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Old 06-08-17, 09:42 AM   #1
jeff5may
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Default Alternative variable speed drives

I am looking for ideas on variable speed drives that can run phase change compressors. I don't necessarily have to use a dedicated steel pot hermetic compressor. The main goal here is cheap and reliable. Something that can drive a belt or shaft is fair game. If it is electric and can drive a 3 phase compressor or inverter compressor without major modification, that might work if a common source of these types of compressors could be discovered.

One idea I have been tossing around lately is the motor and drive inside the new front load (HE) washing machines. They are showing up in salvage yards and landfills every day with problems like bad hinges and latches. The vast majority of these units don't have drive motor failures. They seem to do a pretty good job tossing around a big drum filled with wet clothes and water for years, so they shouldn't have much trouble running an auto AC or shop air compressor. I just so happen to have a guinea pig unit to look at right now...

Another one is the drive inside all those treadmills found at garage and yard sales every weekend. Watching all the youtube and facebook videos of people being thrown by them, I would think they have enough torque to start and run a compressor. Plus they have an automatic soft start built in...

I don't mind devising a belt drive with pulleys and sheaves to match RPM requirements if needed. But what RPM ranges do the previously mentioned candidates operate? And how is that power factor? Do these motors gobble up VA while not running at full HP?

I have read that commonly available VFD units can run refrigeration compressors, but where can these compressors be found on the cheap? Once a suitable pot is found, how much fun is matching the VFD to the compressor?

Feel free to educate me on the holes in any of these ideas. I get told every week how what I am doing will never work. I'm a "Git-er-done" type of person, not a "Go buy a new one". There you go, run it til it breaks. Or not, I hope...

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Old 06-10-17, 01:00 PM   #2
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There are a number of options for motor speed control, it all depends on how big the motor needs to be and how cheap you want it.

Simplest is probably a dc motor from a treadmill, scooter or wheelchair.
You already mentioned washing machine motors which give several speeds and can be found as scrap.

Also for a shaft drive compressor you could just use a 3 phase motor and inverter.

For sealed compressors you need some sort of VFD either single or three phase.

Somewhere i have an old (Probably 15 years old) 12v to 240 inverter, i once took it apart to see what was inside ans found a potentiometer that controlled the output frequency. I remember trying it with a single phase motor of some kind and it did control the speed.
I would guess that modern inverters are microprocessor controlled and therefore have no easy way of altering the frequency.

Another option could be a frequency converter, these were often used to generate high frequencies for motors before inverters became economically viable. We used to use one to create a 300hz supply for hand held die grinders. They consist of a motor driving a generator which has far more poles(6x in this case). We only required a fixed high frequency but the drive motor could be either dc or 3phase with a VFD to create a variable frequency for a sealed compressor.

One more very wacky idea which may yield similar results in a heatpump or refrigeration application, no idea on the efficiency implications though.
From measuring power consumption vs heat output from an ASHP, the power consumption is reasonably relative to the amount of heat being moved.
Therefore by leaking a variable amount of heat from the output to the input of the compressor you could reduce the output and power consumption which i guess is what your after. I've never tried this but see no reason why it wouldn't work to some extent.
Will see if i can look up some actual measurements on this from my past data logging.

Steve
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Old 07-24-17, 01:44 PM   #3
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I just run across this on Youtube. He is speed controlling a Grundfos circulation pump with a microprocessor pulse width modulating a solid state relay. Watch the whole video as he explains the process and even shows the signal results on a scope. I did not know an AC motor could be controlled this way. Wonder if this results in energy savings. He even has the PCB and schematics available.

This could likely also be used on blower fans too, but what about compressors?

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Old 07-26-17, 06:52 AM   #4
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A blower or low pressure pump can be controlled in that manner. A mechanically coupled compressor could probably be made to work also with or without some sort of flywheel. I doubt a hermetic compressor would run with that rig. Every time the line current dropped out, the thing would stall.
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Old 07-26-17, 07:07 AM   #5
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Another thought. Most of the new washing machines have inverter drive motors. Wonder if that could be hacked
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Old 08-27-17, 07:38 PM   #6
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I think Jeff is well into hacking the washer motor and inverter - I had wondered about pairing that with an auto or truck compressor (R134 I think) too - does anyone know the btu rating or horsepower requirements of automotive compressors??? They are made to run at widely varying RPM so might be ideal. A washer has a huge starting torque to spin so unless they are really mismatched would be able to start the compressor even if you had to use pulleys to mate up the torque and rpm.
Most of the front load washers are direct drive and I think at least top out at less than 1000 rpm - so might even not need pulleys. I believe the washer motors are intermittent duty only tho.
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Old 09-27-17, 12:31 PM   #7
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I found a YouTube video of a guy controlling a washer motor (and its dedicated control) over a serial interface with his laptop:


