Honeywell Thermostat mod??

[Dave, I can't do that]

Hi All,

Just upgrading the 4-wire baseboard thermostats in the house to these digital 2-wire ones. I bought one to try and it is working well. It's 240vac into 2 x 1500w baseboard heaters in series. I like it and will replace some ofthe others in the house.

http://www.homedepot.com/p/Honeywell-Digital-Electric-Baseboard-Heat-Thermostat-RLV310A/203166440

But, it has no on/off switch which means before going to bed I need to holdthe "Down" button while is clunks down to 40F. With four more in the houseI will have to start half an hour before bedtime. OK, kidding a little there.

Can anyone help with a schematic and then directions where to cut and I will hack at the circuit board traces and solder the leads for a switch?

I'd like the switch to safely disable the TRIAC control circuit without interfering with the current settings. I don't care if it displays the temp when it is off or not. That's the normal mode, but it doesn't matter if it isdisplayed or not as long as the settings remain, well, until the next power outage. {gasp}

Thanks

Dave

 

[Jasen Betts]

Hi All,

Just upgrading the 4-wire baseboard thermostats in the house to these digital 2-wire ones. I bought one to try and it is working well. It's 240vac into 2 x 1500w baseboard heaters in series. I like it and will replace some of the others in the house.

http://www.homedepot.com/p/Honeywell-Digital-Electric-Baseboard-Heat-Thermostat-RLV310A/203166440

But, it has no on/off switch which means before going to bed I need to hold the "Down" button while is clunks down to 40F. With four more in the house I will have to start half an hour before bedtime. OK, kidding a little there.

Can anyone help with a schematic and then directions where to cut and I will hack at the circuit board traces and solder the leads for a switch?

I'd like the switch to safely disable the TRIAC control circuit without interfering with the current settings. I don't care if it displays the temp when it is off or not. That's the normal mode, but it doesn't matter if it is displayed or not as long as the settings remain, well, until the next power outage. {gasp}

Presumably cutting the wire that goes to the gate pin on the triac is
all that's needed, but without circuit details that's just conjecture,


Putting a regular 240V 15A switch in series with the whole thermostat
will always work.

 

[[email protected]]

"240vac into 2 x 1500w baseboard heaters in series"

That sounds like it MIGHT be against code if you're in the US. The 240 here is balanced and grounded in the center. Most 120 units have a dedicated neutral and hot, and almost always the neutral has to be connected to the neutral.

This is how it used to be though, it may have changed. Thing is, how come you have 240 mains and 120 heaters ? Don't tell me to save wire..........

 

[petrus bitbyter]

"Dave, I can't do that" <[email protected]> schreef in bericht
Hi All,

Just upgrading the 4-wire baseboard thermostats in the house to these
digital 2-wire ones. I bought one to try and it is working well. It's 240vac
into 2 x 1500w baseboard heaters in series. I like it and will replace some
of the others in the house.

http://www.homedepot.com/p/Honeywell-Digital-Electric-Baseboard-Heat-Thermostat-RLV310A/203166440

But, it has no on/off switch which means before going to bed I need to hold
the "Down" button while is clunks down to 40F. With four more in the house I
will have to start half an hour before bedtime. OK, kidding a little there.

Can anyone help with a schematic and then directions where to cut and I will
hack at the circuit board traces and solder the leads for a switch?

I'd like the switch to safely disable the TRIAC control circuit without
interfering with the current settings. I don't care if it displays the temp
when it is off or not. That's the normal mode, but it doesn't matter if it
is displayed or not as long as the settings remain, well, until the next
power outage. {gasp}

Thanks

Dave

With the information you provided, there's hardly any usefull answer as far
as an intervention in the hardware is concerned. However, there's an old
trick to fake a thermostat. Place a (power) resistor near the temp sensor.
You'll have to find out power and distance and so on but you can control
that resistor anyway you want. On/off switching being the most simple.

petrus bitbyter

 

[[email protected]]

On Wednesday, November 6, 2013 7:15:06 PM UTC-5, Dave, I can't do that wrote:

Leave the thermostats alone. Mount a power toggle in a knockout hole of thebaseboard junction box. If you have multiple baseboards on the same circuit, so much the better, the toggle can be used to open the feedthrough circuit also, unless you've done something creative. The HD spec says these thermostats remember their settings through the power outage.

 

[Dave, I can't do that]

Thanks people.

