M116A3 Build

[featherliteCT1]

You are displaying some pretty impressive diagnostic skills. My interest is piqued!

[lfhoward]

You are displaying some pretty impressive diagnostic skills. My interest is piqued!

Why, thank you, featherlite!

It has been a steep learning curve. I’ve left all my mistakes and misunderstandings in the previous couple pages of posts. Hopefully they won’t confuse anyone, but rather help others towards a better understanding and a solution if they’re having Propex heater issues. There is precious little on the internet about tracking down any problems with Propex heaters. This could be because they’re just so dang reliable (which I think they are). It could also be that people just send them to the factory to be fixed when something happens. I like to know how things work and how to fix them myself. There are few internal spare parts to be found for the Propex online too, and the flame sensor is not one of them.

[lfhoward]

I finally got all the parts to be able to hook a WC pressure gauge (or manometer) up to the propane line just before the heater. This will allow me to see how much the pressure drops when the heater is running. It needs 37 mbar (15WC for us Americans) to make the flame the right size and make it reliable. This should allow me to rule out incorrect gas pressure as a factor, and dial in my regulator to the right setting for the heater.



Please note that if you are reading this post trying to troubleshoot your Propex, and you bought it in North America, yours is set to run at 11 WC, not 15. I imported mine from the UK, and they use a higher gas pressure over there.

[lfhoward]

One of the other potential confounding issues to rule out is having the intake suck up exhaust fumes and lower the flame efficiency. I don’t have exhaust and intake hoses yet so here is my work around.



I built a temporary platform out of scrap wood I had lying around, and bolted the heater to it. That’s the exhaust pipe you can see there. The intake draws in fresh air from the other side. I can take this jig outside and place it on top of my grill, then hook the line up to the propane bottle. Easy to run tests.

[lfhoward]

Progress!!!

After cleaning the flame sensor very well with a green scotch brite pad, I reassembled the unit and tested it out again. I actually got it to stay burning for about 30 seconds to a minute! The heater shut itself down eventually, most likely because it lost the circuit with the flame sensor. After shutting itself down, it wouldn’t run for more than 5 seconds again. If I let it sit for an hour and start it up again, I can get the 30 seconds to a minute burn, before it reverts to its shutdown behavior.

Since we know the flame sensor is polished up now, I’m thinking I need to turn my attention to the other side of the circuit: the burner housing. Maybe I should polish that up as well? I can polish the igniter at the same time. Maybe there is enough soot and crud on the burner housing that electrons traveling through the flame can’t make it any further? Worth a shot, I think.

Now to take everything apart again, lol.

Alternatively, maybe the flame sensor really does have a micro crack in the porcelain insulator and it opens up as the metal rod inside gets hot and expands, shorting it out.

[featherliteCT1]

I was looking at your battery and wires and was wondering if the wires were large enough to carry the start up amps without suffering a voltage drop. I went back and read your previous posts, and it appears that you have never had a “low voltage” error code.

I just wanted to be sure that you were not having a problems with voltage drop at startup. I would suspect that the unit draws up to 10 amps at startup. On the other hand, it appears that the wire length is fairly short which would mitigate the voltage drop. I would think you would need at least 12 AWG wire. Just trying to help brainstorm and eliminate all possibilities. I use 10 AWG wire for my diesel heater that draws 10 amps at startup.

[lfhoward]

The burner:


The burner is made of brass and has connection to ground. Cleaning it is tricky as a scotch brite pad can scratch brass. Recommendations?

Where the burner lives:


The housing is made of stainless steel and also has no connection to ground unless the burner itself is touching (the clearance is like 1/2 mm). It could possibly have a connection to ground through the white wire to the igniter module (black box), but when the unit is turned off there is no connection between the housing and ground.

However as I understand it, the electrons must flow through the flame. If the flame has a wide spread angle it might touch the stainless steel housing, allowing the circuit to be connected there, but if the flame is long and narrow it won’t touch. (I don’t know what form the flame takes.) I am thinking the electrons probably have a better path back to ground if they go into the brass burner than into the stainless housing, for two reasons: 1. brass is a better conductor than stainless steel, and 2. the burner itself has a sure ground of its own.

