Flame sensor voltage...

[mrcaptainbob]

Can 24 volts be run through a furnace flame sensor? I know it uses continuity for the furnace controller, but I suspect the controller must be sending a voltage through that 'switch' to know whether to keep working. I'm wondering what that voltage might be....

[paul52446m]

Can 24 volts be run through a furnace flame sensor? I know it uses continuity for the furnace controller, but I suspect the controller must be sending a voltage through that 'switch' to know whether to keep working. I'm wondering what that voltage might be....

Why do you want to know what the voltage is going through a pilot? No you can not run 24 volts through a pilot .
The pilot flame produces a very small voltage. It might be like .002 volts.
The different types of primary controls Amplifies this power so it can be read by
the controls. So the voltage that is read depends on the amplification of the control and size of the pilot and how clean everything is. On different units i have seen readings from 5 mille-volts to 30 mille-volts Paul

[HayZee518]

Bob, I have a Reddy heater that uses no electricity, just what is generated by means of the thermopile "in a flame." The capillary and "bulb" is the electrical signal. Inside the bulb end a wire is welded to the inside of the tip. This forms what is called a J-K junction. Two dissimilar metals, one gives up electrons, one freely accepts electrons and so you have current flow. This wire goes down inside the capillary to the little silver bulb which screws into the pilot valve. I got an illustration somewhere here that shows how its connected.

[mrcaptainbob]

Flame sensor info....

I'm learning here. I checked the continuity of that flame sensor and it showed zero when it's in the dark, but infinity when it's in the bright light. I was under the impression, then, that it was merely a conductor to complete a circuit in the controller. If that were true, my thinking goes...(went?) then what voltage did the controller pass through it on that circuit? It's a cadmium-sulfide photoconductive flame sensing device for sequencing oil burner systems. A typical one is Honeywell Cadmium-Sulfide Flame Detector with 60 in. leads, Type "R" mounting bracket and 130367 Cad Cell.

[paul52446m]

I'm learning here. I checked the continuity of that flame sensor and it showed zero when it's in the dark, but infinity when it's in the bright light. I was under the impression, then, that it was merely a conductor to complete a circuit in the controller. If that were true, my thinking goes...(went?) then what voltage did the controller pass through it on that circuit? It's a cadmium-sulfide photoconductive flame sensing device for sequencing oil burner systems. A typical one is Honeywell Cadmium-Sulfide Flame Detector with 60 in. leads, Type "R" mounting bracket and 130367 Cad Cell.

In your first post you was talking about a flame censer. Know you are talking about a photocell or cad cell, which close by seeing light. I don't remember what the power they run through them. Is it important to know this and for what reason? Paul

[HayZee518]

ok a cad cell. it is a device whose resistance changes with or without the presence of infrared light. yeah its a photocell/ put your meter across the leads and shine a flame from a lighter on it. now measure the voltage. do the same but with the meter on resistance.
a properly operating cell will have no more than 1600 ohms across it with light shining on it.

[mrcaptainbob]

Flame sensor...

Hi, Paul. I guess my choice of words got in the way of what I was talking about. My personal focus on this object precluded other sensor options. Apologies for that. The reason I'm asking is because I wanted to refrain from a drawn out story and just get to the point. So, I recently acquired a waste oil furnace and have been in the process of refurbishing it. Although it's a brand name unit, it is so old that the company itself has no records. Manuals are so far non-existent. I am now at the point of firing it up and find the controller sometimes works, sometimes doesn't. Thermostat terminals are jumpered, as is so often the case with these units. The time-of-use on the controller is at 30 seconds to see flame, then it shuts off, making it impossible to further figure this unit out. Resetting the controller is aggravating, as it takes a while for it to reset itself, even after hitting the red reset button. I have since (temporarily) removed the controller and bypassed the wiring. Although I managed to get flame to the unit last night, I need to do further refinement on the nozzle and it's performance. I would like to keep the flame sensor (cad cell) in place while I work on this and was hoping to (again, temporarily) use a relay in place of the controller that was controlled by that sensor/cell. Not knowing exactly how these work, I posted the original question, as I did not want to put voltage through it that might burn it up.
But, Hayzee just cleared that up for me. It produces electricity itself. Stupid me for forgetting that that is what photo cells do! So....the controller reads that power from the cell and makes it's decision based on that information.
Thanks, guys for the help. Sure enjoy this dialogue with you both.....

[HayZee518]

Bob, the last place I worked at had a waste oil heater. The outside box was red in color. the pump/gun assembly was on the right side as you face the unit, an 8 inch flue pipe with a barometric damper is on the left side. This went up and outside the building. On the unit itself there is an input for compressed air, an inlet for waste oil, a bleeder for when the pump primes and a 120 volt heater for the oil. The way it worked is you press the orange button on the protecto-relay. This would start the heater - pre-heat. Once the oil was heated, you'd open the air in valve and turn up the stat. oil would flow out of the nozzle and the ignition would constantly spark. if the unit fired up, the cad cell would detect the infrared flame and the unit would run. Variables are amount of oil through the nozzle, amount of air to atomize the oil. We had all kinds of oil going through ours. Waste diesel fuel, kerosene, crankcase oil, vegetable oil, bio-diesel, old lube oil, gear oil, you name it. Occasionally it wouldn't fire up but kept on pumping. Next time it fired, it blew the stack clean off the burner and I think it cracked the heat exchanger.

[mrcaptainbob]

WOH info....

YIKES! I hope I don't have issues like that! This unit (CleanBurn) is close to what you're describing, HayZee. Heated compressed air, heated oil chamber...should burn most anything. I got it to fire off pretty decent today. I allowed the heaters to do their job and it worked quite well. The fan even turned on/off on it's own! Glad I found that shorted wire (re:another post...). Still am learning. Lots of fine tuning. Once it's to the point I'm satisfied with, then I'll reinstall the controller and cad cell.
I still appreciate all the help from you guys. Thanks.

[hawkins111]

Cad Cell

Bob,

The Cad Cell just completes the low voltage circuit in the primary controller when enough light is present to reduce its resistance and allow current to flow. If there is no light then the resistance is high and no current can flow. The spec from Honeywell says Max Voltage 60VDC or 60VAC. The cell does not generate voltage for the primary control. This is evident when you trouble shoot the circuit by jumping the F terminals. The jumper provides no voltage. When the burner fires you can then check the OHM’s. With a flame you should see less than 1600 OHM’s. In darkness you will see 20K OHM’s or more.

Tom

[mrcaptainbob]

Cad cell....

Great explanation, Hawkins. Sure appreciate the help....