I recently read a post where the person added another LiFePo battery to his system and another post responded saying that if you were charging the one battery with 30 amps that now you should now use 60 amps. Is this true and what is the reasoning?
Do you need to increase charge amps when adding more batteries?
- Thread starter B.T.
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Samsonite801
Solar Wizard
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Yeah, when you parallel 2 batteries say, the volts stays the same, so you aggregate the amp/hour capacity together (as a bigger bucket), and thus the charging amperage requirement would double (if you still desire the same charging rate to full SOC), otherwise it will take twice as long to fill the batteries with the original amperage, as you are filling 2 buckets instead of one (with the same voltage).
In contrast, when you series 2 batteries, now the voltage doubles instead (voltage aggregates, amp/hour stays the same), so you need a charger that can double the volts, but can use same amperage as you were using before, and the buckets can fill at the same speed with same amps, because the voltage doubled.
In contrast, when you series 2 batteries, now the voltage doubles instead (voltage aggregates, amp/hour stays the same), so you need a charger that can double the volts, but can use same amperage as you were using before, and the buckets can fill at the same speed with same amps, because the voltage doubled.
not needed, my 220ah lifepo4 is 2x 110ah batteries in parallel. I charge at same rate as before 8 to 12 amps. It does take longer but any lithium prefer to be charged at lower rates. But technically you can charge at higher rates if you really wanted to since the amps will be divided by the 2 batteries.
Samsonite801
Solar Wizard
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Yeah to augment what jony101 says, you don't necessarily 'have' to charge at higher rate if it's enough to meet your daily power needs, it just takes longer, as it is a bigger bucket to fill. You'll likely get more life out of the batteries by charging more conservatively.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Example.
Typical LFP battery is 1C Charge/Discharge rate capable with a preferred charge rate 0.5C max. At 100% SOC with every cell at 3.65V the cells will take 0A. There are higher capability cells which can go up to 5C discharge and High Charge rates but Big $$$. These are not what people use here. Each and every battery added in parallel needs to be able to be charged. The "cumulative" Amp Hours of all the battery packs in the bank is what needs to be addressed. So if you have 200AH collectively you will need 100A to reach 0.5C, for 400AH = 200A for .5C. Obviously, most folks don't get there unless they are doing a Large System with stacked SCC's and so on.
As Samsonite correctly states, in a properly paralleled battery bank the charge & discharge capacity is shared across the packs within the bank. IF each battery pack is identical (BMS, Cells, Config & Cell Quality [read as matched & batched] ) then the entire process is usually pretty flat across the packs. They will vary a slight bit but will always level up with each other (does not mean cell balanced).
If you have mixed packs, or standard Commodity cells (most of what is used here are these) then there will be fluctuations between the packs in the bank. Individual cell variances affect the specific pack which the BMS will react to accordingly by various means depending on the BMS.
I can use my own system as an example. I run a hybrid of LFP, FLA or Both.
My LFP is 2x175AH & 2x280AH (910AH) @ 24V. So this is a good example of how different packs in a bank can behave.
~ specifics: Chargery BMS8T-300's (passive balancing off), 300A-DCC's, QNBBM-8S Active Balancers on each pack.
Right now actually, I am using Genset to charge the LFP bank (all 4 packs) while also doing Pass-Through AC.
The Charger is pushing 100A out, I am using 6.6A in pass-through, so 93.4A is hitting "the Bank" of 4 LFP.
* This is part of a testing & abuse cycle I am running, so some numbers reported on BMS for SOC etc are out of whack.
As shown below, the individual packs are taking what they want at this stage. As they reach actual Full and the amps accepted reduce, the other packs "can" take it if needed which will increase their charge rates. * The higher rate the more heat is generated in the cells.
Click on thumbnail to expand.
Hope it helps a little.
Typical LFP battery is 1C Charge/Discharge rate capable with a preferred charge rate 0.5C max. At 100% SOC with every cell at 3.65V the cells will take 0A. There are higher capability cells which can go up to 5C discharge and High Charge rates but Big $$$. These are not what people use here. Each and every battery added in parallel needs to be able to be charged. The "cumulative" Amp Hours of all the battery packs in the bank is what needs to be addressed. So if you have 200AH collectively you will need 100A to reach 0.5C, for 400AH = 200A for .5C. Obviously, most folks don't get there unless they are doing a Large System with stacked SCC's and so on.
As Samsonite correctly states, in a properly paralleled battery bank the charge & discharge capacity is shared across the packs within the bank. IF each battery pack is identical (BMS, Cells, Config & Cell Quality [read as matched & batched] ) then the entire process is usually pretty flat across the packs. They will vary a slight bit but will always level up with each other (does not mean cell balanced).
If you have mixed packs, or standard Commodity cells (most of what is used here are these) then there will be fluctuations between the packs in the bank. Individual cell variances affect the specific pack which the BMS will react to accordingly by various means depending on the BMS.
I can use my own system as an example. I run a hybrid of LFP, FLA or Both.
My LFP is 2x175AH & 2x280AH (910AH) @ 24V. So this is a good example of how different packs in a bank can behave.
~ specifics: Chargery BMS8T-300's (passive balancing off), 300A-DCC's, QNBBM-8S Active Balancers on each pack.
Right now actually, I am using Genset to charge the LFP bank (all 4 packs) while also doing Pass-Through AC.
The Charger is pushing 100A out, I am using 6.6A in pass-through, so 93.4A is hitting "the Bank" of 4 LFP.
* This is part of a testing & abuse cycle I am running, so some numbers reported on BMS for SOC etc are out of whack.
As shown below, the individual packs are taking what they want at this stage. As they reach actual Full and the amps accepted reduce, the other packs "can" take it if needed which will increase their charge rates. * The higher rate the more heat is generated in the cells.
Click on thumbnail to expand.
Hope it helps a little.
Okay, thanks for all the great replies. I have my batteries in series and I prefer to charge conservatively to prolong battery life so I believe I will just continue to charge at the same (low) rate. If I get in a situation where I am not getting enough charging then I will up my amps. But as I understand from the comments there is no harm in keeping the charge rate the same and a 'slower" (lower amp rate) charge may actually be good in the long run.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Just a follow up on my wee test today. At one point, as the packs were starting to hit actual full, it was interesting to watch as the amperage was taken up by the remaining packs and they were cycling in the top-off process. At the end when one pack was taking the 95A and sucking it in I was watching the batt temps go up and get warmed a tad...
I tossed this together today, something far too many folks look for.
I tossed this together today, something far too many folks look for.
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