However, the inside of that flame hole is quite dirty. I’m going to clean it up and see what happens. What else should I try? If you’d like to know anything I can test with the multimeter, just ask. (Thinking of you, featherliteCT1)

[lfhoward]

I was looking at your battery and wires and was wondering if the wires were large enough to carry the start up amps without suffering a voltage drop. I went back and read your previous posts, and it appears that you have never had a “low voltage” error code.

I just wanted to be sure that you were not having a problems with voltage drop at startup. I would suspect that the unit draws up to 10 amps at startup. On the other hand, it appears that the wire length is fairly short which would mitigate the voltage drop. I would think you would need at least 12 AWG wire. Just trying to help brainstorm and eliminate all possibilities. I use 10 AWG wire for my diesel heater that draws 10 amps at startup.

Good idea! I tested the amps and the unit draws a momentary 2.4 amps at startup (even while igniting), and quickly drops down to less than 1.7 amps. The spike seems to be only due to the electric fan motor spinning up.

I think the 10 amp draw of your diesel heater could be the glow plug. One of the nice things about a Propex is they use less electricity.

[featherliteCT1]

Well, I am glad you have eliminated that possibility. I hope you figure this problem out soon because it is bugging the heck out of me!

[lfhoward]

Me too! I’d love to get onto heater installation and cold weather camping!! Luckily it’s only getting down in the 50’s at night here so far.

More to think about:







This is how the igniter, flame sensor, and housing look inside of the combustion chamber. If you were an electron making a round trip from the flame sensor back to ground, and you had to travel through flame to connect with anything metal, what path would you take?

[edit: the burner housing is brass too, now that I look closer.]

[lfhoward]

The burner housing polished up nicely.

I’m still a bit sketched out by the chip/crack in the base of the flame sensor.





It makes me wonder if it’s the source of my grief. I put it under my dissecting microscope (I am a biologist after all, and doesn’t everyone have a microscope in their basement?) and there is a longitudinal crack that extends from the chip, maybe 2/3 of the way to the metal ring. My multimeter shows no electrical path from the rod/spade to the mounting ring, which is what we want. I don’t think it is probably shorting out, although the metal should expand when hot and that could change the equation.

[pchast]

in my previous life I was a home boiler mechanic... Just a bunch of unrelated thoughts:

You may still have a short through the sensor mount after the insulator heats up. Check for microscopic cracks and carbon tracking under the mount connection.

Is there a transformer or coil that supplies a constant ignition? that could also heat up and short or open. if you have good pressure and flow, a constant flame would be less likely to be affected though.

Otherwise, you say the burner tube is dirty? There should be very little soot there if there is enough air flow for good combustion.

[lfhoward]

in my previous life I was a home boiler mechanic... Just a bunch of unrelated thoughts:

You may still have a short through the sensor mount after the insulator heats up. Check for microscopic cracks and carbon tracking under the mount connection.

Is there a transformer or coil that supplies a constant ignition? that could also heat up and short or open. if you have good pressure and flow, a constant flame would be less likely to be affected though.

Otherwise, you say the burner tube is dirty? There should be very little soot there if there is enough air flow for good combustion.

Wow, we were channeling the same thoughts. Check out the edit I made to the previous post while you were writing yours. I am thinking you’re probably right about the short in the flame sensor once things get hot. It is consistent with my observations that I could only get a 1 minute burn going when the machine was cold.

The igniter only comes on at the very start of the cycle. It ticks about a half dozen or 10 times or so, then it’s job is done. I do think the flame sensor’s job is constant while the flame is on.

The dirty burner tube may be my fault. I was using one of those bic fireplace lighters to try and get an electrical connection back when I thought I was dealing with a thermocouple. (A flame sensor is a different beast, I know now.) The lighter could easily be the source of the soot, especially since it could use up the oxygen in the chamber and extinguish itself after about 15 seconds or so. Without the fan running there isn’t enough air in there to sustain a flame.

[pchast]

Yes, the safety would be constantly checking the flame.

[lfhoward]

Yes, the safety would be constantly checking the flame.

Thanks for your thoughts, Pete.

Does it ever work to get a universal straight flame sensor and then try to bend it to the same shape and angles of the old one? There are many flame sensors out there for sale on the internet, just not this one. But I could possibly get one that’s close and then bend to match the original?

For example, from EBay: