# relay rating question

Discussion in 'Beginner Electronics' started by krem, Dec 3, 2003.

1. ### kremGuest

I have a relay which is labed to be able to switch 120vac @ 1A. Will i
still be limited to 1 amp if i'm only switching 30vac?

2. ### John PopelishGuest

Maybe yes, maybe no. It depends on whether the current rating is
based on the continuous rating of the contacts (current) or on the
ability of the contacts to handle the flash when the current is
interrupted. I have seen both cases.

3. ### Jerry G.Guest

The ratings of the contacts can be fairly complex, and involve a number of
factors. Basically the contacts should be able to support 1 Amp of
continuous current, not including any peaks upon closure (latching) of the
contacts.

I would normally rate the relay contacts to at least double or more of the
amount of current I want it to handle. This way, a high reliability factor
will be introduced.

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I have a relay which is labed to be able to switch 120vac @ 1A. Will i
still be limited to 1 amp if i'm only switching 30vac?

4. ### Guest

A couple of points:
1) If your relay is really rated to *SWITCH* 1A at 120 vac,
then it can handle more at 30 vac, all other conditions being
equal.
2) A rating to switch 1A *should* limit your design to
switching less than that. It is not a good practice to
run components at their rated maximum.

Essentially, if a hobbyist has a question about a relay's
ability to handle the current in the circuit, he should use
a bigger (higher rated) relay - one *well* in excess of the
maximum expected current.
decision,

5. ### kremGuest

Thanks, the only reason i'm not just going out an buying the higer rated
relays is that i already have 100 of the 1A 120vac around the house and need
to use about 28 for the project i'm working on so its an expensive
proposition. Unless some one knows of a cheep source

6. ### John PopelishGuest

You might improve the contact life of the ones you have with well
designed contact snubbers, but that might cost a significant fraction
of what better relays cost.

Do all the contacts need to carry more than 1 amp, or just a few of
them?
How much current must the contacts carry (worst case) and what sort of

7. ### MichaelGuest

Simple, Try one, see how hot it gets.
Relays can dissappate heat through the pins, so if you are making
your own pcb for them , try to have a lot of copper around the contact
pins.

8. ### SpudleyGuest

If your relay has multiple contacts then I would advise running them
in parallel to double their contact rating.
Else get relays with higher contact current rating.
Perhaps you could divide the loads across multiple relays to reduce
the current imposed on each relay.