discharge the same batteries to 55% would give you a life of 8000 shorter cycles but basically the same power stored and released. I'm sure there are those that would argue that point but I think it's close enough to true to be considered a valid simplification. For me it's the charging that means everything. Low current overcharge kills Li. Slowly but surely.
And not charging to full repeatedly causes memory.
Now to mix batteries with that charging regimen. Well you needed a BankManager to do the charge for the original bank. Just use a second BankManager for the new batteries you add. No restrictions on the size, manufacturer, age difference. What could be better? Well the cost of that second BankManager but if we start selling more than a handful at a time I'm sure I'll lower prices. By the time you need the second one hopefully BankManagers will be much cheaper.
I'm currently working on getting this technology built right into batteries. So each battery will know how and be responsible for charging it's self.
To your direct question. Bluetooth is more of an entertainment than a necessity. The battery control system should not require you to look at what they report. You are human and should have better things to do.
But if you find it fun, get Bluetooth batteries. I enjoyed my time playing with the app.
@@EmilyAndClark thanks for taking the time for your detailed answer, Clark! I really appreciate that¡
I am using 300Ah in parallel with 100Ah. No problem whatsoever. Each 16-cell series balances well and I have no issues whatsoever.
I am an over the road truck driver. I have a question maybe you could help me with. The truck is a Kenworth T680 with the KIMS system. Aka (Kenworth Idle Management System)
It is a battery powered APU that runs A/C, Heat and Hotel load while the main engine is shut off. They typically run 4 AGM batteries that charge while driving and my question is. I want to go with lithium batteries for the Apu but I am still working with the additional 4 lead batteries that run the starter and the truck voltage while the truck is working. Would your bank manager work since all 8 batteries on board are charged by the same alternator ran by the truck engine? I really appreciate your videos and hope to hear from you. Thank you in advance. And thanks for sharing your knowledge.
I have no first hand experience with your system but I don't see any not.
There is most likely a diode between your starter bank and your apu bank so to use the BankManager you should retain some lead in your apu bank or possibly remove the diode to use your starters as your lead.
The BankManager hybrid approach requires some lead battery to always be connected so it is free to remove your Li bank once it's fully charged. This lead would only be used after your Li is empty so it wouldn't be cycled and thin plate starter batteries should serve well.
Thanks for answering my question so soon. Since the Bank Manager is sold primarily to mix Lithium and Lead, wouldn't it be OK to have one mixed bank now and add a second entirely Lithium bank in the future?😮
Yes but you would need a second BankManager at that time
Clark, thanks for the video, I got a lot from it… but, begs a question, if each lithium battery has an internal battery management system, wouldn’t that regulate charging for each battery regardless of age?
And, another question if you have two banks, one lead, the other lithium how do both banks become a supply for the same system without back feeding into each bank?
1 yes. I'm m thinking of making a BankManager BMS and selling it to battery producers.
2 under normal condition the li does fead into the Pb. It floats the Pb to 13.2 or so using a tiny amp flow. Under high load conditions the system voltage quickly drops below 12.8 and the lead "helps out"
I really like your expertise on how to manage and implement battery systems in our boats but it always seems to be on a very simple and well define environment, let me explain myself, I watch your videos about mixing LiFePo4 and lead batteries and the electronic hardware that you sale and that make it super efficient, But in the real life in our boats we have our lead batteries with MPPT and the external BMS, then watching your videos I cannot understand how the hardware that you sale and look super efficient and very convenient when you start an installation from scratch, but how do we integrate your hardware with our existing MPPT and external MBS ? because it is not very realistic for boat owner to throw away the whole installation they already have.
Then please if you could describe how to integrate your product in to our existing installation, that would be great thank you
It really is that simple and the device was designed from the start to work with whatever you currently have. You don't need to change old charge controllers with no li setting, in fact even if you had new controllers you would choose the lead settings.
Take a look at these two videos together. They were filmed on the same day with the same exact setup.
th-cam.com/video/LZwhxDnj7cE/w-d-xo.html
th-cam.com/video/VZSr6o5fLHE/w-d-xo.htmlsi=P8dVMKctJ-3xgNy8
To install a hybrid system with the BankManager you start with a lead system. All loads and charge sources go to the lead. Once that is set up it's a rather simple matter to add Li in parallel with the lead. Connect the ground terminals directly but install the BankManager in the positive terminals between your existing lead batteries and your new li batteries.
