1.5v batteries and LEDs

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1.5v batteries and LEDs

This topic has 9 replies, 6 voices, and was last updated 16 March 2018 at 15:32 by Neil Wyatt.

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16 March 2018 at 00:43 #346304
Ady1
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@ady1
I got a Lidl battery tester the other day because I have dozens of rechargeables for various duties, mainly the AA and AAA variety

One is auto night lights, like a torch, but a sensor detects you and switches it on

3 x AAA powered like most small LED torch units

Anyway, when they stopped working recently I tested each battery and in both cases only the top battery, at the +ve end had been drained out, both the lower (middle and -ve end) batteries were fine and were re-used with a new +ve end battery

So don't chuck all three out if you're using good disposables(duracells etc) in a led torch, two of them may actually be fine

Edited By Ady1 on 16/03/2018 00:58:45
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16 March 2018 at 00:43 #35141
Ady1
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@ady1
16 March 2018 at 07:07 #346311
clogs
Participant
@clogs
Interesting, thanks for that, but I usually check every battery…….sad I know……..clogs
16 March 2018 at 07:20 #346312
not done it yet
Participant
@notdoneityet
Typical of rehargeable batteries. The weakest cell of the battery is likely to get drained completely by the others continuing to perform. Nickel metal hydride cells do not like to be run down to zero volts and then fail or do not recharge properly, so the downward cycle continues, often exacerbated by charging the other cells to an over-voltage situation( if recharged in series), which is also not good for them.

Swapping in a new cell is likely to repeat the downward spiral, but all good fun.
16 March 2018 at 08:24 #346316
Ady1
Participant
@ady1
Nickel metal hydride cells do not like to be run down to zero volts and then fail or do not recharge properly, so the downward cycle continues

One was actually "completely deid"

However I forgot to bin it and the next day it tested a slight charge and the charger recovered it

So it just needed a cup of cocoa and a nights rest

Edited By Ady1 on 16/03/2018 08:24:48
16 March 2018 at 09:31 #346322
Douglas Johnston
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@douglasjohnston98463
I have a few of the torches that use 3 AAA cells, but I picked up another one recently ( I simply can't resist buying them! ) and found it uses a single AA battery. This is a much better idea, although the electronics must be a bit more complicated to operate the LED from 1.5V.

Doug
16 March 2018 at 09:38 #346324
Muzzer
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@muzzer
To ensure that all the cells in a string are fully charged, you need to overcharge the whole string periodically (cell equalisation). With NiMH batteries that results in gentle heat, so needs to be done gently. With flooded PbA it generates gas and requires periodic topping up with pure water. Not good for lithium….

If you run a whole string down until it appears completely drained, the cell with the lowest initial charge (a function of initial state of charge and effective capacity) may end up being reverse biased. Not ideal conditions if you want long life out of it, which is why periodic equalisation is required.

Murray
16 March 2018 at 09:41 #346325
Muzzer
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@muzzer
Posted by Douglas Johnston on 16/03/2018 09:31:46:

I have a few of the torches that use 3 AAA cells, but I picked up another one recently ( I simply can't resist buying them! ) and found it uses a single AA battery. This is a much better idea, although the electronics must be a bit more complicated to operate the LED from 1.5V.

Doug

Not a lot. Unlike the old bulb lamps where you just slapped the bulb across the batteries, you need to control the current in an LED, not the voltage, so there will be a dedicated LED driver IC in there to achieve that. Whether the controller needs to drop or boost the voltage isn't a big deal.

Murray
16 March 2018 at 15:04 #346360
not done it yet
Participant
@notdoneityet
You could convert to one 18650 lithium ion cell 9or even bigger if mounted carefully/separately. Slightly less voltage, but likely satisfactory operation. Very good if the cell has a bms to prevent over-charge and over-depletion.
16 March 2018 at 15:32 #346361
Neil Wyatt
Moderator
@neilwyatt
Posted by Douglas Johnston on 16/03/2018 09:31:46:

I have a few of the torches that use 3 AAA cells, but I picked up another one recently ( I simply can't resist buying them! ) and found it uses a single AA battery. This is a much better idea, although the electronics must be a bit more complicated to operate the LED from 1.5V.

Doug

It is more complex… but the electronics are considerably cheaper than a pair of batteries, NiMH or alkaline!
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