Alt-BEAM Archive

Message #01654



To: "Feser, Jason" jfeser@ea.com
From: Bob Shannon bshannon@tiac.net
Date: Sat, 20 Mar 1999 20:09:35 -0800
Subject: [alt-beam] Re: Solar charger for NI-CAD walker...


Feser, Jason wrote:
>
> Hey gang,
>
> I was going through my 1000 Circuits book from none other than Forrest
> Mims and found a circuit for a solar charger. I was thinking that I could
> implement a solarize my walker by trickle charging a NICAD with a solar
> cell. My question is this - can you be charging a nicad and drawing from it
> at the same time - I think that NICADS have memory, so would this damage the
> battery's ability to store its maximum power level? Also, the circuit I
> have doesn't seem to have any protection against overcharging - anyone know
> how to implement this?

If you limit the charge current to C/25 (one twenty-fifth of the
batteries 'C'
rating, in amper-hours) then you need not worry about overcharging at
all.
When the charge current is a trickle charge at most, you cannot
overcharge
a Ni-Cad cell.

If your worried about memory effect, simply fully charge and fully
discharge the cells on every cycle and it will never develop a 'memory'
at all. If this is too much of a restriction, then use Ni-MHD cells
> I was also thinking that when the power level of the NICAD got below a
> certain threshold, say about 3.5v, it might at that point use a IR recieve
> to get a signal from a IR transmit mounted to a wall wart and then head the
> walker in that direction. Then when you saw your bot scrabbling against the
> wall near the trasmitter, you would know that it was time to juice up. Is
> this a do-able thing? Would it require the use of a microprocessor?

With IR tranceivers, probably.

But you can probably do this with polarized IR LEDS and matching
polarizers over a special set of photodiodes that become active when the
power level is low.

> I've
> never played around with an IR setup before so I'm not too sure if this is
> something that is easily done.

IR detector modules have some funny habbits, and are best used with
microprocessors.

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