P61a Harman issue-Feed motor does not stop when mode knob turned to off. Fire & stove keeps running?

[Don2222]

Hello

What part needs to be replaced? ESP probe, Circuit Board or another part? If another part please explain.

Here is a problem on a 2007 Harman P61a-2 that I have not seen before?
It looks like a fairly newer model with the indent in the ash door for the tile insert.

The stove seams to start up and run fine. Start to fire takes approx 5 mins. However there are a few more pellets in the burn pot so the initial flame is very large! It does settle down and run fine. When the mode selector knob is turned off the stove goes to a low flame but keeps feeding pellets!

Here is my analysis. Please correct me if there is an error.
The mode selector knob in room temp mode uses the room probe thermister to vary the feed motor to keep the room at the set temp. The room probe biases the gate of the feed motor triac probably thru an inverter circuit. and the temperature knob varies the bias level for the heat level desired. (Wish I had a schematic - Does anyone have a schematic of the Harman circuit board?)
When the mode selector knob is in stove temp mode then the ESP probe biases the gate or the triac in the same manner. The mode selector also varies the voltage level applied to the room blower to change it's speed.
Now the mode selector has one more function. In startup and shut down mode it either acts as a gate or controls a gate to bias the feed motor triac.

In this case when the knob is turned to off, there seems to be a hung state and the triac gate is still being biased. The ESP probe just varies a small voltage going back to the circuit board so even though it senses the exhaust temp and tells the board when to shut the room blower off and the combustion blower off, it may have nothing to do with turning the feed motor off.

This stove had no surge protector and there were quite a few power outages last season. ESP probes do not go bad very often so I would say a power surge has damage the CB\ircuit Board. Anyone know what part on the Circuit Board?

SCRs are used in DC circuits so it makes sense that 2 are used in an AC circuit. One to handle the negative cycles and one for the positive cycles of the AC sinewave.

TRIAC operation
It can be imagined from the circuit symbol that the TRIAC consists of two thyristors back to back but with a common gate terminal, and the cathode of one thyristor connected to the anode of the other, and vice versa. This configuration is more correctly termed antiparallel

On a basic level, the operation of the TRIAC can be looked on in the format of the antiparallel thyristors, although the actual operation at the semiconductor level is rather complicated.

When the voltage on the MT1 is positive with regard to MT2 and a positive gate voltage is applied, one of the SCRs conducts. When the voltage is reversed and a negative voltage is applied to the gate, the other SCR conducts. This is provided that there is sufficient voltage across the device to enable a minimum holding current to flow.



(broken image removed)
Equivalent circuit of a TRIAC


In terms of the structure of the device, and its more detailed operation, the main terminals MT1 and MT2 are both connected to p and n regions within the device. The current path depends upon the polarity of the voltage across the main terminals.

 

[Bioburner]

Been more than one thread of bad pot switches. I had our garage Harman come on all by itself. Replaced the pots and have had no issues. Someone stated that they were only supposed to have a service life of around 300 cycles. Just a shot and easy to get and replace.

 

[alternativeheat]

Maybe not related to your problem but a P61a can take up to an hour to completely shut down and I've had my own take up to 30 or 35 minutes to flame out. It feeds pellets once or twice during this process, not a lot of them but it happens early on in the shut down cycle. Maybe you just aren't waiting long enough ?

 

[Don2222]

View attachment 136620 Been more than one thread of bad pot switches. I had our garage Harman come on all by itself. Replaced the pots and have had no issues. Someone stated that they were only supposed to have a service life of around 300 cycles. Just a shot and easy to get and replace.

Thanks BioBurner
I was thinking that myself, it makes total sense!

 

[Don2222]

Maybe not related to your problem but a P61a can take up to an hour to completely shut down and I've had my own take up to 30 or 35 minutes to flame out. It feeds pellets once or twice during this process, not a lot of them but it happens early on in the shut down cycle. Maybe you just aren't waiting long enough ?

It stays on for a long, long time. Maybe your potentiometer is on the way out?

