Thread: Mounting high-amp relays

the 400 watts is probably for the AC side ... so that'd be 120v @ 3.33 amps as you said ... but remember there's no such thing as free power ... extra current is needed on the DC side to get the higher voltage on the AC side. In order to get your 120v @ 3.33 amps on the AC side, you'd need 33.3 amps @ 12v on the DC side. And that's assuming the inverter is 100% efficient (which it's not!)

anyway, in reality you probably won't be pulling more than an amp or two on the AC side.

As long as there's no risk of shorting, you can mount the relays wherever.

Your 400 watt inverter supplies a max 400 watts at 120VAC, and draws a max 400 x (1/efficiency%) at 12VDC. So if it's, say, 90% efficient at peak power, it will be drawing about 450 watts, or 37 amps.

Now even if your relay can't handle the max inverter rating (and in this case it apparently can't), you could still use it as long as your circuit didn't draw more than the relay is rated for. Just make sure to put a <= 10A fuse in line.

Assuming your circuit is your entire PC system, a 10amp relay is probably not going to cut it, as that limits you to 120watts minus all the inefficiencies of alternator and PSU - the system itself will probably need to draw less then 100watts. The solution? Get a 30A automotive relay, they're not expensive

or a decent dc-dc power supply

Originally Posted by mushin

As long as

draw less then 100watts. The solution? Get a 30A automotive relay, they're not expensive

check out www.partsexpress.com the automotive relay is like 1.79 bucks