Lifepo4 Cell Robustness

[markcraven]

We have limited choice here in NZ for Lifepo4 batteries and pack sizes. I have two spaces available in my small Land Rover camper (no serious off roading). I have 400Ah lifeline agm batteries and know a 200Ah Lifepo4 pack is not big enough and I need at least 300Ah. Also since these are Synopoly cells and they don't recommend using greater than 200Ah cells due to structural integrity in mobile and marine applications I will need to parallel some packs. My option for space 1 is to parallel 2x200Ah packs. My option for space 2 is to parallel 3x100Ah packs. Would the 300Ah smaller cell option be better or will the 200Ah cells be robust enough? I also know for option 2 I will need another CellLog 8.

[BruceS]

I read somewhere that cells larger than the 100Ah ones 'can' have a bit of a problem that those under 100 don't. something about the thickness of the internal plates I think it was.
I think Terry recommends to use the 100's & build your 'battery' up with them.
Mark may I suggest you wait for Terry to comment as I think he builds the pack so that you only need to monitor each 3.6V (nom) cell. (3 of cells in each 'cell')
eg. cell, cell, cell + cell, cell, cell + etc etc
So for 12V you only need half of the cellog unit. (Junsi)

[Busman]

See Sir Collyn's comments in the latest Wanderer, it is a big no no apparently (cause enerdrive or someone says so) to couple lifepo4 cells in parallel.

Sheet now I don't know what to do.

I have 64 cells like that in my 24 v pack and been that way for years with no problems, what am I gunna do now ?

William

[bagmaker]

Stop reading negative comments no matter who posts them??

[Busman]

And now no one at all can tell me why it is a bad idea.

Oh dear, what to do.

I know, blame T1, he was the one that suggested it, must be all his fault !

[El Gringo]

Hi Mark,
Please ignore those other 2 eejits..
My only comment really is that no matter which option, you don't parallel the pack, you parallel the cells.
In other words don't make 2 or 3 batteries, you just make one battery of parallel and series connected cells.
From my understanding though 100Ah calls are easier to control.

Cheers,

[Lance]

And now no one at all can tell me why it is a bad idea.

Oh dear, what to do.

I know, blame T1, he was the one that suggested it, must be all his fault !

Yeah, that silly Terry boy just goes about testing stuff himself rather than listen to all the experts.
No damn wonder he gets it right........ most of the time.........

[Mrcoolabah1au]

Very good

[markcraven]

Thanks for the advice so far. I thought I would have to build a custom pack of 3P4S but have read elsewhere that it is OK to parallel packs. Here is one article

http://nordkyndesign.com/assembling-a-l ... ouse-bank/

Just when you think you've got it sorted

[native pepper]

We have limited choice here in NZ for Lifepo4 batteries and pack sizes. I have two spaces available in my small Land Rover camper (no serious off roading). I have 400Ah lifeline agm batteries and know a 200Ah Lifepo4 pack is not big enough and I need at least 300Ah. Also since these are Synopoly cells and they don't recommend using greater than 200Ah cells due to structural integrity in mobile and marine applications I will need to parallel some packs. My option for space 1 is to parallel 2x200Ah packs. My option for space 2 is to parallel 3x100Ah packs. Would the 300Ah smaller cell option be better or will the 200Ah cells be robust enough? I also know for option 2 I will need another CellLog 8.

This is my opinion, which may differ from others. If possible stick with small cell sizes, they have less trouble and are easier to balance in a pack and you can see an example of this in tesla and other Ev's. Plus large cells (100ah up) can tend to heat up internally. The size of your pack depends on what you are going to use, I have a 120ah portable lifepo4 pack which is 10 years old, 700ah house pack, 9 years and 480ah in my bus, 4 years old. The bus has fridge, freezer, large tv, hot water, A/C, induction cooking and charges phones etc run by 1kwx24v solar.

You can parallel packs, but only if they have their own charge controller and balance controls on each pack and theoretically pack sizes should not go over 500ah, again larger packs tend to have heating and balancing problems. Why do you need 700ah on a camper, you have to realise you will get at least double the energy from lifepo4 compared to lead acid and all above 12v. Believe your link also states to parallel packs, you need separate controls on each pack as well.