Can you connect two LiFePO4 batteries in parallel??
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- เผยแพร่เมื่อ 2 ต.ค. 2024
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Welcome to our channel! We’re excited to get into this with you guys and share some of our journey and knowledge of custom Offgrid Power Solutions.
We often get asked whether you can connect two LiFePO4 batteries in parallel or whether it causes problems. In this video, we're going to be talking through the topic of connecting multiple LiFePO4 batteries and talking through what options you have.
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Interesting experiment. It is indeed surprising at the difference in current draw between the two. What would've been an ideal experiment however is 2 batteries with differing capacities that are a bit more significant. Your experiment covered 200 and 202Ah which are extremely close. Would've loved to see maybe 200Ah and 280Ah in parallel and see how they perform.
The difference in amperage was expected, it is not a surprise.
The newer battery with higher discharge rating likely has lower internal resistance. Meaning it will tend to get less hot and be more "willing" to put out the amps you need. The Daly BMS may also have lower total resistance, however it is most likely the cells imo.
Do you think, the Daly MOSFETS have a lower resistance than the copper relay contacts?
Were the battery cables same length?
Hi
Thanks for another informative video.
Looked at your webshop for your switches/breakers and couldn't see them. Whats their ratings and what recommended brands/models to buy for safe operation?
The cable to the inverter is different and looks smaller on the one that’s pulling less amps.. so it’s inevitable.
Also. If you’re running over 150amps it’s a better not to run the full amount through the bms. .. just run it through the switch for the inverter. And the inverter direct to the battery.
Thanks for the comment. All the wiring on the system from the batteries to the inverter is 50mm2 (1/0AWG) apart from the two wires that come off the Daly BMS (going to the battery negative terminal and the bus bar where it then connects to a 50mm2 cable). I suspect that you are correct that is down to the resistance and distance of cables, etc.. that determines how much the inverter draws from each battery.
In terms of running the inverter directly to the battery, I probably wouldn't recommend that as the only protection you have is the low voltage disconnect on the inverter, but if something goes wrong on your inverter, you could land up destroying the battery by discharging it past a safe voltage. We've seen instances of inverters failing and the BMS "turning the battery off" to protect it, so this level of protection would be lost if it was wired directly to the battery bypassing the BMS.
@@offgrid_power if you run the switch for the inverter through a solid state relay to the bms in series. The bms will shut the inverter down.. get it ?
Yep, understand what you mean now. That would work. :)
So then how does the BMS detect Over-Current?
I have a 25V system with two batteries with Dali BMS.
One battery has a small capacity and the other has a large capacity.
In addition, the supply cable for the smaller battery is shorter.
I keep seeing that the smaller battery starts supplying power quicker and runs out quicker.
Then the larger battery takes the most power. I also see that the smaller battery charges on the larger battery.
I want to replace the smaller battery so that I have two batteries of approximately the same size.
I also want to adjust the cable length.
Internal resistance all that matters. BMS has no freaking point here. Same different current can be taken from the individual cell, thats why cell matching is important and BMS is essential for a multicells battery.
Thanks for the comment. 👍🏼
Draw is not even : Resistance is different cable wise OR internal batery => diferent draw.
Thanks for the input!
I recently built a 2nd battery bank (48V, same cell size & BMS as 1st), to put in parallel to an existing bank (~3 years installed/2.5 years usage). I've found that the older bank will draw more amps than the new bank. At some point, the 2nd bank's amps draw rises to match the 1st, then overtakes it. I've only needed to draw down to about 50% total SOC of the 2 banks (560Ah), I'll be interested to see what happens over winter next year.
This exact episode was quite obvious for me. But all you other videos were very helpful. You helped me (and not only me) both save money and get experience.
Thank you.
You're very welcome!
I rather just buy higher c rate cells an build a bigger bank an disable the discharge parameters. An charge an just monitor by temp. LIFEPO4 is almost the safest next to LTO which I highly recommend over the bigger clunky lifepo4 eve cells that can't even deliver much current.. or have a seperate bank for bigger amp loads. One for the capacity factor. Just my opinion nothing more
You share the exact knowledge needed for beginners. Thank you, guys!
Great to hear!
Great video. I have a 280ah lifepo4 batteri which i have Built with 4 cells in series so it becomes 12v. I am thinking of building one more similar pack and put it in paralell with my current pack so i Will get more amps, total 560ah 12V. Both with one separate daly bms and then also a victron smart shunt on the negative side so that i can easy se percentage, draw and other statistics from the battery.
So based om what you have Done this should totally be possible for me i guess?
Thanks for a nice video!
Of course, batteries can be connected in parallel. Why would you think, this was not allowed? Verify with the *manufacturer* of your BMS. Daly has a special Parallel comm board.
@@MrSummitville thanks. I think its allowed, i was just asking again to be sure. Thanks
Surprising results on this test. I was expected to see the winston discharging higher amps, not the other way. Looks like the blues are a strong contender.Thank you for sharing.
Hello
I have a question.
Can i parallel two deferent brand of lifepo4 100 amp battery for example 100 amp Timeusb brand with 100 amp Redodo brand . Thank you
It's generally not recommend to mix completely different BMS & batteries, but it depends on the BMS really. If they use a mosfet to protect the battery, you might be OK.
Not suggest connect in parallel if battery cells not matched…
Thanx !