Priority switch? (Lektricuty question)

[Robatoy]

I have 30 amps of 220 (single phase) available to my shop. When my electric heater (20 amps) is running, which isn't often because the shop is very well insulated and my compressor (10 amps) kicks in, ..mmm let's just say.. the lights dim a little.

Neither piece of equipment runs a lot so I see no reason to bust open the concrete driveway and burying cable to upgrade to a bigger service. So.... it shouldn't be that hard to develop a relay box that simply cuts off either piece of equipment when the other is running.... I mean... shouldn't be that hard for somebody who knows this kinda stuff.

I would be helped a lot if there was name for such a circuit, because then could start digging for a schematic.

Anybody?

Please?

0¿0

Rob

[Charles Spitzer]

house load controllers work this way

[toller]

You simply want to throw a switch and have the compressor power up, and have power cut off to the heater?

Two ways to do it. Get a double pole double throw switch, and hook it up to the two units. Thrown one way the compressor will have power, the other the heater. In the middle neither. It is like a 3way switch, only for 240v.

The more elegant way is to use a 240v relay with normally on contacts. When the compressor switch is off, the relay will allow power to the heater. When the switch is on, the relay will open shutting off the heater.

The DPDT switch is certainly easier, but it may require you to move some wiring around. With the relay everything can stay where it is, with a small cable connecting them.

[Lew Hodgett]

Toller in another post has pointed you in the right direction; however, there is even a simpler way.

Install a DPDT non fused, 250V, 30Amp, disconnect switch that you manually switch.

Leave the switch in the air compressor position.

When you get cold, switch to the heater.

When things warm up, switch back to the air compressor.

Low cost, simple and reliable.

HTH

Lew

[Mike in Arkansas]

Let me ramble for a bit here. As I understand, you want power to the heater available at all times when the thermostat calls for heat and when it does you want to interrupt the power to the compressor it it will not run until the heater goes off. So, what you need is a relay that is operated by the thermostat. Put the coil to the relay across the (probably) 24 vac circuit that will operate the relay contacts. Run the power to the compressor through the relay contacts so that they are open when the thermostat is calling for heat (furnace is on). Simple DPDT relays are cheap and available from Newark.com as well as Grainger or others. I'd get 15 amp contacts for the compressor power and a relay matching the voltage of your thermostat circuit. Simple yet elegant.

[Rob Mitchell]

Isn't that backwards? Wouldn't you want power available to the heater at all times except when the compressor needed to run (seldom and only for a few seconds) Otherwise, you might have to wait until the room came up to temperature before you could drive a nail with the compressor.

The concept would be the same, but pick up the signal from the compressor to switch a relay rather than the thermostat. The higher priority, lower duty cycle device should interrupt the lower priority higher duty cycle device.

[Mike in Arkansas]

Rob Mitchell Feb 3, 7:19 pm show options

Newsgroups: rec.woodworking From: Rob Mitchell =AD; - Find messages by this author Date: Thu, 03 Feb 2005 22:19:31 -0500 Local: Thurs, Feb 3 2005 7:19 pm Subject: Re: Priority switch? (Lektricuty question) Reply | Reply to Author | Forward | Print | Individual Message | Show original | Report Abuse

Mike > Let me ramble for a bit here. As I understand, you want power to the

[Joe User]

This seems to be getting a bit complicated (and expensive). Why not just turn the thermostat up (or off) when using the big tools?

-j

[Larry Jaques]

On Thu, 03 Feb 2005 22:19:31 -0500, the inscrutable Rob Mitchell spake:

I think you read his post wrong. His NC relay would -cut- power to the compressor while the thermostat told the heater to work.

[Secret Squirrel]

Larry Jaques wrote in news: [e-mail]:

compressor.

Which is probably backwards from what you want. The heater will run regularly and potentially for long periods. The compressor will run rarely and for short periods. Would you rather wait 2 minutes for the heat to come back on while the compressor charges, or an hour for the compressor to come on while the heater runs?

[Mike in Arkansas]

If you want the opposite to happen, that is, disable the heater when the compressor starts or is running just parallel the 240 relay coil to the compressor motor wiring. So when the compressor motor is running the same 240 volts will open the normally closed relay contacts that control the voltage to the heater. Either way, it's a simple thing to do.

[Chuck Hoffman]

Maybe you don't need any modifications. The starting surge of the compressor is considerable but only lasts for a short time. If the lights return to normal brightness when the comressor comes up to speed, you may be OK without any changes. That is, unless you blow the breaker when the heater, compressor and another power tool are all running at the same time.

[Larry Jaques]

On Fri, 04 Feb 2005 14:18:42 -0600, the inscrutable Secret Squirrel spake:

My heater and compressor run about the same time, 2 minutes.

[Robatoy]

That is what I have been doing. That is what I no longer want to do, because sometimes I forget to turn it back up.

[Robatoy]

I like. Thank you.

0¿0

Rob.

[Robatoy]

Either way is fine. It doesn't matter which knocks out what, as long as they don't run at the same time.

[Robatoy]

I e-mailed my fax number to you.

There must be other folks in here who could make use of this solution, no?

When the heater runs, the compressor can't kick in till the heater stops. When the compressor is running, the heater can't start till the compressor is done.

I appreciate your help.

0¿0

Rob.

[Robatoy]

I agree that this is by far the simplest(best) solution if I didn't forget to turn the heat back on before locking up for the night. My solid surface sheets need a minimum temp of 60F in order for the adhesive to work... to wait for that in the morning is a PITA....or so I'm told...

[Robatoy]

Excellent lead. Thank you.

[Mike in Arkansas]

Rob, I didn't get your fax number email so you might want to try again. address is [e-mail].