Stoker stroke length vs feed motor run time

Hello - I've been burning a hand-fed for about a year. I am interested in stokers.

I've noticed that most pusher-type stokers (specifically the Harman Magnum) have the ability to adjust the stroke length, as well as being able to control how often the stoker feed motor runs.

Don't both methods produce the same result? Could you theoretically get the same burn/temps by just controlling the feed motor runtime, with a constant stroke length?

I've just been brainstorming the verti-flow stoker mechanism, and it seems redundant to control both the feed motor runtime and the stroke length. However, I'm sure Harman would not have messed with both if they could get by with only one.

Anyone shed some light on this? Thanks

Steinke

To a point they work hand in hand the length of stroke is used to adjust the size of the fire or how far it extends onto the grate . The best mental way to picture it is to just use pilot mode for example and we will round some numbers lets say we have it set to run 5 min on 15 min off in the 5 on I have the stroke pushing 2 inches the fire will come to a certain point out on the grate at the end of the 5 min if I reduce the stroke to 1 inch in the same 5 min cycle less coal will have been pushed and the fire will be smaller hence the stove will run cooler . Remember the harman is also controlled by a wall mounted thermostat when not in the pilot mode .

The coal-trol thermostat that is so popular on the stoker stoves have you set the stroke to max and control the run time of the stoker motor to get the desired results.

gambler wrote:The coal-trol thermostat that is so popular on the stoker stoves have you set the stroke to max and control the run time of the stoker motor to get the desired results.

I think what he means to say is you adjust the stroke to the maximum sized fire without pushing fire off the grate not the maximimum available stroke. At least thats what I hope you meant Gambler

Actually my Harman is set to maximum stroke and the coal-trol determines how long to run it based on the min and max of the run time (running 4 min and 86 max) as Gambler suggested. This set up works best to overcome any problems with damp coal or unusually large pieces of buck. I have been running the Magnum in the house this way for over 3 months if you include the science project dial in time in the garage.

Ultimately you can reduce the stroke to less if you desire, but the concept is way different than the stock Harman control where the stroke is the means for setting high fire.

Just another perspective to consider with the flexibility of the Coal-Trol.

Matthaus wrote:Actually my Harman is set to maximum stroke and the coal-trol determines how long to run it This set up works best to overcome any problems with damp coal or unusually large pieces of buck. I have been running the Magnum in the house this way for over 3 months if you include the science project dial in time in the garage.

Ultimately you can reduce the stroke to less if you desire

Just another perspective to consider with the flexibility of the Coal-Trol.

Mat you should put some of that info in a pdf and email it over to them . The coal trol site made available a pdf with what I guess was one of the first successful installations on a magnum I have a copy of it and it sounds like you may have refined it a bit, I'm sure it would be beneficial .

Generally, the max stoker stroke for me is set to fill the grate with fire, but not push it off, when burning full power. Then, the motor's pilot setting is dialed in to maintain a certain size fire (and amount of heat) when the thermostat is satisfied.

That being said, I do deliberately adjust both the stroke length and timer settings when I feel I don't need as much heat during a cycle, like during a mild spell when a warm stove is good enough but I don't need her to crank up, or when it's mild enough that the thermostat won't call nearly as often. The other week we had a stretch of warm sunny days so I turned the pusher down a turn without changing the timer. The stove ran not as hot, which I wanted since I didn't need as much heat till the weather turned again. When it's really cold out, I set the pilot timers to keep the stove warmer in between calls from the thermostat. In either case, what I try to avoid is long periods of idle (and small fire) punctuated by brief runs of volcano-like heat from a full-stroke stoker.

But like I've said before, I graduated from wood to a small hand-fired to the stoker over the years, so I feel the need to futz with the stove from time to time. Could be old habits die hard...

Thanks for all the input. It all makes sense, but is a little hard to grasp as I don't own nor ever operated a stoker.

I'm just tinkering with ideas to build a stoker (don't laugh). The simpler the better.

Anyone have a guess as to how many rpms the feed motor runs (during operation of course)? Also, I was looking at the fork design of the magnum and thought they could improve it to be beefier, a closed loop instead of a open fork.

I like the design of the verti-flow, as I think it may work with my western bituminous coal. We have little or no swell, but lots of volatiles. I'm interested in trying it, but none of the dealers will give me a straight answer about using it with our bit. coal.

Steinke

steinkebunch wrote:I like the design of the verti-flow, as I think it may work with my western bituminous coal. We have little or no swell, but lots of volatiles. I'm interested in trying it, but none of the dealers will give me a straight answer about using it with our bit. coal.
Steinke

Heres a bit of input on that, a lot of times I see someone who lives in Suburbia USA 200 miles from the nearest piece of coal living in a population where 89% of their neighbors think Anthracite or bituminous have something to do with terrorism or maybe rock music, theses folks get frustrated when they speak to a Harman dealer in their area and the Dealer isn't helpful. Duh . Call a dealer in Coal Country where they have an active market in your case an active bituminous mining market . Should that fail Harman has a top notch group of engineers and specialist working at the plant and in their organization, they are not a small operation in any sense of the word they distribute there product not just nationally but globally, the dealer has access to Harmon engineers whenever needed to solve problems all they have to do is call, sit down with a dealer and present him with your need to knows and request he make the call to the mothership .

steinkebunch wrote:Anyone have a guess as to how many rpms the feed motor runs (during operation of course)?

Most stoker motors run 1 to 6 rpm. IMO, if you make the stroke adjustable you can make most any stoker you design work with that range of RPM. You are correct to think the vertiflow has the best chance of modern stoker stove designs to work with but... the underfed design makes it the only one even close. Another idea would be to design your own underfed firepot (retort) based on the big fellas like efm and gentleman Janitor and use sections of cast grate from a junked stove (or find some suitable cast and drill holes in it) to form the pot with a steel casing for the outside. You can make a tube to feed the combustion air from a fan positioned outside the stove. The auger and tube could be from any number of sources, old stoker like efm or even a pellet or corn stove.

Keep us posted, sounds like another manly man is considering going over to the girlie man side.

If you didn't see this post earlier....here's some stoker pics.

What does a stoker mechanism look like?

My Buddy I work with, built his own stoker (with a little input from me, since I have 2 stoker stoves) with a stepper motor, chute, etc...for his wood/coal boiler....seems to work, even programmed his control system and uses a Laptop....

WINNER of Best Modified Stove