Brake Motor + VFD Help

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olephart

Newly Enlightened
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Apr 27, 2004
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I'm thinking about changing the 220V single phase motor on my mill/drill to a 3 phase AC motor controlled by a VFD. A friend has a Baldor BM 3556T "Brake Motor" that he wants to sell me cheap. I'm not looking for specific hook up info (yet). Just want know if this motor and an inexpensive controller will work together and power the mill.

All I have been able to find out about brake motors is they stop fast when power is removed and are recommended for machine tools. The Baldor info seems extensive, but it's all Greek to me. I did notice that it's 1140 RPM. I should get a max RPM of about 1700 with the existing pulley system. That is OK for me.

I wonder if there is some down side to this type motor and if there any special requirements for the VFD used to control it? Would a Hitachi 200 series controller be OK?


Baldor Specs:
http://www.baldor.com/products/deta...BrakeMotor&winding=35WG1272&rating=40CMB-CONT
 
If it's a truly smoking deal. (Under $200, since you can get at least a 1HP Baldor for that on eBay) then go for it, you should be able to remove the brake, you won't really need it. IMO it'll just add issue since VFD's allow for braking as it is.
 
Not trying to be negative about that motor, BUT ...

It is a 1hp motor at full rpm, meaning that if or when you slow it down to 10% of full speed (which I often do) you have only 1/10 hp. Think sewing machine motor.

When sizing a motor for VFD use, first determine what you want the lowest speed to be - either motor shaft speed or machine spindle rpm. That's the reason I've always replaced 1hp motors with a 3hp motor ... even at 10% of full speed, you have 3/10 hp working, plus you also have 300% of the torque of the 1hp motor.

The biggest mistake I see people making is to go too small on the horsepower & then find out the machine cannot do the job at the slowest speeds.

Would a Hitachi 200 series controller be OK?
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If you mean the current model X200, it isn't suitable for machine tool drive. It's a volts per Hz design, well suited for pumps & fans where the load decreases as the rpm decreases. For a machine tool, look for a vector drive, which often costs little more than a V/Hz drive.

My current favorite drive, and the one that Will Quiles used on his mill, is the ACTech SMVector. Well made (in the USA :D), easily configured, awesome tech support. Three SMVectors are in my shop, plus one Hitachi. http://www.wolfautomation.com/Product.aspx?ProductID=19500

The Hitachi's are very nice, made in Japan. On a per horsepower basis, their price is quite a bit higher than ACTech. Configuring (programming, or parameter setting) the Hitachi is a genuine pain, and I always end up calling tech support.

Hard to go wrong with the SMVector, although the Teco/Westinghouse EV Series does a nice job at a very low cost: http://www.wolfautomation.com/Product.aspx?ProductID=28926

Lots of VFD (and rotary converter) info on the PM forum: http://www.practicalmachinist.com/vb/transformers-phase-converters-vfd/
 
Thanks for all the info. The motor is $100 - its new in da box. I was planning on continuing to use the belt system to keep the motor in the 50 to 100% range to minimize heat. I can produce 100% power at 8 settings between 80 and 1700 RPM. I am mostly drilling and making fairly light cuts in aluminum, so I wouldn't be changing belt settings too often.

I'm rethinking the whole thing. I can do the above for about $250. Going to 3hp with similar quality is around $450. That's more than I want to spend on this. I guess I need to find out what amount of work can be done at 1/2 hp and go from there.
 
That is encouraging. I am looking at the Telco unit you recommended and will probably go with that if I continue. I ran across information that said the motor brake can't be used with a VFD. Apparently it will draw more current than the VFD can supply.

Other folks say it can be used independent of the VFD. The motor brake has to be powered with a separate service and the VFD set to coast rather than brake. I can't find any info about disabling the motor brake, but it may be as simple as removing the power leads from the coils.

I need to research all this and determine the best option. I would really prefer to use the motor brake rather than spending more on resistors for the VFD.
 