This looks very promising indeed! I haven't had time to rig anything up, as the summer has been busy at the real job, plus all of the front load washers I've encountered have been very economical (and profitable) to repair and flip. Doing this gig this summer, I've learned that most all of the people with these derelict units will literally try to give them to you once you show up with a truck and a dolly! On that note, at first, I had people actually get rude with me because I didn't try to knock them down on price...like 50 bucks wasn't cheap enough already! Now when I show up, I immediately ask how low they can go on the price. Dickering and such commences...

I was looking for something on the protocol and such for the motor control for a (whirlpool duet sport) Kenmore HE2 plus washing machine. I have a unit with a dead motor and a serial communication error code. The thing is too cherry to rip its guts apart: there are many somebodys out there who will literally trample each other racing to pick the unit up when it gets fixed and listed for under $200. The unit obviously got something corrosive spilled into the control board, and some traces got ate. I will be doing a quick analysis once the thing gets running again, even if it needs another control board.
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Old 10-13-17, 07:22 AM   #8
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a little update on the washer motor idea:

I have been playing around with the front load units while I have been fixing them up. I couldn't get the serial interface working on the motor control board that isn't communicating (yet), so I ordered a replacement. When I get the replacement board, I'm going to attempt to repair the broken one. It looks as if the power and speed control sections are OK, but the transmit and receive section for the serial interface is either dead or not functioning well enough to operate. Since schematics and block diagrams for these things are pretty much nonexistent to me, I'm going to have to have one that works in front of me to compare with the one that is broken to fix it.

Before I ordered a replacement , I wanted to verify that replacing the motor control board would indeed fix the washer. I picked up another similar washer off the interweb for less than the price of a refurbished or working pull board, and transplanted the (not identical) motor control into the malfunctioning washer. The board communicated with the brain, and did just about everything it was supposed to. However, the transplanted motor control must not interpret ALL of the instructions the same, because it always spins at the same speed. Forward wash, reverse wash, and spin functions do what they are supposed to, but apparently the microprocessor doesn't know what to do with the odd spin speed instructions.

The one unit is a Kenmore HE2 Plus and the other a Whirlpool Duet Sport. Evidently, the models are mechanically close enough in design to swap most of the working parts with each other, but the electronics are programmed different enough that they won't just swap out and work perfectly. This is common among most consumer electronic equipment in general. If the units all had the same firmware in them, then the supply houses and manufacturers would not have to stock a jillion different service parts, and the stuff they did stock would not command a higher price due to scarcity. Gotta love the capitalist sales model.

I have a little TTL to USB serial adapter that I purchased to read codes and log live data out of OBD1 vehicles that should work to sniff packets of data from this washer I have now. Once I get it operating, I will rig it to it and analyze the data stream to see how the interface does what it does to and from the motor control. Since I have spare parts (and hopefully a working motor control board soon), I can do a bench setup with one of these motor sets and an automotive a/c compressor with a belt drive. If I'm lucky, I can control the setup like the guy in the video with my little TTL to USB adapter.
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Old 04-08-18, 11:38 PM   #9
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I know I'm resurrecting a dead thread, but I've been thinking about the idea of picking up the smallest used 3 phase condenser I can find (2 stage if possible), and then doing speed control with a standard VFD.
2 stage usually gets you 2/3-70% of rated output -so for a 5 ton that's 3.5 tons
3.5 tons at 60Hz, running at 50Hz is about 83%, which gets you down to about 3 tons. assuming you can probably turn it UP to 72Hz, that'd get you a 6 ton AC/heatpump with a 50% turndown ratio. a good bit better than stock, eh?

Not sure how far down you can go before oiling becomes an issue on a compressor not intended for low speed operation, but lets say you could get to 44Hz safely (based on the 3 phase 2 stage scroll compressors i've seen rated at 50/60Hz), that'd drop down to 2.5 tons.
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Old 04-09-18, 11:11 PM   #10
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looks like i found it over here: EcoRenovator > Improvements > Geothermal & Heat Pumps > 5 Ton GSHP Build

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