On Jul 7, 2:41*am, Don wrote:
Will this relay work to switch 500 DCv .5 amps? I can't find 500v
relays under big buck prices.
tyco/P&B K10P-11A15-120
http://www.mouser.com/ProductDetail/...0P-11A15-120/?
qs=iO7mgM19OaZKj751FOt%252b%252bQ%3d%3d
Thanks,
Don
Trying to switch a 500Vdc amp rail with a relay can lead to prolonged
arcing between contacts if they don't open wide enough. Few relays I
have ever seen do this unless they are very bulky industrial types.
Using a relay rated for 30Vdc is madness. That same relay might be OK
for 110Vac. However, there are applications where I have wanted to
discharge the +500Vdc B+ caps in an amp very quickly to make an
umbilical cable plug pin voltage go to safe levels within 0.5 seconds.
So I have used a two pole relay meant for 240V mains with both relays
in series and biased at 250Vdc, with 0.1uF x 630Vdc rated caps across
the contacts and with series resistance of 470 ohms at 20W rating
which will take the maximum current of about 1A for a short time when
the caps are discharged.
Even the simplest thing you may want to do with 500Vdc needs careful
analysis and thought or else you'll end up with smoke and regrets. If
there is a choke involved in the 500Vdc rail, it makes matters worse
to design around it, and a suitable diode, say IN5408 may need to be
placed across the choke to prevent back EMF causing voltage across the
relay to go very high when contacts oen and DC flow is interupted. So
you need to know what you are doing. Its usually better to try to
always switch the AC transformer winding producing the 500Vdc. There
are also ways of using an SCR to perform switching instad of a relay.
About 16 years ago I made a bench top PSU capable of 600Vdc at 100mA,
and it has an over current protection circuit with SCR in series with
500Vdc, and the gate control circuit works from a board powered by a
12Vdc supply biased at the Vdc rail, and it includes a relay to switch
the gate signal and turn a red lamp on to tell me when I've gone over
current. I can reset it just by turning off the ac on/off switch. Its
very primitive as most things I made back in 1994 were, but its never
failed, and saved me from smoke and expensive repairs during many
tests of tube gear and finding out the basics myself as you should be
doing.
Patrick Turner.