Help needed with mixing lifepo4 brands in parallel. NO CHOICE. Please read.

[phantomreaver]

Hello and apologies as I now realize this is in the wrong section as I never really use forums. I need some advice on finishing my battery bank. This is my first time trying my hand at solar. I just bought two Redodo 12.8v 230ah lifepo4 batteries with 150a bms. I planned to do a 24v system with two sets of two 12.8v 230ah batteries so I would have a 24v 460ah bank. I couldn't afford the other 2 batteries I would need for my bank all at once so I waited a month and now those batteries have apparently been discontinued and I can't seem to find any that are close in spec. This will be a 24/7 off grid almost 12kwh system. (If I had the other 2 batteries of the same type).

I know everyone says to never mix batteries but without the full capacity my project is pretty much ruined? What can I do?

Below images are of the battery, what connections are supported and the battery setup I was attempting to go for from the manual.

 

[MisterSandals]

Is there a reason you cannot still make a 24V system (desired, no?) with your 2 Redodo batteries?

 

[phantomreaver]

I live in Michigan where we can go quite a few days without sun. A 10kwh capacity would be the bare minimum to be off grid 24/7 without fully draining the batteries and I am stuck at 5.9 kwh.

The plan was to try my hand at this first when I had the money saved up, make sure everything worked correctly then add the other 2 batteries when I could afford to do so. Unfortunatly as I said they stopped selling them within a month of my purchase.

 

[Rocketman]

While not ideal, make sure the battery being added is about as same as you can get. Same chemistry (LiFePO4?), same number of cells and both both have the same charging voltage and start balancing about at the same point.

Also, if you are running a 24v system- it is much better to have a 24v battery- rather than two 12v in series. The reason is the single bms can balance all the cells in the battery- rather than just 4 of them. Also, you don’t end up with the two 12v batteries having different states of charge.

Good Luck

 

[42OhmsPA]

You can parallel pretty much any other brand as long as it's lifepo4 8s.
Why not pick up 8 cells and a BMS and make your own for ~900? You're already confident in connecting the 12v in series to make 24v....

 

[phantomreaver]

That is what I am trying to figure out. I see conflicting answers on whether I can add batteries of differing ah and bms capacity in parallel. I cannot seem to find any other batteries that are 230ah with 150a bms and do not have the confidence yet to try assembling my own battery.

 

[phantomreaver]

While not ideal, make sure the battery being added is about as same as you can get. Same chemistry (LiFePO4?), same number of cells and both both have the same charging voltage and start balancing about at the same point.

Also, if you are running a 24v system- it is much better to have a 24v battery- rather than two 12v in series. The reason is the single bms can balance all the cells in the battery- rather than just 4 of them. Also, you don’t end up with the two 12v batteries having different states of charge.

Good Luck

Thank you for the reply. The problem is I cannot find similar spec batteries even though they wrre just available a month ago. I realize that it is better to just go straight 24v with the batteries but I am doing this on a budget and buying two 12v over one 24v saved me about $400.

 

[Rocketman]

You can mix a 230ah battery with a 100ah and a 280ah battery for a three battery setup - like I said it is not ideal - but as long as you are not pushing the limits you should be fine. Just make sure they are all LiFePO4.

Yes try building your own 24v battery- you will save money and it really helps you understand everything.

 

[phantomreaver]

You can mix a 230ah battery with a 100ah and a 280ah battery for a three battery setup - like I said it is not ideal - but as long as you are not pushing the limits you should be fine. Just make sure they are all LiFePO4.

Yes try building your own 24v battery- you will save money and it really helps you understand everything.

I see thank you for your help.

 

[JBertok]

Any batteries in series, of any chemistry, need to match each other in spec and lifecycle. The main concern with different capacities in parallel is minimizing millivolt differences between the batteries under load.

For example, say you have a parallel battery bank consisting of:
- Two 230Ah 12V units in series
- Two 100Ah 24 units
- Total of 430Ah @ 25.6V (24V nominal), = 11kW.

If I had a situation like this would be trying to balance the loads between the providing capacities of each of the three parallel batteries/sets so they experience equal charge and discharge states. You've no doubt read here that connecting each battery to common busbars with identical lengths and gauges to each battery is optimum. Well, busbars in a mixed-capacity scenario will only work right if the cable gauges and lengths are calculated and adjusted to equalize resistance-induced voltage-drop measured at each of the battery's terminals, under load. That would be difficult to get right and is likely to be endlessly problematic in keeping them balanced. Instead, a parallel cascade/daisy-chain would be preferred.
In the above example, the 230Ah in series would be carrying about 53.5% of the load, and each of the 100Ah units 23.25%.
Then, you have to de-rate the total battery bank ampacity to stay within BMS maximums based on that load distribution; it is not just a cumulative value of the BMS maximums. So, if the 12V units have a 150A BMS, and the 24V units each have a 100A BMS, the 100Ah batteries cannot exceed 65A of load without exceeding the 150A rating of the 12V units. So, effectively the maximum amperage capacity is 280A with that example.

I'd wire them cascaded with no busbars (in that example) like this to keep everything in balance:

 

[chrisski]

There is a few people on here who have lithium batteries paralleled with mixed ah ratings. Stick as close to the capacity as you can. Some have batteries in parallel that are half the rating of other cells; they stay away from charging to 100% and avoid excessive discharge.

I do have concerns about putting two batteries in series due to BMS issues, unless the manufacturer states in documentation then that 12 volt battery can be put in series.

When I bring my RV out, I plan for 3.2 kwh power per day and being able to survive a cloudy day, so at least 6.4 kWh. I found I very rarely need that much power because the heat which is the biggest drain in the RV, so actually the battery bank could typically last days or weeks. IMO, you do have to plan for that worst case scenario.

 

[SolaroSsaurius]

If those are 2 12v batteries with 4 cells each, 230Ah, why not buy 8 extra 230Ah cells (easily available), and 2 BMS plus 2 boxes and 2 class T fuses and make 2 24v DIY batteries?

Basically you would end up with 2 quite similar batteries

Note: first evaluate very carefully the current batteries' cells in order to check if they could be reused (terminals, glues, ...)

 

[DIYrich]

DIY a 24v 230ah battery with 8 Eve LF230 cells.

I am paralleling 48v batteries of different capacity, and they work fine. Draw is proportionate to capacity.

 

[TimE]

Sell the batteries you have and do it properly.
For what you need, it would be easier to buy 16x280Ah cells and build two identical 8s batteries. Use a pair of 200A JK BMS with 2A active balance. You will have a far better set up, with two identical batteries.

 

[JJJJ]

There are still a large number of members who continue to invest in the DIY approach. A number of off grid members have shared their knowledge and builds over the years and they continue to work together well.

Granted the new technology is cool looking and comes in very nice packaging. I personally like the ability to update, repair and configure my cells in the manner I want.

 

[TomC4306]

12v, 230ah

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USA STOCK FAST UPS DELIVERY Docan 12V 105Ah Lifepo4 Battery Pack with with Bluetooth BMS and LCD Display Apply to: home storageColor: blackBuild in LifePO4 battery type: EVE 3.2V 230AhFecommend charging current: 50ADischarging current: 200AFuncation: JBD BMS +LCD scree

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Raw cells

https://www.docanpower.com/index.php?route=product/product&product_id=464