On Wed, 06 Jul 2011 12:41:18 -0400, 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
Switching DC is totally dependant on the size of the air gap of the
contacts. A single break contact will generally switch less voltage than
a double break contact. You can usually just about get twice the DC
rating of a single contact by putting 2 in series, but not always. On
some relays you can even manage 3 contacts in series but the law of
diminishing returns kicks in and you won't get 3 times the DC rating. The
best you can usually get is to use a small 4-pole contactor (about 4kW
rated). These are usually 600vAC/400vDC rated double-break contacts. For
your application you would need 2 contacts in series.
The problem is that DC will produce an arc as the contact opens. The arc
will try to maintain for as long as possible. Some high power DC relays/
contactors use electro or permanent magnets to pull the arc sideways, at
right angles to the contact face, so that it becomes stretched and more
easily broken by the air gap.
Note that the breaking capacity at DC bears no relation to the insulation
breakdown voltage or the contact's carrying or making capacity. Just
because a relay will withstand 500vDC and will make it satisfactorily, it
won't necessarily break it. Reed relays often fall into this group. They
will carry, say 3A at 500vDC, but will only break 0.5mA of DC or 0.5A of
AC.
Always try to switch AC rather than DC. It is easier and far kinder to
the contacts!
--
Mick (Working in a M$-free zone!)
Web:
http://www.nascom.info
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