Is there a Stevco or other Relay that is socket mount ?

Wanting to build another RPC, and it would be a much neater job if
the voltage sensing relay was mounted in a socket.

I haven't seen one in my searching.

Omron makes octal base, voltage sensing relays; the LG2-AB should be the right series.

But they are very proud of them, they run around $200.

digger doug said:

Wanting to build another RPC, and it would be a much neater job if
the voltage sensing relay was mounted in a socket.

I haven't seen one in my searching.

Click to expand...

For eons Potter & Brumfield (now part of TE Connectivity...) built their KA series - KA11-DY a popular one as was found in everything from office copiers to PABX switches - on Octal bases. And then they were copied. Whole tribe gots to be common as dirt, folks like Digi-key or Mouser?

Smaller "Ice cube" format, the auto industry standardized onto sockets, and by the trillions.

The "Voltage Sensing" part (or current..) is a function you can DIY onto ANY sensitive relay with an external circuit.

Of about three components. One of them usually a Zener Diode. Not hard.

Not hard to MAKE a(ny) relay INTO a "socket mount", either. Time was, we bought stock metal boxes already equipped with a plug for those various "custom" tasks.

"Store bought" just makes plug-and-go replacements easier for the kitchen and grounds-maintenance staff.

Tbartoletta said:

Omron makes octal base, voltage sensing relays; the LG2-AB should be the right series.

But they are very proud of them, they run around $200.

Click to expand...

Don't look too promising with a detection range of 200V and an inductive current rating of 1.2A.

For a RPC that operates in the range of 240-250V
LG2 Voltage Sensor/Specifications | OMRON Industrial Automation


SAF Ω

I think it's inside the operating envelope, but yes you would need to control a separate contactor with it.
Set voltage: 150-240
Release voltage: 140-230

It's just watching the generated leg to drop out the start cap or pony motor right? I've never built an RPC so please enlighten me if I'm thinking about it the wrong way.

ANY relay is a voltage sensing relay, once you've determined what it's pull-in current requirement is... just add appropriate resistance to it, such that it doesn't reach pull-in strength until your setpoint.

On my self-starting RPC, I used an ordinary light dimmer as an adjustable, in series with a smallish contactor... and adjusted the light dimmer 'till the contactor pulled in at a desired point.

Only thing to remember, is that there's a fundamental difference between a relay and a contactor:

A relay is a device which pulls in, once coil current reaches a high enough point for it's magnetism to pull in the contact bar. The relay coil draws a constant current, regardless of wether it is dropped out, or pulled in.

A CONTACTOR, is a special relay who's electromagnet pulls in the contact bar, and once seated, the contact bar becomes a magnetic shunt integral to the electromagnet's polepieces. The result is that it has substantially greater 'holding' force, than 'pull in' force. Once pulled in, the shorting bar's contact increases the inductive reactance of the COIL, which reduces the coil's current substantially. As a result, a contactor flows substantially less current once pulled in, than when it is PULLING in... and the other side effect, is that it will HOLD itself in until a much lower voltage, than what was required to PULL in.

So if you're messing around with relays and contactors to make this work (on a much more sensible budget than a specialty solution) you'll know why it does what it does, right?

On my RPC I just used a DPST momentary green push button to energize a NO Contactor with a power loop to keep it energized for the main line power supply using the first pole and a NO Contactor on the second pole feeding my start caps. I push and hold the button to turn on AND start the idle motor, then when I release the button the start caps drop out but the main relay stays energized to keep the RPC running.

I have a 3rd NO contactor on a 5 second delay relay that delays the output from the RPC to prevent the start caps from juicing my machines before they drop out.

On my power loop feeding the first relay I ran (1) red NC momentary push button and (2) e-shut offs and a line from my garage Ceiling light so when I press the red button it all shuts down, or if I trip a E-stop OR if I walk out and turn the garage lights out it still all shuts off!

I also run fuses AND breakers.

My breakers are over sized and only for SHORT circuit protection and my fuses are sized as close to running specs as possible for overload protection

DaveKamp said:

ANY relay is a voltage sensing relay, once you've determined what it's pull-in current requirement is... just add appropriate resistance to it, such that it doesn't reach pull-in strength until your setpoint.

