PP130, proposed wiring modification.

[little-willie]

Or another title could be, "What were the engineers thinking of?!"
The safety snap switch trips when the stove overheats, and shuts power completely off to the stove, which in my Not So Humble Opinion, is DUMB!
On almost any, if not all, modern heating appliance, an overheat condition shuts off the FUEL supply, ONLY. It leaves the indoor blower/convection fan and draft inducer an to run, pulling and and all heat out of the system, as quickly as possible. This is a safety concern.
I wonder why, PP shuts the entire stove down, leaving a fire pot, with fuel burning and still generating heat, and the convection blower shuts down, adding to a heat soak situation.
Any ideas as to why, or reasons to not make the wiring change, so only the feed motor shuts down, in an overheat condition?

 

[johneh]

The whole stove shut down because of overheat
First time in 20 years of working on pellet stove I have never run across this
normally pellet feed is stopped and the combustion fan runs until the stove has cooled
An overheated stove will not start until the sensor is reset.

 

[little-willie]

johneh, that's my thoughts and question, why would the designers NOT want to just shut down the fuel and get rid of the heat as soon as safely possible.
As you stated, the stove could still not restart, until the snap disc is reset.
I'm new at pellet stoves, much less than new of heating service.
I see no reason to not rewire the stove as I described.
I will wait to see if anyone knows of a reason not to do so.

 

[zrock]

so your stove has went into overheat shutdown?

 

[little-willie]

zrock, it has gone into "shutdown", numerous times, from different situations and component failures.
I think that I finally have everything now taken care of, including running on a UPS in case of another "observed power outage", but looking ahead to the future.

 

[Mt Bob]

It is not a "stove overheat" protection device. It is a "burn back" protection device, shuts stove off if it senses too high a temp on the auger tube, meaning the pellets are burning up the auger tube. Unless you have some different model, and it is not mounted on the auger tube.

 

[little-willie]

Mt Bob, it is mounted on the auger tube, but even as a "burn back" prevention safety device, I would think that you would still want the convection/indoor blower running, to get rid of the heat in the stove and firebox.

 

[Mt Bob]

I believe it's kind of like a structure fire, flames go towards the oxygen, and, if you have fire already in the tube, it's a small step into the hopper. Turn off the fan, the oxygen stops. If you are really worried, mount another switch somewhere else, and wire into the auger.

 

[little-willie]

Fire & heat, prefer to travel upward, the way the PP130 is designed, the pellets fall down a chute, from the auger to the firebox. A chute fire, would have to travel downhill, past the auger, to reach the hopper. Not at all like the American Harvest 6039, that we originally had, and did have a hopper fire in. NOT the least bit fun!
The convection fan, only blows air around the heat exchange jacket, supplying now combustion air to the fire box and combustion area.
Higher temperatures promote faster combustion, evacuating the residual heat, still seems like a good plan, but shutting down the draft inducer does seem like a good idea.

 

[Mt Bob]

You can theorize it any way you want, but the vast majority of hopper fires come from the standard, top feed gravity drop stoves, well, even since pressure feed stoves went away. Quad's used a safety switch on the auger tube for years, and may still.

Pellet stove hopper fires?

I had a friend tell me that due to the type of auger feed system in the Harmon pellet stove, if there were a power shortage, it possible for the fire to continue burner backwards following the auger and ignite the pellets in the hopper. Have any of you heared of this, and done it seem possible...

www.hearth.com

 

[tlc1976]

Except for when I had a faulty overheat switch, my overheat switch has tripped once. It was due to a stopped convection blower shortly after startup. It was my own fault for installing the seal backwards after lubing the bearings, but seized bearings or an electrical short could do the same thing. And continuing to provide power in either case could start a fire in external components.

Other than a control board failure resulting in an overfeed of pellets, or a suddenly plugged exhaust, that’s probably about the only thing that could make the stove overheat.

So the lesser of evils is a kill switch, which is what the overheat switch does. At least if a fire does happen, it’s contained to the hopper, and it can’t get much air to keep it going. Mine did it’s job, no fire, shut the stove off well below the threshold of fire.

BTW my switch is nowhere near the auger. It is on the back of the heat exchanger jacket near the convection blower.