Charging individual battery modules from a disassembled pack?

1181 Views 16 Replies 8 Participants Last post by Junk e, Feb 20, 2022

Junk e

Discussion Starter · Feb 18, 2022

I have a 2015 Fiat 500e with a bad battery pack (that is still under warranty but fiat refuses to replace it) and I have a spare battery pack that is also bad. These packs are discharged (common issue with the 500e). what I'd like to do is disassemble the packs I have and try to save the modules. If I could charge the pack without disassembly that would be great but I fear some of the modules may be bad. I'm hoping I have enough good ones to build one pack.

is there a prefered method to charge a assembled pack vs individual modules? I still have to figure out how many cells each module has and how much voltage each module should have. Is there a minimum voltage needed before i start to charge? What equipment is needed to charge?

I'm new to this so any other info is very welcome as well. Thanks everyone.

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remy_martian

· #2 · Feb 18, 2022

Your bms might get upset if it sees one cell ramping up in charge while the other cell friends weren't invited to the party.

For a number of reasons, including getting killed, disconnect all the cells, then constant current charge them, one ar a time, physically removed from the pack, to 3.5V.

Miss the window to shut off the charging and you'll have the 4th of July in your garage.

I would do this kind of futzing outside, away from everything, including the pack of other cells. Water hose nearby and ready to use.

What you're doing is risking electrocution and is a major fire risk, especially with dead cells.

john61ct

· #3 · Feb 18, 2022

Water hose LOL will not be any use if you hit thermal runaway go fireball and start spouting toxic fumes & smoke

might help cool down a bit if you are monitoring cell temps while charging

but then you should've just stopped earlier.

Do not do this stuff inside or even near a building with human living spaces

Shed across the lawn or down the driveway, maybe. Middle of pavement area, dirt yard...

remy_martian

· #4 · Feb 18, 2022

Meh. I've lit off cells before, so stop being a drama queen about The Lithium China Syndrome 😂

I told them to f*ck with one cell at a time if they're going to be stupid about trying to recover dead cells or about messing with 400V without WANTING to disconnect it all to take its venomous fangs out...a garden hose should be able to cool one cell down vs a blazing pack...because there's no hurry and you can do one cell an evening while reading your latest edition of Pyromaniac Weekly.

Yes, it should never go there. But no accidental fire is supposed to. Garden hose. Cuz most people don't have an irrigation pump or fire hose at the house. Not in the house. At the house. If you must do really dumb things...

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piotrsko

· #5 · Feb 18, 2022 (Edited)

Brother who retired from fire department just watches them until they're cold, says he didn't have enough water available. Swimming pool might work.

For single unattached cells perhaps a hobby charger with adjustable auto turn off set to a low point but that will take lots of time. The better ones have a temp probe, adjustable current and panic button disconnect

Dxta

· #6 · Feb 18, 2022

You got to also have a fire extinguisher close by, just in case.
A fan blowing air on or across the modules, should also help with cooling.
I have replaced some modules on a Hyundai sonata hybrid modules gotten off of eBay before, and reconditioned the pack (lifepo).
What kind of charger(s) are you intending to use for your rebuild?

remy_martian

· #7 · Feb 18, 2022

Great. What process did you use to restore the "dead" cells?

piotrsko said:
Brother who retired from fire department just watches them until they're cold, says he didn't have enough water available. Swimming pool might work.

For single unattached cells perhaps...

Again with the drama...you're supposed to create evangelists here, not spread lore. ONE CELL, not a pack.

Good idea with the auto shutoff hobby Li-ion charger on a single unattached cell, though.

piotrsko

· #8 · Feb 18, 2022 (Edited)

Merely commenting that professional people do not consider lithium to be extinquish capable using water in any amount, at least not the 2500 gallons onboard the typical pumper fire truck which COULD BE more than a garden hose....

Crud, after ten plus years, no BMS, I am still waiting for the meltdown of my pack into a fireball as predicted by the pundits here. Hasn't happened yet, don't expect it ever will.

I also dont see the OP separating cells to do the recovery one at a time.

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remy_martian

· #9 · Feb 18, 2022

At least he won't live to see the fire due to electrocution...a 1.5V cell at the top of an otherwise working 400V stack is sitting at 398.5V

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piotrsko

· #10 · Feb 18, 2022

I appreciate you keeping a friendly positive attitude on this effort. Gawd knows there's enough consternation in the world already

lj516

· #11 · Feb 18, 2022

2

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While there is danger in reviving dead cells, the overall danger is very minimal when thermals are considered while charging. I used my stick welder providing 1-2C charging current on each cell until they are above 3V, then charge the group in series to 4.1ish. I use high current so that internal shorts are immediately obvious through heat.

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remy_martian

· #12 · Feb 18, 2022

Wow. I never would have thought a stick welder's output would be clean enough. Nice.

Is that 84 amps? Hard to tell it's not 184, lol.

brian_

· #13 · Feb 18, 2022

Junk e said:
I still have to figure out how many cells each module has and how much voltage each module should have.

Assembling snippets from other discussions, it appears that the 500e has 18 modules, but they are not identical... it appears that there are two different sizes (different numbers of cell groups in series, but of course the same capacity of each cell group): some 5S, and some 6S. With typical lithium-ion cell chemistry (not LiFePO4), nominal voltage would then be 5 or 6 times about 3.7 volts, with minimum and maximum at corresponding values (e.g. maximum over 4 V per cell or 20 or 24 V per module). jl516 shows a 5S module being charged (by his welder) in his post.

piotrsko

· #14 · Feb 19, 2022

lj516 said:
View attachment 127708
While there is danger in reviving dead cells, the overall danger is very minimal when thermals are considered while charging. I used my stick welder providing 1-2C charging current on each cell until they are above 3V, then charge the group in series to 4.1ish. I use high current so that internal shorts are immediately obvious through heat.

Never thought that way.
1-2c charging isn't considered that fast in the hobby battery business. How fast do they get to too hot to touch (approx 125 degrees F)? Or is it obvious immediately in a cell pack? How do you stop the process when a bad section is found

reiderM

· #15 · Feb 20, 2022

1C charge rate for EVs generally falls under the category of "fast charging." 2c charging, a lot of EV batteries won't be able to sustain that without substantial active cooling.

john61ct

· #16 · Feb 20, 2022

Depends on the chemistry, mass/volume, packaging. And longevity preference.

Hobby LiPos are tiny, fragile thin skin and many hobbyists happy to get a couple dozen cycles since discharge rate can be 30+C continuous

so 2C and higher is not that fast between races out in the field.

LTO as widely used on urban buses, lasts 10,000 cycles even when charged at 5+C, can do a 5-min refill at a passenger stop every hour or two.

But standard EVs the packs are massive, insulated do not dissipate the heat well, and longevity in daily use for years expected.

Junk e

Discussion Starter · #17 · Feb 20, 2022

2

I checked the voltage of the entire pack yesterday by measuring voltage at the contactor on opposite sides shown in the picture circled in red. I had 16.51 volts for the whole pack

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