Do you need a DC to DC Charger for lithium?
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- เผยแพร่เมื่อ 27 ก.ย. 2024
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In this video, we're testing a question that we are asked regularly by people that we meet at trade shows: do you need a DC to DC charger for a lithium battery? Can you use a lithium battery without a B2B charger?
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Interesting way of explaining this situation. I did not expect that. I watched this video because I figured I want to see what experts say about charging LiFePO4 batteries. What I understood before watching this video is that the life of the LiFePO4 battery degrades when charged at a high rate. For example, my 100Ah has a 100A BMS but the manufacturer recommends charging at 20A. It appears to charge fine at a much higher amperage than that but I am concerned about the long term effects of continuing to charge the battery at a rate higher than 20A. I currently have the battery in the vehicle keeping the refrigerator running when the vehicle is not driven. Sometimes but rarely I see current go as high as 70A for a while then drop 0 after approx 30 minutes as both batteries achieve full charge. regularly I see between 50 and 60 amps. I have a smart battery isolator installed between the batteries and it prevents the engine from pulling a heavy amp draw from the LiFePO4 battery when starting. The isolator makes a connection to the LiFePO4 battery after about 10 seconds after the engine starts. So my main question is, does the LiFePO4 battery degrades when charged at a high amperage even for half an hour or so? My battery is made from prismatic cells and I am unsure of the max safe charge rate this type of cell can sustain during this type of use.
Interesting experiment. Would be very interesting to see the results with the leisure battery at say 20% state of charge.
Have a great rest of the week and weekend, all the best. David 👍
That's a good idea! We'll do that next. :)
It's my understanding that the DC to DC Charger is to protect the Rectifier in the Alternator more than anything .
Main Power wiring should always be rated to the prospected Maximum A/h rating of the Battery anyway .
Again One of those Useless videos made by a person that do not Know Much about batteries and electrical power
Glad you're enjoying our videos, Peter. We appreciate your support!
Fuse size is rated by the cable, not the load........that's how it works, bro.
*It seems that you are using a stock alternator and stock alternator charging leads. These are still , even these days already quite undersized In the old days like in the 70's USA they would use a 20 gauge wire. Thats it! In a 2007'ish I would think about a 6 awg at best. Therefore I would run 4/0 and wire like audio buffs do dubbed the Big 3 or 4 (battery Neg to body ground, another lead Battery Neg to Engine Ground, next from the Pos main alternator stud to your battery Pos and then finally from your alternator ground to from the alternator Ground to Body Ground. (I added a 5th jumper to eliminate resistance in the fuse box with some 2 AWG also Copper Welding Cable on my 2000 Dodge Grand Caravan and also 2002 Dodge Caravan and once on a 1998 Dodge Caravan 2.4, on the 2.4 it really livened up the engine because the ground straps from the factory are thin crap.) add a high amp alternator because you need some 30-50 amps to run the engine and most of these alternators being rated at say 110 or 140 amps might only offer the 30 or 35 at idle as the rest is relegated to the engine. While I see you have diesels, a small 4 or 6 cylinder gas engine needs 13-16 DC amps to just run the engine, spark plugs and such, Then add 20-40 amps for the radiator cooler if it is electric. Finally add dash lights and headlights and taillights and headlights draw 55 watts high beam and 45w low beam per headlamp)*
Just adjust the maximum amps that can be used for charging in the BMS, Then BMS won’t draw anymore from the alternator and prevent its damage.
It could blow up the alternator if lifepo4 is at 20% soc or under because my 12v 20A battery charger blew up as soon as I connected it to my lithium that got depleted to under 10% when it's voltage was 12.0V and bang AC-DC charger went toast in 5 seconds, before that it was working fine for almost 10 months because I never depleted battery under 12.9-13.0V however just from all that charging experience I noticed that at 13.3V SOC my 20A charger wasn't charging more than 13A but when soc was 20% or about 12.9V the charger was pushing 20A and being very very hot that I needed another usb fan to blow air over it even though charge had small internal fan so judging by my experience I would say that if you tried using alternaror on lithium that's 20% soc or less you are going to see some crazy charging numbers like over 100A 😌
What is Amp rating of the alternator in the Hilux?
What? When charging how the current can flow to the system blowing something? My understanding the current only flows to battery
Most motorhomes have the power flowing from the engine battery through the electrical system to the leisure battery.
I have my doubts that Lithium can beat Led Acid for Cold Cranking Amps.
It cannot. You'd be looking at a peak draw of perhaps 3 or 4C from the battery with a 280Ah Lithium battery - far in excess of what the cells or the BMS is rated for. If you wanted to use a LiFePO4 battery as your starter battery, you'd want to have a bank of supercapacitors that actually deliver the cranking current, and then separate those supercaps from the battery with a contactor that closes when you prime the ignition and opens when you crank the starter.
@@madvlad1 very well said
Yeah, I wouldn't use lithium for that. It's not what it's designed for.
Good response! :)
Keep up with the latest. There are now specifically designed lithium starter batteries. Yes, deep cycle vs starting batteries are different animals but manufacturers now have it sorted. I've been running a lithium starter for nearly a year. It's good tech!
before you have to get through all this rambling about nothing....the simple answer is NO you dont need a DC to DC charger. In reality the answer is YES. Your car alernator will not output the 14.2-14.6 volt needed to completely charge your lithium battery. In most cases you can use the 12v source of your trailer plug if you stay under about 20 amp of charging current. If you want to run a 40 amp or higher output for charging you have to make sure that your alternator will support said load. You also have to run cable directly from the alternator if you want to use more than 20 amp. Victron has a 12/12/18 charger that works perfect. Your battery also needs a Shunt. You also should consider that the dc charger will get very hot during operation, even more so the 40 amp units.