I like Jasen and Bloggs.Fred suggestion. My only question now is, is it OK to open-circuit the output of the TRIAC?

The old thermostat had four wires, the new only two with everything now in series. ASCII art coming up...
OLD:
Mains----O O----1500W-+
|
Mains----O O----1500W-+

NEW
Mains--TRIAC--1500W-+
|
Mains---------1500W-+

I am assuming the suggestion is to

Mains--TRIAC--O-Switch-O--1500W-+
|
Mains---------------------1500W-+

Is that correct? Opening the TRIAC output?

I can live with manually setting the temp after power outages. They are a way of life out here in the boonies, about 20+ per year.

Thanks to all who helped.

 

[[email protected]]

Thanks people.



I like Jasen and Bloggs.Fred suggestion. My only question now is, is it OK to open-circuit the output of the TRIAC?



The old thermostat had four wires, the new only two with everything now in series. ASCII art coming up...

OLD:

Mains----O O----1500W-+

|

Mains----O O----1500W-+



NEW

Mains--TRIAC--1500W-+

|

Mains---------1500W-+



I am assuming the suggestion is to



Mains--TRIAC--O-Switch-O--1500W-+

|

Mains---------------------1500W-+



Is that correct? Opening the TRIAC output?



I can live with manually setting the temp after power outages. They are away of life out here in the boonies, about 20+ per year.



Thanks to all who helped.

Okay, was looking at the installation manual and some other stuff on the RLV310A
https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-1869ES.pdf

There is no battery installation so that means the battery backup, if any, is a permanently installed lithium probably. The main thing is the unit goes to sleep or shuts off entirely on power loss. This means a toggle switchthat opens the circuit to the heater will be seen as a power loss by the tstat, which is what you want because, battery based backup or not, the tstat operation and longevity are unaffected. The requirement for a minimum 2A load has to do with keeping the tstat electronics powered while it's stealing power ( something Honeywell is very clever about) during heater ON operation and does not apply to the idea of a toggle switch interrupting power to the heaters.

 

[ehsjr]

Thanks people.

I like Jasen and Bloggs.Fred suggestion. My only question now is, is it OK to open-circuit the output of the TRIAC?

The old thermostat had four wires, the new only two with everything now in series. ASCII art coming up...
OLD:
Mains----O O----1500W-+
|
Mains----O O----1500W-+

NEW
Mains--TRIAC--1500W-+
|
Mains---------1500W-+

I am assuming the suggestion is to

Mains--TRIAC--O-Switch-O--1500W-+
|
Mains---------------------1500W-+

Is that correct? Opening the TRIAC output?

Yes, but you needn't think of it as output. You are opening the
circuit, and you can do that before or after the triac. My
preference is before, with a switch between the service entrance
circuit breaker panel and the triac tstat, like this:

breaker--hot---switch---triac_tstat---heater---neutral

Both the switch and the tstat must be connected in the
hot (black wire) side, NOT the neutral (white wire)side,
per the electrical code.

Ed

 

[[email protected]]

Yes, but you needn't think of it as output. You are opening the

circuit, and you can do that before or after the triac. My

preference is before, with a switch between the service entrance

circuit breaker panel and the triac tstat, like this:

His tstat only sees one mains wire, not two, it is completely in series with the load. When he breaks that one wire circuit, there is nothing to turn the TRIAC on with, and in this case the internal control has the smarts to not even try, it goes to sleep. It makes no difference where he breaks his circuit, the baseboard is the most convenient place.

 

[rickman]

That sounds like it MIGHT be against code if you're in the US. The 240 here is balanced and grounded in the center. Most 120 units have a dedicated neutral and hot, and almost always the neutral has to be connected to the neutral.

This is how it used to be though, it may have changed. Thing is, how come you have 240 mains and 120 heaters ? Don't tell me to save wire..........

What? A 240 volt load doesn't need to be grounded in the middle. My
furnace has multiple kW heaters as back up and they are just two wire
and 240 volts. Why do you think you need to ground the middle of a 240
volt load? Or do I misunderstand what you are saying?

Actually, if you use two 120 volt heaters, you would be able to ground
the middle connection between the two heaters safely. I'm just not
following what you are thinking.

 

[ehsjr]

His tstat only sees one mains wire, not two, it is completely in series

with the load.

