M116A3 Build

[pchast]

Sorry, the short answer is I don't know. Is the rod about the same size?

I've never worked with one of those. The gas flame sensors I worked
with were a bulb and capillary. Its been almost 20 years.
Can you get a manual from the manufacturer? I'd love to know.

Or just ask: [email protected]

[lfhoward]

I found a brand of flame sensors that are universal, and they say to bend and cut them to match your original sensor. So I think it can be done. I ordered a couple of straight sensors that are the right length and have matching mounting hardware, and they should be here by the end of next week. I will give that a shot. I got two because they were inexpensive and because I thought I might break one.

Also, I am in communication with Propex UK and have asked them if they can ship me an OEM flame sensor for this heater. If they say yes, I’ll not need the sensors above, and I’ll use the one that they send. I’ll keep you all updated!

Assuming one way or another that I can get this heater running reliably, the next steps would be:
- Order exhaust and intake pipes, and heating ducts from VanCafe.
- Repaint the VW Westfalia tank and install the valves, then get it purged, filled, and tested.
- Install the propane tank under the trailer.
- Cut holes for exhaust, intake, and gas in my trailer floor, and install the Propex.
- Connect the gas line and run the wiring. Seal the gaps to make it weatherproof.
- Go camping!! Our next trip is in the middle of October, so I bet it would be nice to have heat by then, especially up in the mountains.

[lfhoward]

The “new to me” flame sensors arrived tonight. They are pretty close to the OEM Propex sensor in terms of mounting hardware, ceramic insulator diameter & length, and rod thickness & length. I’m going to have to bend the rod to shape, and grind down the spade where the wire clip attaches, but really. I think this will work! (There is a second one in case I break the first one.)



After bending the rod and filing down the connector:



Pretty excited to try it. It’s dang close to the original, but (hopefully) without a microcrack in the insulator. If anyone is wondering how I bent it, I drilled a hole with a 1/8” drill bit (same diameter as the rod) in a piece of wood, then inserted the rod, checked my angles, and bent it. Using the wood instead of a vice made sure I wouldn’t leave any scratches or grooves in the steel rod to collect carbon and cause it to malfunction later.

[lfhoward]

Here is a question for you electrical engineers and HVAC techs out there:

How is it possible I’m reading 30+ micro amps on my flame sensor circuit? This causes an immediate shutdown of the unit, because I’m thinking it’s probably expecting about 5 mA. This only happens with my multimeter in-line. The rest of the time (direct connection), it does the normal shutdown after 5 seconds (2 flash flame sensing error).

Hey, at least we have micro amps now, right? The cracked flame sensor didn’t work at all. Now I just need to figure out why this one is reading so high. It’s just a steel rod?! Not too much to it. Maybe it needs more cleaning?

[edit: I just realized the mA setting on my multimeter is milliamps, not micro amps. So, my multimeter may not be sensitive enough to detect the flame sensor’s current.]

[lfhoward]

Sort of bummed. I haven’t done anything on the heater today. I really had hoped the problem was the flame sensor. I don’t think we will have heat for our camping trip in 2 weeks.

[bdosborn]

Did you measure the resistance of the sensor between the spade connection and and the base? I always thought it was the resistance that changed with temperature on those probes. I'd put the tip in a flame (lighter) and see how the resistance changes. It might be that the resistance isn't in the the correct range for the furnace to keep a flame going?

Bruce

[lfhoward]

Thank you. I should probably take the sensor out and test it to verify there is electrical connectivity between the spade and the rod, using the ohms setting. Maybe I busted it internally when I bent it. I haven’t read that there should be much resistance though, because it’s supposed to connect a circuit through the flame to ground.

Another question I have is what voltage I should look for on the upstream side of the sensor, coming from the circuit board. On home furnaces, it’s an AC voltage of something like 120 V, which gets rectified to low amperage DC as it travels through the flame. But the Propex is a 12 VDC heater, not 120 VAC. I’d love to know what to test for to make sure that the board is putting out the proper electrical signal in the first place.

