Never leave a plugged-in battery charger unattended!

Phil Pilgrim (PhiPi) · 2010-02-28 19:50

Here's a lesson I learned the hard way. But it could have been so much worse. Last evening, when I came into the house from the shop, I detected what smelled like burnt plastic. I had just done a load of clothes in my ancient washer and figured its time had come, so I turned on a vent fan to air out the house, and the odor dissipated. About an hour later, I heard a sizzle and pop and saw smoke coming from the NiMH battery charger on the kitchen counter. I quickly yanked the plug and tried picking it up to throw it out the back door, but it was much too hot to handle. So I grabbed an oven mitt and carried it out to the picnic table in the yard, where it spent the night. Here's what I found the next morning:

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I've heard of Li ion chargers and/or batteries doing this, but never NiMH. If I had not been home, this thing could have burnt down my house! As it is, I'm just thankful all I lost was the charger and some batteries. Plus, I don't have to buy a new washer and dryer -- yet. Maybe I should build a concrete "charging bunker" some distance from the house, though.

-Phil

Tracy Allen · 2010-02-28 20:09

Take it back to the Shack!! NiMH chargers are supposed to have a temperature sensor. The end of charge on NiCd and NiMH batteries is often detected by the hump in dV/dt, but that is unreliable, and a good backup is dT/dt and ultimately a full switchoff at around T=40 degC.

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Tracy Allen
www.emesystems.com

Phil Pilgrim (PhiPi) · 2010-02-28 20:17

Tracy Allen said...
Take it back to the Shack!!

I would if I wanted another one like it in exchange, but I don't want another RadioShack charger. I guess they should at least be alerted, though, in case a recall is necessary.

BTW, what do the rest of you use for AA NiMH batteries? Is there anything out there that I can trust not to leave me homeless?

Thanks,
-Phil

kf4ixm · 2010-02-28 20:30

I use the Rayovac PS-4 one hour rapid charger, i've used this one for over 4 years and it's never gave me any problems. in fact, it's charged other NiMh batteries that other chargers just refuse to charge. works with AA, AAA and 9 volt's. It also charges each cell individually unlike most that charge them in pairs.

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Post Edited (kf4ixm) : 2/28/2010 8:45:43 PM GMT

W9GFO · 2010-02-28 20:34

I use the Maha charger. I prefer to use chargers that charge each cell individually rather than in pairs.

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

hover1 · 2010-02-28 20:52

Phil,

I use the exact same Radio Shack charger! I'm going to have to monitor it a little more closley.

I have a small fire safe to charge my Li-Po batteries. Those can be nasty and destructfull!

Jim

Phil Pilgrim (PhiPi) said...

Tracy Allen said...
Take it back to the Shack!!

I would if I wanted another one like it in exchange, but I don't want another RadioShack charger. I guess they should at least be alerted, though, in case a recall is necessary.

BTW, what do the rest of you use for AA NiMH batteries? Is there anything out there that I can trust not to leave me homeless?

Thanks,
-Phil

Beau Schwabe · 2010-02-28 21:08

You should also exercise caution when it comes to the Ni-Mh batteries you are recharging...· I recently ordered 20 Ni-Mh from E-bay and two of them decided to 'leak' during charging...· The fluid is conductive (go figure) and leaked into the Charger causing it to go nuts.· It was a decent 'Energizer' Ni-Mh brand charger too, capable of doing AA's and AAA's.· Fortunately I didn't have a charger melt-down, but I should have been more curious about the noticeable odor than I was.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Leon · 2010-02-28 21:14

When I worked at Racal Comms there was a loud explosion in the lab. It transpired that someone who should have know better put a manpack radio NiCd battery on an ordinary lab constant voltage supply, instead of using the proper charger. Luckily. it was lunchtime and the lab was empty. No one owned up, of course.

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Leon Heller
Amateur radio callsign: G1HSM

John R. · 2010-02-28 21:19

Another comment on charging (and using) multiple cells: It is not a good idea to mix types/brands of cells on a charger like this. It appears that there were at least two different types in the picture Phil posted. Different brands of batteries may have a slightly different construction and/or chemistry, and as a result, a different internal resistance and charging rate.

This can contribute to the problems Phil saw. The charger still should have shut down, but if one cell has a lower resistance than the other, it will get more current, especially when they are charging as a pair in series, as appears to be the case with this charger.

It is also generally not a good idea to mix brands/types on the "usage end" either. The mixing also applies to old and new cells. When multiple cells are used in an application (series and/or parallel), these slight differences can be significant to performance, safety and battery life.

In terms of "what won't leave my homeless" - about the only option would be a "trickle charger" (if that). Any of the "quick chargers" can be a risk, not so much because of the charger, but all it takes is one bad battery to make a mess. The higher the energy density, the more risk (i.e. NiCad => NiMH => LiPO in order of increasing risk). The faster the charge, the greater the risk.

When all is said and done, high performance charging should only be done in an "attended" situation. 90% plus of the time there will be no problems, but "the consequences of failure can be extreme".

