Priority switch? (Lektricuty question)

Page 1 of 2  
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?
00
Rob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

house load controllers work this way

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Excellent lead. Thank you.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Robatoy" Writes:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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...<G>
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike in Arkansas wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Rob Mitchell Feb 3, 7:19 pm show options
Newsgroups: rec.woodworking
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 in Arkansas wrote:

<Isn't that backwards? >
Maybe, but it was my understanding that because the heater only came on so rarely that he could live without the compressor for the very short time it was on. BTW, I was assuming that there was an external thermostat involved in the previous suggested method. If not, and the heater has an internal thermostat without 24 vac, then the relay coil would need to be 240 volts and would be wired directly to the heater element connectors inside the furnace. Be glad to fax a drawing to OP if it will help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
00
Rob.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<<I e-mailed my fax number to you. >> Rob, I didn't get your fax number email so you might want to try again. address is snipped-for-privacy@aol.com.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I tried using the mail function of my newsreader. No cigar. Those darned computers!!!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 03 Feb 2005 22:19:31 -0500, the inscrutable Rob Mitchell

I think you read his post wrong. His NC relay would -cut- power to the compressor while the thermostat told the heater to work.
--
The clear and present danger of top-posting explored at:
http://www.netmeister.org/news/learn2quote2.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
spake:

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 04 Feb 2005 14:18:42 -0600, the inscrutable Secret Squirrel


My heater and compressor run about the same time, 2 minutes.
--
The clear and present danger of top-posting explored at:
http://www.netmeister.org/news/learn2quote2.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Either way is fine. It doesn't matter which knocks out what, as long as they don't run at the same time.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I like. Thank you.
00
Rob.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.