Trying to replace a lawnmower part with a contactor/relay to use an arduino and need help

Here is the original piece and need it to be 35Amps DPDT 36VDC and preferably output as DC. I’ve been looking for a part similar enough but have no luck. Thanks for any parts you recommend.

Hi @Rustery, I’m not seeing a sole relay that could interface directly with an Arduino 5V output that can switch a 35A/36VDC load.

The only solution I’m thinking of right now is to add in extra control circuitry. As in, the 5V output from the Arduino can switch on a FET to toggle the contactor’s output. Full disclosure, I’m not sure if that’s a viable option. But maybe others from the forum have other suggestions…

Hello Rustery,

Agreeing with Lindsay, I don’t see we have a finished device that will achieve this. It would be a retro fit of a few different parts, depending how comfortable you are with soldering/wiring. Maybe other suggestions will come through…

I found below SSR but is normally open, and missing the normally closed aspect making it not able to work for your application on its own:

Thanks for both of your answers. If I was to get that part any recommendations for the 2nd(The normally closed)? I have this additional part, does this fit the specs needed for the normally open I need? I used it but it didn’t work because I think I needed to have a normally closed as we because one of them broke when I tried it. Thanks again for the fast replies!

Hi Rustery,

Below relay daughter cards may be a good choice since these accept logic signals. You could use this in conjunction with the SSR that you have, otherwise can use these on their own. These are SPDT, so one relay could be your normally open and the other relay can be the normally closed.

There are dual and quad relay board options, you may have to double or triple up relay boards to achieve the required current rating, but this should work if configured correctly.
Click here for 1597-1646-ND | 1597-1647-ND

Welcome to the forum.

Switches that can handle 1.23kW DC are rare, relays are even rarer, and AFACT there are no DPDT relays with that much DC power handling. @ Digi-Key.

However the switch schematic in the photo shows it isn’t DPDT, it’s DPST 1 Form A (NO) + 1 Form B (NC) so that makes it cheaper to figure out a workaround. I would use 3 relays:

  1. 35A @ 35VDC SPST Form A (NO)
  2. 35A @ 35VDC SPST Form B (NC)
  3. Low A and V SPST to drive the two coils above. You’ll need a transistor switch for Arduino compatibility, or for ease of construction an Arduino compatible relay shield if you don’t know how to design a transistor switch for a relay.

However there is a potentially disastrous failure mode that may be avoided by the switches internal construction.
What happens if only one of the two circuits switches?
At those power levels it could be a fire hazard depending on the rest of the circuitry connected to the switch.

If you are unsure of the specific consequences of switching only one circuit at a time, than you might consider a mechanical actuator to push the switch via the Arduino rather than changing to relays.

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