I have two oler P61a stoves that I rebuilt - I replaced both circuit boards and the pellets stop feeding immediately when switched off.

 

[alternativeheat]

It stays on for a long, long time. Maybe your potentiometer is on the way out?

I have two oler P61a stoves that I rebuilt - I replaced both circuit boards and the pellets stop feeding immediately when switched off.

Maybe but I don't think I'm alone on this. I read here where others experience the same thing with their P61A's. Mine is less than a year old, it's done this since new but I read here at the forum where others said this was normal so never thought anything of it.

 

[Bioburner]

Been talk of how long the exhaust fans stay on. Up to and hour but not very often about a stove not shutting the feed down when turned off.

 

[alternativeheat]

Been talk of how long the exhaust fans stay on. Up to and hour but not very often about a stove not shutting the feed down when turned off.

Mine runs a couple more cycles of feed, they are shorter than the average feed but it does it. I just assumed the board doesn't react as an instant off situation. It then stops feeding. Of course the flame takes a long time to die out all together as well, it has to burn the existing pellets off. As long as the exhaust fan is running the flame is getting air. This is an ESP function I assume. As long as there is heat sensed above a certain temp the blower runs. This is not fresh on my mind incidentally since I have not run the stove since the end of April or very early May. But I do recall hearing the tinkling sound of pellet feed on the early phase of shut down. I wondered if this is to avoid too far a burn back into the auger assembly ?

 

[Bioburner]

Mine runs a couple more cycles of feed, they are shorter than the average feed but it does it. I just assumed the board doesn't react as an instant off situation. It then stops feeding. Of course the flame takes a long time to die out all together as well, it has to burn the existing pellets off. As long as the exhaust fan is running the flame is getting air. This is an ESP function I assume. As long as there is heat sensed above a certain temp the blower runs. This is not fresh on my mind incidentally since I have not run the stove since the end of April or very early May. But I do recall hearing the tinkling sound of pellet feed on the early phase of shut down. I wondered if this is to avoid too far a burn back into the auger assembly ?

I can understand a couple of short feed cycles during shutdown for the reason of preventing a smoldering fire into feed tube but not a continuing fire like its in manual mode if this is what is being described. Wish I too could remember the exact shutdown of the Harman as I have a Hestia that feeds into fire almost 20 minutes after shutdown is input but that maybe so that it can ramp up if stat calls for heat. That stove has some interesting cycles. To many stoves with different programs

 

[alternativeheat]

I can understand a couple of short feed cycles during shutdown for the reason of preventing a smoldering fire into feed tube but not a continuing fire like its in manual mode if this is what is being described. Wish I too could remember the exact shutdown of the Harman as I have a Hestia that feeds into fire almost 20 minutes after shutdown is input but that maybe so that it can ramp up if stat calls for heat. That stove has some interesting cycles. To many stoves with different programs

Maybe another P61a user will chime in, a younger guy perhaps !!. But when I get it up and running again this fall I will pay closer attention on shutdown for cleaning and report back. Actually it will be shoulder season so it will shut down anyway then. In a way I can't wait but oh too long a winter so no rush !!

 

[Tonyray]

My P61A takes approx 45 minutes to an hour before the stove completley shuts off..
as someone said, there is No Instant Off..
It does feed some pellets for a bit in the beginning, then the Burnoff starts.
My flame starts to Slowly drop within 10 minutes or so..
Exhaust fan will run till no more smoke from the Embers or heat is detected.
that seems to be what takes the longest....
I am assured that the above is normal function with the Harman P Series since the Harman Installers after showing me how to start it &.made sure all was working correct,, went back to their shop, came back 40 minutes later, showed me how to shut it off, and then we talked and had coffee while they cleaned up for close to an hour before the Blower finally went to sleep and they signed off on it.

