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Discussion Starter #1 (Edited)
Hello my 2013 wheego life has a large pack of 36 3.2v 260ah winston prismatic cells but it sat for 3 years and completely discharged how should I recharge the pack? Can I bypass the bms (turns on at 80v) and put 120v dc into it directly?

More info in Production EV forum section; "Ultra-Rare 2014 wheego life" thread.
 

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There is no question if truly dead flat, the cells have suffered irretrievable damage, in the sense their longevity will be a fraction of what it would have been if cared for properly.

It is IMO very likely they are now unusable, will not hold decent capacity, of scrap value only.

Yes, an adjustable power supply direct to the cells is called for.

I would do this one cell at a time.

In your case advise at least consulting with an experienced professional as to the right protocol, voltage and current settings.

Otherwise start out low, say 3.2Vpc and at a .1C rate. Once 3.2 is reached, isolate for an hour, measure V and report back here.
 

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Discussion Starter #3 (Edited)
There is no question if truly dead flat, the cells have suffered irretrievable damage, in the sense their longevity will be a fraction of what it would have been if cared for properly.

It is IMO very likely they are now unusable, will not hold decent capacity, of scrap value only.

Yes, an adjustable power supply direct to the cells is called for.

I would do this one cell at a time.

In your case advise at least consulting with an experienced professional as to the right protocol, voltage and current settings.

Otherwise start out low, say 3.2Vpc and at a .1C rate. Once 3.2 is reached, isolate for an hour, measure V and report back here.

Thanks for the advice your reply is much appreciated. Any chargers you'd recommend for lifepo4? one that can do multiple cells because 36 will take a long time one at a time.
 

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Power supply with ability to vary the max current and set voltage very precisely. HP, Agilent, Sorenson, TDK (Lambda etc).

Do not do in a flammable space, back shed or outdoors.

Maybe do the initial low-current lower-voltage testing wired all in parallel, but to do accurate constant-current load / capacity SoH testing really need to work at the individual cell level.

A 20-hour load test is not required as with lead since Peukert is so close to 1.0 with LI, maybe 4-5 hours?

Buying or renting multiple PSUs helps speed things up.
 

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To echo the -
Do It OUTSIDE on a concrete or gravel surface

Your chances of having something go pop ARE AT LEAST 100 TIMES NORMAL!
 

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Discussion Starter #6
Decided to charge the whole pack in the car, as it is around 60v not as bad as I thought. using a 4a 120v dc charger

Would it be wise to at first only use 60v, then slowly ramp up the voltage volt by volt and current ? Or just put 120v into it and it should be fine?
 

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Well 4A into a 260Ah pack will barely keep up with self-discharge :cool:

3-4 days?

Really should be monitoring with known-good instruments, in this case cell temperatures will stay ambient but watch anyway, and of course climbing V

Going that slow will make things tedious.

I would Bulk / CC only, cut off at reaching 120V, no Absorb / CV and test capacity.

If you can get to 122V that will be very close to Full.

Not go over 123V until you get a faster charger, 80-100A, in which case 124V then hold CV until acceptance drops to say 10A would be OK for longevity.
 

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Discussion Starter #8 (Edited)
Well 4A into a 260Ah pack will barely keep up with self-discharge :cool:

3-4 days?

Really should be monitoring with known-good instruments, in this case cell temperatures will stay ambient but watch anyway, and of course climbing V

Going that slow will make things tedious.

I would Bulk / CC only, cut off at reaching 120V, no Absorb / CV and test capacity.

If you can get to 122V that will be very close to Full.

Not go over 123V until you get a faster charger, 80-100A, in which case 124V then hold CV until acceptance drops to say 10A would be OK for longevity.
Thanks a lot john.

https://www.easycalculation.com/physics/classical-physics/battery-charge.php

According to this, 3 A 120v it will take about 80 hours to charge.



I think if they have slowly been discharging to around 60v, then lower amps, slower charge would be better no?

also trying to pick out a charger, would something like this work?

https://www.ebay.com/itm/Astec-Powe...366869&hash=item25f27573aa:g:L8oAAOSwGW9axTQK

looks like good quality electronics for less than a $300 adjustable psu.

this one is from china but only $70 and looks simple enough, what could possibly go wrong? Looks like it adjusts volts only not amps.

https://www.ebay.com/itm/DC-0-120V-..._trksid=p2060353.m1438.l2672&autorefresh=true
 

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Lower current means you need to stop at the lower voltage to avoid overcharging, fast rates you can go higher V terminating, because you get the drop to resting V.

When the total charge cycle current is lower than what you'd use for an Absorb / CV stop point you need to be even more conservative.

And an automated stop control becomes more necessary with such a long cycle, just because you're more likely to fall asleep, unless you've got a crew taking shifts.

But yes if you hope to resuscitate, get a little more lifetime gentler is good at least for the early stage, first few cycles, just avoid going all the way to the top.

A $3-400 charger is just the minimum baseline I'd expect, sure you can get lucky, or even try cheap Chinese off eBay, just make sure you keep watching the cycle, and do it outside far from anything you care about burning.

And of course voltage adjustability is important, but getting high amps for safe production use more so, 60A really would be my minimum for a big working pack IMO.
 

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Discussion Starter #10
Lower current means you need to stop at the lower voltage to avoid overcharging, fast rates you can go higher V terminating, because you get the drop to resting V.

