Wind up torch not holding charge for long, doesn't appear to be a battery issue

[SolderSucker]

I have a wind up torch that I've had for about four years.

A while back I noticed that it wasn't holding its charge for very long and this has only become worse.

Thought it must be the battery - it had inside three 1.2V, 80 mAh NiMH batteries wired in series to give 3.6v - these are stacked to form a small pyramid.

I didn't have a spare of that exact same type so replaced it with one of these:

https://uk.rs-online.com/web/p/button-rechargeable-batteries/0525843

so the same voltage, mAh and also NiMH

however, the problem remains - irrespective of how much I wind it up the charge doesn't last long.

What else could be wrong?

There's not much inside the battery - just the motor/coil/whatever it's called that you wind up, the LEDs, a few wires and the on/off button. And that's it.

[edpalmer42]

You need to put some numbers on this.

How long does it hold a charge.  Hours?  Days?

How long do you need to crank it to *fully* charge the battery.  5 minutes?  5 hours??  I suspect most people stop cranking long before the battery is fully charged.  Then it looks like the battery isn't holding a charge.

Disconnect the battery and check for leakage current in the circuit.  A leaky diode is all it takes.

Ed

[wasedadoc]

Not clear what is meant by "Not holding charge for long".  Which of:

1.  Wind the handle a lot. Immediately switch on briefly.  Works OK.  Leave switched off for a period of time.  Switch on but dim or no light.

or

2.  Wind the handle a lot.  Immediately switch on.  Works but goes out much sooner than previously running the same test.

[SolderSucker]

Thanks guys, to clarify some things:

As a test I crank the handle for one minute, when the torch was new this would power all three LEDs for at least half an hour. Now after a minute of winding and leaving it on the LEDs start to noticeably dim after two minutes and go out after about five minutes.

I'll take it apart again and see if there's anything that I'm missing, but would welcome any more suggestions if any come to mind.

[wasedadoc]

Disconnect the battery and charge with a power supply and suitable resistor for appropriate time.  Reconnect battery and test the run time.  If it is as when new there is something amiss with the generator.

[IanB]

If it's a new battery you should condition it before use. Remove the battery from the torch and charge it from a constant current supply at 8 mA for 16 hours or so.

Then place it in the torch and see how long it runs when fully charged like that.

However, the above is what the data sheet calls a standard charge (taking 16 hours). A rapid charge would normally be about 1-2 hours.

Note there is no indication that such a battery can be charged in 1 minute. Attempting to do so would surely destroy it. 80 mA for an hour would be 4.8 A for a minute. There is no way the battery could withstand that, nor I doubt could you crank the handle fast enough to generate 4.8 A.

Sometimes these torches are "fake" and have a hidden primary alkaline battery somewhere inside them to give the appearance they are rechargeable. Have you looked carefully for one?

I'm rather puzzled how such torches can actually work. Unless it's not close to using the 80 mAh capacity of the battery and is  only using something like 5 mAh instead? Or maybe it's just that 1 minute of cranking gives 1-2 minutes of light, or something like that?

[BILLPOD]

Good Morning SolderSucker,   If you could post the make and model of the torch/flashlight, it would help in diagnosing your issue.

[floobydust]

There should be a blocking diode to prevent the battery from discharging into the generator? You can measure leakage current from the battery as well.

The really tiny micro batteries like Seiko lithium only have a specified life of 50-100 cycles and it's quite harsh to charge them up in seconds. Their micro NiMH are the same.

[themadhippy]

could it be a mechanical problem ,maybe a slipping gear or something .

[p.larner]

the battery was possibly 90% charged when you first got the torch so missleading things?.