Firewood Processor Controller

I worked on this project about a year ago.  I realized recently that I had just enough pictures and a fuzzy enough memory to pull off a blog entry.  Enjoy...

A friend of mine has a firewood processor that was having some electrical issues last year.  The manufacturer didn't use an enclosure that was rated to be outside in the rain, so the inside was always damp and he was replacing components regularly because of corrosion and rust.

Original controller

Oh, the humanity!

It took some convincing, but he brought the machine over to my shop, and I got to work.  The plan was to keep the design of the controls the same, but to use higher quality components.  I started by making a parts list for the new controller, which included new pushbuttons and cable glands that would maintain the NEMA 4 rating of our new enclosure.

In case you don't know, NEMA is the National Electrical Manufacturers Association.  They created a standard that dictates how resistant electrical enclosures and other components are to the ingress of dust, water, and other things you won't want mixing with the pixies in there.  NEMA 4 basically means that when assembled correctly, it will be waterproof (within reason).

With our parts on order, it was time to figure out how the existing controller worked.  I spent some time rooting around in there, writing down connections between components and poking arounf with a multimeter.  It took a few tries, but I was able to sketch up a schematic that appeared to match the existing controller.

After the new parts were delivered, I had to transpose the schematic because the terminals were configured differently on the relay sockets. This involved comparing the old and new sockets with a multimeter and making a table that related the terminals on the two versions.  Then I had to redraw my schematic.

Final schematic, drawn with handiCAD

With my new schematic in hand, it was time to start building the new panel.  I started by mocking up the new relays and terminal blocks on a section of DIN rail, and laying it on the subpanel of the enclosure. I kept it towards the bottom of the panel because I would need room in the panel for the cables (all eight of them) to enter the enclosure, and also because the height of the relays would interfere with the pushbuttons.

Once I was happy with the locations of everything, I drilled and tapped two holes in the panel to mount the DIN rail.  I then screwed the rail onto the panel and snapped on the components.  I then drilled three 7/8" diameter holes in the front of the enclosure for the pushbuttons.  I kept the layout of the front identical to the old enclosure so that I wouldn't screw up my friend's muscle memory when he was running this thing later.

With the components in place, it was time to use my schematic to connect the components on the panel together with some 14 gauge THHN wire.

New controller before the notch was added.

In a prime example of my supreme planning prowess, I now had to disassemble what I had constructed so that I could add clearance in the subpanel for the eight cables to pass through.  I took the components off of the rail, and drilled two holes to serve as the inside corners of the area I was going to remove.  Then, I went to the bandsaw to cut from the edge to the holes, and then from hole to hole - making a nice notch with rounded inside corners.

After a little filing to smooth out the edges, it was almost time to reassemble - after I drilled holes in the back of the enclosure for the new cable glands.  I laid them out to be as close as possible so that the cables coming through them would fit neatly inside my newly cut notch.  With the holes drilled, I could install the cable glands, and reinstall the subpanel and all my components.

With the new controller assembled, it was time to remove the old one from the machine.  To maintain order, I labeled the cables as I removed them, and then unbolted the old box from the machine.  To maintain it's NEMA rating, the new enclosure needed to be mounted from the back into four threaded inserts that the manufacturer installed.  This meant making a pair of uprights with 1" angle iron, drilling matching holes, and welding them to the frame of the processor.

Octopuss.  The old enclosure can be seen in the background.

When mounting the new enclosure, I decided to lay it back at an angle.  I did this for two reasons: First, it felt more comfortable to me, so it seemed like a better choice from an ergonomic standpoint.  Secondly, after removing some of the ends of the cables due to corrosion, some of them didn't have quite enough slack to land in the box when it was perfectly upright.  Dang!

I had some cans of knock-off John Deere green spray paint that was a surprisingly close match to the paint on the machine, so I shot the new brackets with a few coats to keep the rust to a minimum.  After the paint had dried and I mounted the new controller, I used the schematic and my labels to land the cables in their new home.

Inside the new controller, after the install

It was all done.  Nothing left to do but test it.  Would it work?  Would it explode?  My friend came over to help me find out.  He fired the machine up, put it through its paces, and... it operated just as it should - what a relief!

Having lived with the previous, janky enclosure for a quite a while before, he was suspicious that this new box would hold up to the elements.  To put his mind at ease, we sprayed it with the garden hose for a few minutes (he seemed a little shocked at my testing methods).  We did find one very slow leak at one of the cable glands, thanks to a burr on the edge of the hole, but that was a breeze to fix.  Once it was reinstalled and tightened up, the whole enclosure proved to be tighter than a clam with lockjaw.

Its been a year, and as far as I know, it's still operating perfectly.

New controller in place

Thanks for reading!