BLDC or 3-phase-AC for mill motor replacement ?

[maxime.levesque]

I'm considering getting a used ZAY7045 mill with a 3phase 575v motor that I will need to replace, as I only have single phase 240v and 120v.

It is a gear head mill, with two gear knobs/levers (H, L) and (S1, S2, S3), for 6 combinations (see photo).

The motor plate has 2 numbers for RPM: 1730 amd 2850.

It's not clear if that means the motor has 2 wiring for each speed, or if the speed change is entirely driven by gears.

Needless to say, If the motor has 2 speed configuration, it will be harder to find a 3-phase motor that has the same specs.

Questions:

1) If I get a 3-phase motor with 1740 RPM, and a VFD, am I likely to get problems running it at 2850 RPM ?

2) How about a BLDC motor with a controller ? I see kits at reasonable price, with controllers, would like to get recommendations.

	I	II
L1	90	180
L2	200	400
L3	300	600
H1	550	1100
H2	960	1920
H3	1700	3400

 

[mattthemuppet2]

I would get a 220v 1ph > 220v 3ph vfd and a transformer to bump that 220c 3ph up to the voltage of the motor.

 

[strantor]

It's not clear if that means the motor has 2 wiring for each speed, or if the speed change is entirely driven by gears.

It can be wired for one speed or the other. Plus speed changes by gearing. It is not clear to me either specifically how it is configured, but I suspect the H/L lever is an electrical switch and the 1/2/3 lever is a gear selector.

Needless to say, If the motor has 2 speed configuration, it will be harder to find a 3-phase motor that has the same specs

You don't need to look for another 2-speed motor. Going on my previous assumption of 2 electrical speeds and 3 gear speeds, I would get a 2-pole (3600rpm) motor rated 2.2kw/3HP (double what's on there) and a VFD. That will allow you to hit the high speeds of the original motor when it was in the "H" mode while maintaining the torque that it had while it was in the "L" mode. The motor will offer the bonus of being able to hit the high speed and high torque at the same time, and since it is a common motor will probably cost less than the two-speed option if you manage to find it. 3HP also seems to be the ceiling for VFDs that step 120V single phase up to 240V 3 phase, so that works out nicely.

 

[matthewsx]

Is the price really good?

Would be much easier to just buy a machine that works with available power.

Adding a VFD to a 3 phase 240v is easy. Wiring existing controls isn’t difficult if you are electrically inclined.

Have you found a suitable replacement motor? For that type of mill (direct drive I’m guessing) you probably need an exact replacement.

So, all I’m saying is factor in all the costs and hassle before you commit.

John

 

[mksj]

It is a metric motor 90S frame size, dual speed motor 4P and 2P, 1.5Hp. So it would be best to replace it with a 2Hp metric motor, 1750 RPM (4P). There is no issue with running it above the base speed so something like a range of 20-100 Hz (600-2900 RPM), below 20Hz there can be cooling issues with TEFC motors above 100 performance typically drops off with a standard motor. Technically they use the same bearing in 2P as 4P motors so mechanically they can operate above 100Hz for a 4P motor. Better to overspeed a 4P motor then under speed a 2P.

The issue often with a motor replacement on these types of gear head mill motors is that both the mounting and shaft dimensions are non-standard. So the first thing I would recommend is pulling the current motor and getting the mounting dimensions and shaft dimensions. The shafts are usually longer and smaller in diameter. Leeson, Marathon, WEG metric motors are common replacements. My recollection on someone that had a similar mill was that only the 2Hp metric motor would fit but there was an issue with the shaft diameter.

PM932 Mill Motor Upgrade

Hello group. I haven't posted in quite a while; however, I read most of the posts here daily. I have a PM932PDF mill that I am in the formative stages of getting ready to think about upgrading the motor to 3 phase with a VFD. I figured the best place to start would be with the motor. Below is...

www.hobby-machinist.com

 

[maxime.levesque]

Is the price really good?

Not great, which is why I'm trying to find a used replacement motor before, to know the real cost beforehand.

There are many nice used mills at great price, but unfortunately most of them are too big.
I can only have a bench mill, as I will have to move it to my basement.
Bench mills are much more expensive for their weight and quality, there are too many of us basement machinists, we drive up the demand !

 

[matthewsx]

Personally, I’d keep looking. I tried to find exactly what frame motor you have when you posted previously but I couldn’t determine it from the motor plate.

Take a look at the parts breakdown for an RF-45 to get an idea of what you have to do to adapt something different. You might need a mill to fix your “new” mill.

And, read a few of the threads on here about moving equipment into and out of basements. If you have the vertical clearance there’s probably a way to get a full size mill down there.

John

 

[Chipper5783]

What are your longer term plans? If you get a phase converter (couple good options for this first step) + a transformer, then you can simply connect the machine and away you go. Then any other 240 or 575 three phase machines are easily powered up. Three phase and higher voltage machines tend to be higher quality (numerous exceptions aside) and there is less competition, because folks have a hard time sorting out the power. The venerable RPC is one good option, and they are quite easy to make yourself (many people here on HM have done so and can direct you to the plans to make one), then a small transformer can be purchased used (may have to be patient). If you are handy at putting electrical stuff together, and with some searching and patience, it can be done pretty inexpensively.

This arrangement works well (I have been using such a set up for about 10 years, have quite a few machines hooked up to it). You may well be able to do a motor swap and VFD cheaper - but still not cheap, cheap - it is a chore to match up the motor and only addresses that machine.

 

[PNW_Guy]

Have you considered a VFD? It would allow you to run the 3 phase motor on single phase 220, and even give you a bit more RPM range. They can be purchased for as little as $100.

 

[Huub Buis]

If using a VFD is not an option, i would use an AC servo motor that runs 3000 RPM. You can run these from 0..3000 RPM and they hold their RPM constant and deliver a constant torque at the whole RPM range. You can overload them 300% for a short time. Works great for tapping.