KN-4 Booster Motor Replacement - DC motor for speed control?

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M

moose_grunt

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I'm a Fish!
I bought a KN4 off here a couple of years ago, and it came with a Dayton 2 HP (single phase) Farm Duty motor. It's been running like a champ, but it's scary fast filling 2L oxygen rebreather bottles, and it's quite loud. I'd like to reduce both of those in anticipation of moving to a smaller place with closer neighbors.

One solution I'm brainstorming is to replace the AC motor with a DC motor from a treadmill or similar, as it would allow speed control (to slow down fills) and would presumptively be a bit quieter than a motor designed for farm use. Has anyone tried this? Any motor gurus care to comment?

Thanks,
Jim
 
I was under the impression that VFD didn't work on single phase, and that the cheapo router speed controllers 1) are questionable anyways and 2) would be too small for a motor that's rated at 20 amps.

Motors aren't my area of expertise, though, so if you've got a link of something that'll work...
 

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I don't believe you can make that one run on a VFD but your real option is to replace it with a 3 phase motor and run it on a variable frequency drive. None of the small dc motors you will find easily will be able to output 2 hp.
 
BRT:
I don't believe you can make that one run on a VFD but your real option is to replace it with a 3 phase motor and run it on a variable frequency drive. None of the small dc motors you will find easily will be able to output 2 hp.
Click to expand...

thanks for confirming my suspicion. That might be a post-lockdown project for later this summer, if I decide to go that route. A local motor place might make me a good deal on a swap, who knows.

For a DC replacement, I was thinking of a treadmill motor, honestly. Plenty of those on eBay and in surplus, or I might enable to pick up a whole treadmill locally for cheap through craigslist or such. Something like this is listed at 4 HP, or am I thinking about this the wrong way?
 
@moose_grunt a 2hp dc motor is going to be hard to find and expensive, plus you have to have a transformer to run it. Finding a 2hp single phase VFD is going to be a bit difficult, so you'd have to use a 5hp for 3-phase, not a problem, just a thing. You won't find anything over 1.5hp for 110v because of normal 15a circuit restrictions.

If you go with that DC motor, you do have to have a transformer that is big enough to run it. Your booster is currently running at ~1800rpm since it is direct drive from the motor. The motor you linked is rated at 5110rpm, so you'd have to run it at less than 25% to have any sort of meaningful reduction, but that's going to generate a lot of heat. You also have to figure out how to adapt it to the motor plate, and the input shaft. BIG project to even think about getting that to work.

AC motors do come in any lower RPM ratings than what you have on there now, but they're BIG, HEAVY, and $$$$. You have a 4-pole motor in there now, and to cut that RPM in half, you'd have to get an 8-pole motor which is basically 2x as expensive as what you have now since there is twice the copper in there. It may also not physically line up with the motor mounts and input shaft. Half the rpm, means half the HP required which is good though.
The benefit of the VFD though is that you can always speed it back up if you need to.

Ideal situation, though not the cheapest.
Replace motor with a 1.5hp, 6-pole, 230vac, 3-phase motor. ~$350 per the last one that we bought at work.
This link is a random online link, but you'll probably get better prices from your local motor suppliers
Buy Motors at Wolf Automation
Buy a phase converter VFD with 110vac 1-phase input, and 230vac 3-phase output. $400 ish
VFD, 1.5hp, 120-240V, Single Phase, NEMA 1,

Call it $800 to convert, but you can probably sell that motor for at least $100, or keep it for something else. You get a motor that is more efficient with power since 3p motors are almost 50% more efficient than 1p motors and you get variable speed to make it go exactly the speed that you want. Filling a bigger tank? Go faster. Filling tiny breather bottles, slow it down. The 6-pole motor will limit the top speed to about 2/3 of what it is now, but you can go with a 4-pole motor if you commit to 230vac and need to the speed. Reduces the cost of the motor, but doesn't change the VFD to go to 2hp instead of 1.5hp.
 
That's why I ask on here, to get advice from the people who actually know what they're talking about! Thanks again, everyone, for the advice. Gives me a bit to read and think about.

Of course, the low-tech solution would be to use the booster like the Soviets intended and just attach the manual pump arms :rofl3:. That would fix the noise and certainly the fill speed!
 
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