In a message dated 7/3/2006 12:21:40 PM Central Standard Time,
spamiam@comcast.net writes:
> Regarding electronics, I was planning on using something like a 1N4007
> diode. I believe that it the 1000V/1A type. I have some 27V bidirectional
>TVS's
> around, and I will use one. Do you think the 1000uF cap adds anything to
> the protection vs a 0.1uF that the regulator needs routinely? It seems as
>if
> you think that there is no other component that I should add to the power
> supply to further protect it? I am not too concerned about maintaining a
> super-regulated voltage, I just want to avoid blowing the regulator. I am
>not
> experienced in the design of power supplies in general, expecially not for
>such
> a nasty environment as the car. I would love to see what an oscilloscope
> would show in the power in the car. I have no scope, however.
>
A capacitor on the down side of the diode will act like a peak detector
causing voltage spikes to linger longer. Series impedance will limit the
current
available to charge the cap in which case the peak voltage will be less. I
would say yes, a larger cap will have benefits over a smaller one especially if
you add some series resistance.
I'm going by memory but ISTR that the expected environment in an automotive
environment includes voltage spikes in the +/- 150 volt range. 1N4007's cost
about the same as a 1N4001 so making the leap carries little or no financial
burden so why not? But I always include reverse polarity protection just in
case someone hooks the battery up backwards. It is so much nicer to just flip
the battery and see everything still work than to have to replace a bunch of
stuff that burned up as a result.
Also, if you do have an intermittent ground fault on the gauge feed line an
LM317 regulator (or just about any IC voltage regulator) is current limiting
and will survive happily - unlike the old mechanical devices which may burn
contacts as a result.
Dave
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