I describe it as simple because it's really as simple as that. No changes to your existing system and add a li battery bank in parallel with a BankManager.
wont the bms shut down charging on the battery that gets fully charged first, preventing over charging?
A lot of people think that..
Nope a BMS is to keep the cells from electrically destroying themselves and to protect them from thermal runaway. That's their job.
For a long life you need to stop charging when they are full but you can't tell full from voltage alone.
That's why people buy the BankManager.
Clark, maybe use the term FRUGAL rather than cheap! You're not cheap.
Im cheap. Don't believe me? Just ask my ex 😂
Everyone is always looking for a good deal that is cheap that's just common sense right Clark😅
A little off-subject but still in scope, I think. What if I buy 3 batteries of the same brand, same voltage, same ah, but only one is internally heated? Should this be a problem?
The first question is should you care at all if the batteries are all close. The pair I used were the opposite ends of the spectrum. Age can be important I believe.
But it comes down to, do they charge at the same rate. They would have different BMSs so could be different. My answer would be I don't know but most likely they'd be OK
I am interested in the HVAC business you mentioned in the last video. I am not in HVAC but am experienced with residential electrical and am currently finishing up my A&P classes (Airplane tech).
Send me a message to emilyandclarksadventure@gmail.com
Really loving these videos. I've been experimenting with different batteries recently for powering a simple cheap Minn Kota 40 pounder for my tender - silent, indestructible, lightweight and clean. Do you think the Redodo 100Ah is suitavle foe that? Max draw of ~52A at full power in hot weather.
I also wanted to warn you about Renogy. I bought their 12V 50Ah unit last year. First one was faulty - 9.3V was as far as it would go - and it took months of legal threats to make them honour the warranty.
Once the warranty battery was received, I tore down the old one. Turns out they had full-on left out four 26650 cells, meaning it was short an few amp hours. On top of this, the case was horribly built - almost three quarters of an inche of wasted space in all directions, and the BMS is extremely poor quality. They've ignored my emails about the fact that they are lying about the product they are selling. Dont give them a penny, don't even bither testing their stuff. I really appreciate the work you're doing.
Sorry about your renergy experience. I'd actually like to review your actual battery but you already opened it. A mistake I've made with this series is I only accepted batteries that looked great to me. I should review crap batteries as well. I have a bad battery from a friend I'm going to review. To start with it only weighs 50lbs (so I'd likely 200ah) but says it's 500ah.
Yes Id use the little Redodo as a dinghy pusher. It's so small it would be easier to transport.
@@EmilyAndClark thanks for the info. I am building a second version of my waterproof battery box (knockoff pelican with appropriate breakers, meters, and waterproof ports) using the still-good parts of the dead battery with replacement cells and a different BMS, but it'll only be 54.3Ah... having 100Ah would be a game-changer for being out and a about in the dinghy.
Clark, hope you don’t mind me asking on here.
Saw an interview with a guy who had a break on the shaft of his propeller drive shaft so that it didn’t rotate when not in use.
Never really thought about this.
Wondering if you or anyone else had a view on if this is a good idea.
I wish I had one. I had one once but it wasn't very good gear and poorly supported.
You only need a break if you have a hydraulic transmission. Otherwise just put it in gear and your prop won't turn
@@EmilyAndClark that’s what I thought but wasn’t sure. Thank you for taking time to reply. Much appreciated.
Any thoughts on 12v vs 24v systems?
Same thing.
But if your 24v system was made up of 12v batteries you should include an isolated balancer.
I used one in the "Duffy" video. There is a link to it in our Amazon store (link in description). The same company makes one that only balances 2 batteries for 24v guys. They are all inexpensive.
Can I ask, what do you think of the Redodo 410 ah plus battery?
It's the same physical size as 4 x 100 ah mini. But one does not need all the connection wires.
I really don't know. They won't send me one for review.
In theory I like one big battery better than 4 small batteries.
@@EmilyAndClark Thank you.
Redodo has been asking me to review a new battery serise they have coming out. The initial offering is only 100ah.
