Hobby King MultiStar Shocking Overcharge Tolerance

[LyonNightroad]

So a couple of weeks ago I did a dumb dumb thing. I have 2 6s 16000mah HK MultiStar 10 C LiPos. They have behaved pretty well, and are staying well balanced. I have a 14s lipo charger for another 18650 pack I constructed. One day I was feeling impatient and didn't feel like pulling the batteries out and hooking them up to my rc charger. So I figured I would just hook them straight up to the 5amp charger and come unplug them after a little less than 2 hours since they were at 10% SOC. DUMB DUMB. Of course family kept me busy and I completely forgot about the battery for 4 hours! When it hit me that I forgot I was stricken with fear. Why isn't there a fire in my garage? I go out and check the pack. I approach with apprehension. It looks like the pack isn't swelling, good. I cautiously feel the pack. Not warm, good. I unhook the charger and hook up my watt meter. 54.2v. Not good. Okay, I need to discharge this pack ASAP. So I take the bike out. I ride and ride and ride, WOT everywhere. The voltage is hardly dropping. It takes 7ah to get the pack back down to 4.2 volts per cell. So I say F it. Let's see how far this thing will go. I hit 20ah. Still going, haven't fell off the voltage cliff. It's not until 22ah that the voltage starts to plummet. At this point I figure my cells must be way out of balance. But no! Everything is within .02 volts even at 5% SOC. WOW! I end up using this pack cautiously for 20 more cycles (not overcharging). I experience no loss in capacity and the cells are still staying balanced. Crazy. I've heard that lower C rating packs tolerate abuse better, maybe it is true.

 

[Syonyk]

Ouch. So 4.5v/cell (12s pack at 54v)?

It sounds like it's probably fine, but that's still scary, and damaged cells can let go at some point later with no warning.

Fix your charging connectors so you can't do that anymore!

 

[nutnspecial]

4.5 might be a record or something. Possibly a slow enough charge on a fresh enough battery shifted odds in your favor for not exceeding damage to anode and cathode resulting in heat and co2, and then venting/ignition.

If no puff, likely little cell degradation, and long term effects would show as capacity lost imo. Amazing that much extra ah was realized. Would you say 20%?

 

[bionicdan]

I did exactly this on one cell that used to discharge itself. Charger set to nicad and accidentally went out. Anyway I got similar numbers to you but was higher than 4.5v but cant remember the exact number due to panic and trying to discharge asap. cell still works as it did ie not very well lol

multistars now do a 4.3v high voltage lighter pack which could be somehow linked

 

[DAND214]

Bionicdan wrote:
multistars now do a 4.3v high voltage lighter pack which could be somehow linked

What does that mean?

Dan

 

[Gregory]

It means there are LiHV Multistars, here, which I read somewhere they are charging to 4.35V.

Isn't there also an 18650 that charges to 4.3V?

 

[dogman dan]

It's never been like you charge to 4.31v and blammo they catch fire. Racers overcharge to get exactly the edge you noticed, but don't expect 3 years of service from the pack afterwards.

You shouldn't trust that pack now, and actually, why are you trusting a "good" pack to be charged in the garage with a family in the house? No, I'm not saying it's likely you'll burn your house down, but you really want to take any chance of making your kids homeless, or worse? If you have a really fire resistant charging and storing area in your garage that's different. But most have something flammable within 3-4 feet. Garages are rarely uncluttered.

 

[LyonNightroad]

It's never been like you charge to 4.31v and blammo they catch fire. Racers overcharge to get exactly the edge you noticed, but don't expect 3 years of service from the pack afterwards.

You shouldn't trust that pack now, and actually, why are you trusting a "good" pack to be charged in the garage with a family in the house? No, I'm not saying it's likely you'll burn your house down, but you really want to take any chance of making your kids homeless, or worse? If you have a really fire resistant charging and storing area in your garage that's different. But most have something flammable within 3-4 feet. Garages are rarely uncluttered.

I do appreciate the concern in case I was not aware of the risks. I am aware of the risks, my lipos are charged in a lipo bag in the center of my garage about 7 ft from anything flamable with the garage door open. My biggest concern is the toxic residue. I've talked with my insurance agent, he says this would be covered.

 

[LyonNightroad]

I've finally got a nice 14s charger coming that has a built in IR meter. Can't wait to compare the IR of these overcharged cells to brand new cells. If I didn't have so doggone much capacity at this point (64mah in lipos - 2 16ah 12s 'backup' packs and building a 14s 32ah pack + 20ah in 14s 18650) I might consider doing some long term experiments with overcharging these cells to say 4.25 or 4.3.

 

[Syonyk]

...I might consider doing some long term experiments with overcharging these cells to say 4.25 or 4.3.

Do you have some sort of highly fire and caustic gas proof place to do those tests? Or were you planning to just do them on your ebike/in your garage?

Testing lithium packs beyond their rated limits should be done in the type of environment where you can fully contain the thermal runaway and venting of the entire pack under test, with a good margin of safety. It's not something to casually frock around with.

 

[LyonNightroad]

...I might consider doing some long term experiments with overcharging these cells to say 4.25 or 4.3.

Do you have some sort of highly fire and caustic gas proof place to do those tests? Or were you planning to just do them on your ebike/in your garage?

