nuckollsr(at)cox.net
Guest
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 Posted: Tue May 15, 2007 11:17 am Post subject: Circuit Protection upstream of crowbar module |
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| Quote: | I have been comparing the opening times between ANL (Bussman) limiters and
electromagnetic CBs from Carling.
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Crowbar OV protection is always used downstream of a circuit
breaker. A quality miniature is fine.
| Quote: | If they are being popped by an OV crowbar, the time delay seems to be
related to the %overcurrent. This current will depend on the
on-resistance of the SCR when triggered, as well as other resistanc in
the circuit. Can you tell me what the actual overcurrent will be? From
the delay curves for these devices it looks like 300% will give a trip
delay of less than 100 ms.
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The ship's battery will hold an alternator at bay for
seconds . . . OV trips are generally all over in 50 mS.
| Quote: | Will this protect avionics, or should transorbs be used as well?
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Transorbs are for transient (spike) protection. These are
short duration, very low energy events quite apart from
an OV condition caused by a runaway alternator. When used
as described in the Z-figures, crowbar ov protection will
generally produce a 100+ amp opening event on a 5A breaker
and get it open in 15-30 mS . . . plenty fast. Transorbs are
not helpful in an OV situation.
Fuses should not be used upstream of a crowbar OV system.
Use a miniature thermal breaker like:
http://www.aeroelectric.com/Pictures/Breakers/circuitbreakers.jpg
available at:
http://www.bandc.biz/cgi-bin/ez-catalog/cat_display.cgi?7X358218#CB1
and elsewhere.
Bob . . .
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( IF one wishes to be "world class" at )
( anything, what ever you do must be )
( exercised EVERY day . . . )
( R. L. Nuckolls III )
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