I'm not certain which sensing method we're discussing (there were two of
them, one current-sensing, the other voltage-sensing), but the
voltage-sensing setup is probably not going to like having the sense
lead driven to a higher (or lower) voltage than the power supply ...
This is truly ancient stuff (as auto electronics go), it wouldn't be
surprising to me if it didn't have any reverse-polarity protection.
Early stuff certainly had the reputation of being quite fragile (which
is part of the reason many cars still had points even in the mid-70s).
Randall
Bill Babcock wrote:
>
> Probably nothing since it's the power supply leads that we're talking
> about, not the signal lead. I don't know about ancient tech like an
> electronic smith tach, but all electronics for cars have to accommodate
> the difference between a poor battery state (which might be down around
> 10.5 volts) and a full charge state (might be 14.5).
>
> -----Original Message-----
> From: Ed.Barnard@MARCONI.COM [mailto:Ed.Barnard@MARCONI.COM]
> Sent: Wednesday, August 08, 2001 2:05 PM
> To: Bill Babcock; Ian Cowie; FOT
> Subject: RE: Smiths tach
>
> Bill;
> The only issue with that method may be the .7 volt drop between each
> diode. What will that do to the accuracy of the tach reading?
> Ed Barnard
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