New PE Blower hum

[Sisu]

I have a PE Pacific that was purchased in 2005. The blower is fairly quiet but certainly audible. However, I do not use the fan.

My insert is in the basement internal masonry fireplace (bungalow house). When I first purchased the insert, I experimented with the fan on vs. off. I discovered that when the fan was on, the upstairs (ground floor) was cooler, since the fan was cooling the masonry of the chimney. Meanwhile the basement was very hot. When the fan is not used, the masonry in the ground floor radiates the heat, and distributing the heat more effectively to the ground floor.

You can run this insert safely without using the fan. Try experimenting and see if you get the same heat with the fan off. If so, your noise problem is easily solved.

 

[begreen]

The problem is the 3,000 rpm motor. If you run it full speed you get a lot of air noise. If you try to run it too slow you are going to get a hum due to the rheostat applying too much resistance to the system. You are trying to throttle back the motor too much and it doesn't like it and will eventually overheat and fail. A better choice would be to select a lower rpm motor like a 1,250 and run it at full speed.

Either that or the three mounting points are too flimsy and you are getting a vibration in the housing. Stiffer is better. So you could stiffen the sheet steel with some ribs or try a band-aid fix of applying damping material.

In our case, the 60Hz hum is always present, even at full speed, it is just masked by the blower noise. The hum is the same whether the motor is running at 3000 rpm, 1500 rpm or 500 rpm. The blower suspension in the case is quite well done, not flimsy. The noise is transmitted by resonance. Surfaces that resonate around 60Hz make it much more noticeable.

FWIW, my old Fasco test fan used to run at medium-low speed all day long when we had a fire. It was too noisy at high speed. The motor never overheated or even got overly warm and still works fine. Maybe a bad controller? PE's controller seems to limit the lowest speed to about 1000 rpm? I'm going to run it for an hour at lowest speed and will then take an IR temp reading off the motor.

 

[cycloxer]

1,000 rpm is okay on the 3,000 rpm motor. I wouldn't run it lower than that, but that is a matter of how much life you want to get out of the motor. The slower you run it, the more you are stalling your motor. If you feel the transformer on the motor when it is running you can figure out the minimum speed you can run before it stalls too much and overheats, eventually burning out the motor. The rheostat increases the resistance of the circuit and limit the current to the motor. That's why they tuned the pot the rheostat for a minimim speed.

As for the housing, if it is resonating, the only way to get rid of that is to stiffen the housing or dampen it out. The motor could be causing the rear heat shield to resonate at certain speeds. If you stiffen the shield that is resonating, you will increase its natural frequency and that is what you want. Another way would be to apply a dampening material like Dynamat (though I have no idea if this stuff is combustible). Check it out:

(broken link removed)

 

[begreen]

I think the controller design is the factor here. You may have tested with a controller that allows the motor to almost stall. I don't think a stove maker would ship with a controller that allowed that. They use a rheostat that has a range suited for the motor. After running the fan for an hour (off the stove) at lowest speed, I got a motor temp of 77°F with room ambient of 70°F.

Thanks for the tips on the isolation. I don't think it gets very hot at the bottom back of the stove. Will check. Tom suggested fiber washers which are easy to get and I will try. I was also wondering if I put a layer of flat stove gasket between the blower case and the rear shield if that would isolate it.

 

[cycloxer]

Rheostats usually have a main control knob and then a smaller pot that has a recessed adjustment that is accessed with a small flat head screw driver (see yellow arrow). You have to adjust the pot to set the range. On mine it is actually labeled 'min speed adjust'. The Jotul's use this style. I haven't taken apart a PE blower assemby to see if their rheostat has an adjustable pot, but I would imagine it does. You may not be able to see it from the panel side as they may have purposely hidden the access screw so that people don't muck with it and blow out the motor.

 

[Chuck Pearson]

<<apply a dampening material like Dynamat
The specifications say it can withstand up to 300 degrees F.

 

[begreen]

I'm thinking this is mostly me and not an issue. The blower is very quiet, so one hears new sounds. I loosened her up and used a bit of flat gasket material as a spacer/decoupler. Works fine.

FWIW, just checked the temp at the bottom of the heat shield after a good fire's been going for about 4 hrs. It reads 87°F.