[Al_The_Man]

I don't know what type of controller you are using, but you really need one with a current limit adjust set to the right limit for the motor.
You may not have noticed any rpm difference, or you may have adjusted the controller to compensate for the possible load difference , ANY increase in load at ANY armature voltage results in an immediate increase in current.
A way of monitoring the current would be nice also.
Al.

[LongRat]

It's the stock controller that comes with the machine. They are well know for poor reliability in the smaller '20' mills. I have no reason to assume the larger controller is any better, if indeed it is a different controller.
They have a load balancing circuit that I think increases the voltage to the motor under load, thus increasing current and raising torque when you are taking a heavy cut. I haven't adjusted mine, but when the load on the spindle goes up my motor actually starts to increase RPM slightly, so something isn't perfectly adjusted. But it has always been like that. I'll open up the controller and see if there are any adjustments I can make to decrease the arcing.

[digits]

Congratulations on the belt conversion LongRat!

As for your motor - sounds pretty similar to what happened to my first one. My controller would speed up by about 10% on heavy cuts - I did have a go at adjusting the current limit lower, but I think it was too late. Not long after it went bang!

I have had better luck with the second one so far, but I think the real solution is to go for an induction motor and VFD. The main problem though is that most ac motors with decent torque seem to have lower base rpms than the stock dc one.

[LongRat]

Yeah, I won't be buying a replacement DC motor. Looking into an AC motor and VFD combo now. I'll be adjusting the current limit a bit tomorrow to see if that helps. Did yours spark and pop in the same way before you adjusted the limit - and did that make a difference?
Hopefully the low-speed performance won't be too much of an issue. I still have 2 pulley ratios on my belt drive, and I basically never use the machine at very low speeds.

[mrcodewiz]

Why are you opting for an AC motor over DC? I replaced mine with a 1.5 hp treadmill motor. It seems to run much stronger than the oem and doesn't really get hot at all.

[LongRat]

Well, I would rather not have a commutator and there seem to be a lot more good quality VFDs around than there are DC controls in the same power range. I wouldn't rule it out but I have seen some nice 3-phase stuff in action for a reasonable price and would take some convincing to go to DC over those.

[mrcodewiz]

Ah. Just curious. I have never used a VFD setup.

[Maglin]

Mrcodewiz holy crap that was a lot of arcing. I would be scared of getting electrocuted by the machine if it wasn't earth grounded.

As for the lower speed of AC motors. That is usually rated at 50/60 hz. With a VFD you are controlling the speed by changing the frequency of the power from 0-400hz. Most AC motors can handle 2x speed ie. 100/120 hz operation. Past that you really start to lose power and increase possibility of motor damage. So that 1650 rpm motor at 60 hz will run 3300 rpm at 120 hz. And past 6k Spindle rpm you are getting in dangerous territory for your tools balance along with malfunctions possibly causing serious injury to you or those around the machine when something happens.

I never thought about the solder being thrown off the comm. when it over heats. That explains a few things I couldn't get past in my head.

[LongRat]

I played around a bit with the controller for the motor tonight. After tripping the power and tracing it to (another) fallen off wire, I am fast losing all confidence in this thing.
Turning down the CL (current limit) pot did nothing but slow down the motor. The arcing remained. I didn't touch any of the other pots. The controller itself seems to be very similar to a KBIC beased on reading the manual for the KBIC. But it isn't the same. Spoke to a company about getting a 2HP 3-phase motor and VFD and currently sizing it up to check it will fit, but I am pretty sure that will be the way to go.

[Al_The_Man]

The arcing remained. I didn't touch any of the other pots. The controller itself seems to be very similar to a KBIC beased on reading the manual for the KBIC. .

Usually if you see that degree of arcing, its too late!
Al.

[tef9]

Hi Longrat,

Have you thought about using a treadmill motor?

Andy

[arizonavideo]

A 2HP three phase is really a large motor for that mill. I have the same mill and a spare 2hp motor and I just wouldn't put something that big on that head.

