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| Lathe HP motor upgrade? |
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| Miner:
Chazz, Just like computers, My electrical knowledge is very limited. From what I've read, And I don't quite understand everything about them, Some of the newer vector drives offer really high tourque levels and at fairly low RPMs. I bought a pretty pricey Baldor industrial rated VFD about 5 years ago. ($1400) At that time I was advised by a Baldor tech. That SOME motors, (not specified as to what motors or types because even Baldor didn't or couldn't pin point for sure.) Anyway they didn't survive with a VFD. If? the motor didn't survive VFD use. It could be specialy rewound by a good competent electrical motor rewind shop specificly for use with a VFD. My 3 hp mill motor is a Taiwan/Asian frame size, So a rebuild/rewire for VFD use if needed would be the only way to go. (About $800 for my motor to be rewound 5 years ago.) It hasn't needed to be done yet or at least so far. Since Baldor do not build a drop in replacement frame size for my motor. I'd have to build an adapter plate to use one of their or other North American built frame sized motors. Baldor did and may still do offer a special motor designed and built to be used as a 100% tested and compatable combination of a VFD and motor that is/was ultra smooth for operation. It wasn't cheap at around $1800 for a 3 hp 5 years ago. But I will say I did really trust the Baldor techs. information. He or his company had nothing to gain with what he told me. I'm maybe a little paranoid about burning up a motor due to replacement costs. I have a belt change Bridgeport type mill with a back gear. I'll obviously vary the speeds with the VFD, But normally or never go 30% higher or lower on what the normal motor RPMs should be. Low RPMs and extended run time result in really increased motor heat due to a slower cooling fan speed, I can do a quick belt change to keep the motor RPMs fairly high for larger cutting tools like fly cutters or drop into back gear for really low spindle speeds if I was boring large oversize holes with a boreing head. I personally think that a belt drive mill verses a variable speed belt drive type is the way to go if your going to use a VFD on a mill. High RPMs? I really don't know the exact quality of the motor bearings. I'd suspect fairly low quality, So I don't personally think it's a good idea to overspeed this motor too much. A decent spindle speeder from Tormach is about the same money as a motor rebuild and I can get over 8,000 rpm out of that for real small cutting tools and no changes or worrys about my mills bearings or motor. So, I've added some non topic information for you, But you now know everything I know about VFDs and motors with VFDs. Maybe some of this helps, Maybe it doesn't. Before I bought my mill I spent far more time with my power supplier than what should have been nessisary about what exactly was the best system between Solid state 3 phase converters, Rotary 3 phase converters and VFDs. I never did get a clear cut answer from them. Luckily I decided on a VFD because I knew far less about them then than I do now. If your only dealing with a single 3 phase motor instead of multiple motors on the same machine a VFD really is the best way to go. And 3 phase is MUCH smoother than single phase. I'd think you'll see an immediate improvement in your surface finishes using it on a lathe. Pete |
| Chazz:
@Pete, again my minisquile(sp?) understanding of why some AC motors don't like VFD is due to the design of thev VFD, (in some design cases?) ie one VFD type will use one leg for starting the motor and when the motor hits a predetrermined set-point, passes off power distribution or runninig mode off to the other two legs, that is, the motor is running on 2 of 3 legs.....not good for some motors. The VFD I'm looking at uses all 3 output legs to start and run, as well, it is programable for a 'soft' start, meaning I can program the motor to 'ramp-up' to 1,800 RPM and take 5~7 seconds, or more, to do so. :scratch: Again, to any sparky types, added, newer and more importantly, corrected info appreciated, Chazz |
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