Author Topic: Can anyone repair Li-ion battery circuit? (Read 49,454 times)

Fred Nerd · « **on:** February 21, 2011, 10:57 AM »

I'm a carpenter as a day job, and I had a Makita 18v lithium ion battery fail on me today after being drained too far.
Which made a conversation topic and I found out the following info:
This is a VERY common problem; there are heaps of dead batteries out there.
Often its a case of the charger saying it HAS to be dead because its so low, but actually it isn't, and if you can trickle a bit into it, then it will work again.
Also, there are plenty of sites on the net showing you how to pull them apart and replace the faulty cell.

BUT, here's the killer: there is an on board circuit in the battery. And if you get a 'fail' 3 times in a row, it stops it from ever trying to charge again.

Now, if someone with a bit of circuit knowledge can find out how to remove the block, there would be good money in restoring old batteries. And/or it would help a lot of people (new batteries are about $200 in Australia, and there's only a one year warranty on them)

Anyone want a project?

Fred

Clara Listensprechen · « **Reply #1 on:** February 21, 2011, 05:50 PM »

I've got more projects than I can handle at the moment but I've never heard of a circuit on a battery (cell). I can diddle with circuits but that sounds like a microcircuit totally defiant of the soldering iron. But you have my curiosity up--I'm definitely gonna do more research on that.

Nicads and metal hydrides have an inherent characteristic like that, without any extra circuitry as it happens. Lead-acid batteries require deep cycling to avoid going bad, so each type of battery has its own inherent peculiarities even without circuitry.

I found this just now:

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...Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.

Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.

Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the battery should be partially charged during storage. The manufacturer recommends a 40% charge....

Apparently, there is an additional safety issue regarding what you suggest and so I would advise against it.

Fred Nerd · « **Reply #2 on:** February 21, 2011, 07:43 PM »

There is a safety issue if you try to revive a dead cell, but the killer is that I took my battery and connected the teminals to another, charged battery, and let them equalise for an hour or so, and then dead one had a healthy (probably about 1/4) amount of charge. And I imagine that if the circuit hadn't blocked it, it would now be a working battery.

Here's a link to what's inside: http://hackaday.com/2010/01/12/makita-battery-pack-repair/

From the pic I guess its micro circuits, so its probably not a soldering job, but there might just be a jumper or something simple, or make a pc interface (apparently Makita can read the amount of times its been charged, so there' s bit in there).

And its a very common problem, there are heaps of dead batteries out there, if you want one to play with, I could send you one, but international postage might be high. Are you friends with anyone in the construction industry? They should be able to get one to pull apart.

Clara Listensprechen · « **Reply #3 on:** February 21, 2011, 09:20 PM »

Thanks for the link. The pic shows a battery pack that clearly has a cell leakage problem on the right side of the pack. I've disassembled many similar packs to keep the individual cells that are still good and use them for different purposes. Temperature is an issue with these cells and the connections between them are micro spotwelded. Before you defeat the circuit board, you need to replace the leaky cells or the other good cells will go bad and/or you ruin the circuit board from faulty operation.

In NICads I've successfully soldered the spotwelds back to fresh cells using a low-watt soldering pencil (45 watts, tiny tip, with heat sink arrangements), but it's my understanding that the Li Ions are much fussier. In my considered opinion, I think your best option for salvage is to just separate the good cells from the bad and use them individually in other things. That pack, as a pack, is shot (except for maybe the circuit board).

I'd sure like to see the schematic of that board, but I'll betcha it's proprietary.

This cautionary comment on that article is wise to make note of:

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It’s a bad idea to replace a single cell in a pack like this. If the cells don’t discharge evenly you can get in a situation where a strong cell reverses a weak cell. That will drastically shorten the life of the reversed cell or even destroy it (depending on which battery chemistry it is).

This is the same reason why instruction manuals for everything state to use only matched, new batteries when you replace them. You can get away with a lot in something like a remote control, but in a high-current application you have an opportunity to rupture a cell.

This is further debated in the comment thread, but having experienced overheating batteries and batteries that went boom, it'll take experience for those in-favor guys to change their minds. I'm hoping it doesn't have to come to that for the wise who find it better to learn from the mistakes of others in preference to making their own.

Fred Nerd · « **Reply #4 on:** February 22, 2011, 11:08 AM »

Thanks,
The thing is, I don't think the battery is dead. I haven't taken it apart to see, but I think the charger just registers it as too low, it HAS to be dead, when in fact if it got above their cutoff voltage, it would come good again.
I have seen a charger give a 'dead' sign a few times, and just taking the battery in and out fixes it.

As you say, the chip will be all in secret code, and impossble to reset, but if you could, you could save a lot of batteries, I reckon.

Clara Listensprechen · « **Reply #5 on:** February 24, 2011, 04:30 AM »

You can't save a leaky battery, alas. What you say is true about a lot of rechargeables, as it happens. What you're doing is putting a charge on the battery's electrodes and its internal chemistry re-forms the dielectric somewhat. An auto's lead-acid battery will recharge somewhat from a bundle of AA cells simply because there's a charge applied to its plates enacting a chemical process. It won't charge enough to be able to deliver the full rated current, but you might could get it to crank your engine a couple of times if you've got a small car with a small starter and an easily turned engine. Get the engine started and the system charges the battery with full current delivery.