relay current draw

Hi

I want to run 3 amps and a digital voltmeter on my capacitor from a relay off my Alpine CDA-9807 head units remote output. The manual doesn't list current ratings for the remote so is it ok to use a relay with a coil resistance of 66 ohms and a current draw of 160 ma? The Relay I am considering using is Radio Shack part #275-226.

The remote turn on shouldn't have a problem with that.  My general rule of thumb is to not exceed 500mA on the remote turn on.

I, personally, wouldn't use the Radioshack relay - they are overpriced and generally a lower quality.  If convenience is your only concern then it will work, but there are better places to get relays (and harnesses).

I would be surprised if your three amps and digital meter would pull more then 100mA of current.

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Kevin Pierson

If I fused my remote wire with a fuse small enough to protect the remote output say a 1/2 amp fuse I could try running it and if it keeps blowing the fuse then I would need to use a relay. What style fuse do they make for car audio that comes in 1/2 amp?

you would need to find a small glass fuse

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Kevin Pierson

which brand and model # of relay do I need? I have a HELLA and a Prolink relay but I dont know how much current they draw off the remote output.

Most automotive relay solenoids are around the 60 to 80 Ohm range (Hella, JIDECO, etc), hence around 200mA.

EG: V=IR, hence I=V/R = 12/60 = 0.2A = 200mA.
Or at upper charging voltage of say 14.4V = 14.4/60 = .24 = 240mA

If the total solenoid load is too high but you are switching a 12V supply with at least one of them, use that relay output to turn on the others.
Or have a dedicated "master" relay to turn on the others.

FYI:-
If its voltage dips that you are trying to monitor with the voltmeter, keep in mind that digital meters sample at intervals so you often miss the dip.
But if you are checking for undersized alternators at whatever load and RPM, then that's fine. But a small battery in place of the capacitor will have a much better effect and be much cheaper. (IE - I suggested a Yuasa 12V 7AH Recombination aka AGM battery. They have low ESR, can be legally use in enclosed spaces, and are cheaper than their wet counterparts - eg ($AUD) $35 vs $50. And they have HEAPS more energy than more expensive cacitor counterparts.)
But neither cap nor battery will compensate for the 1 Volt or more lost from a strained alternator (but a small 1.2AH battery will hold up much longer than a cap).