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Thread: Mounting high-amp relays

  1. #1
    Maximum Bitrate KyleYankan's Avatar
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    Mounting high-amp relays

    Hi everyone. I'm working on a startup circuit and need some help. I need to mount these somewhere, and they don't use standard PCB connectors. There about the size of a 9v battery but fatter. Can I just use a 9v battery clip? Maybe tape it off?

    Also - my relays ae only 10amp. My inverter supports 400 watts. Is that 400watts at 120v or 12v?
    If beleive that's 120v, which means I'm getting 3.33 amps, which these can handle. However, it's it's 400watts of 12v, It's 33.3 amps, which these cannot handle. What can I do?

    BTW, These are my Relay markings - i'm assuming 10 amps?
    IEC255
    10a 110VAC~
    -------------------
    1/2HP 120VAC
    12A 240VAC
    -------------------
    (Switch schematic)
    10A 220V~AC1
    10A 24V~DC1

    These relays are going between the battery and the inverter. Will they be enough to power my inverter?

  2. #2
    FLAC shakes's Avatar
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    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.
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  3. #3
    Maximum Bitrate mushin's Avatar
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    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

  4. #4
    FLAC shakes's Avatar
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    or a decent dc-dc power supply
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  5. #5
    Constant Bitrate minghi's Avatar
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    Quote 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
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