Mix Matching LiFePO4 Batteries

[SolarAntics]

Hi,

In a best effort to not kill myself doing what I love doing; I would greatly appreciate y'all's thoughts and advice on my plans to build my first solar power system; starting here with the battery bank. I have 3 different brands of lifepo4 batteries, with different capacities, that I want to combine to make a 24v bank.

(I have decided to keep my developmental progress recorded here on this first post for context and quick reference. The most current plan and system information is at the bottom - also here is a link to my full build - it's a work in progress - https://diysolarforum.com/threads/m...kw-lifepo4-2500w-inverter.95256/#post-1283778)

The idea is to connect two Brand A 100ah batteries in parallel to a first set of bus bars, and a Brand B 180ah battery to those bars - but in series connectivity to the bars to make 24v from them to the main bars.
Then, connect those bus bars to two main bus bars; which are connected to two Brand C 180ah batteries connected in series.

So this should look like a 24v 740ah battery to the MPPT charger.
(MEGA MISTAKES - please disregard this diagram)


REWORKED DUE TO MEGA MISTAKES ABOVE

I haven't boughten the yellow brand b battery yet, so it sounds like I will need to buy two 100ah to make another 24v pair to make two relatively close capacity groups.


EDIT 3
Thinking wiring bus bars to MPPT staggered like so - Is it better to wire the pos closer to one group versus the other due to group capacity variations (200ah vs 180ah)?


(Above has stupid wiring creating shorts)

EDIT 4 (based on recommendation of using a balancer)


EDIT 5 (fixed balancer mistake and created closer capacity groupings for parallel connection between 180ah group and the 200ah group)



EDIT 6 (Need to balance each series independently)


EDIT 7 - (I am stuck with Brands B and C 12v batteries, and find that purchasing a 24v battery is nearly the same as the cost of two 12v, a balancer, and the extra cabling. Save some space as well)


Context on full system build plan:

• For my RV

INVERTER:

• A 24v 2500w pure sine wave inverter by VEVOR
  • Most draw at one time would be the microwave/air fryer that pulls 1700w plus the RV lighting, water pump, some draw for the water heater startup, and a 45amp 120vac rv converter to charge and maintain an independent 100ah lifepo4. I will likely be adding a 12v fridge that would pull 60w (will plug into 120vac).

CHARGE SYSTEM:

• MPPT 24v charger is from LiTime rated at 30a output and 100v max input >> Connected to 800w total of solar (two 400w arrays in parallel (each - OCV=47.2v SCC=11a))
• The 120vac charger (LiTime 29.2v 40a) is isolated for charging by means of a generator for emergencies only.
  • I will cut the solar charger off to batteries using a switch when not connecting solar panels and/or using the generator (panels will be disconnected anyways). The 120vac charger goes to an outlet facing outside my rv (again to reiterate, this is completely isolated from any other system) to connect my generator to.

Questions:

Will this work, and does anyone have any advice?
When making parallel connections, those cables need to be of equal length?

Thanks for your help!

 

[SomethingAppropriate]

The yellow one as drawn is wired as a short.
That would blow up pretty quick.

Your capacity figures seems all off....

If you are wiring the blue batteries in parallel you have 12v 200 Ah.
I am assuming the pos and neg is also correctly wired in parallel so you have 380 ah at 12 volts on the left.
On the right you have 360ah at 12v

Put that in series and you can only use the lesser capacity of 360Ah

When wired correctly, You will have essentially a 360 Ah 24v battery.

 

[SolarAntics]

The yellow one as drawn is wired as a short.
That would blow up pretty quick.

I don't understand , what do you mean? Please disregard the diagram scaling. The length of the lines are arbitrary y'all.

 

[SomethingAppropriate]

I don't understand , what do you mean? Please disregard the diagram scaling. The length of the lines are arbitrary y'all.

In your drawing: yellow neg goes to red positive bus bar. where the 2 other pos go to. the pos of the yellow battery goes to the neg bus bar and would create a catastrophic short. All three batteries would be shorted here. With one in reverse polarity.

 

[SolarAntics]

I don't understand , what do you mean? Please disregard the diagram scaling. The length of the lines are arbitrary y'all.

The yellow one as drawn is wired as a short.
That would blow up pretty quick.

Your capacity figures seems all off....

If you are wiring the blue batteries in parallel you have 12v 200 Ah.
I am assuming the pos and neg is also correctly wired in parallel so you have 380 ah at 12 volts on the left.
On the right you have 360ah at 12v

Put that in series and you can only use the lesser capacity of 360Ah

When wired correctly, You will have essentially a 360 Ah 24v battery.