I've been trying to get them to send me a 410 for review as I no longer want to review small batteries. I sent them your comment and said I'd review their new 100ah if they also sent me a 410 for review.
Clark, if I may ambush you with a question while you're online; I've heard conflicting commentary on number of batteries that can be connected in parallel. I'm thinking of getting 4 self heating Li batteries but want to keep it 12v. Any thoughts?
There is no hard right or wrong number. 4 seems a reasonable max. Use big wire or bus strips between the batteries in parallel. Then, very important...run the positive wire to the first battery and the negative wire to the last
Of course if you are made of money you could put a BankManager on each battery and they would all be charged perfectly with individual attention to their different needs. :)
Clark you have been so gracious to respond so quickly to so many questions in the past couple of days I've decided to join your Patreon group... This is the first and only time I've done this. I feel that I have finally found a genuine person who has the heart to help others. I'll have questions as I build out my rv(cargo trailer) solar system and appreciate your occasional advice in the process. Hope you and Emily are well. ps. I'm, unfortunately, not made of money. Can you explain the advantage of a bank manager over a regular charge controller? Do you have a spec sheet laying out the advantages? I'm a mechanical designer for a biogas company but am ignorant when it comes to electrical. I can tell you about Roots blowers, heat exchangers, and Schedule 10 SS pipe though....lol! @@EmilyAndClark
I'm frustrated that I can't seem to find a complete and easy to understand schematic for a solar system.. I have 4 Renogy 100w panels, plan to buy 3 to 4 100ah li batteries. I want to connect to shore power which means I'll need a switch( don't know what to buy here) that connects to both my inverter and the shore line( I think). Would like to charge via shore so that will need some sort of charger( don't know what to buy here). Some sort of monitoring device, a fuse(s). I know just enough to fry everything I buy.... stress! Starting with the 4 panels and knowing that I want to be able to run two bougerv 30qt fridges, an AC through the inverter, a few lights, a couple of oil radiator heaters for warmth, and an occasional appliance I'm not sure how to move forward with components. First calculate total wattage and assume a certain percentage of that always on for 24 hours. Fridges will cycle. AC with cycle. Appliances used for 10 to 60 minutes at a time.... I'm out of my comfort zone for sure on knowing what to buy.
For the BankManager start here.
www.emilyandclarksadventure.com/bbms
It does a lot of great things that I guess a lot of people don't know they need. But chiefly it actually charges li correctly for long life, unlike Victron or any other so called Li charge controller out there. Really it's the only way to charge li correctly.
As for the rest of your system. Watch ALL our videos I guess. A lot of what you need to know is there.
But the system you describe can't operate the loads you mention. Solar isn't magic.
In engineering terms, "Good Enough is the enemy of Perfect". It doesn't have to be perfect, but it does have to be good enough.
😎
If the smaller battery charges faster, wont it's impedance increase as it becomes nearly full and thus reduce the current that it accepts? The larger battery will continue to accept current until they are both charged and then voltage will rise to the cutoff set by the charge controller or the 14.4V cutoff in the BMSs of each battery. I'm failing to see how this is a problem with different capacity batteries in parallel.
Everything you just said would be true for lead.
Almost none of that applies to Li.
For example you don't charge li to a voltage and certainly don't let the BMS be the charge limited. Do that and your nice 15 year Li battery will likely die in 3 years.
It's really a different animal. Conrad's article linked to the bottom of this page tells it well.
www.emilyandclarksadventure.com/bbms
Won't the bms prevent over charging
Nope
Its job is to stop terminal immediate damage and thermal run away. Don't charge to a voltage Your batteries won't last much beyond 3 years. And don't charge to the BMS, they won't last that long.
If you're pulling enough power long enough to drain the smaller capacity battery to the bottom of the curve it'll start leeching current from the larger battery but then contribute back to the load eventually. Worse case is heat from undersize conductors if the unregulated current rises too high. Nothing is actually being lost. If your in a net gain and one of your batteries tops out and over charges, you've got a bad or cheap BMS. It's job at the very minimum is to turn the battery off at 3.65 or 2.5 volts (sorry cell voltage). It should actually give a little more grace than that but shady companies do shady work.
