Hello. I’m new to the site so apologies if this is the wrong place for this post.

Ive been trying to find either a pre built module or circuit for a thermostat with one momentary on and one momentary off output.

I have a diesel powered air heater with a remote control that has on and off monetary buttons. The unit has its own thermostat control but for the situation I’m using it in even the lowest setting heats the room to much. So I’m looking to have an on/off switch linked to an external thermostat.
My plan is to piggyback the thermostat outputs to the tactile switches on the remote so when the thermostat reaches a predetermined temperature it switches the heater off and visa versa to turn the unit on. The thermostat outputs need to be on for approximately 1 to 2 seconds
I’d be very grateful if anyone knows of an existing unit or a simple circuit diagram to make something to do the job.

Many thanks in advance.

 

Can't you just wire a thermostat in to break the control circuit when it gets hot? Put the sensor in the units return air flow and set it to knock it off at 22c

 

Can't you just wire a thermostat in to break the control circuit when it gets hot? Put the sensor in the units return air flow and set it to knock it off at 22c

Hi.
Thanks for your reply.
Yes I could hack into the main controller to do that but it still needs to be momentary on/off.
The main controller talks to the control board digitally and I’d rather not hack into the control board if possible.

 

Maybe there's a solenoid valve you can interrupt? How does the circuit board switch the heating off?

 

The start up and shut down is controlled by a processor.

The heater is stoped by the processor turning off the diesel pump then it goes through a cooling down cycle. When a temperature sensor on the heat exchanger case detects the case is cool enough enough the fan is switched off.


The startup goes through a process of turning on the fan and glow plug. Once the glow plug is sufficiently hot enough the pump is started pushing fuel over the glow plug which in turn ignites the fuel. Once a temperature sensor detects enough heat the processor turns off the glow plug.
To hack into the main board would be a nightmare. This is why I prefer hacking the remote.

I don’t want the unit to just switch off. I need it to turn on when the temperature drops below the set temperature.

 

OK then ...
A simple approach would be to automatically change the resistance of the sensor so that the processor starts the shutdown procedure.

A thermostat could switch in a resistor either in series or parallel with the sensor. Maybe it would take a bit of experimentation but once done it's quite a simple modification.

Other way is probably to use a micro controller.

 

This is an interesting challenge, so now a few questions: Is this a mains powered heater or a battery powered heater? Do you have a manual for it? Providing an isolated momentary start and a momentary stop will require knowing if the buttons are normally open or normally closed, or one of each. And also how long the button must be pushed to make the command register.
The best approach will add two relays, one for start and one for stop..
The solution depends on the answers. Anybody's solution. Almost.

 

OK then ...
A simple approach would be to automatically change the resistance of the sensor so that the processor starts the shutdown procedure.

A thermostat could switch in a resistor either in series or parallel with the sensor. Maybe it would take a bit of experimentation but once done it's quite a simple modification.

Other way is probably to use a micro controller.

Ok the temperature sensor is nothing to do with the thermostat or regulating the room temperature It’s a safety device to monitor the heat exchanger temperature only.
The thermostat is in the control panel which is separate from the main board. Any mod has to be done in the control panel or the remote fob.
The heater is in a caravan and is to efficient for the small area.
All I want to do is have an external thermostat to turn it off when the ambient room temperature is too warm and turn it on when the ambient temperature drops. This is the only way I can solve the problem.

 

OK, now we know that the control is strictly ON/OFF, with two buttons.
Is the start command simply a momentary (very short) button press, or do you need to hold the button in for that whole long start cycle described in post #5. ? I
t seems that the heater has no built in temperature control, except you switching it on and off.
If the start is a simple normally open button and the stop is simply a normally closed button then it might be quite simple. It might be as simple as two thermostats, one to operate the start relay and another to operate the start relay.

 

This is an interesting challenge, so now a few questions: Is this a mains powered heater or a battery powered heater? Do you have a manual for it? Providing an isolated momentary start and a momentary stop will require knowing if the buttons are normally open or normally closed, or one of each. And also how long the button must be pushed to make the command register.
The best approach will add two relays, one for start and one for stop..
The solution depends on the answers. Anybody's solution. Almost.

Your solution is what I’m looking for. There are devices that thermostatically control a relay. But the relay has an on or off state. What I need is a thermostat controlled circuit that triggers two relays for approximately 2 seconds or longer. I could then piggyback the relays to the momentarily tactile switches or remove the switches from the board and link the relays to where the switchers were.
There are to buttons on the remote. One for on and one for off. These switches are normally open.
The remote control is battery operated.
The remote thermostat needs to be powered separately so I can turn it off or it will turn the heater on and off indefinitely.