Yes - that is what I drew.
" breaker--hot---switch---triac_tstat---heater---neutral "

It makes no difference where he breaks his circuit,

Yes, that is what I said with respect to the hot wire.
" You are opening the circuit, and you can do that before or
after the triac. "

However, he must NOT use the switch to interrupt the neutral
wire. That violates the electrical code.
"Both the switch and the tstat must be connected in the
hot (black wire) side, NOT the neutral (white wire)side,
per the electrical code. "

the baseboard is the most convenient place.

Here we disagree. If he modifies the baseboard to include
a switch, he'll have to bend over every time he wants to
operate the switch. (And that assumes there is room in the
baseboard to add the switch.) A switch between the service
panel and the heater can be mounted at a convenient height,
and requires no modification to the heater itself.

Ed

 

[[email protected]]

However, he must NOT use the switch to interrupt the neutral

wire. That violates the electrical code.

"Both the switch and the tstat must be connected in the

hot (black wire) side, NOT the neutral (white wire)side,

per the electrical code. "

He's using 240, there is no neutral. His cable should be two insulated hot wires (120VAC relative to house GND each) plus bare copper GND. There's no neutral present to interrupt.

Here we disagree. If he modifies the baseboard to include

a switch, he'll have to bend over every time he wants to

operate the switch. (And that assumes there is room in the

baseboard to add the switch.) A switch between the service

panel and the heater can be mounted at a convenient height,

and requires no modification to the heater itself.

Well, okay, if he has mobility problems then that's the way to go. Many baseboard heaters like this have an option for mounting a thermostat on the baseboard itself, so there's not a lot of overwhelming objection to that location.

 

[Dave, I can't do that]

" breaker--hot---switch---triac_tstat---heater---neutral "

Ed, thanks for that, but I was hoping to use a small switch to open the Gate lead of the circuit board.

http://www.allelectronics.com/make-a-store/item/SMTS-4/SPDT-ON-ON-SUB-MIN-TOGGLE-SWITCH/1.html

Cut the track and then run wires to the switch that I can mount in the thermostat housing as there is plenty of room for a small switch.

I can't measure the Gate voltage as the tstat will not work with the front panel removed as the buttons are on that panel.

That's why I was asking about the possibility of damage to the TRIAC if theswitch simply open-circuited the Gate.

Jasen Betts suggested it might be possible in the first reply to my OP. Butbefore trying that I wanted to know of the risk level to the TRIAC. I can see where to cut on the circuit board as it is pretty simple with well spaced components. The only unanswered thing is, will flicking the switch be likely to wreck the TRIAC?

Thanks

Dave

 

[ehsjr]

Ed, thanks for that, but I was hoping to use a small switch to open the
Gate lead of the circuit board.

Grrr. That was not clear in what you said earlier:
"Is that correct? Opening the TRIAC output? "

http://www.allelectronics.com/make-a-store/item/SMTS-4/SPDT-ON-ON-SUB-MIN-TOGGLE-SWITCH/1.html

Cut the track and then run wires to the switch that I can mount in the
thermostat housing as there is plenty of room for a small switch.

You can try it, and it should work fine, but don't use that
switch.** (** = More on that, below)

I can't measure the Gate voltage as the tstat will not work with the front
panel removed as the buttons are on that panel.

Gate voltage doesn't matter for what you want to do, if
you use a switch rated at 240 VAC or higher.

That's why I was asking about the possibility of damage to the TRIAC if
the switch simply open-circuited the Gate.

Not likely to be a problem for the TRIAC - but as Jason said it's
impossible to predict what will happen without having the circuit
schematic.

Jasen Betts suggested it might be possible in the first reply to
myOP.But before trying that I wanted to know of the risk level
to the TRIAC. I can see where to cut on the circuit board as it
is pretty simple with well spaced components. The only unanswered
thing is, will flicking the switch be likely to wreck the TRIAC?

Or wreck the part of the circuit that drives the gate of the triac,
or burn out the switch or ??? You're doing surgery to the thing,
so there can't be any guarantees. It will also make you legally
responsible for any disaster that arises because of the surgery.

Back to the switch. Without the schematic and without knowing
the gate voltage, you have to assume mains voltage level for
the switch rating. The switch at the url you posted is rated at
125 VAC, but you indicated you have 220 VAC mains, so you have
to assume that switch is not good for your modification.

Ruining the TRIAC is almost irrelevant - they're relatively
cheap, and it is not likely to fail because of an open circuit
to the gate.

Now aside from all the negatives above, my best guess is that
it will work fine. Buy you _do_ need to use a properly rated
switch.

Ed