Possible alternative to the STEVECO potential relay

Hi All-

For those who build their own RPC, the frequent choice for start-capacitor control is the STEVECO potential relay.

Because it's a for-purpose device, it is often challenged to be used starting some frequently much-larger-than-intended loads in our rotary phase converters. Because of the way they're internally wired, it's not a simple task to connect them to a repeating contactor to get higher current capacity.

I was looking through the documentation on other products and stumbled upon this:

Motor Starters - Universal Motor Starting Relays | HVACR Industry Leader of Electronic Controls | ICM Controls

I immediately realized that it may be a viable alternative. The wiring sheets diagram it in much the same way as the STEVECO (that's the type of product it's intended to replace), but I believe they may have made it in such a way that it could be utilized for start-cap control in a typical Fitch Williams or similar setup.

I have not tried one, but I have used other ICM products- delay timers and replacement furnace controllers, and I'm extremely pleased with the results... IMO, they've got some fine products going.

Possibly.

I don't see a reference to adjustable cutout voltage. The fact that it says "universal" and that it has a 110 to 270V input rating suggests that it has a ratio-based cutout voltage, based on some probably fixed proportion of the input determined by the electronics inside. You might have to delve into the innards to change that if needed.

If you go to "details", and select the "zoom" function next to the picture, you can see the wiring diagram clearly.

it says it's 'differential based'. I haven't checked with 'em on it, but their 'style' is to be robust and predictable, so I'm sure they've got a good operational method. I'm sure that their tech guys would respond with substantial information density if asked... they may even offer a variation or mod... they may have those other (unused) set up for perhaps isolating the sensing from the contact circuit, which would mean it'd be suitable for driving an external contactor. The installation doc shows the diagram and connection notes as well. They identify the current rating... 30A or 50A.

I have used standard relays converted to current sensing with the coil replaced by a few turns of heavy wire, like #12. I had to use stronger springs and sometimes put a spacer on the pole to reduce the holding power, producing a release at a higher current. I wonder if anyone has tried a normal relay with back to back Zeners to alter the pull in voltage.

Bill

Here is another link to look at http://www.stearns.rexnord.com/pdf/Cat_902/16-17.pdf

I haven't built a rotary converter yet because I personally don't need one. But if I did, I would probably consider one of the newer type potential relays that are adjustable.
This should make tuning a tad bit easier.
Supco

I have used the Sinpac/ Sterns electronic start switches for single phase motors mentioned above, and they do work well when ordered for the proper pick up voltage.

SAF Ω

I have used the Supco relay for a similar purpose (not in an RPC). I had to modify the trip point for what I was doing, which involved changing a resistor value to move the range a bit.

Inside, there is a chinese copy of a standard P&B "T9" relay (now P&B is "TE Connectivity, and even their relays are chinese copies of the real thing). Has 30A 277V rating, and a HP rating (nowhere near 5HP, but this use is for the start winding only, not total motor current).

You will need an external contactor for any bigger RPC idler, for sure, and I am not 100% sure of the 5HP rating. That rating involves some guessing of the probable start winding current.