I hope I’ve explained things clearly.

 

OK, now we know that the control is strictly ON/OFF, with two buttons.
Is the start command simply a momentary (very short) button press, or do you need to hold the button in for that whole long start cycle described in post #5. ? I
t seems that the heater has no built in temperature control, except you switching it on and off.
If the start is a simple normally open button and the stop is simply a normally closed button then it might be quite simple. It might be as simple as two thermostats, one to operate the start relay and another to operate the start relay.

As you say the control is on and off. One button for on and another button for off. The button press needs to be greater than 1 second for on or off. The remote is a wireless fob.
the unit does have a thermostat. This is built into the control panel.

I think I should explain there are three parts to the heater. A motherboard which is the brain. A control panel which communicates with the motherboard to turn the heater on or off, control the room temperature and various other functions.
Then there is a remote fob which has the ability to turn the heater on or off and set the thermostat to the desired room temperature. Via the control panel.

 

OK, so will a remote thermostat wired to connect across the thermostat in the control panel be OK for the application?? That could be simple to implement, if it is a switch type of thermostat. Not a resistance type.

 

OK, so will a remote thermostat wired to connect across the thermostat in the control panel be OK for the application?? That could be simple to implement, if it is a switch type of thermostat. Not a resistance type.

No that won’t work. The problem is nothing to do with the thermostat or the heater not working correctly. As I tried to explain (obviously not clear enough) in my initial post the heater is way to efficient for the area it’s heating. Having a second thermostat connected to the one on the control panel will not charge the fact that even at the lowest temperature setting on the heater it still supply warm air to the area.
The only way to solve my problem is to physically turn the heater off when the area gets to hot and turn it on again when the area gets to cold.
All I’m asking for is a thermostatically controlled device that will do this. I can find devices that are similar but they have latching relays. I need something that closes a relay only for approx 2 seconds then releases it.
Ideally a thermostat with 2 relays. One is triggered when the ambient temperature falls below the target temperature (thus turning the heater on) and another that is triggered when the temperature rises above the target temperature (thus turning the heater off)

I know this is a tall order but I’m hoping someone knows of such a device or can design a circuit to do just that.

 

are you space constrained at all? Adafruit and Sparkfun have dev boards with relays of various kinds but you'd have to do some programming to get them to cycle how you want as well as read the temp sensors you'd need. https://www.sparkfun.com/products/16566 as an example. Is this the route you were looking for? The linked is for a relay board. https://www.sparkfun.com/products/15795 is for an arduino to control it. I don't know how accurate the on chip temp sensor is for your application, but if it isn't, the quiic ecosystem on sparkfun does make connecting an I2c temp sensor pretty easy.

 

are you space constrained at all? Adafruit and Sparkfun have dev boards with relays of various kinds but you'd have to do some programming to get them to cycle how you want as well as read the temp sensors you'd need. https://www.sparkfun.com/products/16566 as an example. Is this the route you were looking for? The linked is for a relay board. https://www.sparkfun.com/products/15795 is for an arduino to control it. I don't know how accurate the on chip temp sensor is for your application, but if it isn't, the quiic ecosystem on sparkfun does make connecting an I2c temp sensor pretty easy.

Thanks. They look like something I can use. I’ll investigate further.

 

"" The heater is in a caravan and is to efficient for the small area. ""

This is a VERY DANGEROUS idea.
You could easily be killed by Carbon-Monoxide Gases.
.
.
.

 

"" The heater is in a caravan and is to efficient for the small area. ""

This is a VERY DANGEROUS idea.
You could easily be killed by Carbon-Monoxide Gases.
.
.
.

No exhaust gases are released into the living area. When installed correctly the heater is safe to use.
I understand your concern but please don’t make wild assumptions without knowing the facts.

 

Take two relays, one SPDT and one DPDT.
Connect the coil of the first one directly to the thermostat. Connect the second to the thermostat with a resistor/capacitor delay.
wire the n/o contacts of the first via the n/c contacts of the second to the start button.
Wire the n/c contacts of the first via the n/o contacts of the second to the stop button.

 

Take two relays, one SPDT and one DPDT.
Connect the coil of the first one directly to the thermostat. Connect the second to the thermostat with a resistor/capacitor delay.
wire the n/o contacts of the first via the n/c contacts of the second to the start button.
Wire the n/c contacts of the first via the n/o contacts of the second to the stop button.

That sounds interesting. I need to do a schematic to understand it better but my initial thought is it could be what I need. Simple and does what I want. Thanks

 

My suggestion would switch off the heat at some setpoint and on at a lower setpoint.