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98mrd 12-23-2011 02:57 PM

Help with baseboard heater relay
 
Hi - just joined the forum. I have been trying to figure out a problem for a while now and decided to (finally) ask for help.

My house is heated with baseboard heating. It was built in 1971. I recently replaced all the heaters with dimplex linear convectors and all the thermostats with honeywell digital programmable line voltage thermostats.

Everything is fine except for one room which is wired differently. Because the room is quite large, the heaters are powered off of two separate 240V 20A circuits. These are controlled by a White Rodgers 24A06G-1 relay connected to a 24V thermostat in the room. (The relay is connected to the electrical panel.) The problem is that it only supports a 2 wire thermostat, and I'd like my thermostat to match the rest of the thermostats in my house, so I need 3-wire.

I modified the relay itself, splicing in to create a separate neutral to power the tstat. That worked fine, except that the transformer can't generate sufficient current to power the tstat and also power both electromagnets that trigger the relay. The tstat works fine except only half the baseboard heaters go on (the ones on one circuit).

I'm looking for a new relay that will control 2 240V 20A circuits off one 24V 3-wire tstat. Does anyone know of such a product? Alternatively, anyone have any advice on another way to solve this problem?

Thanks in advance.

carmusic 12-23-2011 03:02 PM

since they are on different breakers it is not recommend to do that (you would need 2 relays). how many watt are the heaters, can you join them on the same 20A circuit?
best solution is to get rid of all relays, put them on same circuit and use a regular line voltage tsat but this mean a lot of rewiring

98mrd 12-23-2011 03:07 PM

That's not a possible solution. I would need almost 40 amps - that's why they are on two circuits. I'm in no way connecting the two circuits together. They are kept isolated at all times. The relay on there now is designed to control two circuits. Two separate electromagnets are activated which turns on both circuits - they don't connect at all.

Even 10 gauge wire would be insufficient for the amperage. If you start at 30 amps, subtract 20% since they run continually, you are at 24 amps, which is nowhere enough - also it's about 100 feet from the panel, so there is some loss to that too.

I have to preserve the two separate circuits, I just need to find another relay that runs two circuits at the same time, or possibly alter this relay by replacing the transformer to increase the current.

See the wiring diagram here: http://www.platt.com/CutSheets/White...1%20Instal.pdf

EDIT: BTW, a licensed electrician installed the existing relay. It is up to code - the issue is that it only supports a 2-wire 24V thermostat.

carmusic 12-23-2011 03:10 PM

you have over 4800w of baseboard heaters in one room :huh:

darren 12-23-2011 04:05 PM

You have to use a 2 wire thermostat. Why would a thermostat have 3 wires?. Line voltage stats are either 2 wire or 4 wire.

98mrd 12-23-2011 05:30 PM

I have around 8000W for that room (2 2000W 50inch dimplex linear convectors on each wall - 4 total) - and that's barely enough to heat it when it gets cold. The room is large and has cathedral ceilings too.

It's not a line voltage thermostat... it's a 24V thermostat. That's the point of the relay. It controls two 20 amp circuits with a 24V thermostat. It has always been different from the rest of the house (for 40 yrs now) because no single circuit / line voltage thermostat could be used (other than something very industrial I suppose).

The two wire 24V thermostats are the old mechanical ones - that's what I just replaced. The third wire is a neutral so that the digital thermostats can be powered and light up the LCD.

joed 12-23-2011 05:34 PM

Quote:

except that the transformer can't generate sufficient current to power the tstat
Simple. Get a bigger transformer.

Missouri Bound 12-23-2011 09:36 PM

Take the thermostat out of the circuit and short the wires. See if that operates the relay. It's hard to believe that the thermostat would need more than the relay to operate. It's almost always the other way around. And when you modified the relay, you took away it's UL listing....just sayin'. Where did you get the neutral from anyway? From looking at the schematics it looks as if the relay is intended to work off a mechanical tstat. Have you checked the voltage that the xformer is putting out. Just because it says you can use a 24v thermostat doesn' mean it's a 24v output. Just some things to think about.

a7ecorsair 12-23-2011 10:07 PM

Quote:

Originally Posted by 98mrd (Post 801338)
I'm looking for a new relay that will control 2 240V 20A circuits off one 24V 3-wire tstat. Does anyone know of such a product? Alternatively, anyone have any advice on another way to solve this problem?

Thanks in advance.

Your relay is designed to support two 240 volt loads at 25 amps each.
The relay requires .2 amps at 24 volts
Have you already bought this three wire t-stat? what is the brand and model?

98mrd 12-24-2011 12:11 AM

Disconnecting the thermostat and shorting the red to white activates all the heaters. You can observe the relay functioning (it's electromechanical) and both electromagnets power on and close the switches activating the 240V circuits.

