Harman Control Board DIP Switches 1,2,3 set the heating range

This week while my Harman P68 stove was down, I had the chance to take things a part, look
over parts closely, and pull information off the Internet. The Harman control board which is used
in two dozen models of stoves has a bank of red switches, called SW2. For reasons of cost, the
control board is made to be general enough to be used across many products, but has switches to
tailor the control board to a specific stove. DIP switches 1,2, and 3 are set for the heat range of the stove.

I will explain this in more detail. As all Harmon owners know, the stove heat output is controlled by the
settings of the room temp/constant burn dials (two) and the feed limit dial (one). The settings of these
three dials, determine the heat output (and pellet feed rate) of the stove within its operating range. In addition,
the three DIP switches position the heating range, dependent on the model of stove.

You can move the stove heating range up or down by the setting of DIP switches 1,2, and 3.
Look closely at this:

http://rs.woodmanspartsplus.com/company_41/Harman Dipswitch Reference Chart.pdf

There are eight settings of the three DIP switches. The most common setting is 000, which is the middle
point.
Harman does not want owners changing these switches. Harman has labelled these as "Ignition Feed Time
Offset Adustment." And Harman talks about "Offset Time" This could also be called heating range.
But that is not the whole story. Look over all four pages above and think about it.
Harman uses the same control
board in two dozen models of stoves, of varying physical characteristics -- auger and burn pot dimensions.
The three DIP switches is how Harman tailors the board for the heat output range of a particular model of
stove. From the middle setting of 000 (decimal 0), the heating range is moved down ward with settings of
decimal 1 to 3. Conversely, from the middle (decimal 0), the heating range is moved upward with settings of
decimal 4 to decimal 7. Harman has labelled 000 as the middle, probably because that is the most common
heating range of the Harman products (You can see that from the dipswitch reference chart.)

So what I actually did. My P68 puts out too much heat during warm days and the shoulder seasons,
even with all three panel dials set
at the lowest settings, what I call constant burn 1/2. I changed the DIP switches of my board from 101
(decimal 5) to 100 (decimal 4). You want the power to be off, when you change these switches. When
the control board powers-up, it reads the switches "to see what stove it is in."

After I changed from 101 to 100, my P68 was throttled down to a lower heat output, while the three dials
of the panel were at the lowest settings. The top of the
heating range was also moved downward, but I do not care, because I only have ever ran the stove
at full output maybe a dozen times in the past 8 years. In essence, DIP switches 1,2, and 3 control the
range of the firing rate of the stove.

There is no harm in under-firing a stove. The same efficiencies still exist (or even a bit higher)
because the same physical dimensions still exist of heat exchangers and burn pot. Ever notice how much
more heat is conducted through the walls of the fire box, right after the ash, acting as insulation, has been removed from the inside walls?

However, be very careful in your testing if you try to over-fire a stove.
I would recommend to shift the heating range by only one step (out of the eight) at a time and see how it
works for a few weeks.

Switch bank 2, the red bank is easy to access from the panel. Just tear off the black plastic covering a
square hole over the DIP switches 1,2 and 3. The square hole is under the AN of the HARMAN letters
on the top of the control panel. You can get access to DIP switches 4 to 8 by bending out the sheet metal
cover until it breaks off. It is designed to happen that way. But I do not think many people will need
access to DIP switches 5 to 8.

It is understandable that Harman does not want average customers changing the DIP switches. The
information that Harman publishes about what the DIP switches 1,2, and 3, really do is somewhat obscure,
intentionally.

 

I don't know Harmans, but I read that chart as saying switches 1, 2, & 3 only apply to the initial feed of pellets... to pre-load the burnpot before ignition.

 

That is correct….the only thing that those switches control is how many seconds the auger runs to fill the burn pot upon startup….

 

That part is true, but not the whole story. The DIP switches tailor considerably, more
as I described above.
Harmon states that as an explanation of what the DIP switches do, but Harman does not
want people adjusting the heating range of the stove -- for good reasons. Harman wants
only
Harman repair technicians changing the switches when a new control board is installed
into a specific stove.

Please do not take this as me bragging or being argumentative. As an engineer or an
engineering project manager, I have worked on design teams of many products,
seen the products go to manufacture, and brought to market. I am aware of the economics of
scale. The Harman control boards in nearly all models of Harman stoves have nearly all the same functions.
But are tailored for each model of stove via the DIP switches. That is just the
way products are developed and marketed in the industrial age.

The average computer or cell phone has many more features than what are "turned-on" in the
particular model. Another model has a different set of features "turned-on".
This is done for economics of large scale manufacturing and providing different models at
different price points.

The reference chart of the DIP switch tells this if one studies the board numbers, heat output,
auger RPM gearing, etc. -- keeping in mind that the same control board is used in two dozen
models of Harman stoves. Plus a some knowledge of product design, manufacture, and
marketing helps.

 

So it does affect the normal run-time feeding?

 

Yes. I share this information with some caution. Be very careful about moving the heating range upward.
Move only one step at a time and then test for a few weeks. In general, the community on this forum is
quite knowledgeable, so I think it is probably safe to share this information.