When the total charge cycle current is lower than what you'd use for an Absorb / CV stop point you need to be even more conservative.

And an automated stop control becomes more necessary with such a long cycle, just because you're more likely to fall asleep, unless you've got a crew taking shifts.

But yes if you hope to resuscitate, get a little more lifetime gentler is good at least for the early stage, first few cycles, just avoid going all the way to the top.

A $3-400 charger is just the minimum baseline I'd expect, sure you can get lucky, or even try cheap Chinese off eBay, just make sure you keep watching the cycle, and do it outside far from anything you care about burning.

And of course voltage adjustability is important, but getting high amps for safe production use more so, 60A really would be my minimum for a big working pack IMO.

Thanks for the replies all the help has been much appreciated. A 60a charger sounds nice but I don't have $500, the goal is to get the pack charge above 80v so the bms can take over but 115-120 sounds good too.

i think ill try the 4A $70 Chinese, 3-4 days to charge isn't that bad.
 

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goal is to get the pack charge above 80v so the bms can take over but 115-120 sounds good too
What do you mean by the BMS taking over?

At 80V you're only at 2.2V, won't be useful for anything at all practical.

In fact, those cells should never be allowed to go below 3Vpc, treat that as 0% in practice.

Once you're charging to somewhere near Full, as outlined above, the resting voltage range between 3.05V and 3.2 or so is really where they should remain for the rest of their useful life,

if any.
 

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Discussion Starter #12
What do you mean by the BMS taking over?

At 80V you're only at 2.2V, won't be useful for anything at all practical.

In fact, those cells should never be allowed to go below 3Vpc, treat that as 0% in practice.

Once you're charging to somewhere near Full, as outlined above, the resting voltage range between 3.05V and 3.2 or so is really where they should remain for the rest of their useful life,

if any.
bms wont charge car when it falls below 80v. Otherwise id just plug it into the wall and let it charge.
 

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Well BMSs don't actually charge as such afaik.

So you are saying, besides the charger you've been talking about, which you've wired so that it bypasses the BMS, that

there's also another charger built into the vehicle, which you don't know how to hook up to use getting it to bypass the BMS.
 

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Discussion Starter #14
Well BMSs don't actually charge as such afaik.

So you are saying, besides the charger you've been talking about, which you've wired so that it bypasses the BMS, that

there's also another charger built into the vehicle, which you don't know how to hook up to use getting it to bypass the BMS.
There are 3 chargers in the car controlled by bms. They wont charge the batteries below 80v.

and no, I never tried bypassing the 3 chargers on the bms to charge the pack.

This is likely possible but there are no instructions on how to do it and I don't want to damage the car any further.

the original problem with the car was it wouldnt charge, so it was left sitting, indicating perhaps 1 of the 3 chargers failed, or some other component, or a cell in the pack.
 

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You are taking serious risks -

I hope the car is on concrete a few meters from any buildings

I would be removing the whole pack and charging individually with a lot of monitoring
 

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My experience with very low voltage LiFePO4 cells is that a very small current will quickly bring them up in voltage - unless they are well and truly dead. Best way is to look at individual cells (which you should probably do anyway) and see if they respond. You know the pack is low : do you know if this is because all the cells are low or could it be half the pack is sitting at 0 volts? (can 't remember if you have checked this yet)

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Yes, break the pack apart and treat each cell independently is the ideal.

OP apparently is not able to afford the proper gear to do this.

But even at the pack level with nothing but a good ammeter, should with info on that setup, be able to bypass the BMS and live - troubleshoot a restore attempt using one or more of the onboard chargers.
 

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Discussion Starter #18
You are taking serious risks -

I hope the car is on concrete a few meters from any buildings

I would be removing the whole pack and charging individually with a lot of monitoring
ahha well i think charging em all up at once relatively quickly is way less risk than trying to wire up 36 little cells individually, but u are right its probably best to do it that way for accuracy and cell health.

I think the pack is only around 60v, which is half of its full charge.

Yes, break the pack apart and treat each cell independently is the ideal.

OP apparently is not able to afford the proper gear to do this.

But even at the pack level with nothing but a good ammeter, should with info on that setup, be able to bypass the BMS and live - troubleshoot a restore attempt using one or more of the onboard chargers.

I like this idea, as I wont have to buy a 3-500$ dc power supply. Ill research this a bit more before buying one.

Thanks again all especially john for all the help.
 

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No worries

I think the pack is only around 60v, which is half of its full charge.
Doesn't work like that.

Ah capacity and SoC are the relevant measures.

For that bank, 0% Full doesn't even start until resting voltage gets past 110V.

100% at 125V while fast-charging, then resting at around maybe 115V.

In between those two, only an Ah counting gauge can estimate SoC accurately, voltage tells you nothing.
 

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ahha well i think charging em all up at once relatively quickly is way less risk than trying to wire up 36 little cells individually...
No need to wire all the cells. Recharge each cell one by one. 2 per day is realistic and you will need 18 days.
It's long, but it's the best way to go. Little rc charger are cheap and work well. With some charger and few wires you can be able to balance 6-8 cell at same time.

Back to 2014 I had many Lifepo4 cells at 0.1V after I found my 156V battery pack at 4V.
I've tried to recharge individually every cells at 0.1V and over and many came back at regular voltage with 70-80% of original capacity.
I used some of there's on a e-bike and 12V back-up battery since with great success. There are still working well today.
Good luck
 
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