Grainstoves from J. A. Mitchell Marketing

Chapter Six: Auger Operation and Feed Rate Adjuster

We will now go over the relevant components and controls of the PC-45 grain stove. You will need to understand these components to make the grain burn efficiently. We start at the beginning. The grain is fed into the burn pot through a patented bottom-feeding auger.

Other grain and pellet stoves use an auger to bring the fuel above the burn pot and then drop the grain/pellets into the pot. Rather than dropping the grain, the PC-45 pushes it through the burning process. This bottom-feeding technology was adopted from Harman’s coal auger. Since the grain is pushed rather than dropped, there is constant pressure throughout the burning process. This constant pressure creates a system that allows for the systematic burning of grain and removal of ash. Furthermore, because the auger speed can be controlled precisely, the entire process can be adjusted to burn many different types of grains. This pressure system also pushes the ash out of the burn pot once it has been burned. This is the most effective ash removal system on the market today. Mechanisms that drop the grain into the burn pot have no way to get the ash out. These other mechanisms are much more likely to clog and require much more cleaning because they do not have a process to move the ash out of the burn pot (some competitors do have a mechanism that dumps the entire burn pot when the thermostat shuts off, but this is messy and does not empty if the fire is burning constantly - as stoves do on cold days).

The most important control related to this patented auger bottom-feeding system is the “Feed Rate Adjuster.”

The Feed Rate Adjuster controls the amount of grain that can be fed into the burn pot. It can be set between 1 and 6. The higher you set the control, the more grain that will enter the burn pot. This control is not intended to be used as a method to control the temperature by constantly adjusting the amount of grain being fed into the burn pot. The Feed Rate Adjuster is intended to be used a governor. It should be set to the maximum feed rate the stove can handle for this particular batch of grain. Needless to say, this feed rate will be different for different types of grains, and will even be different for different batches of the same type of grain, depending mostly on the moisture content. Generally, the feed adjustor only needs to be set once for every batch of grain.

At this point we should probably point out that grain stoves feed slower and adjust to changes in the feed rate setting more slowly than pellet stoves. The reason is that grain is a much more compact fuel than pellets. In other words, there is more fuel in one cup of grain than in one cup of pellets. For that reason, grain has to be fed more slowly into the burn pot or it will smother the fire. Pellet stoves generally operate on one minute cycles and can feed for 30 to 40 seconds out of every minute cycle. The PC-45 feeds on 15 second cycles. The default feed setting for the PC-45 is set to feed 2.1 seconds out of every 15 second cycle when the dip switches on the circuit board are set to the recommended grain burning settings (dip switches 3,4,7 and 8 on the circuit board should be set to "on" for burning grain. These dip switches should be set by your dealer). If dip switch 4 is on and dip switch 1 is off (which is the recommended grain-burning setting), the stove will feed for a maximum of 6 seconds out of every 15 second cycle. On the other hand, if dip switch 1 is on, the stove will feed for a maximum of 15 seconds out of 15 (this is the setting for burning corn). If dip switch one is on and the stove is set to feed for a maximum of 15 seconds out of every cycle (or constantly) the “Feed Rate Adjuster” dial is simply not sensitive enough for the precise adjustments necessary to achieve efficient grain-burning.

For example, the feed adjuster setting for wheat should be somewhere around 2.8 to 2.9 seconds per cycle. When the entire range of the adjuster dial only moves the feed rate between 0 to 6 seconds, it is much easier to set the feed rate to precisely 2.8 or 2.9 seconds. On the other hand, if the feed rate dial adjusts the rate between 0 and 15 seconds, it is much more difficult to find a precise setting of 2.8 because even a slight movement of the dial changes the feed rate significantly. Additionally, the recommended dip switch setting provides for a more intuitive feed rate operation because each number between 1 and 6 on the “Feed Rate Adjuster” dial will roughly correspond to the number of seconds out of 15 that the auger will feed the into the burn pot. In other words, if you set the “Feed Rate Adjuster” to 4, the auger will feed grain into the burn pot 4 seconds every 15 second cycle.

As you can see, grain stoves spend far less time per minute feeding fuel into the burn pot than pellet stoves. In addition, grain stoves feed this fuel in smaller increments because they operate on shorter cycles. It is precisely because grain-buring stoves are more sensitive to changes in the feed rate and are more likely to go out as a result of over-feeding, that Harman has been very careful to limit how fast the feed rate can be adjusted. In the PC-45, the fastest that the feed rate can be increased or decreased is by 1/10 of second per cycle. Therefore, if the auger is feeding for 2.1 seconds every 15 second cycle, and you adjust the “Feed Rate Adjuster” to 3.3, it will take 3 minutes to get the stove to feed for 3.3 seconds out of every 15 second cycle. Therefore, when you adjust the feed rate, you should keep in mind that it will take a little while for you adjustment to take effect.

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Warning, J.A. Mitchell Marketing Ltd. is not the manufacturer of the Harman PC-45 or any other product. J.A. Mitchell Marketing Ltd. is not responsible for any loss or damage caused by the Harman PC-45 or any other product. J.A. Mitchell Marketing Ltd. provides no representations or warranties. If you are confused or unsure at any point, contact your local Harman dealer.