Auger Protection

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New Member
Hearth Supporter
Apr 15, 2008
Central Maine
With all the talk in this forum about burning up augers, I decide to build a protection device for the two auger motors in my Engalnder 25-PDVC.

Considering using a CT with a rectifier and quad op amp to feed DC current into a PIC microcontroller. Program the pic to activate a solid state relay if the current draw was too great after a short time delay. Prototype circuit seams to be working well. PIC seams to detect current wihtin +/-10% as measured by an ammeter on a steady load. I'm going to connect it to some type of LCD display and maybe a small buzzer.

Are all the augers used for pellet stoves about the same?

Mine appears to be a 1RPM final gear auger attached to a 120 VAC motor with a full load amp rating of about 0.5 amps.

I've designed the circuit to measure 0-5 Amp RMS AC with motor cutouts under two conditions:

125% FLA (.75 Amps) for for 5 seconds "high load"
200% FLA (1.0 amp) for 1 second "locked rotor current/jam"
Ummmm.... what did you say????

Not sure I understood most of what you wrote, but I can cofirm that the auger motor in my empress is about the same (1 RPM, 120V, .48 amps)
If you are that worried about burning up an auger motor, just get a back up motor. The motors are not that expensive. I have seen new motors (1 RPM) from $36 to $150 new. If you pay more that is your fault.

There's something about just replacing an auger motor without knowing why it failed that rubs me the wrong way. Before I replace a broken part I like to know why it failed so the second unit does not fail prematurely as well.

Monitoring the current draw can tell you if the motor jammed (something stuck, gearbor or the auger hung ups) or cutout on high load (carbon buildup, bearings, pellet dust, etc). If you have voltage but no current, the motor probably failed. If you have voltage with a small current draw the motor decoupled from the auger or the gearbox failed. Sometimes they just fail too.

A new auger motor for my stove runs about $90 to $125 each.

A motor protection circuit runs costs around $25.

If the pellet stove was my only source of heat, I'd probably carry another motor on the shelf, just in case.
FWIW Harmans run @ 4 RPM
Also the ratio on them is somewhat over the 800-1 area
which is why I went with the clutch to protect against overloads...
By the time I approached Full load either the chain would skip and fall off or the mount would bend.
however direct drive is a bit different, sounds like a good fix you came up with...
tyru, did you build a circuit board for the PIC microcontroller, or is there a development kit available? How about a picture?

The PIC has a lot of capability for the buck. I can think of a lot of things I could use it for.
GVA: Thanks for the info. You make a good point that even though the motor may be rated for X full load amps does not mean that the rest of the auger system can handle the torque at that amperage. I'm going to stick an ammeter on my motor to see where it typcially runs.

I have obtained a couple 10A, 1000:1 CTs. I'm still working on the analog circuit to obtain a stead DC signal. Can't seem to get the circuit to generate over 4 VDC.

FYI to anyone following this thread:
The wire that carries the current (primary current) to the auger motor is passed through the hole in a current transformer (CT). Using a 1000:1 ratio CT, the current (secondary current) generated by the CT is 1/1000th the current in the primary. A current of 5 amp AC primary gives a 0.005 amp or 5 mA current signal in teh secondary. The hard part is the circuit that takes the AC current and converts it to a 0-5 volt DC signal for the PIC. A PIC is a small programmable micro controller which can monitor input (such as the a 0-5 VDC signal corresponding to the current draw of the auger motor), show the current draw on an LCD and then activate a relay if the current draw is too high.

I already had a PIC programmer and a prototype board with an LCD which I use to do various projects on.

I'll post a video specific for to the project when I have it further along. Here is a sample video for another project using a PIC programmed to activate a solenoid and then release after a delay period (used for a pneumatic gun).

Pic Prototype Board
Very cool. Is the prototype board available from Microchip?
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