Automatic transfer switch that works off a relay?

[signal15]

Looking for a 100amp ATM switch. Most of them monitor your primary power source, and when it goes down it switches to the backup. I need one that I can control via a relay or some other method.

This is because I'm having another power source installed that is cheaper during certain times of the day, and need to change things over on a schedule.

Does anyone know of anything?

If someone doesn't make one, I'm thinking I can use an off the shelf automatic transfer switch and some sort of huge 100amp relay. Except I would need a single huge relay that could handle both phases, or one relay for each phase.

Thoughts?

 

[tmbrown97]

I'm curious - there's systems out there that use Solar when it's available and supplement with grid power... would something like that work?

Otherwise, google Contactors - they're the big heavy-duty relays that can handle the load you're after. You'll probably have a lower voltage relay trigger the contactor.

 

[JimS]

Some ATS have a manual override switch. It shouldn't be too hard to tap into the panel button/switch (low power) to activate the main switch. If they have provision for a remote mounted switch that makes it even easier. Or break the low current path to the control circuitry so the ATS thinks the utility power has dropped. With an ATS you already have the high current relay - why pay for another one and have another possible point of failure? You might even be able to find an ATS with a computer port for status and control.

 

[fcwilt]

Well it's one thing to have the transfer switch activate after you have lost power and the start-up delay for the generator has elapsed but I wonder how the appliances, equipment, etc in a home would react having the transfer switch activate while still supplying power?

 

[signal15]

Well it's one thing to have the transfer switch activate after you have lost power and the start-up delay for the generator has elapsed but I wonder how the appliances, equipment, etc in a home would react having the transfer switch activate while still supplying power?

The only stuff that's going to be on this is going to be some refrigerator/freezers, electric heat, and a server rack with a UPS in front of it.

 

[signal15]

Looks like if I cannot find an automatic transfer switch that does everything I want, I can place a 100amp contactor in front of the primary feed on an ATS and then control that with a relay.

I'm waiting for a call back from an electrical supply place.

 

[Ira]

It depends on the type of ATS. For Generac residential setups (arguably the most common residential units), the "decision" to switch in either direction is made by the controller in the genset instead of the ATS. In other words, the controller in the genset tells the ATS when to switch to genset power, and when to switch back to utility power.

The ATS I have switches so fast that you don't notice it in the home when it switches back to utility power (and it is a "whole house" genset).

 

[JimS]

If you are running refer/freezers then momentary outages can be hard of them. I wouldn't want to be doing this on a regular basis. What happens if the unit is running is that the compressor has built up pressure and then stops with the interruption. When power comes back on the motor may not be able to start against the pressure, the motor over temp protection trips and cycles until the pressure goes down enough for the unit to start. It is hard on the motor and many programmable thermostats have delays to prevent this from happening for AC units. Since you don't have any loads that can't tolerate short interruptions you would be better off shutting off power for 15 minutes and then powering up again. That is enough time for the pressure to bleed off. Not sure how you do that easily.

 

[signal15]

If you are running refer/freezers then momentary outages can be hard of them. I wouldn't want to be doing this on a regular basis. What happens if the unit is running is that the compressor has built up pressure and then stops with the interruption. When power comes back on the motor may not be able to start against the pressure, the motor over temp protection trips and cycles until the pressure goes down enough for the unit to start. It is hard on the motor and many programmable thermostats have delays to prevent this from happening for AC units. Since you don't have any loads that can't tolerate short interruptions you would be better off shutting off power for 15 minutes and then powering up again. That is enough time for the pressure to bleed off. Not sure how you do that easily.

If the automatic transfer switch does it's thing fast enough, there shouldn't be a problem. The phases are in sync on the two meters/panels since they are off the same main feed from the pad.

 

[JimS]

No matter how fast the transfer switch is I doubt the generator will start fast enough when the utility power drops to prevent a short interruption.

I didn't follow the thing about the phases being in sync. Do most transfer switches make sure the generator and utility are in sync when they switch? I don't think so but could be wrong.

 

[michelkenny]

I think some people are missing the main point in the OP... He doesn't need power to switch when he looses utility power. He wants to flip flop between two power sources that are up at the same time, as they cost different amounts at different times of the day.

 

[tmbrown97]

:hesaid: - it should happen fast enough the motors shouldn't stop moving. I'd still want a UPS on my sensitive electronics to ride it out though.