Folderol wrote on 8/29/2017 1:33 PM:
> On Mon, 28 Aug 2017 18:56:01 +0000
> Jim H  wrote:
>
>> On Wed, 23 Aug 2017 22:29:55 +0100, in
>> , Folderol 
>> wrote:
>>
>>>
>>> First off, charge voltage is inversely proportional to temperature, and one
of
>>> the companies I contacted was kind enough to send me a schematic of a
simple
>>> compensated voltage regulator, with a thermister which had to be *in*
*Thermal*
>>> *contact* with the battery under charge.
>>
>>
>> Would you care to share that schematic? Please?
>>
> I'd be more than happy to, only that was a long time ago, and that along with
> many other documents of the time have long since disappeared.
>
> From memory there wasn't much to it. An op-amp driving a power transistor as
an
> emitter-follower, then a diode to protects against the battery feeding back
> when the power was off. Control was from a high resistance feedback path from
> the battery terminals (so negligable drain on the battery) and somewhere in
that
> lot was the thermistor and a preset pot.
>
> Current limiting was crude - just a resistor in series with the transistor
> collector.
>
> Not a lot of help I'm afraid :(
>
> Hmmm, thinking a bit more. The thermistor and preset weren't directly in the
> feedback but in the potential divider producing the reference voltage.
>
> Actually it's remarkable what you remember once you actually start thinking
> about things. One resister from the battery + to the inverting pin of the
> op-amp. Something like 470k I think, and the same from there to the common
> ground.
> A resistor from a zenner reference to the non-inverting pin of the op-amp,
then
> resistor - preset - thermistor from there to ground. No idea what the values
> were, nor what specific thermistor it was

I believe I saw a modern copy of that circuit.  Instead of the opamp, pot
and many other components it has an MCU.  Otherwise identical...

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

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