jump starting caveat - Warning!

[ngant17]

Jump starting dead 60v lithium ion batteries. Caveat. Please note.

I just want to put out a warning for anyone trying to do a 'jump-start' trick to revive a dead lithium ion battery. I just tried out that technique to try on my 60v 4ah Greenworks battery. Although it seemed to be relatively harmless and possibly help the older battery when I hooked it in series to a lower amp-hour 60v battery (2ah).

However the real fireworks happened when I tried jumpstarting the old battery to another one of same 60v, 4 amp-hours. For whatever reason, it totally melted the contacts and clips I was using to connect both batteries, in addition to producing a intense shower of sparks from the old battery. Therefore, based on personal experience, using the same amp-hours between the 60v 4ah batteries for jump starts is a serious hazard and I would discourage anyone from trying this so-called “quick fix” to resurrect dead lithium ion batteries.

Tearing down the batteries and isolating bad cells is the smart and safe way to do rebuilds. And this specialist job should not be taken on by amateurs, which includes me.

 

[amberwolf]

What is a "jump start"?

If you mean hooking a charged battery to a dead one, directly, that's a REALLY BAD IDEA, and is NEVER RECOMMENDED.

EVER.


The all caps is just to make it absolutely clear to any battery noobs that come by in future to read the thread.



The only way I would *ever* recommend attempting to recharge a cell that has gone too low for a BMS to allow recharge on is to use a very low current, maybe a few dozen mA at most, until it has reached a point that the BMS will recognize it as "safe" again.

I would ONLY do this while being physically present, in a place where you can quickly get rid of the pack if something serious happens (because there are all sorts of reasons a cell might have gone too low, and some of them can give very unhappy results if current is pushed thru the cell again).

And also keep in mind that the cell may not actually *be* safe to recharge, or discharge, but you won't know this until something goes wrong with it later, however seriously or mildly.

 

[billvon]

This is a bit of an odd post.

I don't know anyone who has intentionally done what you describe (connecting a charged battery lithium ion battery to a dead one) for any reason. It's a bad idea for a lot of reasons, and I have not seen it done as a way to "revive a dead battery." Nor is "tearing down the battery" a good first approach.

A better approach:

1) Measure cell voltages. If cell voltages are at or near zero, then those cells are dead. Discard the battery (after discharging any remaining cells.) You may want to save any cell that is > than about 3V for another project if you like.

2) If all voltages are above about 2.7 volts then you can try to save it. (Battery voltage > 2.7*S is a way to tell this without opening up the pack, but is less reliable.) Get a power supply and set it up to trickle charge the battery at a rate of C/20 or less. If the BMS has a balance function then this should serve to rebalance the pack as long as charge rates are low.

3) If all voltages are above about 3.3 volts then charge normally.

Other notes -

If the battery pack is intended to take a balancing charger then you can do the same trick - but charge each cell slowly at C/20 via the balance connector until it gets above 3.3V, then you can go to a higher rate to complete the charge.

In many cases a battery pack that appears dead has just tripped its BMS. At that point opening it up to check cell voltages is prudent. In some cases this is good news; it means the BMS has protected the battery and it may be possible to charge it and reset the BMS.

 

[john61ct]

Maybe got that "technique" from a "what not to do" website?

 

[flippy]

well, that is about one of the dumbest things you can do with a battery.

might want to take up a differeny hobby, something a little less dangerous like making DIY explosives.

 

[Philaphlous]

Ive shorted 18650 before and dang.... Almost made me want to quit my hobby... I agree with reviving cells. It's super dangerous and FYI Sanyo cells and notorious for being "heaters" which they get hot when charging due to extended periods of time below minimum voltage and dendrites form which can cause internal shorts/self discharge/increased IR/Lower capacity....if the battery is at 0V or well under 2V per cell you should probably just pitch them.

 

[kcuf]

some bms disco under heavy discharge

refuse reset lacking external potential

connecting to charger normally resets bms

possibly done in field using 2nd battery

not wise unless understand current limiting

healthy cell groups

and short circuit protections

 

[fechter]

When Li-ion cells are over discharged below about 2.0v/cell, bad things can happen. If a pack was left sitting unused for a long time and the cells were slowly drained by the BMS or other parasitic load, they have to be "revived" by a very low current charge until they get back above 3.0v or so. Normal charge current into a really low battery will damage the cells. Charging at something like C/100 to bring them back into the healthy range is the only thing I've had success with. Even then, if the cells were over discharged at a high rate, like riding a bike, they may be toast.

