mixing LFP with different capacities & manufacturer

[cx415]

A slightly different question than I've seen asked here before...

I have two 12v 100ah Weize LFP batteries, in parallel.
I want to buy one 12v 200ah LiTime or AmpereTime LFP battery.
And put the two sets together in series to make one 24v 200ah battery bank.

I've been able to locate enough information that tells me the charging and discharging voltages of the different manufacturers are exactly the same (Low/Under/Over/Float voltage disconnect/reconnect).

As a matter of fact, the user manuals for Weize and AmpereTime are almost exactly the same, word-for-word, down to their use of color and layout. Weird!

How's that sound to everyone?

I like the idea of having 12v LFPs because even though my new inverter is 24v, I'd like to be able to use the batteries with my old 12v inverter if needed.
I want the 200ah capacity, and also want to keep the weight limit of any individual battery to <50lbs.

Thanks!

 

[sunshine_eggo]

A slightly different question than I've seen asked here before...

I have two 12v 100ah Weize LFP batteries, in parallel.
I want to buy one 12v 200ah LiTime or AmpereTime LFP battery.
And put the two sets together in series to make one 24v 200ah battery bank.

I've been able to locate enough information that tells me the charging and discharging voltages of the different manufacturers are exactly the same (Low/Under/Over/Float voltage disconnect/reconnect).

As a matter of fact, the user manuals for Weize and AmpereTime are almost exactly the same, word-for-word, down to their use of color and layout. Weird!

How's that sound to everyone?

I like the idea of having 12v LFPs because even though my new inverter is 24v, I'd like to be able to use the batteries with my old 12v inverter if needed.
I want the 200ah capacity, and also want to keep the weight limit of any individual battery to <50lbs.

Thanks!

So you want to put two older batteries in parallel together and then put them in series with a larger new battery. It's VERY important that elements of a series string of batteries be as identical as possible. The last thing you want is for the 12V portions of the 24V battery to be problematic.

Hopefully, when stated that way, you might have some intuitive sense that it's not be best idea.

Would be WAY better idea to:

Put your 2X batteries in series.
Get 2X new 100Ah batteries and put them in series.

then put the two strings in parallel with each other.

That way you can be reasonably confident that the "old" 24V will have comparable elements and the "new" 24V will have comparable elements.

In this 2S2P configuration, EACH 12V could be monitored and checked without being masked by a 12V being in parallel with another 12V.

Lastly, if you ever need to use them with your 12V inverter, NEVER just connect the inverter to a 12V in the 24V. Parallel them into 12V and pat yourself on the back for not making a huge mistake.

 

[cx415]

Thanks for your reply @sunshine_eggo, I'll buy the 2 more Weize 12v 100ah batteries. Was trying to make it less cables to wire up but doesn't sound like a good idea.

>NEVER just connect the inverter to a 12V in the 24V. Parallel them into 12V...
Definitely would not do that. But thanks for pointing it out.

 

[sunshine_eggo]

Thanks for your reply @sunshine_eggo, I'll buy the 2 more Weize 12v 100ah batteries. Was trying to make it less cables to wire up but doesn't sound like a good idea.

>NEVER just connect the inverter to a 12V in the 24V. Parallel them into 12V...
Definitely would not do that. But thanks for pointing it out.

Glad to hear. Not everybody realizes that, or they think some small device pulling from one 12V is fine. It's not.