Electrical conundrum!

[cathead]

My torpedo heater decided to run a few seconds and shut off so the problem has to be somewhere in the
photocell circuit. I replaced the photocell with a good one with the same results. There is a circuit breaker
that shuts down the unit when there is no fire, I can understand that. On disassembly, what I can't understand
is how could the photocell that is connected to a small circuit board which is connected to the breaker with only
ONE WIRE have any effect on the circuit breaker? I did disassemble the little box and found what appears
to be a bad transistor(overheated). Actually it looks like a small signal transistor but in actuality it is an SCR
(silicon controlled rectifier), an X0203 to be exact. Well, I didn't have one but did have another SCR so
soldered that in and tried it. Well, the heater fires up and runs but doesn't shut off if you disconnect the
photocell so I know I need to find an X0203... Sure, I could throw some money at this thing and get a new
fire sensing unit but that isn't going to happen because they seem to sell for somewhere in the 100 dollar range.

In the meantime.... I connected the breaker wires together and of course the heater works even without
the photocell of course. That's probably not the safest thing to do but will provide 150,000BTUs of heat
as long as it isn't left unattended. I have another one so it isn't a big deal...

So, now for the next step I intend to find an X0203 and solder it in and see if it solves the conundrum.
The photocell leads to the blue and white wires that go to the circuit board and only one wire connects to
the breaker. I just don't get it. Maybe someone else on here can understand this but for the time
being, I am truly perplexed. If you look at the photos and expand them, you can see the single wire going
from the board to the breaker. How can this be??

 

[Flyinfool]

Digi-Key has that SCR for less than a buck. Heck, Digi-key is in Thief River Falls, MN, so almost in your back yard.

Discrete Semiconductor Products | Thyristors - SCRs | DigiKey

Discrete Semiconductor Products - Thyristors - SCRs are in stock at Digikey. Order Now! Discrete Semiconductor Products ship same day

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There are 2 big terminals on the breaker, are you sure a connection did not fall off before you pulled it off? I can see marks on one of the terminals that says there was a wire on it.

 

[markba633csi]

One lead must have fallen off, Cat. It wouldn't work otherwise
Why a photocell in a heater? Is this a gas fired heater? The SCR controls a gas valve?
BTW (and this is for everyone) got to post smaller files- takes a light year to open them when they are 5 meg +
-Mark

 

[cathead]

I'm positive there is (and or was) only one wire to the circuit breaker! The two spade terminals are for powering the
unit of course. The photocell senses the fire and dumps the breaker if the fire is lost, a safety feature to be sure.

 

[markba633csi]

That doesn't make sense. Breakers don't normally work that way- the photocell circuit must be cutting the gas valve when you lose flame
How does this heater normally operate? Is there a start button? Or does the breaker act like a start button? The "breaker" could be a latching relay, that would make more sense.

 

[cathead]

Normally, one just plugs it in and it fires up. If the flame should fail for any reason, it dumps the breaker somehow
and with one wire(and I'm sure on that part).


Edit: It's a 150,000btu Reddy heater.

The breaker will act as a start button if the flame sensor has caused the unit to fail.

 

[markba633csi]

I was going to say, it could be a sensitive gate SCR in that circuit. A regular one won't work, which explains your substitute not working
There is a gas valve though, right? A sketch would help

 

[cathead]

There is no gas valve. The fan motor has an air pump on the back of it and it causes the fuel to be siphoned
from the tank and atomized.

On the bottom right are the two spade terminals. One of the spade terminals is connected to hot(black)
and the other goes to the load(fan). The arrow in the photo shows the single wire going to the breaker.
It runs on kerosene or #1 fuel oil.

It looks like MAGIC to me! Stuff like this really gets me so I can't leave one turn unstoned!

 

[markba633csi]

No gas valve!? Hmm..yep it's magic all right. OK, I'll bite- where does the neutral connect? Don't tell me there isn't one LOL

 

[cathead]

The X0203 is a sensitive gate SCR according to the data sheets...

Thanks to Flyinfool and to markba633 for your responses. I ordered from
Digikey a few SCRs so will try to follow up when I get the control unit
put back together and hopefully working.