Any "revived" packs should be charged very carefully in a fire safe location.

 

[ngant17]

Got this dangerous quick fix on someone's YouTube channel. Seems to be repeated by others on YouTube. Well, if I saw it on YouTube, it's gotta be true, right.

By this so-called "jump starting" technique, that is connecting a dead Li-ion battery to a good Li-ion battery to try and resurrect the dead, you are letting the charge trickle over to the dead battery and hope it will revive it. The other trick it to stuff in in your freezer overnight and that's supposed to fix it.

Jumping a 2aH 60v to a dead 4aH 60v seemed like it was working, no problem at first. But as I stated in beginning (hooked up in parallel not series, sorry for the mistype), when I next tried a good 60v 4aH battery to jump a bad 60v 4aH battery, all hell literally broke loose. Would have worked as an interesting fourth of July event, but no kentucky fried fingers fortunately.

Anyway, I've developed a healthy respect for DC electricity that I didn't have before. Hope a lot of people can read this FYI. Battery building and maintenance should be approached like high voltage electrical work. You want to be coming in on the level of an apprentice electrician with a master to guide you at very least, IMHO don't start this thinking this is a simple hobby as you can burn down the house very easily.

And I agree, you're doing something that's not very far removed from building IEDs and DIY bombs. Sure, you won't have BATF breathing down your neck but it's potentially just as dangerous. Although this may sound a little too communist to some, I definitely would like to see federal or state level regulation wrt Li-Ion battery rebuilders, amateurs need to be warned to stay out of this just to introduce safety and public security for common good. Right now it's like the Wild West and statistics are going to be pretty ugly as DC electric power hits mainstream more in future.

 

[amberwolf]

By this so-called "jump starting" technique, that is connecting a dead Li-ion battery to a good Li-ion battery to try and resurrect the dead, you are letting the charge trickle over to the dead battery and hope it will revive it.

It is

NOT

"trickle" charging anything.

It is allowing FULL current for the difference in voltage between packs, at whatever equivalent series resistances the two packs are at, to flow.

Let's say one pack is at 60v, and the other is at 45v, and the total packs' resistance is very high at 100mohm. That's 15v / 0.1ohm = 150amps. !!!!

The cells can't really output that much current without so much voltage sag it would significantly decrease the current, and the BMS probably won't allow it, and would shut the pack output down. So the actual current would probably only be just at the limit of whatever the BMS won't shutdown at, but it is still likely much more than the packs would normally be charged at, much less what it is safe to charge an overdischarged cell at.

If the BMS does not limit the current by shutting down, then much higher currents than otherwise will flow, and heating and cell damage (to *both* packs!) is even worse.)


That's why it is very dangerous.

Especially with a pack that has cells in it that have forced the BMS to shut it off and refuse charge in the first place.

The whole reason for the BMS to prevent recharge is that the cells are in a state where it is no longer safe to use the pack *at all*.

The cells may be damaged to where using them normally could cause a fire.


These are not little bitty fires.

These are big fires that burn your house or apartment building down.



Look around just here on ES, and you will see some results of cell problems (and pack construction or other problems) that have burned houses, bikes, cars, etc.

Often this happens during charging, whcih is usually unattended, making it very much more dangerous.

The other trick it to stuff in in your freezer overnight and that's supposed to fix it.

That's just going to chill the cells, which means that *for their temperature* they will have a higher charge state. As soon as they warm up they're back to the way they were...except they've been frozen so if there's any moisture in places there shouldn't be, it'll have formed crystals that could rupture membranes, etc. (probably won't, but if it does, you won't know until the next really bad thing happens).

But it doesn't fix anything.

At best, it "tricks" the pack into allowing you to recharge damaged cells, with unknown and unpredictable future consequences...but with a higher risk of fire, every time the pack is recharged.






There are "safer" ways to revive packs that won't recharge because the BMS has disallowed it for safety reasons, but just hooking up a charged pack to a dead one ain't one of them.

