Potential relays

Don Gitzel · Jan 13, 2021

What do you think about using potential relays to start a RPC. I found them finicky and troublesome. I usually wire the start relay to the start button momentarily energizing the start relay and releasing the button when the idler comes up to speed. If remotely started, I will use a time delay relay. I think potential relays are more meant for single phase refrigeration loads.

JST · Jan 13, 2021

Don Gitzel said:
What do you think about using potential relays to start a RPC. I found them finicky and troublesome. I usually wire the start relay to the start button momentarily energizing the start relay and releasing the button when the idler comes up to speed. If remotely started, I will use a time delay relay. I think potential relays are more meant for single phase refrigeration loads.

They have worked for a lot of RPCs, so they are not that bad.

The one serious problem I see is that unless added parts are used to prevent it, if the voltage drops, such as under an abnormal load, they will connect the start caps again. The electrolytic type cap will likely be destroyed by that, but one can use oil filled capacitors rated for the voltage.

A time delay relay is pretty positive and won't reconnect.

Phil in Montana · Jan 13, 2021

2nd time delay,...Phil

Strostkovy · Jan 13, 2021

JST said:
They have worked for a lot of RPCs, so they are not that bad.

The one serious problem I see is that unless added parts are used to prevent it, if the voltage drops, such as under an abnormal load, they will connect the start caps again. The electrolytic type cap will likely be destroyed by that, but one can use oil filled capacitors rated for the voltage.

A time delay relay is pretty positive and won't reconnect.

My RPC was a dual motor 10hp/40hp idler. The 40hp motor was a dead short, and attempting to connect it after it was up to speed dropped the 240V line to around 160V or less, causing the potential relay on the 10hp idler to kick back in. The only ill effect was fusing the contacts on the potential relay together, as I don't think they are really meant to close under load. The start capacitors were fine, but the 10hp idler would immediately spin up and then "growl" very loudly until you hit stop/start a few times and the contacts properly seperated.

I find potential relays are finicky only when connected incorrectly.

thermite · Jan 13, 2021

Don Gitzel said:
What do you think about using potential relays to start a RPC. I found them finicky and troublesome.

That, they are. Age and other variables thing. Not just connection.

Not new.

Many of us have the same problem between our ears, and for the same reason, flat batteries not included.

Next subject?

rons · Jan 15, 2021

Don Gitzel said:
What do you think about using potential relays to start a RPC. I found them finicky and troublesome. I usually wire the start relay to the start button momentarily energizing the start relay and releasing the button when the idler comes up to speed. If remotely started, I will use a time delay relay. I think potential relays are more meant for single phase refrigeration loads.

The only praise for them comes from the people selling them.

9100 · Jan 21, 2021

My first converter came with a potential relay. I converted a standard AC coil relay to a current relay by rewinding the coil with a few turns of 12 ga enameled wire. Worked great. I don't know what this hangup on potential relays is about.

Bill

rons · Jan 21, 2021

9100 said:
My first converter came with a potential relay. I converted a standard AC coil relay to a current relay by rewinding the coil with a few turns of 12 ga enameled wire. Worked great. I don't know what this hangup on potential relays is about.

Bill

Because the net and youtube. The tube has a ton of first-timers advertizing their first works, and of course people copy....

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