BUNN LPG - Back From The Dead

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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Postby Robot » Mar 11, 2012, 5:02 pm

About a month and a half ago I picked up an used BUNN LPG from a local Italian restaurant. The owner originally wanted $350 for it, but after some time, I showed up with $160 and waved it in front of him and he accepted. :lol:

I took it home and immediately took it apart for a good cleaning. I even found a dead cockroach inside! The hopper was yellowed and cracked, the solenoid operated 'gates' were scary and the entire unit was far too big for what I was using it for, which is a cupping/Chemex grinder. I promptly removed the hopper and used a piece of PVC pipe to go over the motor assembly to prevent stray beans from popcorning out during grinding.

Then I had the 'great' idea to get rid of the solenoids and gates, get rid of the huge switches on the front and operate the entire unit using a pushbutton. The idea was that I could hold down the button to turn the grinder on, and let go to turn it off. Simple enough. Trouble was, like a tool I didn't look at the wiring diagram and I miswired the darn thing. I blew a fuse, and after a lot of time I finally connected the motor to the AC line. It 'moved' and I assembled everything back up. When I put beans it, I found that there was no grinding, the motor was moving but it was more of a vibration than a revolution. My worst nightmare had come true, the control board and fuse that I blew out during my failed experiment was actually converting the AC current to DC current, and this motor was DC!

All sorts of crazy ideas came through my head at this point. Should I get a three phase AC motor from craigslist, modify it and use it as a new motor? I already have access to 'free' AC drives from my company. After a lot of thought, I decided it would be best to scrap the entire control board, streamline the profile of the grinder and attach a Variable Frequency Drive to the motor. I wanted everything to be clean and minimalistic, and I made the top portion of the machine 'modular' when it comes to wiring. This means I can disconnect 4 wires and remove the entire top of the unit to service the burrs when need be.

Have a look, I hope you enjoy.

One more thing, the 'plug' which you see on the side is actually an 'explosion proof' unit that I took from a dumpster at our company's R&D facility. The box it came in had Japanese writing on it and when I saw the quality of it, I was shocked that they threw it out. I had no idea what I would do with it many months back, but I knew it had a purpose. Now, it belongs on the machine and looks the business.

The issue of popcorning: I start the machine with the slowest setting for the motor which is a complete standstill. From there I add a little bit more power until the shaft starts to rotate. At this point, the shaft might still lock up due to the torque required to grind the beans. I then adjust out the power until the shaft is rotating as slowly as possible but NOT locking up. I've found that at this speed, popcorning is not an issue. I've also created a temporary cardboard cutout to put over the opening just in case.

Once I put the Ditting burrs in, I would like to do some experiments to see how the speed of the grind influences its consistency.


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Postby cannonfodder » Mar 12, 2012, 9:26 am

I had thought about putting a speed controller on my grinder when I tore it down for a cleaning and found that it had a DC motor in it. Never got enough ambition to do it. The yellow hopper, just stick some coffee company bumper stickers on it to mask the color. I used some cleaner made for plexy that I use on the faring of the motorcycle to keep it clear and clean. It cleaned it up for the most part. It also had a couple of cracks in it. Get a bottle of thin formula CA (super glue) and put a single drop on the crack. The thin CA is designed to wick into hairline cracks and will seal it up.
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Postby scareyourpasenger » Mar 12, 2012, 1:19 pm

This looks different then my lpg. Which model is it specifically? Did it have a partition?

Neat idea but even with most of the bulk removed mine didn't have enough WAF to stay on the counter and now I have to sell it.

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Postby Robot » Mar 12, 2012, 11:41 pm

I believe it is an LPG-2E. It did have a partition originally. the profile of it really changed. The only important elements of the grinder to me were the motor, steel casing and the burrs. I think this profile really lets the basic elements shine. Now if only I could get the Ditting burrs, it would be almost perfect.

Question, you mentioned that yours didn't have enough WAF to stay on the counter. What do you mean by WAF?

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Postby Sherman » Mar 13, 2012, 12:49 am

"Wife Acceptance Factor"
Your dog wants espresso.
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Postby entropyembrace » Mar 13, 2012, 2:24 am

Wow....that looks like the kind of hacked together stuff you find in an experimental physics lab :mrgreen:

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Postby Robot » Mar 13, 2012, 10:50 am

"Wife Acceptance Factor"! I love it! Luckily my wife knows I'm crazy, and the 'experimental physics lab' look is exactly what I like about it. If I had it my way, all coffee equipment would look as scientific and lab like as possible. We are a strange mix of techies, artists, chemists and freaks. I'm my opinion, we are super lucky to have found this passion. But YES, looks freaking crazy on the counter top. Very Robot though!

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Postby UltramaticOrange » Mar 13, 2012, 11:34 am

Just need some sort of science surplus jar for a hopper and the physics lab look will be complete. The thing cleaned up nicely. Glad its up and running!
If your tiny coffee is so great, then why don't you drink more of it?

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Postby TomC » Apr 24, 2012, 1:05 am

I want to bump this thread and hear how you think of it all so far. I'm going to be doing a mod for a better non espresso grinder in the next few weeks. Likely a G series Bunn with a set of Ditting burrs ( inspiration via JohnB) I like Dave and Jim's idea using the much nicer looking and lower profile LPG, but I think the popcorning is more likely on that design due to the lack of the auger (?)

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Postby another_jim » Apr 24, 2012, 11:31 am

I use an LPG bought new as my cupping and brewing grinder. I am very satisfied; and the Bunn G series grinders are used in cupping labs all over the country. The Ditting burrs may provide better coarse grind quality; but I doubt it makes a large difference. The drawback of using the LPG as opposed to the G1-3 is that it is not really designed to single dose. You need to do some massaging to ensure the beans all grind.

That said, I was very impressed by the quality of the brew delivered by the Baratza Vario's new steel burr. The ergonomics of the W model makes it nearly ideal as a cupping grinder, especially if counter space is limited, and I'll be doing a close comparison soon.

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