Once you get to 3.65 slow damage is happening. Don't count on a BMS for charge control You shorten the life of your cells if you overcharge them and that can happen at any voltage over 3.37.
You just can't charge li properly to a voltage and different batteries in parallel are essentially charging each other to a voltage.
That's why I developed the BankManager.
www.emilyandclarksadventure.com/bbms
Generally speaking, as long as the voltage is the same, LiFePO4 batteries can be put in parallel. Age doesn't matter, capacities don't matter (within reason, see below), manufacturer doesn't matter either. The only thing that matters is that the internal number of cells in series is the same and that the chemistry is the same (aka LiFePO4) for the batteries you are paralleling.
"12V" LiFePO4 batteries are always 4-cells in series internally. "24V" LiFePO4 batteries are always 8. "48V" LiFePO4 batteries are typically sold as 15-series or 16-series cells internally so in that case you have to make sure that the batteries are compatible.
It is a very good idea to parallel at least two LiFePO4 batteries together for robustness (if
the BMS in one disconnects, the BMS in the other is probably still connected). And sure, if designing a new system its a good idea to make all the batteries the same manufacturer and model. But if you do not have that luxury, they don't have to be.
You can connect ANY NUMBER of same-voltage LiFePO4 batteries together in parallel, with two provisios.
First, the internal BMSs can handle only so much short-circuit current and still be able to disconnect. Typically this is 3 or 4 of same-type batteries. So when connecting more than approximately 3 batteries in parallel start thinking about fusing to stay within the short circuit current limitations of the (worst) batteries in the set. And of course, the pack as a whole should have a series fuse (usually on the main positive) sized generously but within the limitations of the wiring and batteries, as well as a master DC breaker sized to worst-case charge or discharge currents in real life (which adds safety and makes working on things easier).
The only other provisio when doing this with different manufacturers and/or capacities is that you have to limit charge and discharge current to the worst possible case (all the BMS's in the batteries have disconnected due to low or high voltage except the worst battery in the bunch, or all the batteries are connected but only the worst one is accepting or providing current due to relative SOCs at the start or end of the discharge curve). So if you have a 200Ah battery and a 100Ah battery in parallel, you have to limit charge and discharge current to what the 100Ah battery can handle (typically 100A).
More sophisticated systems with more professional LFP batteries that have BMS comms can adjust charge/discharge limits based on the actual state of the paralleled batteries.
--
CHARGING:
Generally speaking, once you've done an initial full charge of the paralled bank to put all the batteries at the same SOC, then batteries of different capacities will divide up their current proportionally, charging or discharging.
You can also initially connect batteries up in parallel that are at different SOCs, just as long as the voltage differential does not cause excessive current between them. You can then charge them up in parallel and just hold the charge target for a few hours to bring them all up to 100% SOC.
During normal charging (and discharging) operation, there WILL be a small SOC offset between the batteries of different manufacturers due to differences in internal resistance. But these differences are essentially overwhelmed by ANY appreciable charging current due to the voltage drop caused by the current and the internal resistance of the cells inside each battery. In otherwords the SOC's for the batteries will remain in lockstep, just with a small offset.
This means, generally, that if you have (for example) a 100Ah and a 200Ah LiFePO4 battery in parallel, the 100Ah battery will charge/discharge 1/3 of the current and the 200Ah battery will charge/discharge 2/3 of the current and they will remain in approximate SOC lockstep (with a small SOC offset, typically no more than 10%). This is NOT an exact ratio... there will be differences at different parts of the charge/discharge curve and also depending on the charge or discharge current. But again, all that will happen is that the SOC offset will shift around a bit. It will still stay within a 10% range and otherwise remain in lockstep.
At the end of charging the batteries will radically slow down current acceptance at different times, but still almost universally within, oh, 20 minutes of each other or so.
As I said before, with an appropriately selected charge target voltage (typically 14.2V), YOU CANNOT ACCIDENTALLY OVERCHARGED PARALLELED PACKS. It is perfectly fine to hold the charge target for several hours before dropping back to the float. In fact, you HAVE to hold the charge target voltage for at least an hour to give the BMS's in the batteries time to balance their internal cells.
