Replacing worn out LifePo4. Some help please.

[acollins22]

Hello everyone,

I have recently started on my first EV project, the recommissioning of a Citroen C1 Evie from 2009. It has been pointed out to me that it is a lost cause because of its faults but being a hands-on rather than off-the-shelf kind of guy and also because it owns me money, I'm in up to my neck.

The first problem is the batteries which were beyond reclamation and have been scrapped. It's in their replacement where I need your help.

There were two trays of Thundersky 160AH/3.2V LifePo4 cells. Sixteen under the bonnet, 9 under the rear seats where the fuel tank would have been. They were wired in series and so I should have 80V. There are 400A fuses in each battery tray.

I have sourced a number of EIG C020 LiPo cells (20AH/3.2V) that I plan to use but I could do with a bit of guidance.

A bit more background... There is an AC charger in the car, a 12V DC/DC converter, a bespoke BMS (monitor and balance only) and Curtis motor controller.

If I was to replace the LifePos with the same power LiPos, I would need 22S8P which would give me about the same power at about 81V. Close enough for folks.

I would like more power though and here's where I have dilemmas.

I would like 200AH cells rather than 160 provided by Thundersky. To get that, the obvious way is 22S10P but I an not sure that 10 cells paralleled up is a good idea. Is it?

Failing that, I could go for two strings of 22S5P but would need to replace the existing BMS with two new ones. Is that wise? Would I need some more control kit than just two BMSs in parallel?


What do you think?


Thanks for your help.

Andy.

 

[fechter]

It should be no problem to put as many cells in parallel as you need. Look at a Tesla. It has dozens of cells in parallel. That way you can use a single BMS.

 

[john61ct]

There were two trays of Thundersky 160AH/3.2V LifePo4 cells. Sixteen under the bonnet, 9 under the rear seats where the fuel tank would have been. They were wired in series and so I should have 80V.

Yes nominal at 25S

What exactly does the charger put out? 86V? 91V?

Can test the full profile and termination logic with a small bank of LFP cylindricals.

Assuming you want to repurpose the charger. What model? Is it adjustable?

Same with DCDC, check input range?

BMS likely not reusable?

_______
> I have sourced a number of EIG C020 LiPo cells (20AH/3.2V) that I plan to use but I could do with a bit of guidance.

LiPo ? with 3.2V rating seems should be LFP

do you just mean pouch format?

Google says

Nominal voltage = 3.65v

That needs clarifying for sure.

______
I would like 200AH cells rather than 160 provided by Thundersky. To get that, the obvious way is 22S10P

So same chemistry as original, good batteries.

But why 22S if original was 25S ?

And 200Ah cells are pretty big, you're really talking about lots of them in parallel?

I think would not fit

> but I an not sure that 10 cells paralleled up is a good idea. Is it?

As long as all your paralleling is down at the lowest 1S voltage level, not strings, no problem however many Ah you want.

I advise against paralleled strings and multiple BMS.

 

[acollins22]

Thank you fetcher that's great.

It should be no problem to put as many cells in parallel as you need. Look at a Tesla. It has dozens of cells in parallel. That way you can use a single BMS.

I didn't know that about the Tesla. Do they have some kind of fuse-able links between the cells that are paralleled do you know or just bus bars?


Cheers,

Andy.

 

[acollins22]

Hi john61ct.

The charger has a sticker on to say that it was adjusted to 93V in 2014. I haven't checked it yet.

There were two trays of Thundersky 160AH/3.2V LifePo4 cells. Sixteen under the bonnet, 9 under the rear seats where the fuel tank would have been. They were wired in series and so I should have 80V.

Yes nominal at 25S

What exactly does the charger put out? 86V? 91V?

BMS likely not reusable?

I don't know anything about it yet. I thought if I was going down the two BMS/strings route I had better get identical BMSs.

I've nothing against the fitted one. It doesn't have any low/high temp cut off. I'm not sure if that matters at this point.

LiPo ? with 3.2V rating seems should be LFP

Sorry, that's my mistake. They are 3.6V

That's why I was talking about 22S10P

And 200Ah cells are pretty big, you're really talking about lots of them in parallel?

I think would not fit

There is some unused space that I can use.

As long as all your paralleling is down at the lowest 1S voltage level, not strings, no problem however many Ah you want.

I advise against paralleled strings and multiple BMS.

That's great.

Thanks very much for your advice.


Cheers,

Andy.