Testing lithium packs beyond their rated limits should be done in the type of environment where you can fully contain the thermal runaway and venting of the entire pack under test, with a good margin of safety. It's not something to casually frock around with.

I've used, litteraly, hundreds of LiPos. Abused them in every manner possible. It's just inherent to the RC hobby. Packs get slammed into the earth at 70 mph all the time. Discharge rates get exceeded. Pack get overdischarged. I added some flavor to my story, but I do always charge my LiPos assuming they are going to randomly ignite. Anyway, my experiences aside.

Charging to 4.25 or 4.3 is very unlikely to result in sudden and unexpected failure assuming your lipo charger is measuring cell voltage accurately. All you would expect to see a more rapid loss in capacity. However, I do have safe places to charge the battery. A quick google search shows that this type of testing has been done and the results vary from battery to battery. My understanding is that lower C batteries tend to tolerate overcharge conditions better.

All that being said, I don't intend to test this because, as I mentioned earlier, I have no practical need for the extra capacity and if as I expect the cycle count is significantly reduced, it would have been cheaper to just buy more batteries.

However, in a world where I have unlimited time and money... I would enjoy testing several batches of these batteries, For Science!

 

[dogman dan]

Good, sounds like you know what you are doing with the lipos.

Please don't take it too personal, I often write these warnings aimed at the hundreds of others who will read this. Lots of people out there with no experience, with cluttered garages that have bare walls ready to burn real nice.

Some long term testing would be interesting. I tend to get about 2 good years from lipo, and that didn't change much when I went from storing them at 4.2v to storing them at 3.8 ish. The most recent batch was never charged more than 4.15v average, though sometimes one cell would get to 4.22 or .23.

It would have been nicer to charge to 4.3v and have that bit of extra range, if it still got me 18 months of good use. Charge and ride immediately I mean. Timing it right buying them, two warm seasons. It's the warm climate I think that limits my lifespan, combined with fairly hard use of 10 ah packs. (40 amps, riding dirt so lots of amp spikes)

But the burn your house down thing does concern me, and is why I now (bulk charging) charge to 4.15v . I would have a hard time considering cells charged to 4.5v safe. But if they did not puff, and still have normal resistance after a few more normal cycles, I would keep them in service for sure. But just take the kind of precautions you do when charging them, and then store them outside the house.

 

[LyonNightroad]

Yes, It is remarkable how much variance there is in a lipos ability to tolerate storage at a 'full' charge. I see this with my hobby lipos all the time. I have so many lipos and they are so cheap that I can't be bothered to switch to storage voltage and then recharge again. Remarkably, most of the packs tolerate this just fine. 1 or 2 will become unbalanced after the first use after an extended period of no use. I wish all cells were tested for this too.

 

[parabellum]

Looks like Samsung uses 4.4V bats now

 

[ScooterMan101]

Any word / plan on Multistar making 7 s packs ?

>

It means there are LiHV Multistars, here, which I read somewhere they are charging to 4.35V.

Isn't there also an 18650 that charges to 4.3V?

 

[andresg72]

Hello, I have also made a mistake of overcharging a 6s Multistar lipo up to 4.5v each cell! Yikes, I expected an explosion.... but no. The pack did not puff nor heat. I imediately started a slow discharge until 4.2v
I will try to use it on the bike and post here the results. Can these 10c batteries survive 4.5v charging?

 

[andresg72]

So a couple of weeks ago I did a dumb dumb thing. I have 2 6s 16000mah HK MultiStar 10 C LiPos. They have behaved pretty well, and are staying well balanced. I have a 14s lipo charger for another 18650 pack I constructed. One day I was feeling impatient and didn't feel like pulling the batteries out and hooking them up to my rc charger. So I figured I would just hook them straight up to the 5amp charger and come unplug them after a little less than 2 hours since they were at 10% SOC. DUMB DUMB. Of course family kept me busy and I completely forgot about the battery for 4 hours! When it hit me that I forgot I was stricken with fear. Why isn't there a fire in my garage? I go out and check the pack. I approach with apprehension. It looks like the pack isn't swelling, good. I cautiously feel the pack. Not warm, good. I unhook the charger and hook up my watt meter. 54.2v. Not good. Okay, I need to discharge this pack ASAP. So I take the bike out. I ride and ride and ride, WOT everywhere. The voltage is hardly dropping. It takes 7ah to get the pack back down to 4.2 volts per cell. So I say F it. Let's see how far this thing will go. I hit 20ah. Still going, haven't fell off the voltage cliff. It's not until 22ah that the voltage starts to plummet. At this point I figure my cells must be way out of balance. But no! Everything is within .02 volts even at 5% SOC. WOW! I end up using this pack cautiously for 20 more cycles (not overcharging). I experience no loss in capacity and the cells are still staying balanced. Crazy. I've heard that lower C rating packs tolerate abuse better, maybe it is true.

So I used my overcharged multistar battery after discharging from 4.5v to 4.2v. I used the bike normally and with heavy load in several steep climbs and the result was normal... no puffed pack, the range was normal and at the end of the cycle the 6 cells were totally balanced!!!
Like LyonNightroad observed before: this was a crazy outcome! These multistar batteries indeed have incredible tolerance.