On 04/19/2015 02:17 AM, firstname.lastname@example.org wrote:
The only way to absolutely know is to look at the relay and observe the
manufacturer's marked specifications. Automotive relays typically have
their contacts rated at 14V DC.
If the contact ratings are marked 115v AC/DC then it would be OK to
Bottom line is that unless it's specifically marked for 115v ac or
higher , due to safety concerns I would not use the relay.
Why not just get a proper relay and use it. I hope that the auto relay you
want to use is not a starter relay. The problem with them is most of them
have the coil and contact connected internally as the battery input. This
would present a problem with the coil voltage inseparable from the contact
On Sunday, April 19, 2015 at 8:34:25 AM UTC-4, bob_villa wrote:
Your experience is wrong. It's not just voltage and current that
are involved. There is the fundamental difference between AC and
DC. With AC, the current reduces to zero on each cycle. Unless the
relay is designed to allow for that, the contacts can release. That's
why there are AC relays, DC relays, and some that will do either.
I've never seen an auto relay rated for AC or 120V.
On Sunday, April 19, 2015 at 9:05:06 AM UTC-4, bob_villa wrote:
While you're right that he said contacts and didn't say what
he was going to drive the coil with, you still don't know what
you're talking about, because you implied
it's OK to do. As for the contacts, what's up with this?:
"120 rated points can't handle 12 volts at the typical automotive use amperage"
There is no typical automotive use amperage or 120V amperage.
There is only what the relay is designed and rated for. If you have
a relay with 120V 10A contacts, the contacts could handle 10A at 12V.
On Sunday, April 19, 2015 at 9:37:59 AM UTC-4, bob_villa wrote:
Really, burn up? With *any* DC voltage or current? I never said relay
contacts rated for 10A, 120VAC could handle 10A, 120V DC.
When you have contacts rated for both, the DC amperage rating will be
substantially less at the *same voltage*. But were talking about
going from 120V to 12V at the same time, a factor of 10X,
in which case, the contacts rated for 120V, 10A, can probably handle
the 10 amps at just 12V. And even more to the point, he's actually going
from 120V to 12 volts and from 30A to just 1 amp.
But the right answer is that the relay should be rated for the application.
And it would probably be more productive if he told us what he's really
trying to do.
On Sunday, April 19, 2015 at 10:55:35 AM UTC-4, bob_villa wrote:
I guess the point would be to clarify WTF you're talking about.
Typically switching contacts rate for AC can also be use with DC
at derated voltage and/or current. So, contacts rated for 120V AC, 10A,
will probably be OK at 12V DC, 10A.
Here's an example of a common relay data sheet that shows exactly that:
Note that the contacts are rated for 10A, 250V AC or 30V DC,
it's one example of a relay that does just what I said. It would
be fine at 12V and 10A.
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