With a VFD you can over speed a motor and program the power output. A 1.5 HP motor will make 2 HP at a 25% over speed. AC motors are also under rated by a fair amount where the China DC motors are not really 100% duty cycle at full power.

I would get a 1HP or at most a 1.5 hp three phase motor. With a 2HP VFD you can zip that 1.5 HP motor to 5K and get a easy 2 HP.

[LongRat]

According to the data sheets I am looking at, that is not necessarily the case. Torque derating over design RPM is quite substantial. Check it out, graphs at the bottom - http://www.drivesdirect.co.uk/Downlo...20Lite%204.pdf
Plus, the 2HP motor I am looking at isn't that much bigger than the current DC motor on the mill. How big is your 2HP motor?
Also, with the cheaper, non-vector VFDs you also lose a mountain of torque when running very low RPMs too. Seems to me it is the combination of motor and VFD that must be considered together. I'd like to go for a smaller motor if possible, and if anyone has any evidence that that would be a good solution then please post. But judging at the rate I was able to rip off metal at 5000 RPM I'm not sure if I would risk going too small when overdriving a motor well over 50Hz.

[Al_The_Man]

Here is a tech sheet from Baldor may help in the decision, also touches on 100% torque down to 0rpm, as a general rule I don't run non-vector rated 2 pole motors over the base speed, if 4 pole then I run these up to double the normal frequency.
Baldor Vector rated 4 pole motors will allow going up to 6000rpm.
http://www.scrcontrols.com/docs/BR400_2_05.pdf
Al.

[LongRat]

Hi Longrat,

Have you thought about using a treadmill motor?

Andy

Yes I have, it does appeal in many respects but until the cause of the current problem is found I am unwilling to risk it. I would rather dump both the motor and the controller. I don't want to spend forever hunting down this problem either, I just want it solved. If that means buying a 3-phase and VFD which I am sure I wouldn't regret, its not so bad.

[Al_The_Man]

DC motors are commonly limited to around 2500~3000rpm tops, non-brushed, non-wound rotor motor rpm is usually limited by balance and bearings.
Al.

[pete from TN]

What is the standard line voltage speed rating of the Baldor motor that runs to 6k? I am using a 1725 RPM motor and I run my vector drive on it up to around 120 or 130 HZ.... If that is a 1725 RPM motor and it will take 6k that is amazing and I should look at getting one of those. That would substantially increase my SAFE available spindle speed assuming Torque remains relatively constant and make for one badass mill.... What are your thoughts here...I did not wish to gear for the moon and sacrifice available torque just for the sake of speed. Peace

Pete

[Al_The_Man]

If you look up page 9 of the Baldor link Post #34, it show the 220/440 4 pole motors rated for 5k & 6k rpm.
I think anything above 3600rpm for a standard motor is pushing it.
Al.

[digits]

Yeah, I won't be buying a replacement DC motor. Looking into an AC motor and VFD combo now. I'll be adjusting the current limit a bit tomorrow to see if that helps. Did yours spark and pop in the same way before you adjusted the limit - and did that make a difference?
Hopefully the low-speed performance won't be too much of an issue. I still have 2 pulley ratios on my belt drive, and I basically never use the machine at very low speeds.

Sorry for not replying sooner, my broadband is on the blink

IIRC I don't think I had any warnings before it went quite literally bang! I did readjust the pots following the instructions someone posted, and using a multimeter to check the current limit once I'd got a new motor, and it does seem more stable. If anything, there's just a slight bogging under load - much more what I would expect to see and hear!

Are you sure your air-blast hasn't sent fine chips into your motor?

[arizonavideo]

The IH milling machine came with a 2 HP which I replaced for now with a 4 HP.

The mounting flange is 8" the head of the Weiss is 6" wide.

I don't think a 2 HP is too much power just you may want to look for one of smaller frame motors so it will fit better on the head.

Most of the 3,500 RPM motors have smaller rotors so can have a smaller OD and may fit better.