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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 04-08-2007, 02:53 AM   #1
bigdumbdane
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Default how do I test a lipo with a multimeter?

So I keep reading that you should test your lipos with a multimeter..

So I grabbed my switched mulimeter, set it to DCV 20 (figuring a 7.2 volt battery wouldnt register any more) and touched the red to the red wire and the black to the black wire.

I heard some buzzing, and this odd smell.... coming from an e-flite 7.2 volt battery.

So the battery is outside in a clay pot, and I am wondering what I did wrong, and if I toasted the battery. It looks fine, didnt warm up or swell, but the wires did get hot...

This is where I should admit I have no idea how to use this multimeter - a cen-tech p30756 that I use in this manner to test my AA batteries. Usually it reads 1.3 or so...
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Old 04-08-2007, 08:14 AM   #2
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Dane,

Unfortunately, it doesn't sound good for your battery. I have never tried checking voltage of my LiPos using a multimeter, I use a watt's up meter (watt meter), but I have used them for my NiMH Rx battery with excellent results.

I'm not sure what could have happened as it sounds like what you did was fundamentally correct. Not knowing what type of meter you have makes it hard to diagnose your problem.

Here's a tutorial on multimeter usage if you are interested.

Frank
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Old 04-08-2007, 10:54 AM   #3
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What you describe doing is correct and I've done many many times with no problems.

What you describe as happening sounds like you've short circuited the battery which usually means the multimeter is set to measure current NOT voltage.

That might happen if you have the red lead plugged into the wrong place on the multimeter i.e. the 10ADC socket.

Steve
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Old 04-08-2007, 12:07 PM   #4
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Need to subscribe. I don't have a wattmeter yet and use a multimeter in the mean time. I had no idea that I could ruin a battery with it. I don't know how to describe the settings so here is a pic.

Was you checking at the balance plug for individual cell voltage and maybe touched the leads together or do you think it was the settings on the multimeter?


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Old 04-08-2007, 02:34 PM   #5
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If the multimeter was set up like this, it should be good. Definitely sounds like a short or the meter was set to measure current like mentioned above. That would cause a short.

Frank

Picture borrowed from here.


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Old 04-08-2007, 04:36 PM   #6
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Originally Posted by smokejohnson View Post
Need to subscribe. I don't have a wattmeter yet and use a multimeter in the mean time. I had no idea that I could ruin a battery with it. I don't know how to describe the settings so here is a pic.

Was you checking at the balance plug for individual cell voltage and maybe touched the leads together or do you think it was the settings on the multimeter?

This looks just like what I did... or I thought I did...
I am nervous to try it again with a lipo, I will try a car nimh battery to see what happens.
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Old 04-08-2007, 04:40 PM   #7
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Well good luck. Read over that tutorial above if you have time. Lots of good info.

Frank
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Old 04-08-2007, 04:55 PM   #8
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Yours seems to be set exactly as I use mine. In my pic, I am not showing the leads, but they go in the black and red holes on the RIGHT. The only thing I can think is that you crossed the leads. That is, touched them. If your put the probes on the opposite sockets on the balance plug itself, I think it just reverses your reading (makes a positive number negative).

I use the pointed probes, which have a lot of bare metal in close proximity. And I can't get a reading in the balance plug itself. So I porbe the face of the plug where the wires anchor. It is extremely easy to jump slots or accidentally touch the probes.

Good luck.

Incidentally, I haven't killed a battery yet by shorting it. I've allowed the battery charge leads to touch while soldering (scary ). But the battery didn't puff and still operated fine after I got the plug soldered on. Keep an eye on yours and then try to get a reading again. It may not be damaged. Do it in the clay pot though maybe.


EDIT: I have mine set as Smokejohnson has his. I thought that was your pic.


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Old 04-08-2007, 05:29 PM   #9
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Well the lipo is fine, and I have my multimeter set just like everyone else. I got brave and tried it again, and it worked fine..

I have no idea what I did the first time. I guess I probably shorted it somehow and was not aware..

I shorted out a 3 cell lipo when soldering as well.. I was doing it on a metal table (duh!)
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Old 04-08-2007, 05:31 PM   #10
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Dane,

That's good news but I'm concerned about the "buzzing and odd smell." I'm no expert by far, but that doesn't sound good.

Hopefully someone else can chime in on that.

Frank
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Old 04-08-2007, 07:32 PM   #11
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BIG, your settings were right. The only thing that makes sense is that the leads shorted the battery out by touching when you checked it, as suggested above.

I've had a few sparks from very momentary shorts that had no effect on the life or performance of the battery- but sometimes the bear just eats ya!

Alienx made a good point- if the voltage shown is negative, its simply because the leads are reversed. In the Voltage mode, it is a huge resistor that doesn't allow current to flow.

Having had the long probe leads short out while servicing a 440V commercial condensing unit once, I can assure you it is very easy to do- and can be quite spectacular! I put a length of shrink wrap on the probe leads since only the tips are needed for contact- all the rest of their length is nothing but sheer RISK!

Probably best to get a WattMeter and never have any more questions about any of the electrical parameters of the battery or the power system!
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Old 08-05-2009, 04:44 PM   #12
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Well, I'll resuscitate this thread, since it helped me a bunch... But, I'm confused-- my 2s lipos are testing @ 7.4 V (3.7 per cell), but still taking charge... How is the best way to test how much charge they have left using a multimeter -- if it can be done...

Thanks,

Gian
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Old 08-05-2009, 06:18 PM   #13
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You need to do a little reading. A FULL lipo reads 4.2V. At 3.7V it's almost empty.

See http://www.wattflyer.com/forums/showthread.php?t=48334

Steve
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Old 08-05-2009, 06:34 PM   #14
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Excellent! Thanks for the link.

All the best,

Gian
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