3V AA sized rechargeable battery???

[Steve]

We have a solar powered alarm clock which automatically synchronises with the terrestrial time signal. The clock is marked 'PRECISION', 'SOLAR POWER' and 'RADIO CONTROLLED'.

The display became faint and eventually it stopped working. I took a look inside. There was an unmarked AA size battery (leaking blue liquid which I cleaned up). I measured the battery's voltage which was 1.6V, well above that of a normal rechargeable (1.2V?).

I presume the battery is the source of the problem. I tried replacing the battery with both rechargeable and non-reachargeable AA ones, but the unit still didn't work.

I suspect that the original battery was much more than 1.6V - maybe 3V? But I can't find any references to rechargeable AA-sized 3V batteries. Can anyone suggest where to get a replacement battery (or other ideas)?

Cheers.

[Graham.]

terrestrial time signal. The clock is marked

inside. There was an unmarked AA size battery (leaking

1.6V, well above that of a normal rechargeable

battery with both rechargeable and non-reachargeable AA

can't find any references to

replacement battery (or other ideas)?

Any sign of damage to the PCB from the leaking electrolyte?

I think you are reading too much into the >1.5 terminal voltage with no load.

[Gareth]

Was that with it in circuit of after you removed it? If it was in circuit and being charged when you measured it then 1.6v may be correct for a normal AA rechargeable battery.

Lithium ion batteries are around 3V when discharged and 4.2V when fully charged. The 14500 lithium ion cells are AA sized (14500 = 14mm diameter and 50mm long). However, beware that lithium ion cells can burst in to flames if incorrectly charged so you want to be sure it should be lithium ion before fitting one. If you do fit one, I would recommend that you buy a battery with the protection module built in.

These came up after a quick Google:

[Steve]

Thanks for replying Graham. There's no damage to the PCB. Also, I've never seen a rechargeable with >1.5V (even under no load); the battery (I should say 'cell' really) is the most likely cause of the problem. I may risk conecting a couple of 'normal' AAs in series and see what happens.

Cheers

[Steve]

> >

Gareth. The 1.6V was with the battery removed. The Li-ion ones you identify look interesting; you may have hit the nail on the head. As I said to Graham (previous post) I may try connecting a couple of normal AAs in series to check if 3V does the job. If so, a Li-ion should work well.

Cheers

[Gareth]

>>> > >>

As I said, you do need to be sure that your clock was designed to work with a lithium ion cell as they can burst into flames if incorrectly charged. If you do try it, make sure you get cells with built in protection modules and don't blame me if your house burns down.

Gareth.

[Robin]

Idiot boy questions for my education : might it have been an "ordinary" lithium battery - i.e. not rechargeable? Unless the paperwork specified the "solar" recharged a battery might it have been cheaper for the manufacturer to stick a non-rechargeable in given the likely long life with such a device - i.e. well beyond any reasonable claim for a refund under the Sale of Gods Act?

Would the presence of a charging voltage and current from the clock (when in bright light) be one test?

[Alan]

In message , Gareth wrote

Is it a rechargeable battery or just a lithium (long life) cell designed(?) to run the clock for 10 years, supplemented by the solar cell only when there is enough light? If it is the latter then there should be no problem with recharging.

[The Natural Philosopher]

LiFe cells.

Not sure if AA available.

[The Natural Philosopher]

plenty of batteries of the non rechargeable sort have 3v voltage..LIPO are about 3.7 in the rechargeable arena, and LiFePo are about 3.3.

But I don't think any 3.3v rechargeables come in AAA format.

More likely the whole unit is a con, and its a non rechargeable battery that is actually being slightly recharged by the solar power.

However I am puzzled: for reasons of cmapitbility, most AAA cells are of similar voltage.

[Steve]

>>>>> >> >>>

>>> Thanks Gareth. The 1.6V was with the battery removed. The Li-ion ones >> you

Thanks Gareth. Noted!!!

[Steve]

(I can't measure the current through the clock without 'breaking-open' the circuit (ammeter must be ins series), which I don't want to do.)

Cheers

Cheers.

[Steve]

It's nmarked (so can't tell if it's rechargeable or not). The cell in your link may do the job.

Cheers

[Steve]

>>> > >>

> try LiFe cells.

Lithium-Iron is available in AA, but is only 1.5V.

[Andy Burns]

Or less than 1/3 of the RS price

[Tinkerer]

Triple A? Would you care to borrow my glasses?

[Graham.]

the terrestrial time signal. The clock is marked

inside. There was an unmarked AA size battery (leaking

was 1.6V, well above that of a normal rechargeable

>>> > >>

> try LiFe cells.

NiZn cells are 1.65v and rechargeable. They are reputed to come in AA size but I've never knowingly ever seen one.

[Robin]

I'm probably missing the point but I'd thought that you would have access to the terminals to which the battery was connected and so could connect across them a resistor of (say) 470k [1] and then measure the voltage and current when the cells are in sunlight.

[1] total guesstimate based on a Lion cell requiring a charging voltage of ~3.6V and anything less than a few microamps not being worth the candle

[The Natural Philosopher]

Think I need to..:-)

Mea culpa!

[Steve]

Thanks Robin, but I don't have any 470k (or other) resistors to hand. Just a multimeter that I use for checking electrical things.

In any case, surely measuring the current though a resistor between the terminals would only tell me if the charging circuit was working (solar cell delivering current to the battery). It wouldn't tell me if current was being delivered to the clock

- to do that the meter would somehow have to be in series with the clock..

Steve