On my self-starting RPC, I used an ordinary light dimmer as an adjustable, in series with a smallish contactor... and adjusted the light dimmer 'till the contactor pulled in at a desired point.

Only thing to remember, is that there's a fundamental difference between a relay and a contactor:

A relay is a device which pulls in, once coil current reaches a high enough point for it's magnetism to pull in the contact bar. The relay coil draws a constant current, regardless of wether it is dropped out, or pulled in.

A CONTACTOR, is a special relay who's electromagnet pulls in the contact bar, and once seated, the contact bar becomes a magnetic shunt integral to the electromagnet's polepieces. The result is that it has substantially greater 'holding' force, than 'pull in' force. Once pulled in, the shorting bar's contact increases the inductive reactance of the COIL, which reduces the coil's current substantially. As a result, a contactor flows substantially less current once pulled in, than when it is PULLING in... and the other side effect, is that it will HOLD itself in until a much lower voltage, than what was required to PULL in.

So if you're messing around with relays and contactors to make this work (on a much more sensible budget than a specialty solution) you'll know why it does what it does, right?

Click to expand...

Not quite. A relay as you describe is a DC switch. There are also AC relays. The difference between the term relay and contactor is largely just convention. Most in the industry would say a relay is a 10 amp maximum switch, a contactor is anything more than that. I haven't seen a Stevco so I can't comment on their method of control, nor have I designed any sensing relays. What I know about magnetics is that there must be auxiliary controls to get reliable switching control. The reason for this is that in the open gap condition, the pull is strongly influenced by small mechanical variations. In order to over come these problems, a control needs to have sharp switching points that are best done with Zener diodes and associated circuits.

Tom

TDegenhart said:

What I know about magnetics is that there must be auxiliary controls to get reliable switching control. The reason for this is that in the open gap condition, the pull is strongly influenced by small mechanical variations. In order to over come these problems, a control needs to have sharp switching points that are best done with Zener diodes and associated circuits.

Click to expand...

In my RPC, the external control device, is the dimmer, and it has proven itself more than sufficient to very reliably handle the circumstances of the last 20 years' use. The circumstance of a self-starting RPC (which is where guys are using the STEVECO relay) isn't particularly critical about the point at which the relay pulls in, as long as it does sometime after the idler motor has kicked itself off in the right direction. Hitting 30% of the idler's design RPM is enough to assure that it'll spin up the rest of the way on it's own (without capacitive phase shift).

By limiting the effective power flow thorugh an AC contactor's coil with the dimmer, it prevents the armature from pulling in until there's significant generated leg voltage... which meets the same end as the STEVECO... with the advantage that, once pulled in, if the RPC's generated leg is pulled down hard, the contactor's armature is not likely to drop out and cause a (somewhat catastrophic) re-engagement of the starting capacitors. My personal experience with the STEVECO was just that.

The STEVECO was intended to be a direct-controlling start-capacitor relay for fractional horsepower single phase motors, usually for HVAC applications. They're NC devices, and open somewhere around 171 to 184v... and drop out at 90v. When guys use them for an RPC, they're basically stuck (by virtue of much higher current capacity) using it as a control-element for driving a contactor to engage the starting capacitor bank. IIRC, the logic circumstance is reversed, too (apologizing for my memory... it's been a long time since I built mine). I found that just putting the dimmer on a 120v coil, and dialing up the desired pull-in voltage, worked great.

Because of all the inductive punishment, I wouldn't personally feel good about putting a semiconductor in there and expecting it to survive well... especially not a ZD... there's just too much snubbing that'd be required to keep it from taking an electromotive beating.

Whatever works. The issue is if you want fine control over the pickup and dropout points simple magnetics may not be the answer.

Tom

I'm thinking a small P.L.C. would doo everything.

Including timing (if voltage does not come up fast enough, abort starting caps, to save them)
Running voltages & currents, other monitoring/adjusting.

Need to be *very* careful when trying to combine mains voltage measurements and low voltage controls.

An isolating stepdown transformer, bridge rectifier, and smoothing cap to bring it within the limits of a 0-10V analogue input would be feasible.

i moved on from the sensing relay
used a second set of contacts on the start button to bump the caps. just dont hold the button for more than a sec
cant be any worse than the flying v-belt technique
no smoke yet