Different Capacity Batteries in Parallel - Current Sharing Explained
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- เผยแพร่เมื่อ 16 ก.ย. 2024
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Have you ever hooked up two batteries in parallel with a different capacity, thinking they’d share the load equally, only to find out that one battery is doing all the heavy lifting? It’s a common mistake, and in this video, I’m going to show you why that happens and how to fix it!
I started with a simple setup: a 100Ah battery and a 200Ah battery wired in parallel. I expected them to split the current according to their capacities-one-third for the 100Ah and two-thirds for the 200Ah. But when I checked the current draw with a clamp meter, the results were far from what I expected. This led me down a rabbit hole of research, where I discovered the crucial role of internal resistance in how current is shared between batteries in a parallel setup.
In this video, I’ll take you through the entire process step by step. First, we’ll measure the internal resistance of each battery using a straightforward test, and I’ll explain why internal resistance is so important. Then, we’ll dive into some calculations using Ohm’s Law to determine the conductance of each battery. This will allow us to predict how much current each battery will actually carry in the circuit, which is often very different from what simple capacity-based calculations would suggest.
I’ll also give you practical recommendations on wire and fuse sizes to make sure your batteries are working together as efficiently as possible. I’ll show you how to size your wires correctly based on the load, and how to choose the right fuse to protect your system. Whether you’re using batteries of the same capacity or different ones, these tips will help you avoid common pitfalls and ensure your setup is both safe and efficient.
We’ll even do some live measurements to see how close our calculations come to real-world performance. By the end of this video, you’ll have a deep understanding of how to wire batteries in parallel, taking into account not just their capacities, but also the internal resistances, wire lengths, and fuse sizes.
This video is packed with useful information for anyone working with batteries, whether you’re setting up an off-grid solar system, building an RV power system, or just curious about how to get the most out of your batteries. So if you’ve ever been frustrated by uneven current sharing in your parallel battery setup, or just want to optimize your system, this is the video for you.
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Great explanation on current sharing and internal resistance!
I make sure to share your Videos all over FaceBook Solar Power group page & Reddit…you’re the only YT’er guy…keep the vids coming
Thanks! I have a few interesting ones coming.
what if.. instead of parallel you connected both positives to a bus bar and both negatives to another bus bar. now you have two bus bars positive and negative to draw power from. how would the batteries perform in this scenario.
They would perform the same. I tested this before. The only small difference will be a small length of wire which is almost negligible. It was wired like the diagram you can see at the end of the video.
This guy is a genius
Can't believe we're getting all of this for free!!
Thanks a lot man ❤
Subscribing immediately 🔥
Welcome aboard!
Very good, clean and concise! I never knew how battery internal resistance was done before this. I know you just can't use an ohm meter! I guess internal resistance plays a big part in my older FLA batteries, since the voltage drop gets considerable as I apply heavier loads.
Yes, no ohm meter can be used. You will get readings in Ohms, not milli Ohms. Indeed, lead-acid batteries have a higher internal resistance.
How do you place a battery monitor ?
I made a video about it. Search for 'shunt'
Calculating the internal resistance of the battery, the voltage should be measured at the battery terminals, not on inverter, to avoid cable voltage drop mistake.
As I've said I'm measuring the resistance of the whole circuit. Don't forget wires, lugs and fuses also have resistance.
Question. I have a Magnasine MS4448PAE. I have 18-325 watt solar panels feeding my off grid system. We think our gens still run too much. Can I add 9 more solar panels facing more east to catch the morning sun? Or will that be too much for the inverter? Probably get 6-9 400 watt panels. Wire coming into the house is #1 THWN so I plenty of capacity in the wire. I just want to know if my inverter will take it.
Thank you.
Your book is great!
I have a 48Volt system. 8-6 volt Fullriver AGM 400AHr batteries.
The inverter you mentioned is an inverter/charger without solar input. You need a separate charge controller to charge the battery. You cannot combine different panels. Check my video about wiring mismatched solar panels.
@@cleversolarpower thank you!
@@cleversolarpower the charge controller is a Midnite solar Classic. Should have mentioned that! Thank you. Will look up the mismatched panels….
i want to connect my 12v 200ah powerqueen to a new powerqueen 12v 200ah in series so that i have a 24v system.do i need a balancer?some say yes and some say no...
Yes, batteries in series require a balancer. Overtime the voltages of the two batteries will drift away from each other. That's why there is a BMS in every battery to balance the individual cells in series inside of a battery.
An interesting video would be one where the solar panels and batteries are together on a ground mount pad, and then the inverter is remote (100+ ft away) by the panel and grid connection, perhaps in a garage that is too small to also install batteries into.
It would be interesting to see the calculations for whether it would make sense to do this transmitting 48v DC over a long distance, or if there is a good way to boost the battery voltage for the long run, or if the most practical option would be to just invert to 120v AC at the pad and just transmit that to the house.
That would be a very bad idea. The cables from batteries to inverter are large, so the cost of these cables and voltage drop do not make up for that. It's better to have the wires from the solar panels longer because the voltage is higher, thus less voltage drop and thinner wires are required.
@@cleversolarpower It would be interesting to see a video comparing the pros and cons of placement of the various components at different distances.
I see a lot of people wanting to put batteries near ground mount panels a far distance from the house because they don't have room in their roof and garage.
For a scenario like this, you could also show whether AC coupling to the panel in the garage or 48v DC lines to an inverter in the garage would be better or worse.
I am confused by the topic of this video, as I can't find any battery manufacturer that discusses or recommends using dissimilar capacity batteries in either a series or parallel configuration.
It's mostly too complicated to explain, and to avoid confusion and liability issues, they do not recommend doing so. It's NOT possible in series.
What is the cost of these 100ah and 200ah Battery and
how much hour does 100 ah battery run 2, 32inch television with full efficiency
And how much time it take to charge and their weight
And how to control the heat of the battery
1. I have posted the batteries in the description.
2. you can check out my video 'How Long Can a 12V Battery Run a TV?'
3. check my video 'How Long Does it Take to Recharge a Battery?'
4. no need to control the heat as lifepo4 batteries are 98% efficient, so almost no heat generation.
Why do your videos use a safety factor of 1.25 instead of 1.2?
1.25 is from NEC (national electric code) handbook.
What I learned from this is to use matching batteries and skip the math.
You can perfectly use different capacity batteries, as long as the cable is thick enough. As I mentioned you can use the same cable thickness as the inverter, no worries.
Or use an amp meter .and also skeep the math.
@@ilanozana9652 That requires you to have wires already
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12V 100Ah battery in video: amzn.to/3Xwv12w
12V 200Ah battery in video: amzn.to/3ARErwO
12V 200Ah 5% discount EU use code 'clever': cleversolarpower.com/go/eu/red12V200Ah