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John R.
Click here to see my Nomad Build Log

mikediv · 2010-03-01 00:02

Phil do you have any idea what happened?? did you put a battery in backwards ?? I to have the same charger but to be honest its very old but I still have not ever used it not even once yet no reason just haven't needed it but I am very curious if you have any thought on what went wrong..

I have a Sears 6-12 volt Trickle battery charger I use for my tracker and jet skis and ATV batteries the thing is about 12 years old sometimes I would string about 30 NI AA together and charge them all at once

John I did not know a lot of that , that is very informative I have so many different batteries I would always just charge them together never giving it a thought thank you

Post Edited (mikediv) : 3/1/2010 12:07:51 AM GMT

Phil Pilgrim (PhiPi) · 2010-03-01 00:16

mikediv said...
Phil do you have any idea what happened?? did you put a battery in backwards ??

No idea. All the batteries were inserted the right way, and they're all NiMH. The pair of batteries that I removed to swap with the mouse batteries that had run down were fully charged. But, as John R. points out, it's not a good idea to mix brands, which I've done with seeming impunity — until now.

-Phil

mikediv · 2010-03-01 00:28

Wow that would bother me ,, I keep my charger right in the middle of all my other very flammable Smile well I used to lol I'm glad nothing bad happened beside loosing your charger and batteries .. And thanks for posting this I really didn't know about mixing batteries
that was really good info I would figure AA is AA right? Anyway I guess I will not go ahead with my plans to try and charge the Parallax SureFire 3 volt Lithium Battery I bought a bunch for my flash light like 30 of them but they just don't last very long they are a bit expensive
I thought I could get away with charging them but after seeing this I will probably just toss them .. Phil is there anyway to get any more use out of a Lithium after its dead??

Whit · 2010-03-01 00:34

Phil,

I use an Energizer 15 minute charger. It has a fan. I set a timer and check it in 15 minutes and the batteries are most always charged in that time. Some times I notice them charged more quickly and remove them then.

I figured with the fifteen minute charge, I would never be tempted to just leave them charging. I don't know the pros and cons of such fast charging vs. slow charging. My batteries and charger are all the same brand - so I figured it would probably be okay.

No problems yet - but this is a good warning.

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Whit+

"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Phil Pilgrim (PhiPi) · 2010-03-01 00:39

mikediv,

Lithium primary cells (e.g. CR123) should never be recharged. I bought a couple Tenergy rechargeable Li ion cells with a CR123 form factor once, along with a two-cell charger. It was a year before I decided to try the charger, but by then the cells had ruptured and started leaking, even though I had never used them. I tossed the whole lot.

-Phil

Phil Pilgrim (PhiPi) · 2010-03-01 00:45

Whit,

I had always left my batteries in the charger to continue on trickle, since NiMHs self-discharge so quickly. That way I was always ensured of a fresh set, ready to swap. But a 15-minute charge might obviate that need. How many charges do you get that way before charge life starts to wane?

-Phil

erco · 2010-03-01 01:46

Phil:

Glad you found this before anything serious happened. On a lighter note, those batteries in your photo look·much·like charred hot dogs. Remember the Presto "Hot Dogger"? It was a hot dog cooker that ran 115 VAC through your hot dogs. Seems like your charger tried something along those lines.

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·"If you build it, they will come."

Whit · 2010-03-01 01:51

Phil,

My set up is pretty new. I really don't know yet. Maybe I shoud be keeping a log though, just to see.

I only have AAs. The highest mAh, I found locally is 2500. That is what I am using. I do not know if the mAh rating would have anything to do with charge time or recharging life. I only have 12 cells (batteries) right now. My charger will only charge 4 at a time. I charge them all - that gives me two runs on the Scribbler or Stingray. Great for the Scribbler, but I am going to upgrade the Stingray to an RC 7.2 volt system (which I have - but really want to upgrade to a higher mAh rating).

Once you have the charger though, the batteries really aren't that expensive. Mine all came from Wal-mart. By the way Phil - that is one·scarey (sp?)·photo! Glad no one was hurt!

@ erco,

For my seventh grade science project (1970), I put two nails through a piece of plywood (with little stick on rubber feet). I attached an old extension cord to each nail. I then slid a hot dog on the nails (which were hot dod length apart). I plugged in the cord and in about 20 seconds -·a delicious, steaming hot hot dog was ready. I honestly can't believe they let me bring it to school!

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Whit+

"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Post Edited (Whit) : 3/1/2010 2:03:09 AM GMT

Duffer · 2010-03-01 01:53

Phil-

Some of my "rules of survival": Anything that generates heat can over-heat. Anything that uses electricity can short-circuit. Never trust any machine over 30 (that last might apply to your washing machine). ;-)

I never charge batteries overnight or where I can't get to them in about two steps. I use an old "cooler size" fire safe with ceramic blocks under the charger(s)·and a fan to get rid of the heat and I never leave a charger connected to a live circuit, even if it's enpty.