Removing and replacing the transformer is possible, assuming I could obtain one with the proper ratings (not sure what that would be - I can't find detailed specs). It also increases the risk of potentially running too much current over the small tstat wires.

I know I too away the UL listing - and ideally, I'd just like to get a new relay that would do the job. I can't be the only person ever to encounter this issue.

The voltage has always been under 24V. I've checked it with a multimeter and it's around 21.5V AC. I'm not sure why this is. However, it functions fine at that voltage normally (it's the same when the thermostat is not hooked up, and in the original configuration, and it doesn't seem to affect the thermostat running, so I think it's unlikely that is the issue).

I have already bought and hooked up the tstat, and I'm using it now - it provides some heat (half the heaters go on). It works fine aside from its inability to get the second circuit on. The thermostat is a Honeywell/Aube TH115-A-024T.

I got the neutral from the other side of the transformer. I just wanted a 24V circuit to power the tstat - I already had a lead from one side of the transformer. I needed one from the other side (but before it gets to the relay switches).

a7ecorsair 12-24-2011 08:41 AM

1 Attachment(s)
Are there separate connections for the two coils on the relay? They need to be connected in parallel.
You should not, can not, have a neutral from the primary side of the transformer connected to the t-stat. The t-stat operates on a transformer isolated 24v class two wiring. Your transformer may be connected to 120 vAC instead of the 240 as shown in the manual for the t-stat in which case you will have separate 240 wiring to the baseboard.
This is from your operator's manual.

Missouri Bound 12-24-2011 08:51 AM

Which tstat are you using? You may be able to add a seperate xformer for thermostat power, and still use the internal xformer for switching the relay.

Speedy Petey 12-24-2011 09:38 AM

Can you tell me what a "3-wire thermostat" is???

Every lo-volt t-stat I have ever seen was able to be used as a heat-only stat requiring only R&W.

You CAN use those 2-circuit WR relays with one t-stat.

joed 12-24-2011 10:09 AM

Quote:

Removing and replacing the transformer is possible, assuming I could obtain one with the proper ratings (not sure what that would be - I can't find detailed specs). It also increases the risk of potentially running too much current over the small tstat wires.
The stat will use what it needs for current. The transformer is not part of the equation. It does not control current flow unless it is too small for the application and is being overloaded.

98mrd 12-24-2011 10:24 AM

Good points a7 - but don't worry. Yes, there are separate connections for each of the two circuits. The operators manual for the tstat shows a different relay (probably one of the aubes) that doesn't control 2 circuits. This one has lugs clearly marked for circuit 1 and circuit 2 by the manufacturer. Also - regarding the side of the transformer, I should have been more specific. I am completing a circuit which goes from transformer to tstat back to transformer - without having to pass through the electromagnets that would activate the heaters - but ALL on the secondary side of the transformer and all in he 24V wiring section. I've also tested it with the multimeter and it's getting a bit under 22V on that line. You are completely correct that connecting somehow over to the primary side would be dangerous and a bad idea (and I'm guessing would blow the t-stat, since it would be one of the 120V hots from the panel). That isn't the issue here. It's also part of why I was willing to tinker as much as I did. I knew it was only limited current 24V wiring that I was modifying on the 2ndary side.

Can I get two regular, single circuit relays and connect in parallel? What would the wiring diagram look like? That might be a solution. I'm not averse to spending a few bucks - I just want it to work.

As for the 120 vs 240, both baseboards are 240V, and the relay interrupts one leg of each (hence the reason the old thermostat was a SPST mechanical honeywell - one leg was always energized). There are a total of 4 lugs, 2 per circuit. It's like a switch just opening or closing one of the 2 hots on each 240V - so it would be 120V vs ground/neutral. When the tstat is off, they test as 240V (the return path is ultimately to the other hot on the bus). They both get 240V as wired.

Missouri - see above for the exact tstat model number. a7 also pulled from the manual.

Speedy - The tstat clearly states that it requires 3 wires. This is true of thermostats that have display screens and do not use batteries as a general rule. To complete the circuit and draw power, they need to return power, but with a 2 wire the only return passes current over the magnets and activates the relay. I added a neutral return wire between the transformer and the magnets so that the thermostat could draw some power and still not activate the heaters (to run the display, etc.)

joed - I agree with everything you are saying. My working hypothesis at this time is in fact that the transformer is too small and is overloaded right now. The tstat is pulling what it needs (just as when you plug in a nightlight it doesn't try to pull 15 amps on the circuit, it's ohms law, resistance, etc. - I get that). I think the transformer is overloaded though and can no longer supply enough power to activate both electromagnets and the tstat simultaneously.


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