Using a relay to switch high current

xpusostomos
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Using a relay to switch high current

Unread post by xpusostomos » June 8th, 2016, 1:57 pm

Hi all, I want to put an external anderson plug on my car. But I want an internal switch to enable it, in case some smarty were to plug into it and drain the battery. The switch I want to use is a Carling style rocker switch which is rated to 20 amps.

I could probably survive with a 20 amp outlet, but I was thinking another option would be to put in a relay rated to at least 50 amps. This would also save me running relatively heavy cable all the way to the switch, and it would also allow the outlet to handle a full 50A.

But I don't know anything about relays. I heard that maybe relays don't work unless you actually switch high current. So like if I install a 50A rated relay and then only plug 3A into it, it might not be enough to make it switch.

Has anyone got any recommendations on how to go about this?

Muckinhell
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Re: Using a relay to switch high current

Unread post by Muckinhell » June 8th, 2016, 5:02 pm

if you look up winch solinoid that might be what you are wanting regarding that many amps, it has seperate switching wich you use a remote switch like the carling to activate it so it wont matter what current you draw, also a winch solinoid will cater for inrush currents that more smaller relays mighten cater for and they have nuts so you can lug your 6 b&s cable and fit easily.

xpusostomos
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Re: Using a relay to switch high current

Unread post by xpusostomos » June 8th, 2016, 5:24 pm

Muckinhell wrote:if you look up winch solinoid that might be what you are wanting regarding that many amps, it has seperate switching wich you use a remote switch like the carling to activate it so it wont matter what current you draw, also a winch solinoid will cater for inrush currents that more smaller relays mighten cater for and they have nuts so you can lug your 6 b&s cable and fit easily.
I think a winch solenoid is just one particular type of relay. Any relay handling big amps will tend to have big nuts to connect the wires.

But the question is still, will a high-amp relay work properly when you aren't actually drawing big amps? It works with a winch which will always suck big amps, but what if I connect a light drawing 1 A? I thought I might have read somewhere that a big amp relay might not work unless you are actually pulling big amps.

NZ LUX
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Re: Using a relay to switch high current

Unread post by NZ LUX » June 8th, 2016, 9:24 pm

The small "remote" switch only energises the solenoid coil which magnetically pulls in the set of high current contacts. That's all it does, it doesn't know whether it's actually switching 1 amp or 100 amps.

Red04VXE
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Re: Using a relay to switch high current

Unread post by Red04VXE » June 9th, 2016, 7:56 pm

A 70amp Relay is cheap and easy solution for a 50amp Anderson Plug. 8 B&S cable would be perfect.
New Toy, 1982 HJ60 2H 4spd 33's soon to have F&R LockRights and LongFields.

Red04VXE
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Re: Using a relay to switch high current

Unread post by Red04VXE » June 9th, 2016, 7:58 pm

New Toy, 1982 HJ60 2H 4spd 33's soon to have F&R LockRights and LongFields.

Muckinhell
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Re: Using a relay to switch high current

Unread post by Muckinhell » June 10th, 2016, 5:19 pm

the problem with those relays is they use spade terminals wich arnt the most reliable connection unless you put a small screw through them to secure to the pin. they may work loose over time and corragations etc. And yes you use a user selectable swith to turn the relay on and off it doesnt matter the load then. just dont do it if you can avoid it while there is a load ready to go IE:a compressor hooked up and switched on.

hdcoffeeboy
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Re: Using a relay to switch high current

Unread post by hdcoffeeboy » June 11th, 2016, 10:01 pm

I'm in the process of doing something similar. I've mounted a fuse box in the back, along with a 100A relay (http://www.ebay.com.au/itm/281968121688) which will allow the whole fuse box to be turned on and off with the ignition. The whole lot is fed by 6B&S cable, which will also run to an Anderson plug on the tow bar.

I know 100A is overkill, but it has screw terminals.

Image
The wiring is incomplete, but you get the idea.
Tim

2004 Challenger LS Auto. Build-up photo gallery.

Red04VXE
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Re: Using a relay to switch high current

Unread post by Red04VXE » June 12th, 2016, 7:45 am

100A isn't overkill. That fuse panel would be rated to 100amp so it works out well.
New Toy, 1982 HJ60 2H 4spd 33's soon to have F&R LockRights and LongFields.

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