This test is essentially invalid. To do this properly a calibrated shunt should be used to measure the SOC of the LFP battery, have it at a reduced SOC of say 50% or less, then go for a drive, a few hours. see what % of full the alternator system can achieve in the LFP leisure battery. This would reproduce a real world test of a simple battery connection as used with a VSR or other type of battery isolator. It is my belief it will work, but the LFP would only achieve (best guess) about 80% of a full charge. Since the alternator system typically charges the cranking battery with 14.2v to 14.6v all electrical components in the automotive side of the system must be made tolerant of these voltages, thus the higher voltage of an LFP cannot harm them. Also the LFP being charged from these alternator voltages would not likely achieve its highest potential voltage regardless. The BMS can give an idea of SOC but they are a poor method to judge the TRUE state of charge. Shunt is the only way to be sure. Your test did show that there was potential of the LFP absorbing a high level of amps yes, but keep in mind that in an RV that has always been an issue, even with PB battery in the RV, if it was deep discharged, high amps could be driven into it by the charger voltage. Believe it or not, in old RV's the distance of the wires and the gauge of them was used to take advantage of voltage drop to limit the amps from the alternator. Ya, seems crazy but that how it was done in the old days via simple relay connections before the MUCH better method of a DC2DC charger was introduced. A bit later and still used are the diodes in a battery isolator as they acted as to introduce voltage drop.
The test just shows DC-DC converter is a scam , my car alternator is 140 amp so I don’t really need DC-DC converter for 12v 100AH battery to protect the alternator for 30-50 amp max surge,…to have over thousand watts , I think is plenty juice to keep the car fridge refrigerator running for week 😂
Except the test shown didn't prove a max current as we don't know state of charge. What will a fully discharged 280A LFP capable of 1C charging draw? This didn't answer that.
anybody else notice that as soon as he turned off the vehicle there was a pull of 2.2 amps going to the lead acid battery.
Yeah, that's because the lithium battery has a higher voltage than the lead acid batteries.
This test is flawed.
Nobody will (or should) connect lithium without a relay or solenoid. Doing so will discharge the car battery when lithium is used.
This means you need a relay/solenoid and to stress test it see amp when the lithium is at 5% SOC and then the relay/solenoid connects. Given lithium voltage will be 10v-ish and alternator will be pushing 14v+ the current can be VERY significant, likely limited by wires, alternator or BMS.
A cheap way to current limit would be to use a power resistor though that means some power loss and might need to be cooled to dissipate the lost energy.
Exactly! That’s why we recommend using a DC to DC charger that’s designed for charging lithium properly from your alternator.
@@offgrid_powerThere are several problems with DC to DC charger:
1. Cost (most are $100+)
2. Size - in some vans they require to much space
3. Some installs place the batteries under the van and most DC-to-DC are not weather resistant - very common when doing AGM to lithium replacement on Class B vans
4. At least some require an additional 'dc+' wire which means you need to find a source for switching DC-to-DC on (ignition signal is not great as ign might be on but engine/alternator might still be off in ACC mode) - though Victron has a solution for this, their equipment cost is ridiculous
Have you bumped into DC-to-DC that are weather-proof and small?
All valid points, depending on the vehicle you're working on. :)
I believe that Redarc make a DC to DC that you can use in the engine bay of your vehicle, so assume it is fairly waterproof.
> Nobody will (or should) connect lithium without a relay or solenoid
He made that point disclaimed the setup at 8:30. It's not like people drive around with a battery pushcart cabled to the side of their truck.
> the current can be VERY significant
In most relay scenarios the negative return is through the chassis, providing ample resistance in the circuit.
IMO if someone is running their LiFePO4 down to 10v regularly they've undersized their bank for the use case and/or they need an external LVD. Luckily for the alternator the shape of the voltage curve means the bank will pop up to the flat middle of the curve rather quickly and current acceptance normalize.
I can't listen to this guy 'ah uhm ah but .. but couldn't come up with any sufficient explanation except some gimmicky blah bah blah
What a daft exercise ... to show what NOT TO DO. I'd use a white board to explain WHAT TO DO.
Your explanation did not address or answer the question you posed at the beginning. 🙄
Glad you enjoyed the video! 🙂
It could blow up the alternator if lifepo4 is at 20% soc or under because my 12v 20A battery charger blew up as soon as I connected it to my lithium that got depleted to under 10% when it's voltage was 12.0V and bang AC-DC charger went toast in 5 seconds, before that it was working fine for almost 10 months because I never depleted battery under 12.9-13.0V however just from all that charging experience I noticed that at 13.3V SOC my 20A charger wasn't charging more than 13A but when soc was 20% or about 12.9V the charger was pushing 20A and being very very hot that I needed another usb fan to blow air over it even though charge had small internal fan so judging by my experience I would say that if you tried using alternaror on lithium that's 20% soc or less you are going to see some crazy charging numbers like over 100A 😌
Rerun your tests without a lead acid battery in the circuit and include tests turning the bms on and off while the engine is running.