DISCHARGING:
Discharging works the same as charging, just in reverse. Batteries of different capacities WILL current share in approximately proportion to their capacities. There WILL be an SOC offset so in the last 10% before being completely discharged some batteries will stop providing current while others continue providing current. This is not a big issue as long as you ensure that you do not over-current (based on the worst battery in the bunch).
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Is it ideal to mix battery capacities? No, it is not. But does it work? Yes, it does. It does not require anything fancy, it will not prematurely wear out any of the batteries beyond what would have happened to them anyway, and it will not damage the batteries.
I would go as far as to say that you can even situate additional batteries in parallel (again with appropriate fusing on the runs), quite far from your main house battery if space permits elsewhere in the boat or the RV, without doing the "first battery main positive, last battery main negative" trick. That trick is great when the batteries are right next to each other, I do it myself. But it is not absolutely required if you wind up having to situate additional batteries away from the main group. The secondary group will wear differently, but not by a whole lot. The lifetime will be roughly the same... nothing you'd have to worry about for 10+ years.
Using higher house system voltages makes all of this even easier, but most boats are still wired for 12V rather than 24V or 48V house voltages, so I'm not gonna get into that here.
12:02 I am a little surprised Clark doesn't respond to your statement. I have 2 SOK 100Ah batteries which have been used for 2 seasons on my boat and I bought a third 100 Ah SOK to add to the bank. Based on Clark's video I should not do it, based on your statement it is not a problem. I tend to agree with you but I am confused., any thoughts?
We are all captains of our own boats and can do anything we want to do.
Hell, there are guys charging until the BMS shuts down. Is it good for the batteries NO. But it won't kill them in a year so if that's how they want to treat their gear it's their choice.
Mixing cells with different personalities only works at all because you are driving one group into the hockey stick and oversaturating them.
If you don't care, fine.
If you want to do it right I offer the multiple BankManager approach. Expensive but cheaper than totally replacing a big bank when you add more, likely.
@EmilyAndClark thank you for your response. Your point is valid as you clearly showed in the video. But what if the batteries only differ in age (as in my case) and capacity, type and brand are the same? It is obviously not perfect and I don't want to shorten live of the bank considerably. Would 1 bankmanager be enough?
The rule of thumb out there seems to be within 3 months of heavy use.
I have personal idea as I haven't done any studies of aging of cells myself.
I'd fully expect a mixed pair under BankManager would fare much, much better than a mixed pair without one. Just because the normal "low current overcharging" is avoided or minimized.
And of course these things aren't going to last forever no matter what we do. This might all be well into the area of diminishing returns. My goal is to offer every possible cell protection and let users decide.
I personally expect the biggest factor to the death of my batteries is that I use them in the tropics at 35c. I accept that because I want to live in the tropics. So if I get 12 years instead of 15 years out of them I can accept that.
@@BS-ce9jq It literally doesn't matter. LiFePO4 batteries "age" by losing capacity, as in amp-hours. The charge and discharge curves and related voltages don't actually change.
In addition, when you parallel LiFePO4 batteries (of the same voltage, obviously), the batteries will roughly current-share according to their relative capacities. There WILL be a small SOC offset in addition to that, generally no more than 10%, but that's it (because of differences in cell internal resistances).
Since when paralled the voltages are more or less in lock-step, none of the batteries in the mismatched bank will be over-discharged or over-charged.
So basically, paralleling LiFePO4 batteries of different ages is fine. Think about what you mean by "shorten the life of the bank". If you parallel a new LiFePO4 battery to an existing 2-year-old bank, will that "shorten the life of the bank" ? No, it won't. It will extend the life of the bank. Why? Because (1) The mismatched batteries don't cause any stress to each other and (2) Now you have more capacity to cycle through, meaning you are now cycling your bank less as a whole.
If you parallel batteries of vastly different capacities, such as if you were to parallel a 50Ah 12V LiFePO4 with a 200Ah 12V LiFePO4, then you have to be sure not to charge or discharge faster than the lowest-capacity battery in the set can handle (obviously).
If you exceed the paralleling limit (typically 4 same-capacity batteries) of the manufacturer, you just add appropriate fusing (this is just a safety limit for how much shorting current a BMS can handle if other batteries in the bank dump into one).
