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From: Kevin McMurtrie
Subject: Re: Overvoltage Schematic Wanted
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Sat, 14 Sep 2002 07:34:12 GMT
NNTP-Posting-Date: Sat, 14 Sep 2002 00:34:12 PDT
In article <3D82A9C1.EA2CF8B6@hotmail.com>,
Joey <"joeyga"@hotmail.com> wrote:
>I'm looking for an overvoltage schematic that meets the following
>criteria. If anyone
>has one I would appreciate a copy and be willing to pay any expense if
>My email is firstname.lastname@example.org
>1. For a 12 volt circuit that would trip at about 16 volts
>2. Does not use any relays
>3. Has three wires to device, one + in, one ground, and one + out.
>4. If the + in exceeds the set voltage then there is no output.
>5. Input must be cut off and back on to reset
>Such a device is used on aircraft to cut off voltage to the alternator
>fail and normal voltage exceeded. I've seen the clam shell type and the
>type but never a schematic for the type I've mentioned above. ANY help
>will be greatly appreciated. Thanks.
I think you mentioned relay failure before. How about using a relay to
cut only the field coil? It wouldn't need to carry more than about 5
amps so you could use a high quality relay without spending a fortune.
I'm not sure you could get better reliability from semiconductors
without going through a lot of trouble. The circuits will need heavy
protection from atmospheric ESD, RADAR pulses, and all the spikes
normally on a 12V vehicle system.
Is number 5 strictly required? It seems like a better solution would be
to auto-reset the safety when the battery voltage falls below 12.0
volts. At that point the battery is in a position to absorb lots of
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