Alternating relay

I am looking for something that will allow me to alternately close one relay and then, after an adjustable delay, open that relay and close a second relay. And then possibly a third relay.
The goal here is that I have several 120V relays that activate 240V electric heating units. I am hoping to do a little peak shaving by rotating them on and off so as to avoid having them all on at once.
This a fairly low-budget project as it is for my church.

Welcome to the forum

There are many ways to do what you’re asking with price tags ranging from around $50.00US to $5000.00US, and with risks of burning your house down from low to high.

The best solution for you depends almost exclusively on your capabilities and resources. Here are a few questions to help narrow down the options.

Can you …

  • Solder wires?
  • Solder through hole circuit boards?
  • Solder surface mount circuit boards?
  • Program personal computers?
  • Program microcontrollers?

Do you know…

Even if the answer is no to all the above there are still potential solutions. The solutions will likely just require more resources than other solutions.

Final questions, what’s the most amount of money you are willing to invest and end up with…

  • A useful solution?
  • No solution?
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Hello Smithgordonm,

Yes, I understand. The utilities can be a significant burden for a congregation especially if you live in the far north such as my home in Northern Minnesota.

Normally, I don’t do this, but I’m going to recommend against this project.

Implementing a control system such as you described is not simple or low cost. The cost is associated with safety and reliability. It is critically important that the system be electrically safe. It is also important for the system to be failsafe. For example, it would not be good if a failure caused the heaters to run at 100% on a warm summer day. At best this would cause the candles to melt, at worst it could cause a fire.

May I recommend you consider installing heat pumps. These devices offer increased efficiency over electric heat. Recommend:

  1. Contact your electric utility to find out if they offer discounts or extended credit for the installation of heat pumps.

  2. Contact a local HVAC installer to determine the cost of heat pump(s). It may be useful to explore an incremental approach. Instead of installing all the units at once, you could install a few at a time. In this area is common to see churches with multiple heat pumps.

Please share your results with this community. We are curious about your solution(s).

Best Wishes,


P.S. DigiKey can provide solutions such as this alternating relay. DigiKey also has programmable logic controllers which are a natural fit for this application.

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Can you …

  • Solder wires? Yes

  • Solder through hole circuit boards? Not sure about circuit boards, I have repaired things like failed thermostat boards and other control boards where the solder holding a component had failed.

  • Solder surface mount circuit boards?

  • Program personal computers? I was lead programmer for a software development company for a number of years, so, yes

  • Program [microcontrollers]? I have done some work with the programming of PLC’s

Do you know…

  • [Ohm’s law]? Yes
  • [Logic circuits] Yes

Even if the answer is no to all the above there are still potential solutions. The solutions will likely just require more resources than other solutions.

Final questions, what’s the most amount of money you are willing to invest and end up with…

  • A useful solution? $150 - 200
  • No solution? I’d like to think we could come to a decision about whether it would work or not before investing much

As far as the remarks about safety mentioned by another contributor, I am not sure I see the concern. Currently we have low-voltage relays that turn the electric heaters on and off reliably and have for the last several years. The relays are designed for this use. Each heater has a relay. All I am trying to do is to divide them into groups that take turns. For example… in one large room I have 4 heaters… let’s call them A, B, C, D. I’d like to have A and C come on for, say, 3 minutes and turn off. Then B and D come on for 3 minutes and turn off. Then back to A and C. This would reduce my demand by half. It might take a little longer to heat up the room, but probably no one will notice. Obviously the master control for this system will be an ordinary low-voltage thermostat. The relay / timer gadget I am envisioning could actually run continuously but it would only activate the heaters when the thermostat was calling for heat… which is the way it works now except for the alternating part.


Could you provide the part number of the relay you are already using, I think I might have a solution but I need to see the specifications from the relay you are currently using to make sure it will work.

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Thanks for answering my questions, it helped narrow down things a lot.

You should definitely check with the insurance provider for the building to make sure they will cover fire repair/liability (and frozen pipes if applicable) damage when there is a non-UL rated heating control installed (UL testing would cost many thousands so not practical for DIY). Many insurance carriers will not honor their coverage if they discover non-UL certified devices were installed in a building.

Currently my best idea is an Arduino with a relay shield PCB accessory for under $60.00US. Since you can write code, the chance of success approaches 100%.

Arduino R3’s

Relay Shields

With an Arduino in the mix you can even add multiple other environmental sensors (remote temperature, humidity, presence of people, etc.) to more effectively tweak heating power vs. rate of rise to achieve a best balance of comfort vs. cost.


Paul, we were discussing this idea yesterday and a question came up that you might be able to answer. We came to the consenus that there are ways that this could be done, however due to the time it takes for electric heaters to warm up and produce heat, we don’t think doing this will really save a significant amount of energy. What are your thoughts on that aspect, will he save enough to make any of this worth it.

I am currently using an Aube RC840 control signal device. It takes a 24V input and controls 1 heating unit. On one system I currently have 4 of these devices with their inputs wired in parallel and tied into the thermostat.

This looks great.
Thank you.
Is there any advantage of the 0073 vs the 0066?
It appears that I would need just one of 0110 to do 4 relays, correct?
Do I need a special power supply?

PS… I don’t expect to save on kWH’s, just on the demand charges.

I doubt there will be significant savings in total energy use. If I wanted to reduce energy usage for myself, I’d make normal system efficiency upgrades (e.g. insulation, heater, and controller).

Nothing significant for most people, one is through hole parts and the other is surface mount parts.


Arduino is very flexible on its power supply requirement, it has both USB and a wide voltage range coax power jack.
DigiKey has a nice introduction video:

The official documentation covers just about everything else.

Hi smithgordonm,

As an intermediate alternative, “Time Delay Relays” integrate the timing and relay functions into a single device. A typical operation mode would be to engage and disengage a relay(s) or switch between two outputs of a relay (“double throw” relay function) with a preset time interval when a signal is received. This would seem to meet your requirements.

Admittedly, it would be less fun than programming an Arduino - which offers greater flexibility and provides a greater level of satisfaction when one succeeds in completing a project - but it would undoubtedly take more time and be less well understood by anyone else who may need to adjust operation in the future.

Here’s a link to some timers which could likely do the job. Note that they have various input and power requirements, and their physical form factors, mounting methods, wire interconnect methods, and human interface characteristics vary.

Another option would be to install a smart wifi enabled thermostat to each heater or heater sections through a relay(s) if needed. A multi-channel output thermostat may exist to control all heaters or sections. The insurance company would be happy if wired up to code in your region, and this would allow remote temperature/humidity monitoring, and also the ability to adjust or modulate the heaters (or the AC) before or after service & anytime you choose remotely. Most smart thermostats have programmable output functions such as on/off delay times, calendar/clock heating/cooling time preset modes, home/away settings mode, along with other programmable features.