View Full Version : Check my wiring diagram for 2 electrical heaters with magnetic contactors?


DanWheeler
01-13-2008, 12:51 AM
The plan is to get 2 dayton red-box heaters 19,000 BTU each w/ thermostat for my 24x30 insulated garage. It should be enough.

Dayton Heaters:
http://www.grainger.com/Grainger/items/3VU36

I'm going to put the heaters on opposite corners of the same wall switched using a 2-pole magnetic contactor. I realize a 2-pole is not completely necessary but I'm hoping my X10 components will work better if the motors are completely disconnected when not on. (large motors "suck" X10 signals)

These are the magnetic contactors i'm planning on getting:
http://www.grainger.com/Grainger/items/5B124

I will then use a 24v power supply:
http://www.grainger.com/Grainger/items/6WU91
to control both magnetic contactors. I will put a regular light switch and transformer by the main entrance door. The light switch will control 24v to the magnetic contactors which will be located by the heaters. At some point, I could replace the light switch with a thermostat.

I'm hoping if I set the built-in thermostat on the Dayton heaters very high I will be able to control them using a single Honeywell or equivalent thermostat on the wall by my entrance door.

http://dano.smugmug.com/photos/242737689-L.jpg

is my thinking right here?

thanks in advance,

dan

jeff77indy
01-13-2008, 07:37 AM
Dan;
Looks good.
Where are you going to pull the 110V for you control transformer? From the lighting circuit maybe? You may want to fuse the control circuit.
When you order your contactors make sure you get 24VAC coils and not 24VDC.
Jeff

Franzę
01-13-2008, 12:26 PM
As far as your diagram goes it is workable.
The main drawback from my viewpoint is that you are slamming the complete load to the service. You're using far more endangered electrons than necessary, on warm days, and AlGore will be showing up to insist you buy some carbon credits.

I'd opt to sequence the second heater on a little after the first, and what the hell, just for entertainment probably throw a flip flop in to keep hours of operation equal on both units.

DanWheeler
01-13-2008, 01:57 PM
Dan;
Looks good.
Where are you going to pull the 110V for you control transformer? From the lighting circuit maybe? You may want to fuse the control circuit.
When you order your contactors make sure you get 24VAC coils and not 24VDC.
Jeff


thanks Jeff, I didn't even think about AC vs DC for the control circuit. I had actually assumed DC but it looks like the contactors and transformer I spec'd are both AC.

How would you recommend putting a fuse in the control circuit? Do you happen to know what gauge wire is required for the control circuit? I have some security wire laying around I could use but not sure if its thick enough.

thanks,
dan

DanWheeler
01-13-2008, 02:00 PM
As far as your diagram goes it is workable.
The main drawback from my viewpoint is that you are slamming the complete load to the service. You're using far more endangered electrons than necessary, on warm days, and AlGore will be showing up to insist you buy some carbon credits.

I'd opt to sequence the second heater on a little after the first, and what the hell, just for entertainment probably throw a flip flop in to keep hours of operation equal on both units.

woah, you lost me there Franz... At first I thought endangered electrons was a real technical term - but now I think you were just joking :)

how could I delay the second heater? Or what is a flip-flop and how would I implement one?

thanks for your ideas

dan

Franzę
01-13-2008, 09:24 PM
To delay the second heater, instead of pulling both relays in with the thermostat,
Relay A pulls in with thermostat running heater A and time delay relay.
When TD relay reaches preset time it pulls in relay B to fire second heater.

Flipflops or A/B sequencers are frequently used in situations like lift stations or multiple compressor installs where it is desired to keep hours of operation equal on both machines. It's nothing more complex than a device that switches which machine is primary on the next startup. Each machine cycle the flipflop switches the primary for the next cycle.

Electrons are enfangered in many places in the US. Haven't you heard we all gotta switch to compact fluorescents to conserve electrons. If we don't more coal fired plants will ahve to be converted to natural gas fired plants to help drive the price of NG up.

nyjets53
01-14-2008, 06:57 PM
I don't know how the graingers work, My King Pic A Watt electric heater runs for a time after the thermostat disconnects, I assume it is to keep the air moving while the coils cool off a bit...

Franzę
01-14-2008, 07:45 PM
You better hope it does Rich, if the fan didn't continue running the heating elements would cook themselves to death a hell of a lot sooner.

Your fan is probably controled by a heat sensor in the unit. The thermostat only fires the heating coil.

jeff77indy
01-15-2008, 12:06 PM
thanks Jeff, I didn't even think about AC vs DC for the control circuit. I had actually assumed DC but it looks like the contactors and transformer I spec'd are both AC.

How would you recommend putting a fuse in the control circuit? Do you happen to know what gauge wire is required for the control circuit? I have some security wire laying around I could use but not sure if its thick enough.

thanks,
dan

You would have to use a 24VDC power supply to get 24VDC, with the transformer shown in the drawing it would be 24VAC.
You could use an inline fuse holder inside the transformer enclosure and use a 250V glass tube fuse.
I'd run the controls in at least 18AWG.
A sequncer could be picked up at a HVAC supply house or Grainger, it would allow one heater to come on then the second would come on line at a set amount of time after the first.
Jeff

Franzę
01-15-2008, 12:31 PM
I'd stay away from DC control mainly to minimize multipathing possibility.

The size wire you'll need in the control circuit is dependant on distance from the thermostat to the relay. Yuo're really not talking about a large draw with a relay coil, so your leftover security system wire may work.

Fusing the transformer is a nice idea, but not really necessary.