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Converting 7kw propane generator to wood gas or both

 
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Location: North-Central Idaho, 4100 ft elev., 24 in precip
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Ben
We currently live off grid with solar, wind, and a propane generator for back up. I am working up a plan to convert the existing generator to run on wood gas. Its a 7kw Generac EcoGen designed specifically for off grid back up (so relatively new model from Generac). So my question is how feasible would it be construct a gasifier large enough to run that size generator, how involved would it be handle the throttling of the generator as loads increase, and would the existing air/fuel mixing system be appropriate or modified/replaced, etc.?
Thanks for your insight.
 
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I tried to get some specs on the engine but I didn't see if it was a single cylinder or a twin cylinder. I have used both and the twin cylinder has a more steady air input which makes it easier to control with an air control box we call the Electronic Carburetor. It takes an O2 sensor and uses the signal to control an air inlet valve that keeps the air fuel ratio dialed in a tight working range. I made a step by step book on the process, here is a video that explains more:



For that engine the load control would be handled by the generac electronic speed control governor. It will take care of itself. You would get roughly 3.5 - 4 kilowatts of output on that generator with woodgas. There is some nitrogen in the gas that makes it less potent than propane, but still good.

Your build could work fine I think, but it is probably as small as I would go in engine size. Small engine don't pull as much air inside to break down the wood, so you compensate with smaller 1" branch rounds or cubes. Softwoods would be preferred during operation. There is a chart in my book that tells you exactly what dimensions to use in the hearth.

I like generac stuff. Can't go wrong with propane.


 
Dave Dahlsrud
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Location: North-Central Idaho, 4100 ft elev., 24 in precip
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Does anyone know of a quick way to transition back and forth from wood gas to propane? I'm thinking of something like a bypass or quick connect fittings...something along those lines. Or is just going to be pulling the intake off the generator and replacing it with whatever set up you are trying to run at the time?
 
Ben Peterson
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Dave,

In the Electronic Carburetor Workshop book I made the genset able to switch back and forth between the two gases with the flip of a couple valves. It was a little more work, but it is convenient.
 
Dave Dahlsrud
Posts: 531
Location: North-Central Idaho, 4100 ft elev., 24 in precip
46
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Awesome thanks Ben.
 
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