Duffer

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Any technology, sufficiently developed, is indistinguishable from magic.· A.C. Clark(RIP)

Phil Pilgrim (PhiPi) · 2010-03-01 03:18

erco said...
On a lighter note, those batteries in your photo look much like charred hot dogs.

They sure didn't smell like hot dogs, though!

erco, Whit,

One of the projects available to build when I was in 7th grade shop class was a hot dog cooker like the ones you describe. But, sadly, our present nanny system of education would never allow anything like that. (BTW, I opted for the buzzer project, instead. Hey, it made noise!)

Duffer said...
Never trust any machine over 30 (that last might apply to your washing machine).

I'm sure it must. It came with the house when I bought it in 1984. It was old then.

Duffer,

I like the idea of a fire safe to contain any charger blow-ups. 'Probably a bit cheaper than the concrete bunker I had in mind.

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 3/1/2010 3:25:00 AM GMT

sam_sam_sam · 2010-03-01 03:57

The only Battery Charger that I use are the Pulse Battery·Chargers that Radio Shack use to sell
This battery charger is very picke· in what·it will charge and it will let you know if something is wrong with that cell
when this happen I very slowly charge these cells and retest them to see if they are good

The only other battery charger ·that I use have·a·range ·of 50 to 300 ·milliamp charging rate and only charge battery that·are 1800 amp hour or more

Phil Pilgrim

I had the same thing happen to me one time I was charging a battery pack that was giving some problems so· I fast charge at a rate of ·1 AMP
everything was fine about a hour later I start smelling something burning then a big pop and a lot of smoke and that was it

I was· some what watching but i was doing other thing as well

after that I will not leave any battery on FAST charge with really watching it

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··Thanks for any·

·that you may have and all of your time finding them

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Sam

BradC · 2010-03-01 13:15

W9GFO said...
I use the Maha charger. I prefer to use chargers that charge each cell individually rather than in pairs.

I used to think Maha chargers were pure quackery until I bought a couple. Can't say enough good things about them.

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You only ever need two tools in life. If it moves and it shouldn't use Duct Tape. If it does not move and it should use WD40.

Whit · 2010-03-01 14:51

W9GFO and BradC,

The Maha charger does look really nice. I also like the 2700 mAh cells!

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Whit+

"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Searider · 2010-03-01 18:00

I also use the Maha charger and have been very happy with it. I also NEVER leave NiMH on the charger un-attended and be sure to have a smoke detector in the room you are working in. No mater how much you spend on a charger it can fail and the downside is pretty ugly.

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Searider

Kenny Gardner · 2010-03-01 18:44

This charger is awesome. I can't say enough good things about it. There is also an 8 cell charger.

www.amazon.com/gp/product/B00017LRCC/ref=oss_product

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Kenny

davejames · 2010-03-01 19:54

We use two of the above Ansmann chargers at church and they are left on 24/7.

DJ

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rjo_ · 2010-03-02 05:11

I leave mine plugged in all the time...nic cadmium 7.2V RadioShack...
On the other hand... today I found out exactly what happens when you let
your soldering iron touch the power cable that connects it to the wall...
By golly... if you haven't tried it, it is worth a walk in the dark to find the
circuit breaker. First there is a huge pop... the lights go out and a little glow worm
crawls along your desk.... fabulous. For a moment I thought I was back in Vietnam...
and then I remembered... I was never in Vietnam.

Javalin · 2010-03-02 20:25

just be glad it wasn't a lipo charger...! Seen nasty pictures of them going bang (or the batteries to be more precise!)!!

James

Humanoido · 2010-03-04 22:17

When I worked in the Laboratory, we frequently charged batteries for scientific equipment. The batteries had to be up to specs or equipment performance could fault. I had spent years studying the battery and charger characteristics. Sometimes I could tell if a particular battery was going to fail, just by looking at it or touching it. One day, my partner was loading a battery into the charger and he commented that it seemed unusually hot. I told him to immediately remove it. He wondered why, and I explained that if it continued to rise in temperature (outside of the charger), it could explode. Immediately he took it out of the charger, and indeed the battery rapidly continued its upward heated climb until it started burning his hand. I yelled out, "Explosion!!!" and we hit the deck. Moments later, it ruptured into a flinging splatting mass of chemicals and goo drops hurled across the table onto the nearest wall! Even if you attend the charging of a battery, be prepared to take cover!

humanoido

Phil Pilgrim (PhiPi) · 2010-03-28 03:25

POSTSCRIPT: I've considered all the very helpful advice offered here, read the reviews, and settled on the Ansmann Energy 8 from Thomas Distributing. It came with some 2850 mAH AAs, and I augmented them with some 2500 mAH long-shelf-life AAs. For use with my DigiCam, the shelf life was more important than raw energy capacity, since NiMH batteries tend to self-disharge rather quickly.

A warm thanks to all for the insight and advice offered in this thread! I've charged up all my new batteries and have unplugged the charger. I will sleep well tonight!

-Phil

Never leave a plugged-in battery charger unattended!

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