I bought a low quality LED flashlight. Put in 3 AA Memorex alkaline batteries. After about an hour later, I picked up the flashlight and its handle was HOT. The flashlight wasn't on. Took the batteries out, 2 of them are not hot and the last one was. (The middle one was a bit warm, actually, due to contact with the third).
My question is, based on the limited info above, can you tell whether the battery was defective or the flashlight? I guess it most likely be the battery, but is it possible for a defective flashlight to create this condition? If so, how.
Ken, I put the batteries in correctly. The flashlight worked. How did you conclude that the FL was defective? I am ignorant WRT to this matter. Thanks, Kathy
This is the arrangement I had: Bulb [+AA -][+AA -][+AA -] The third battery from the bulb was hot.
Your explanation sounds perfectly logical to me. Just to confirm though, in case I indeed made a mistake, if I have this arrangement: Bulb [+AA -][+AA -][-AA +] then the third battery can become hot?
This theory is a nice one, except that it doesn't quite hold up. The 1.5v remaining is not enough to light a red LED, let alone a blue or white one which these flashlights usually use. Kathy does say that the light worked ...
Just for sport, I connected three batteries up with the third one ' wrong ', and hung a red LED across the string. As expected, it did not light with
1.5v across it. I then substituted about 10 ohms worth of R across the string, and measured about 85mA being drawn. Now this would be a pretty high current for a LED flashlamp. With current being drawn through the battery string, the voltage across the R remained at about 1.5v, and the voltage polarity remained correct across each cell - as it must for the 1.5v of the reversed cell to correctly subtract from the series'd 3v of the other two.
So effectively, I was drawing 85mA ' backwards ' through the third cell, which I suppose you might consider as the two trying to charge the one. The bottom line was that after leaving this arrangement for some time, there was no appreciable temperature rise in any individual cell.
I would think that the problem is more likely to be a short occuring between the case of the flashlamp, which is almost certainly common to the - end of the furthest battery from the LED, and the upper + terminal of that cell. This would leave 3v remaining, which may just be enough to get a blue LED going ( VF typ = 3.2 to 3.5v ) and perhaps a white which has a VF a few decimals higher yet. It would certainly be enough to get a high intensity amber going. Bear in mind also that sometimes, these flashlamp devices have some electronics in them to buck the voltage from the battery so that several LEDs can be series connected. The short created across that cell would cause a large current to be drawn from it, which would cause the cell to hot up in the way described. Interesting theory problem. I'm not sure that I can think of a mechanical way that such a short could occur, but it would be present at all times, which would account for the hotting up, even with the flashlamp switched off. More mileage in this one yet, methinks ...
This is just a guess, but it sounds like the hot battery was shorted out in some way when it was installed in the flashlight. Did all the batteries have their plastic film covers completely intact? Is there any chance that there was some other piece of metal in there which could have shorted out the battery.
I assume the 3 cells were all in a row. Which position was the hot one in?
I believe all alkaline cells have the body + with the - terminal the flat one at the rear. If the rear contact of the flashlight was poorly designed, it might be able to short between the center - contact and the rolled lip around it, which is +. If this is the case then you either have to fix the contact or forget it.
In a normal flashlight you could fix this by putting all the cells in backwards, because an incandescent bulb doesn't care about polarity, but the LEDs DO care, so this won't work in this case.
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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA
But... Some LED flashlights have electronics in them. I have a CMG Infinity Ultra that uses ONE AA cell. The electronics step up the voltage to run the LED. Generally, the higher the frequence (red to yellow to green to blue), the higher the voltage required. White is sometimes blue with a phosphor.
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If you had read on to the bottom of my posting, you would have seen that I already made the point about some LED flashlights having electronics in them to buck the battery voltage ....
Thank you all for your comments. I inspected the inside of the battery tube and the probability of a shorted battery as Jim described is high. The coil connector presses against a piece of metal which goes along the length of the flashlight. The 'hot' battery also had its film cover damaged (before or after the short, I don't know.)
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