So insofar as paralleling LiFePO4 goes, there just isn't an issue.
And for gods sakes, charge the LiFePO4 batteries properly. That means charging to 3.55V/cell (e.g. 14.2V) at a minimum and holding for 1-2 hours so the BMS can properly balance the internal cells. All charging to lower voltages does is prevent the balancers from working properly and internal cells will actually both undervolt and overvolt over a period of months to a year, even though the bank voltage looks ok.
Then after the 1-2 hours of absorption at 14.2V, you drop back to a float of roughly 3.35V/cell to 3.375V/cell (13.4V to 13.5V). The float allows full load support while maintaining the SOC without stressing the batteries.
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Now, paralleling LiFePO4 with LEAD... that's a whole 'nother ball of wax and to be honest it makes no sense to risk expensive LiFePO4 batteries that are supposed to last 15+ years by doing it. You more or less instantly exceed paralleling limits for the LiFePO4 due to Lead's short-circuit current capability and you can no longer use the proper charging profile for either. A proper DC-to-DC charge controller is just $100 to $200.
Or better, use a proper topology... a higher voltage lithium bank (24V or 48V) and then a 97%-efficient $100 charge controller to go from the lithium bank to the 12V Lead starter battery. Along with other insundries (this is a whole 'nother conversation, too).
And no alternator should EVER directly charge a lithium bank. Period. Smart or dumb alternator. Always go through a charge controller and for the same reason... why reduce the life of your expensive lithium bank because you didn't want to spend money on a small $100 charge controller? Why put unnecessary stress on the alternator? There is no need.
I watched the video twice. I am beginning to understand the difference between batteries. I am doing something of what you recommended for now, I plan to purchase two Redodo 200AH batteries now. In the real world, what would happen if a year from now I purchased two more Redodo 200AH batteries and added them to original two in parallel without your Bank Manager?
Much as I said in the video. They would likely charge differently. As batteries age things change.
How fast, I don't know.
Rule of thumb seems to be 6 months is OK. But I've done no tests and don't know anything about why at this point.
But a second BankManager would solve any issues.
I guess if one hooked up two li banks with two equally set up BankManager there would be things to learn. If they stopped the charge cycle at nearly the same time it would prove the batteries could all live together under the same BankManager. If at different times then they need to be treated differently.
one place two 100 AH batteries are better than one 200AH battery... if you use them for dinghy motive power and you want anyone to be able to hand the batteries to you. Maybe not electrically optimal, but 30 pounds is an I get help and 60 pounds is an I will be doing it myself point. A 90 pound AGM 100AH is a whole other thing.. I do have a 60 pound 6HP (it could be 8 hp since I tuned it) I tried looking for a lighter 2 or 3 hp motor... they have all gone 4 stroke and seem to weigh the same 60 pounds as my 6 hp :P Sorry for the rant. My new dinghy only needs to go hull speed... it has lots of rocker so not going to plane well. so electric, my wife can hand me the motor, hand me 100AH batteries, one at a time. It works :)
It seems all your information could be applied to rv's as well.
Absolutely. We use our BankManager in our truck camper
You can, with lithium. Will they be as good as they could be? Not likely. But yeah. as long as they're the same chemistry and same voltage, go for it. The weakest link will be the BMS. Don't exceed the capacity of the weakest BMS, just to be safe. Different capacities will be the most likely to suffer. DIfferent ages wont be much of an issue, but you'll lose capacity based on the oldest battery. Lead... Well. I don't care. I don't use lead any more. :)
using bus bars< will this solve the problem of mixed batteries
It's a step in the right direction but if the batteries are different, they charge differently.
The only real solution is a second BankManager but I realize that costs a lot.
Love your tech talk video's. However, I get distracted every time you forget to take off that massive electrical conductor on your wrist (your watch) I'm just waiting for sparks to fly!
On this video every +/- pair are spaced wider than my wrist.