People hack and reverse engineer products all the time. While at MIT, I knew of some young EE students that hacked the
photocopy machines

 

LOL,no. Harman Lover is right, or Harman has been lying to all the factory trained techs for many years.
I wish "Mr Harman" Lousy Weather was here, he would explain it better, I believe there is actually an old thread where he did.
So,first,Harman never made "two dozen models"of stoves, and, a P68-c is still a P68, same model.
The most common control board fits, I think, 8 models, the furnaces and some other models have different boards.
So,lets look at the basics. Harman has different feeders. This usually means nothing, in the overall picture, except the newer one is supposed to be better.
They have different burn pots, which are also sized to match the fire box and heat exchanger. This is the key to some of the settings,but not the #1-#3.
#1-#3 are for the startup, as said, and become null after the probe reaches a certain temperature.
Now, #7 and #8, are listed as " max esp temp". But, as I was told this "in effect" tells the board what burn pot/ heat exchanger settings are needed, you will notice models that use the same burn pot use the same 7-8 settings.
There are 2,I think, differences, probably from what testing showed.
So, want to get crazy? Mess with the #7 & #8 settings. It's your stove.Tell your P68 it is an Accentra, run for a week or two and get back to us. At your own risk. Remember, these stoves go through many hours of testing, for durability,life and cleanliness. Yes, they also are calibrated to meet emissions.
The first 3 are acceptable, once in a great while an adjustment is needed, like for a very tall chimney,auger motor out of spec, or such, and that is why they freely give out such info.
Anyway, that is what I have learned from Harman techs, If Lousy was still around he could probably explain it better, and more.

 

Thanks for sharing the information about DIP switches #7 and #8. These two DIP switches may be more directly in control of the burn temperature.
A total of two DIP switches, #7 and #8, would mean four different settings: 00, 01, 10, 11. I wonder whether Harman has a total of only four
auger assemblies and burn pot combinations? I agree that one should be very cautious about changing DIP switch #7 and #8, or not change
them at all. Harman has made it more difficult to get access to DIP Switches #7 and #8, probably for some very good reasons.
I see that a P68 has DIP Switches #7 and #8 set to 11 (decimal 3), independent of the auger RPM. Whereas a P61 has DIP switches set to
10 (decimal 2). Does anyone know how much difference exists between the auger assembly, burn port of P61 vs P68? Does anyone know if the
the parts have the same part numbers?

I wonder if DIP switches #7 and #8 directly control burn pot maximum temperatures, as seen by the ESP, whereas DIPS Switches #1, #2, and #2 control
the range of the pellet feed rate (which in other words, controls the range of heat output?)

My old house has a tall (about 40 ft.) old brick chimney about 5 ft. square, so I think it produces a great deal of draft. (Taller chimneys produce more draft
at a given temperature difference.) I am trying to reduce the bottom of the heating range of my P68, so that it I can allow it to run longer in mild
weather and shoulder seasons. In other words, I am trying to reduce the bottom of the pellet feeding rate range. This will make my P68 a nicer stove
for shoulder seasons. And I have made progress in reducing the heating load of the house over the past eight years. I estimate that I have reduced the
heating load of the house by about 30% in the past eight years. More planned for the future.

My P68 was installed in July 2014. The installation people started-up the stove for 3 minutes to show me that it ran, but no other testing or
adjustments were done. (I doubt they knew how or even cared to spend the additional time.) Moreover, measurements during the summer would not
mean much.

On the subject of what boards are used across numerous Harman stoves.
I see that control board 3-20-05886 is used across nine stoves. The
first nine stove of the DIP switch reference chart -- Advance, Accentra and P-Series.

I see that control board 3-20-6142 is used in four stoves.
I see that control board 3-20-6143 is used in six stoves.
My guess is that the above two boards are nearly the same.

I see that control board 3-20-05887 is used in three stoves, the corn burning stoves.
I see that control board 3-20-05888 is used in two stoves, that have either fin igniter or pressure igniter.
My guess is that the above two boards are nearly the same.

And control board 3-20-05892 is used across four stoves that run on 230 volts.

O.K. so the same control board is not used across 20 models of stoves, but each control board is used across five to ten stoves.

It would be great to receive some information from Harman Technicians on what they have been taught. Or better yet,
some current or former Harman Engineers to tell us about the design of the stove control system and the reasons for the
design. Having worked with or supervised 100's of engineers during my career, engineers are trained to think outside
the box and to find ways to solve problems.

 

THANK YOU…

 

I'm not sure what to tell you. Get a smaller stove, or realize your stove will work off a thermostat, the built in one or a remote add on. Just like a furnace.
If you take a stove, "throttle "it down too much, you will create a dirty, possibly creosoted up stove and flue. All this testing has been done. If it was reasonable, adjustments would be built into the stove. Sorry, I really don't see your thinking as "outside the box". You should talk to Don, here, he has made modifications on stoves, of lesser quality, but to make them burn hotter and cleaner, and he has had good success. You sound like you bought a 454 chevy, but want gas mileage of a pinto.
Any way, you can go to any of the good online parts places, pick a part, look at the drop downs and it will tell you all the models it fits. I could give a basic breakdown, but is time for you to do your own research.

 

Hi Harman Lover007 and Badbob,
I apol0gize for sounding too zealous over believing that the DIP Switches 1,2, and 3 affect the range of the
pellet feed rates and range of heat output. Certainly, the DIP Switches 1,2 and 3 determine the quantity of pellets
augured into the burn pot on start-up, as the Harman Dip Switch chart states. Until I complete extensive testing or
find out from other reliable sources, I should NOT state on this public forum that DIP switches 1,2, and 3 control additional
functions of the stove. I want to say sorry to another forum member, Blithering Idiot; I gave-out some unconfirmed
information.

It is useful for me to follow a path of research and experimentation of DIP Switches 7 and 8. Yes, it has been brought
to my attention one downside in reducing the temperature of the burn pot might result in higher emissions.

I do appreciate the opportunity to brainstorm with members on this forum. Always feel free to send me a PM to
discuss material and ideas that may be unverified and, thus not ready to be stated on a public forum.

 

No need to apologize, because...

I agree. And like anything on the internet, apply an appropriate degree of trust but always verify.