But there is always a risk of fire with recharging any cells that have dropped below the cells' LVC point. The farther they go below it, the worse the risk.

The higher the current recharged at after such an event, the higher the risk of fire.

The damage in the cells could grow worse with every charge cycle, and could eventually cause a fire at any time current is flowing thru the cells.


People *do* revive packs by slowly recharging individual cells that have dropped too low, at a few dozen mA or less, and end up being able to reuse the packs for a long long time afterward, and just ensuring they never let them get that low again. But it doesn't always work out.

 

[ngant17]

Just received a $96 rebuilt 60v 4aH Greenworks battery today. Will do the standard torture test on my mower/weedeater/blower to make sure it is a keeper. Also to count it as a legitimate tax deduction since it's primarily used for business.

Don’t know how the factory in North Carolina can ship these rebuilds out for that price, equivalent to a quality 60v 12aH $300 dollars. Must be a large automaton with slave robots. I know a local McDonald's is using robots to cook French fries at a major tourist area near Disney world. Your big city probably has one, too.

In fairness to those pioneers on YouTube who promote the ‘jump start ‘ trick, it did manage to put one green light on battery strength but that only ¼ power. I need to resurrect all 4 green lights but OEM charger simply refuses to cooperate with the dead battery. No one can rebuild it for $95 or less, so it's currently a paperweight.l

 

[flippy]

it is only 32 cells bought by the pallet from a non-brand factory. its well under 50 bucks in actual cost for them.

 

[larsb]

Tearing down the batteries and isolating bad cells is the smart and safe way to do rebuilds. And this specialist job should not be taken on by amateurs...

...In fairness to those pioneers on YouTube who promote the ‘jump start ‘ trick, it did manage to put one green light on battery strength...

Well, the others already said it but please also remove qouted text in relation to what your topic is.. keep the warning if you want to.. This topic's got nothing to do with reviving cells, isolating bad cells or rebuilds.

Fairness? Pioneers? It's just idiots killing batteries.

No need for a rebuild when the voltage has gone too low, only thing to do is to sloooow charge and hope for the best. Works sometimes

 

[neptronix]

Yikes. watch out for idiots on youtube and facebook. This place has enough electrical engineers ( hobbyist or professional ) to keep most of us out of trouble.

Generally on the internet, the more lo-fi the discussion format is, it seems like the higher the IQ is..

There are many reasons this is a bad idea and has a high chance of resulting in a fire, but there's no need to beat that dead horse.

 

[liveforphysics]

Tearing down the batteries and isolating bad cells is the smart and safe way to do rebuilds. And this specialist job should not be taken on by amateurs...

...In fairness to those pioneers on YouTube who promote the ‘jump start ‘ trick, it did manage to put one green light on battery strength...

Well, the others already said it but please also remove qouted text in relation to what your topic is.. keep the warning if you want to.. This topic's got nothing to do with reviving cells, isolating bad cells or rebuilds.

Fairness? Pioneers? It's just idiots killing batteries.

No need for a rebuild when the voltage has gone too low, only thing to do is to sloooow charge and hope for the best. Works sometimes

It does work sometimes, but make sure you do it outside and away from anything you wouldn't be happy seeing engulfed in flames. Even when it works though, those cells tend to be higher impedance and increased gas production rates reducing useful life afterwards, so it's only a partial win at best depending on the application.

 

[Matador]

Frozen cells will underperform during discharge in terms of capacity and discharge rate.

Charging cells that just were in the freezer is almost garanteed to completely destroy them by electropating... The freezer trick is the worst urban legend ever

 

[ngant17]

ok, You've successfully clue'd me in to this battery rebuild business. No more quick fixes with my 60v 4aH dead batteries. Thanx for all comments.

This 60v 4aH paperweight goes to Li Ion recycling bin.

Will continue to purchase 60v 4aH batteries for business and pleasure, with tax deduction. Have no use for single 60v 12aH single packs, sorry. DC voltage needs a purpose in life for me other than leisure and recreation.

No one can beat price and quality of this brand in 60v 4aH range. The 60v rebuilds hold up on my torture tests so far. So empirical evidence will outweigh personal opinion wrt this specific brand.

I'll continue to educate public on this forum and elsewhere on related safety issues with rebuilding Li Ion batteries. iow don't do it unless you're a pro.