But thanks for thinking of my safety
So how can i hook up two different bank managers to batteries running in parallel ? You didn't make the video. 😭. Now im thinking of just using one battery up, then switching over to the 2nd one when the first one dies. But then wouldn't it just make both of them useless if i want to add more batteries down the line ?!? Should i take the plunge and put them in parallel anyway and keep adding batteries as needed ? Also, please make the video on adding different bank managers to two batteries running in parallel. 😀
I haven't made a video on this but I talk about it in this video.
th-cam.com/video/xjzd3MBnj4k/w-d-xo.html
It's really simple to do. You put both Li banks in parallel to your lead with their own BankManager in the positive cable.
On Temptress I'm running 3 in parallel, story in the video.
It works great
Normally I really like your videos and have found most to be very informative but on this one I must call foul. at 14:10 you said that the front battery would be way over charge because at this point in the test it is taking in twice the current as the back battery. BUT... you stated that the back battery was at a higher state of charge when you paralleled them. The front battery needs more amps just to catch up. What you have totally neglected is that the internal resistance of both batteries will increase markedly as they near full charge. That is the reason that they have the double hocky stick charge curves. Whichever battery gets full first, will get greater IR and will except less current which causes the less charge battery to get more current just like you are seeing. As they both approach full [anything over 13.8v] the charger will reduce current output and both batteries will stay at the set voltage taking in only the current that they can hold without going above the charger CV voltage setting. Neither will be overcharged because neither of them can go above the CV setpoint.
The only way that you will over charge them would be to have the cv voltage set too high AND the BMS fails to protect the cells from overvoltage. If the cells in either battery are very badly out of balance, the CV setpoint will need to be lowered to that imbalance below the max allowable voltage of 3.65v per cell. Many drop-in batteries will have 250 mv imbalance at the top end so I would not ever charge them to more than 13.6v without monitoring them for BMS cutout. If you do not have a Bluetooth BMS, you can find the imbalance by charging them up until the charge drops suddenly to 0A at a voltage less than the CV setpoint. That will happen when the BMS cuts charging to protect the cells. Then set your CV setpoint to 0.05v less than that voltage to avoid tripping the OVP.
While it is true that you can have a battery that takes longer to get to full and empty, it will eventually get there because the faster battery will limit itself both at the top and bottom of the charge curve. The only downside to this is that if you are pulling high amps at the bottom of capacity you will not get as many total amps out before one or both BMS's trip for low voltage cutout, but it will not harm the either battery.
Your "test" does not even address how LFP will limit itself to go "CLICK, I am full" without any help from your expensive bank manager. Take those two completely mis-matched batteries and connected them with proper equal gage and length paralleling cables and then charge them to full with 13.8v max CV and then discharge them to 12.0v and they will play nice together without harming either and you will get the capacity of the two added together at the same voltage limits.
Lots of good points there and I accept that my example was lacking.
But, you are missing the heart of "low current overcharge". 12v Li batteries can be damaged at any voltage over 13.48 if held there after saturation.
When two batteries of different internal resistance are charged in parallel I think we agree that the lower resistance battery gets current first and reaches saturation first
Yes it will nearly stop accepting current but it will accept some current as its partner continues charging. This energy has no real place to go but to plate out the li from its salt into elemental Li which will no longer hold a charge.
It's like drinking kills brain cells. You have so many it's not immediately noticeable but the cumulative effects add up.
This kind of treatment is what turns a 15 year bank into a 6 year bank.
@@EmilyAndClark I agree that LFP should not be held at elevated voltage but if the batteries are properly paralleled, both batteries will be at the exact same voltage. Once the slow battery had hit 13.48, they will both be mostly full and will quickly go up to the set voltage and the charger will shut off. I charge all of my LFP batteries to 13.8v with 5-minutes of absorption time per 100Ah.
@@haydenwatson7987 You need a much, much longer absorption time or the BMS's in those batteries won't be able to balance their cells and you will actually be putting more stress on the batteries instead of less.
Charging to 13.8V is only 3.45V/cell. Most BMS's won't even activate their balancers at that voltage. You are literally forcing the cells in the batteries to go out of balance. This will also have poor cold weather charging performance. It will eventually charge the batteries to 100% SOC if held long enough but there is no real reason to do it with LiFePO4.
It is best to charge to at least 3.55V/cell (14.2V) and hold for 1-2 hours (absorption) before dropping to the float. Holding at the charge target for a few hours DOES NOT HURT A LIFEPO4 BATTERY. I will repeat that. it DOES NOT HURT THE BATTERY. The cell voltage will drop into a relaxed state literally the instant it drops to float mode.
