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From: "Jim Wilkins" <muratlanne@gmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: I Quit
Date: Mon, 8 Jul 2024 08:09:10 -0400
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"Bob La Londe"  wrote in message news:v6filg$mrg8$1@dont-email.me...
>
> I quit screwing around with those 5HP motors.  Now I have not one, but two 
> unused single phase 230V "5HP" spare motors.  ...

-------------------------

Single phase. I've been looking for a reasonably priced 3 phase double throw 
contactor rated for over 40A. Maybe two solid state relays (SSR) operated by 
a small double throw relay would be better for your XOR air compressor 
configuration. A DPDT center off switch could select which compressor runs 
when the pressure is low, or shut both off. The water heater circuit won't 
automatically revert to the high pressure compressor if the low pressure one 
fails, otherwise it should provide backup and enable only one at a time as 
you asked.

The simplest version has the control relay coil in parallel with the LP 
compressor motor and its NC contacts operating a single throw contactor or 
SSR to the HP compressor. This retains the single throw pressure switches 
and uses the relay for the logical inversion. Swapping main and backup 
compressors requires rewiring them, unless you have a DPDT switch rated for 
the motor current. I don't know your exact needs, priorities or intentions 
so I've given multiple possibilities.

I used this to power the time delay relay and SSR on my 120V/240V spot 
welder timer.
https://www.amazon.com/NOYITO-Precision-100V-264V-Indicator-Step-Down/dp/B0B7J8DT2G/ref=sr_1_10?