20KVA Power supply Generator Automiser question

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I want to build myself a system that starts my generator. I know a lot of ready made starters are available but i want to start it remortly and according to my need.

To Start the Engine I Turn a key which cranks the engine. I want to replace this key by a relay. Any idea what would be the relay contact rating required for this purpose? Im pretty sure the main starting current does not pass through this key starter arrangment.

For the change over from mains to generator i wnat to use a c/o relay here. The max rating of relays i can get hold of here is 40A. My manual changeover switches are rated at 32Amps So i was thinking of using 2 relays in parallel per phase for safety sake. Does anyone see any problems with this arrangement?

Let me know what you think.

Regards rodney

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rodney_alm wrote:
I want to build myself a system that starts my generator.

For the change over from mains to generator i wnat to use a c/o relay here. The max rating of relays i can get hold of here is 40A. My manual changeover switches are rated at 32Amps So i was thinking of using 2 relays in parallel per phase for safety sake. Does anyone see any problems with this arrangement?

Let me know what you think.

Regards rodney

Paralleling of relays to increase the current handling capacity is generally not considered a good idea. One relay will almost always close/open before the other with resultant high current and eventual contact damage.

Greg

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For the record, I once opened the starter of my car, and disassembled the whole thing (for cleaning and brush change) and the starter relay (the relay that actually connects the battery to the starter motor) had a 4mm thickness copper disc as contacting "relay". And there were evidence of sparks and solid copper accumulated inside the relay case (many years of use, of course). Nevertheless, the relay is still working despite such wear away.

The moral is: You need an automotive "starter" rated relay to do this. Try to not parallel relays, as Greg recommended

Nachus

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rodney_alm wrote:

To Start the Engine I Turn a key which cranks the engine. I want to replace this key by a relay.

What size wire does the key switch use? My tractor switch replacement had 16 gauge wire and was rated for 5 amps.

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Check out SolarConverters.com in Canada. They have generator controllers and MPPT PV charge controllers and other cool stuff.

Imagecraft compiler user

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If in doubt, measure the start current with a multimeter - then you will be sure. As for the changover relay, sound like you need to use contactors rather than relays - basically they're the same thing but 40A contactors should be easy to source from an electrical supply shop. You probably won't get a changeover contactor but you can use two contactors with a mechanical interlock. Don't expect them to be cheap either!