Thinking about this, the problem is definitely in the flame sensor circuit, but what if it’s not in the sensor itself? The heater can sometimes run for 30 seconds to a minute if starting out from when it’s cold, but the circuit fails when it’s hot. At first I suspected a short from a cracked insulator in the flame sensor. Maybe I have a cracked solder joint on the board upstream of the flame sensor lead? That could be worth a look. If so it’s probably a microscopic crack that opens up as electricity flows through it and warms it. Or it could be a failed board component. I wouldn’t know how to diagnose or fix that.

[pchast]

Okkkkkkkk.

Are there any jumpers on the circuit board or dip switches?
Can you see that the sensor is in the flame when it fires as
I expected? Or is it designed to be only heated by it? Where
is the circuit board in relation to the heat plenum? Is it cooled
by the air flow around it? A silly question: Is it designed to be
installed "this side up"? Have you tested the wire/connector
between the sensor and the circuit board for a good connection?

Last, you stated the sensors are new to you. I'd test one against the
other before bending it!

[lfhoward]

Alright, I’ll see what I can do to answer these. Answers in italics.

Okkkkkkkk.
Are there any jumpers on the circuit board or dip switches?
Still learning terminology... can you define what a jumper and dip switch are?
Can you see that the sensor is in the flame when it fires as
I expected?
No, once the heater is put back together, as it has to be for proper air flow, there is no way to see the position of the flame.
Or is it designed to be only heated by it?
It’s designed so that the sensor rod must be in the flame, but it’s not so much the heat that matters, but that the electrons can travel from the rod through the flame to ground on the gas jet.
Where is the circuit board in relation to the heat plenum?
It’s located in front of the air intake from the cabin (not combustion air, air to heat up)
Is it cooled by the air flow around it?
Yes.
A silly question: Is it designed to be installed "this side up"?
It can only be installed in one orientation.
Have you tested the wire/connector between the sensor and the circuit board for a good connection?
Yes and we can rule that out as a source of the problem. It works fine.
Last, you stated the sensors are new to you. I'd test one against the
other before bending it!
Yeah, I bought used. I should definitely test the sensor to make sure it’s not open. It looks fine.

[lfhoward]

I’ve been corresponding with one of Propex’s customer service people and an engineer in England who understands the functioning of the unit. After going over my heater’s symptoms, checking circuits, and trying the replacement flame sensor (electrode in British), the only remaining conclusion is a faulty circuit board. I got this heater used and not working, so I knew that something like this would be a possibility even as I was hoping for a cheaper fix. Luckily it is possible to get a new board (PCB as they call it) for the HS1600. They cost about $180 USD, and I don’t know about international shipping yet. I figure I’m still ahead considering a new HS2000 is more than $800 and I have only $120 in mine so far. I should know more about final costs and logistics soon. I can say without a doubt that Propex’s customer service is top notch.

For completeness, here are some photos:

The igniter and flame sensor as they sit inside the burner.


The PCB inside the heater. The light blue wire (fourth from the bottom) goes to the flame sensor/electrode.


The PCB closer up and removed.

[featherliteCT1]

We wait with fingers crossed!

[lfhoward]

We wait with fingers crossed!

Me too! I’ll update when I know more.
[edit: new board is on its way here from England 10/9/20!]
[edit: the new board had to be tested and verified before shipping. It passed and should go out tomorrow, 10/15/20.]
[edit: new board shipped 10/15/20. Expected arrival?????]

Meanwhile, maybe the next task in front of me is refurbishing and repainting the WV Vanagon Westfalia propane tank. I also have to fabricate some mounting brackets for it. More to come.

Who says a trailer build is ever really done?

[lfhoward]

While I wait for my heater’s new circuit board to ship from the U.K., I decided I needed to make some kind of forward progress.

I had earlier taken measurements of the bottom of the trailer and the cubby the Propex heater will live in. I made a cardboard template of the cubby floor, and marked it with the locations of under floor beams and other obstructions. I positioned the heater on it, then marked the positions of the intake and exhaust pipes, gas line, and screw holes on the template. This way, I can later put the template on the cubby floor and then I’ll know exactly where to drill.

[featherliteCT1]

Nice progress!

[pchast]

Its difficult to access that board from this view.
I see no heat discoloration. When you check the
back of it are there any indications of a problem...
The burner setup looks Ok from that angle.

I'm glad you were able to get to one of their techs
to trouble shoot this.
Waiting to hear its fixed.