@@junkerzn7312 The problem that I had to overcome was one very low cell when I received the battery. I had one cell that would hit 3.64v, one at 3.51v, one at 3.42v and the last one at 3.31v. I needed to shut off charging at 13.88v or trip OVP. My BMS had unlocked Bluetooth connectivity so I shut off charge and discharge and selected "off" for "charge balance" so that it would balance anytime it was not charging but the cells were above 3.45v. At this point, the highest two cells would burn off 70ma and I would let it go for 24-hours and then charge until the high cell was back up to 3.64v. In this manner, the highest cells were bleeding off the excess for almost 24-hours a day. Doing this, I was able to reduce the delta from 330mv with a max pack voltage of 13.88v down to 50mv at a pack voltage of 14.49v.
I was able to raise the max voltage in the lowest cell from 3.31v to 3.607v. I tested the pack capacity the day after I received the pack and it had 445h or 96.7% of advertised capacity and a top delta of 330mv and a bottom delta of 398mv with a voltage of 11.01 at UVP at 2.501v at the low cell.
After a month of balancing, the capacity had gone up to 480.5Ah or 104.5% for an increase of 35Ah. Well worth the time.
I could have done it by just setting the charger to 14.4v and charge balance "on" and let the BMS shut off charging every few minutes, but I do not believe in using the BMS as a charge controller. It is a safety valve and if I can prevent it from ever tripping, I am a happy camper. I have had them installed for about a year now and they have never been more then 50mv out of balance since. I charge to 13.8v with 1-hour of absorption and then float at 13.3v. balancing comes on at 3.45v which is the average of the cells at absorption, so the high cells passively balance down to close in on the lagging cells.
I don't know man. I don't buy the whole charging with the cables lengths make a difference. (11:10) - maybe if the cables were undersized. I mean, I like the experiment you ran, but I couldn't help but to notice that you measured 1.91 amps and 2.96 amps. Add those up and you only get 4.87 amps. So where did the other 0.13 amps go? Meter errror? Kirchhoff wouldn't be happy with the experiment. What gives?
Well you can do the resistance math yourself. With the crazy low internal resistance of li the cables matter
As to the math. Yes some meter error (it's a clip on of course) but possibly the charge acceptance rate went down as I was testing. I had just started the charge when I took the first reading.
Do you buy any of that?
I don't know, it's hard to think of everything while filming a video. Work is easier when there isn't a camera in your face.
The Redodo product page specifically says that the BMS in the mini has overcharging protection. The Feence on the other hand is a typical sold-only-on-Amazon POS with no specs and no support, so who knows. I don't believe your unsubstantiated claim that the Redodo would be damaged by being charged in parallel with the Feence even if the Feence is slower to complete a charge cycle.
So you trust one Chinese battery company over another???
It comes down to chemistry, all LiFePO4 are subject to the same damage if overcharged. I suggest you read Conrad's article linked to the bottom of this page of you are interested in how LiFePO4 should be charged.
www.emilyandclarksadventure.com/bbms
Sorry, you can't over charge a battery that has a BMS. That's the job of the BMS. It stops charging when it reaches its programmed voltage. Been mixing brands from several years with no issues. BMS protects against over charge, over voltage, under voltage, over temperature and sometimes if equipped low temperature, short circuit and over load. As tong as they are same voltage they will play together and only in parallel.
That's a strong definitive answer. How about backing it up. Have you run this way for 5000 cycles?
Wanna sell those batteries? I got a place for em. 👋
Sure. You want to pick them up on the DR?
No, I'll find boats and others who need them here.
This so not very true The BMS will stop charging the battery when its full and if the other battery still is not full it will keep charging until the BMS says its full! NEVER connect a partially charged LIFPOE4 battery to a full one! you will get a huge pass of current between them to balance! this is very scarry bad information.
A lot of people have this same misconception.
You might find the article by Conrad linked to the bottom of this interesting.
www.emilyandclarksadventure.com/bbms
You are not only a technical engineer but also a good marketing engineer. I believe you are biasing your explanations in favor of selling your Battery Bank Manager.