Shooooot. You are right. The capacities I marked are way off.. I have to go back to the drawing board. Thank you very much!

 

[SomethingAppropriate]

The green batteries look like they are in series. This should not be.
You have 3 batteries on the left making 12v
You have 2 on the right making 24v
Unless you are looking for 36v, this is wrong
Yup drawing board time.

 

[Supervstech]

Will it work? If wored correctly, AND a balancer is used, AND you NEVER draw down below 20 or so percent, it could be ok.

 

[SolarAntics]

So fortunately I have not purchased the yellow battery (Brand B) yet. Look like I will need to get 2 more 100ah batteries in series, and connect those in parallel with Brand A in series.

 

[SomethingAppropriate]

Also, something to consider.

You will have to keep an eye on every 12v group.
One battery could go out of spec before the rest get charged and disconnect. this would stop charging or worse... Dump all the current into 1 or 2 batteries. Then you would have to balance them before reconnect ion.

Your idea may turn into a lot of watching and maintenance.

 

[Supervstech]

Right side needs to ba all in parallel.
+to+ and - to -
Same with ALL batteries on left.

THEN the closest positive on ONE BATTERY on the left gets tied to the closest negative on ONE BATTERY on right.

This makes the entire bank in series.
Now take the furthest positive on right to a bussbar for the inverter positive.
And the furthest negative from the bank on left to the negative bussbar for the inverter.

 

[SomethingAppropriate]

Why are you moving to 24v?

If you dont need to DONT
If you need more power add another 12v inverter.

 

[SomethingAppropriate]

You were not too far off in your drawing. (except for the short)
I think you were trying to have a 24v series config on the left and another series 24v config on the right.

This would work but it would be even more of a headache that my proposed parallel/ series idea since you would have 4 groups to worry about instead of 2.

If you dont understand what I am saying, stick with 12v.

 

[SolarAntics]

The green batteries look like they are in series. This should not be.
You have 3 batteries on the left making 12v
You have 2 on the right making 24v
Unless you are looking for 36v, this is wrong
Yup drawing board time.

Reworked boss - please see updates above

 

[SolarAntics]

Why are you moving to 24v?

If you dont need to DONT
If you need more power add another 12v inverter.

Reduced current

 

[SolarAntics]

Right side needs to ba all in parallel.
+to+ and - to -
Same with ALL batteries on left.

THEN the closest positive on ONE BATTERY on the left gets tied to the closest negative on ONE BATTERY on right.

This makes the entire bank in series.
Now take the furthest positive on right to a bussbar for the inverter positive.
And the furthest negative from the bank on left to the negative bussbar for the inverter.

I had to completely change the diagram above; made some really egregious mistakes. Thank you for your help!

 

[Supervstech]

Reworked boss - please see updates above

It will be better if you follow my advice.

 

[SomethingAppropriate]

It will be better if you follow my advice.

Do you think there is a marked benefit to parallel/series is this config? OP seems sold on series/parallel.
Am I wrong in thinking it would be twice the headache?

 

[SomethingAppropriate]

Reduced current

I need sleep. Ill get back to you.

 

[Supervstech]

Do you think there is a marked benefit to parallel/series is this config? OP seems sold on series/parallel.
Am I wrong in thinking it would be twice the headache?

I dont see three different series setups being very easy to keep functioning.

Having the 180s, in parallel, the 100s in parallel, then series in one place makes balancing and maintaining easier.

 

[SolarAntics]

It will be better if you follow my advice.

Like this? I am under the impression mixing different brands of batteries in series is a bad idea due to internal resistances and BMS conflicts? That is why I was unfortunately opting for the 3 series. I was creating two groups because I am under the impression that you want to have similar capacities when combining in parallel.

 

[SolarAntics]

I need sleep. Ill get back to you.

Thank you very much

 

[SolarAntics]

I dont see three different series setups being very easy to keep functioning.

Having the 180s, in parallel, the 100s in parallel, then series in one place makes balancing and maintaining easier.

Is it bad to mix battery makes when creating a series?

 

[SolarAntics]

Like this? I am under the impression mixing different brands of batteries in series is a bad idea due to internal resistances and BMS conflicts? That is why I was unfortunately opting for the 3 series. I was creating two groups because I am under the impression that you want to have similar capacities when combining in parallel.
View attachment 253464

Wait won't this be a problem because the two banks are different capacities? (360ah and 400ah??) PLUS the issue of wiring differently manufactured batteries together in series?

 

[SolarAntics]

Or is this my best bet in attempts to equalize energy amongst all units:

 

[Supervstech]

No matter what you do, you are going to have difficulties.