Question about 12 volt auto relays

Can the contacts of a 12 volt 30 amp auto relay handle 120 volts at about an amp of AC current?

Couldn't find a car group that was still active.

Reply to
marcus
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snipped-for-privacy@invalid.com expressed precisely :

NO NO you would be exceding the insulation ratings by 10 times.

The contacts can certainly handle 1 amp AC but the higher voltage is way outside the designed safety limits. 8-o

Reply to
John G

I finally found something. According to this page the answer would seem to be no.

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Reply to
marcus

That's pretty much what this page says.

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Thanks for answering.

Reply to
marcus

Very possibly yes. But, the insullation isn't rated for 120 VAC, so it may be unsafe.

- . Christopher A. Young learn more about Jesus .

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Reply to
Stormin Mormon

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 use.

Bottom line is that unless it's specifically marked for 115v ac or higher , due to safety concerns I would not use the relay.

Reply to
philo

My experience says yes...going the other way, 120 rated points can't handle 12 volts at the typical automotive use amperage. The wiring can also handle 120. (although not rated for it).

Reply to
bob_villa

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.

Reply to
trader_4

Actually, twice each cycle...

Reply to
danny burstein

Thanks for the lesson...he was asking about contacts and not the coils of the relays. And I never said they were rated for it...learn to read or not comment.

Reply to
bob_villa

This doesn't answer your question but you can buy some that do. There's one here:

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This link is to Zorro.com. This
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will take you to one of the Allied Electronics pages with relays filtered for 12VDC coil voltage. Allied doesn't sell to individuals but this might give you an idea what's available. I don't have the foggiest notion if NAPA or O'Reilly would have something. I unintentionally learned something long ago. Starter solenoids are rated for intermittent or continuous use. Intermittent really means intermittent.

Reply to
Dean Hoffman

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.

Reply to
trader_4

This, of course, is not true for the reason YOU gave before...DC is NOT the same as AC. The AC 10A rated contacts would burn-up using it for DC. Your area of expertise is clearly not in evidence here.

Reply to
bob_villa

Here's your sine!

(very big grin, my friend.)

- . Christopher A. Young learn more about Jesus .

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Reply to
Stormin Mormon

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.

Reply to
trader_4

What IS the point in even responding to your drivel...you add more words, beleaguer the point and say the same thing...never admitting you're wrong. Stick it!

Reply to
bob_villa

To the op Consider the failure modes and the consequences. The contacts may weld close. Consider the insulation between the contacts and between the contacts and the relay mounting frame and the relay coil circuit. What are the consequences of an insulation breakdown between the 120v circuit at the contacts and the low voltage relay coil circuit?

Mark

Reply to
makolber

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:

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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.

Reply to
trader_4
[snip]

Are you sure about that for the CONTACTS, or is it just that the COIL has to have DC?

Reply to
Mark Lloyd
[snip]

They did when I tried it (around 1980). However, there was a minimum order so it wasn't worthwhile for just one small part.

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Reply to
Mark Lloyd

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