rechargable batteries for solar lights

[z]

I'm generally OK with electronical things, but hardly an expert on
rechargables, from reading the posts here. So, thanks in advance;
here's the question:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

 

[Electronworks.co.uk]

"z" <gzuckier@snail-mail.net> wrote in message
news:66277729-eca4-4745-ad9c-f242d9a92b4b@a26g2000yqn.googlegroups.com...

I'm generally OK with electronical things, but hardly an expert on
rechargables, from reading the posts here. So, thanks in advance;
here's the question:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

Hi Z

Interesting question, as I had the same problem with my rechargable garden
lights. I concluded that, even in the hot sun, the solar cells were not
putting out enough juice to fully charge the batteries. I tried improving
the circuit (a cheap Chinese circuit made up of a whole ton of bipolars) and
could not. I concluded things would not improve so I binned them.

In answer to your question, NiCads and NiMH batteries have roughly the same
charging characteristic, so the charging results should be similar for a
given input current. NiMH batteries hold about 40% more capacity than
NiCads, but NiCads can kick out more current (should not be a problem with
LED lighting). These are the 2 main differences.

I would be interested in any comments on this subject to fill a gap in my
knowledge

Thanks

--
Bill
www.electronworks.co.uk
Electronic Kits for Education and Fun

 

[Nobody]

On Sun, 19 Jul 2009 23:50:21 -0700, z wrote:

So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

I don't know if this is a factor in your application, but ISTR people
mentioning that higher capacity NiMH cells often have higher
self-discharge current.

Wikipedia says that NiMH typically have higher self-discharge than NiCd,
but there exist "low self-discharge" types (LSD NiMH), sometimes sold
pre-charged.

 

[Rich Grise]

On Sun, 19 Jul 2009 23:50:21 -0700, z wrote:

I'm generally OK with electronical things, but hardly an expert on
rechargables, from reading the posts here. So, thanks in advance;
here's the question:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

I'd try a set of Ni-Cads like the things were designed for; in my
experience, NiMH's are crap, and especially with a charger that's
optimized for Ni-Cads.

Good Luck!
Rich

 

[David Eather]

z wrote:

I'm generally OK with electronical things, but hardly an expert on
rechargables, from reading the posts here. So, thanks in advance;
here's the question:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

The output of amorphous solar cells reduces over time and it is a safe
bet they weren't "A grade" material to start with. I liked the idea of
the low self discharge NiMH.

 

[Phil Allison]

"z"

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

** Chances are, you solar cells only deliver a small charge current ( like
25 to 30mA ) so must NOT be used with high capacity cells like 2200mAH
NiMHs.

Charging the above cells requires a steady current input of 100mA for 24
hours or longer - at 25 mA they will barely charge at all or maybe even go
backwards.

Try some AAA size NiCds, usually rated at 250mAH.



..... Phil

 

[NT]

On Jul 20, 7:50 am, z <gzuck...@snail-mail.net> wrote:

I'm generally OK with electronical things, but hardly an expert on
rechargables, from reading the posts here. So, thanks in advance;
here's the question:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity to
store a charge. (trying to recharge the cells with a nicad charger
fails, substituting alkaline AA cells in the lights makes them work)
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
compared to 300 for the original NiCads. I wasn't expecting any better
performance, mind you, assuming that the solar cell output is the
limiting factor; but I'm not entirely sure that I'm not getting less
output from them now. It's midsummer here, max daylight, and these
NiMH are only charging up enough to run the lights for a couple of
hours every night. I'm pretty sure I used to do better than that with
the original Nicads. So here's the part where my knowledge of
rechargables runs out; is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger in the
light? Or is it just my own faulty memory?

NiMH have higher self discharge than NiCd, so will waste more of what
little charge you get from the solar cell. Also a larger capacity NiMH
cell has larger self discharge, so you're getting bitten twice.

You can get 2x 300mAh cells for Ł1 from poundland, hopefully they'll
restore your lost energy. Or 800mAh Ł1 each.

Another trick is to arrange an external reflector that gives more
light to the PV cell at times when the sun isn't full strength. To be
effective the reflected light needs to be diffused a bit rather than
pin sharp.


NT

 

[whit3rd]

On Jul 20, 2:50 am, z <gzuck...@snail-mail.net> wrote:

Like a lot of folks, i have a pile of those solar yard lights with a
couple of rechargable AA nicads, which have lost their capacity ...
It's easier to find NiMH these days so I tried a couple of lights with
newly purchased NiMH cells; these babies were rated at 2200 mAH
...is it possible that the NIMH cells actually
charge less than NiCads on the little cheapo solar charger

Well, on a long dark night the cells will completely discharge.
A day on the solar cell, that would fully (or nearly) charge 600 mAh
NiCd cells, will one-third charge the NiMH. So instead of
deep-cycling NiCd cells (which is OK), you'd be shallow-cycling
partly charged NiMH cells. I'd stick with NiCd, and if
it doesn't work well, I'd assume it will NEVER work well.
I have some lead-acid gizmos of this sort, they killed batteries
quicker than any reasonable person would tolerate...