 

[alternativeheat]

My P61A takes approx 45 minutes to an hour before the stove completley shuts off..
as someone said, there is No Instant Off..
It does feed some pellets for a bit in the beginning, then the Burnoff starts.
My flame starts to Slowly drop within 10 minutes or so..
Exhaust fan will run till no more smoke from the Embers or heat is detected.
that seems to be what takes the longest....
I am assured that the above is normal function with the Harman P Series since the Harman Installers after showing me how to start it &.made sure all was working correct,, went back to their shop, came back 40 minutes later, showed me how to shut it off, and then we talked and had coffee while they cleaned up for close to an hour before the Blower finally went to sleep and they signed off on it.

Right, same experience minus the installers here.. When I clean the stove I don't wait for that entire cycle to take place before getting started I might add. And you can scrape those glowing embers off into the ash pan to hasten that whole process by quite a bit.

 

[Don2222]

I can understand a couple of short feed cycles during shutdown for the reason of preventing a smoldering fire into feed tube but not a continuing fire like its in manual mode if this is what is being described. Wish I too could remember the exact shutdown of the Harman as I have a Hestia that feeds into fire almost 20 minutes after shutdown is input but that maybe so that it can ramp up if stat calls for heat. That stove has some interesting cycles. To many stoves with different programs

Good to know
Does it make any difference when shutting down from "Room Temp" mode vs "Stove Temp" mode?

 

[Bioburner]

Good to know
Does it make any difference when shutting down from "Room Temp" mode vs "Stove Temp" mode?

I have not noticed any.

 

[Tonyray]

Good to know
Does it make any difference when shutting down from "Room Temp" mode vs "Stove Temp" mode?

None whatsoever..
same shutdown time for either.
But, to Split hairs here, if the Fire is raging in Either Mode & you shut down,
it will take a bit longer for the Flames to die down than if it was on Manual Setting and keeping your BurnPot Flame Alive...
Actually, that last bit of Wisdom really wasn't even necessary to mention now that I read it...lol

 

[Don2222]

Thanks guys!

 

[Tonyray]

When I clean the stove I don't wait for that entire cycle to take place before getting started I might add.

Same here... Take advantage of it since the Exhaust will be running anyways..
I use that time to use my 2" Paint brush for all the ash on the heat exchanger and shelfs and everywhere that ash seems finds a home
In my stove...
[this is after the Flame dissapears of course.]

 

[ttdberg]

The P68 shutdown sequence works the same way. A couple cycles of feeding after the power is switched off. Total shutdown time is 45 mins to an hour. I do the same as above, near the end of the shutdown cycle, when the stove has cooled off a bit, I will open the door and spend a minute giving the burn pot a good scraping to get rid of the "harman speedbump" as well as pull any fly ash from the sides where it collects into the ash pan. I like doing this with the combustion fan running because it keeps the ash in the stove rather than floating out into the room. Once it's clean, I shut the door and the combustion fan generally shuts down immediately after that. So simple and easy.

 

[Tonyray]

The P68 shutdown sequence works the same way. A couple off cycles of feeding after the power is switched off. Total shutdown time is 45 mins to an hour. I do the same as above, near the end of the shutdown cycle, when the stove has cooled off a bit, I will open the door and spend a minute giving the burn pot a good scraping to get rid of the "harman speedbump" as well as pull any fly ash from the sides where it collects into the ash pan. I like doing this with the combustion fan running because it keeps the ash in the stove rather than floating out into the room. Once it's clean, I shut the door and the combustion fan generally shuts down immediately after that. So simple and easy.

Exactly my procedure...

 

[Don2222]

Problem Solved!

It was NOT the Circuit Board or Pot, in this case it was the Black ESP probe going to an older circuit board that does not have the click off feeling!

Here is what I found.
Old CB
When turning the stove to off with the older CBs the auger does cycle a few times whether it is in Stove Mode or Room Temp mode.

New CB with click off feeling and DIP switches.
When turning the stove to off with the newer CBs the auger stops imediately whether it is in Stove Mode or Room Temp mode!

In conclusion it also seems the circuitry on the newer Circuit Boards maybe more reliable and shutting down the stove!

I would recommend to update these older Circuit Boards!