Advice on early 1970s Bauer A15 compressor

[2airishuman]

That's going to take a 30 amp 3 phase service to run. Most houses only have a 100 amp single phase drop, and if you have to run it single phase, that motor will cost thousands and be mucho expensive to run.

As you might imagine, I have run large 3 phase motors many times when only single phase is available. It isn't expensive or difficult if you know what you're doing but it's best to tailor the converter electronics to the application, which involves measuring current on each leg while the motor is under load, which has to be done with due regard for safety since the wild leg is around 260 volts to ground and will kill you if you let it. It is also very easy to burn up a stator if you get it wrong and aren't paying attention to the signs or are too cheap to put in a proper motor starter with thermal overloads.

The breaker panel in my house is in the garage, and I can pull enough off it to run 10 HP quite readily and 15 HP with some, er, ingenuity.

The great thing about 3 phase motors is that you can buy them for $5-$10 a horsepower when industrial equipment is being scrapped out somewhere, as long as you're not too picky about what you're getting. I bought a whole pallet of motors for $200 from a start-up once that had hit upon hard times and was shutting down a production line that never quite worked out. I got gear motors, DC motors, 3 phase motors, many of them explosion proof, many the more expensive lower speeds, some with oddball shafts. I ran a lot of experiments and used maybe half in actual equipment, sold some, scrapped the rest. For something like this, who knows, I could probably pick up a nice 20 hp 3 phase motor somewhere and adapt it if the 7.5 runs too slow. The conversions are easiest and cheapest when you have a few extra HP to work with and can afford to derate the output. Anyway, old times. I even converted a 2 phase motor once, something I never knew existed, on a 400 amp DC welder from the 1930s.

Beauty. I don't know if that will turn it fast enough to lube it correctly. Takes a Bauer guy to tell you that.

Will do. Easy enough now that I know what I'm working with.

Does it have filter towers and auto drains?

Manual drains and, from the photo, a repackable filter tower that I would inspect with great care and skepticism before pressurizing, because I like the wall of my garage the way it is.

 

[Wookie]

Sounds like you can teach me a thing or 2 about motors. I'm pretty good, but I've always had 3 phase available to me.

 

[2airishuman]

Sounds like you can teach me a thing or 2 about motors. I'm pretty good, but I've always had 3 phase available to me.

::shrug:: Too many of my formative years spent learning calculus and physics, too much time in an electronics lab, then scaling it all up while farming on the cheap. Farms are usually remote enough that 3 phase is very expensive to bring in, though some do. I had single phase but it was 400A at the pole, and the power company made it clear to me that they were the ones choosing the transformer size and they weren't going to upgrade it unless I managed to burn it up or their fancy electronic meter told them they needed to.

I like to visualize things to understand them, mainly because I'm not that good at math. Induction motors are all about circles. The whole idea is to create a magnetic field that rotates smoothly and put a squirrel cage in the middle of it. Getting three phase from the power company makes it easy to create the rotating field, but you can get a similar effect with carefully chosen capacitors since they introduce a 90 degree phase delay. Not the 120 degrees we would want but close enough, and there are ways to smooth out the waveforms if that's really necessary.

Most of the farms around here that have 3 phase from the utility don't have true industrial-grade balanced 3 phase. The power co puts brings in two hots and ground and one big and one little transformer and calls it good. Run a big motor on that and the phase angle isn't going to stay a consistent 120 degrees and the voltage isn't going to be consistent across phases either. So you might as well brew your own because your motors won't deliver the horsepower you paid for either way.

 

[Wookie]

I've always made my own. 208 wye or 480 wye or 4160 wye, depending on the size ship.