I have a 110v spa pump that is itself controlled (on/off) by an air switch. I want to install a spa heater that is 220v, but when I purchased the heater I didn't realize that the heater should only come on when the pump is on. In other words, if there is no power to the pump then there is no power to the heater. I have been told that it MAY be possible to control the 220v heater (with it's own dedicated 220v curcuit) with the power from the 110v pump. How can this be done???

Although the truelly correct answer may be to get a 110v heater to pair with my 110v pump, I like the idea of having the lower operating costs associated with using 220v. Am I on track? Or could a flow switch be used instead so that when the pump is off, it will "lock out" the heater? If so, is there any need for a t-stat? Seems like, no.


  • \$\begingroup\$ In the past people have made very loud warnings in answers to people wanting to use mains voltage. This is not only making your own solution for 110/220V but also doing it in an environment laden with water that people are in. This also seems like a consumer electronics question, as you do not seem to be interested in designing your own setup for controlling a 220 heater, just a way to easily get something you bought working with a different 110V source being used. Please let me know if I am in error on that note. \$\endgroup\$ – Kortuk Nov 30 '11 at 0:03
  • \$\begingroup\$ If I understand you correctly, yes you are right, I am looking for a simple way to use my 220v heater but insure that it will only be powered when the 110v pump is on. \$\endgroup\$ – Alan Dec 1 '11 at 13:19

I'd guess your best bet would be a relay.

You could connect a small power supply (transformer + rectifier + capacitor) across the pump supply, so that when the pump is on the power supply gives say 12V. That 12V could then power the coil of a relay which controls the 220V circuit.

You could build that circuit for a few dollars.

Alternately you could rectify the 110V and use that to power a relay with a 110V coil, but that could be dangerous and the capacitor to smooth the voltage (and stop the relay buzzing) would be quite expensive at 110V+.

(I have no idea what an SPA pump or SPA heater is, but I assume by the voltages mentioned, that they operate off AC voltage.)

  • 2
    \$\begingroup\$ A spa is a hot tub, like a jacuzzi tub. There are power relays available with 120VAC coils, which are also known as contactors. This would eliminate the rectifier/cap issue and make this a viable solution. \$\endgroup\$ – Tevo D Nov 29 '11 at 19:49
  • \$\begingroup\$ Ah - Spa - context is everything. You don't expect to see people talking about hot tubs on electronics sites... and yes, there are contactors. Not cheap tho - it may well be cheaper to use a low voltage DC one and a cheap PSU \$\endgroup\$ – Majenko Nov 29 '11 at 19:54
  • \$\begingroup\$ A quick search determined that Digikey has appropriate "contactor" style relays with 120VAC coil and 250V/30A contacts for ~15 bucks.... possibly less, that was on the first page of 21 or so. \$\endgroup\$ – Tevo D Nov 29 '11 at 19:59
  • \$\begingroup\$ 5 times the cost of the equivalent low voltage DC relay... \$\endgroup\$ – Majenko Nov 29 '11 at 20:00
  • \$\begingroup\$ For example, part Z814-ND (15.20) is chassis mount 250VAC 30A. It would require crimp connectors, but for a few bucks more screw terminals may be easier to work with (Z1054-ND, 19.50). Again, just examples, there may be better/cheaper available. Would also need to look up local code for enclosure requirements and whatnot... but this is a start. \$\endgroup\$ – Tevo D Nov 29 '11 at 20:07

The relay suggested sounds like a reasonable solution.

Another possibility, depending on how easily things can be adapted, might be to use (if they are available) a DPDT air switch to switch both pump and heater on/off together.


I think the big picture here is that you need to follow the electrical codes. In the US it is governed by the NEC as well as local government. In any case, I would bet the heater must be fed by a Ground Fault Circuit Breaker and controlled by an aproved contactor for wet locations and housed in an appropriate enclosesure. The contactor coil could be controlled by the 120VAC source, as Tevo D has pointed out. While other alternatives will work, safety should be your first concern, not to mention liability.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.