OT: Battery Charger DIY...

Thu Oct 21 11:44:13 CEST 1999

Batz,

  I have seen these aklaline battery rechargers, and they say
you shoudlnt charge a batterymore than 10-12 times..

  NiMh batteries are commonly used in mobile phones, typically
you get 3-4 times the life for the same weight as a NiCd,
the other alternative is Lithium Ion batteris...

  Paul

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-----Original Message-----
From:	Batz Goodfortune [SMTP:batzman at all-electric.com]
Sent:	Thursday, October 21, 1999 5:44 AM
To:	synth-diy at mailhost.bpa.nl
Subject:	Re: OT: Battery Charger DIY...

Y-ellow Y'all.
	I feel a bit guilty because everyone's helping me with my little problem
and not actually offering anything up to Chris with his big problem. But I
thought I'd mention a few things in passing.

At 09:07 PM 10/20/99 -0400, J.G. Wong wrote:
>Hi,
>
>    Unfortunately I am away from my bases on business but I was involved
>in some Nicad research that is related to your charging problem so I can
>tell you a little but no specifics because my stuff isn't handy.

I hate NiCads. NiCads are trouble. And if an article in a PE (Practical
Electronics Magazine) circa 1982 is anything to go on, so say a lot of
other people. I cannot find the article in question right at the moment but
this is off the top of my head.

The author talked about some Swiss (I think) rescue organization which
banned the use of NiCads because they were too un-reliable. Not only that,
but they could pack a whole pile of Alkalines for the same weight as a
single spare set of NiCads. 

Weight and size is my big problem here. Though Barry Klein just told me
about something called NiMh batteries which I've never come across before.
I have some old Military Magnesium batteries. I know nothing about them
either but they're bloody weird. They deliver virtually no volts and no
current initially and then suddenly build once you load them up. If anyone
knows anything about Magnesium batteries I'd be curious to find out.

That aside, what I wanted to mention about the afore mentioned PE article,
was that it was about how to charge Alkalines. Remember this is Circa 1982.
It mentioned in passing that in Japan it has always been illegal to print
"This battery may explode if recharged"  on the side of alkaline batteries.
And that for as long as the author could remember, you could buy Alkaline
chargers over the counter in Japan. Saving them some billions on money and
resources every year apparently. Not to mention the lack of nasty chemicals
filling their land-fills.

It went on to describe a method of charging Alkalines called "Periodic
Phase reversal." Simply put, this half wave rectifies AC @ 1.5 volts or so
(I think) and then a suitably sized resistor is placed across the diode
such that a small reverse spike is applied to the battery as it charges.
This does something chemically to the battery and allows it to accept a
good charge. I'm sketchy on the details but the Author showed pictures of
batteries, even carbon batteries, split open and showing the difference in
composition before and after etc. There are two trade-offs. 1 is that you
shouldn't charge them for any more than 11 hours. 2 you must charge each
cell separately. Not that you can't charge banks of batteries but unlike
ni-cads, they can't be charged in series. Each battery must find it's own
level or something, and charge can't be allowed to migrade between
batteries during charging. Something like that anyway.

Like other, more modern supposed "rechargeable Alkaline batteries" you only
get a max of 25 re-uses out of them.

On safety. I recall him mentioning that all alkaline batteries have to have
safety vents placed in them. It is apparently law in England but I don't
know about other parts of the world. Regardless of which he claimed that it
was far too dangerous for a manufacturer to do otherwise in case of
accidental situations such as short circuits or even placing a bad cell in
with a bunch of good ones. But then this is mainly Union Carbide we're
talking about here and does the name "Bopahl"(sp?) mean anything to you?

Union Carbide's track record aside, I can remember my Ol' man charging
Energizer Alkaline batteries in a conventional fashion years ago. The only
thing I remember being wrong was that he only got about 7 - 10 uses out of
them before the charge would die away quickly.  But when you think about
it, And I should have been thinking along these lines myself, even if you
get 5 uses out of an Alkaline battery, that's a saving of 5 batteries.

And as an aside to this. A friend of mine, back in the early 80s worked for
a mining survey company. They would often be caught up bush, hundreds of
miles from the nearest life form let alone a shop that sold batteries.
What they use to do is get the skillet out and roast their batteries over
the camp fire. By pouring heat into them it caused a chemical reaction
which tended to give them some more charge. You should have seen the
battery box of his portable cassette player. All melted because eventually,
the only way to get life out of them was when they were hot, chard and
crispy. :) But he got to listen to his Monty Python tapes and that was all
he cared about.

The other problem with all this, in my case at least, -and some of you may
remember this from maybe 18 months ago- is the conjuring of a a low
drop-out regulator. I use to have the results on the AEK web site as you
may recall. Using a 723, and external reference and comparator. The problem
with low drop out regs is that it is totally at odds with high current to
run a head-light. Put simply,  the higher the current, the larger the
voltage drop across the device delivering the current. The best I got was a
drop out of 4 volts or so. 3.8 I think? And that supplying a constant
current of 500mA @ 3volts. Some would say that was pretty good but not good
enough to get maximum use out of a large and heavy SLA.

In the end it was weight that killed the whole thing. I couldn't find a
battery that was small, light weight, rechargeable and reliable. But I'm
hunting down the article on charging Alkalines. I'll probably find it in a
week or two. :( If I can find someone who can scan it for me I'll post it
on the web site such that you can see it.

Hope this helps 'n' all that.

Thanks to everyone who wrote with ideas.

be absolutely Icebox.

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