Some Baldor brake motors are set up for VFD control, but this model does not appear to be. Baldor states:

Spring-set brake. Power off operation manual release. Resets automatically. Brakes internally connected to motor on 215T and smaller.
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The BM3556T is built on a NEMA 145T frame, so it falls into the "215T and smaller" classification. Since the brake is internally connected, it does not appear that it can be disabled or controlled by VFD. If you phone Baldor & ask for tech support, they'll be happy to discuss this at length & help you determine if this motor is suitable.

http://www.baldor.com/pdf/501_Catalog/Section14_BrakeMotors.pdf

If not, 1hp 3ph motors are both common & cheap, either on eBay or Craigslist. My local scrap dealer sells them by weight, and I paid $50 for a 10hp motor ... a 1hp motor would sell here for around $20. These are used (surplus) motors, meaning some may need bearings & all will need cleaning & painting. They are cheap, and rarely will you get one that is DOA. My dealer does allow return for exchange if a motor is DOA.
 
precisionworks said:
My current favorite drive, and the one that Will Quiles used on his mill, is the ACTech SMVector. Well made (in the USA :D), easily configured, awesome tech support. Three SMVectors are in my shop, plus one Hitachi. http://www.wolfautomation.com/Product.aspx?ProductID=19500
Click to expand...
+1

I have one used in my 3HP Mill and a second one used in my 5HP (used as 3 HP) Quincy compressor. Definitely first class hardware, great customer support, and fairly easy to setup ;)

My next one will also be an ACTech SMVector when I convert my 12x lathe to Variable Speed sometime (I hope) this year :D
 
My next one will also be an ACTech SMVector
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+1

The easiest VFD to configure is the SMVector ... based on my own experience setting up over two dozen different brands, models, etc. Hitachi is far and away the worst, Square D - TeleMechanique ranks a close second, some Allen-Bradley are easy & some are nightmares (same with Siemens), most Baldor are OK, WEG has terrible documentation (as does T B Woods), Teco isn't bad but is more difficult than the SMVector.

There are (sometimes) great buys on larger drives like Yaskawa, Leeson, Tosvert, Reliance, etc. Research any drive carefully, especially older ones, as there may be limited or no documentation. Also, if a drive has not been powered for a number of years, the caps will need to be "re-formed" ... here's one suggested way to do this (from ABB):

http://www05.abb.com/global/scot/sc...$File/Guide_for_capacitor_reforming_Rev_G.pdf
 
I called Baldor. Very nice people and quite helpful. 2 options. To use the motor brake, cut 2 wires from the stator to the brake coil and attach them to an independently powered (230V) normally open relay triggered by the VFD.

To disable the brake, snip those wires and remove some brake parts. This seems to be the best choice.

Here's a mildly interesting fact I picked up while chatting with the Baldor guy. The various Baldor models have different ratings for speed ratios. Seems that exceeding these ratings will be very hard on the windings. Some are 4:1 which means you should not slow a 60 cycle motor to less than 15 cycles. Many are 10:1 and the premium motors are 20:1. There is supposed to be a chart on p. 189 of their catalog with the ratings if it is of any interest for your application.

I think I'm gonna get the motor even with the required surgery. I place a premium on it's new condition rather than using a cheaper motor in unknown condition. For a bigger motor, I'd probably go the used route and factor in a rebuild.
 
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To use the motor brake, cut 2 wires from the stator to the brake coil and attach them to an independently powered (230V) normally open relay triggered by the VFD.
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That's a nice option, as there are quite a few VFD outputs that can be used for relay control. Set up the drive so that hitting the stop button engages the brake & you'll have instant stop :D

eBay does have smoking deals on new motors.
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The 2hp motor would be a decent deal for about $75 IF they would ship using my own UPS account (which gets 40% off list price).

The 3hp motor is nearly identical to those that power four of my machines with VFD control - the eBay motor is a M3611 (NEMA 182 frame) and my motors are M3611T (NEMA 182T frame). With free shipping that's a good price, especially if they accept an offer of $150-$175.

Motor prices don't go up much as the horsepower goes above 3hp, but VFD prices almost double if a 5hp (single phase input) is needed. The sweet spot for drives is 3hp max, where they aren't expensive.

wonder what it would cost to get 460V power to my house?
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Most motors are able to be wired for low voltage (208-230v) or high voltage (460v). A few machines, especially those from Europe, require 460, 480, 550, etc. For those, a step up (boost) transformer is the least expensive way to go.
 
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precisionworks said:
The 3hp motor is nearly identical to those that power four of my machines with VFD control - the eBay motor is a M3611 (NEMA 182 frame) and my motors are M3611T (NEMA 182T frame). With free shipping that's a good price, especially if they accept an offer of $150-$175.
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As you know, that is what I did :D

I followed your advice and bought brand new 3HP Baldor for about $150 shipped (used in the mill), and the big 5HP Baldor for about $175 shipped (planned for the 12x).

The key is to have patience. And wait. And wait some more. Until the right deal comes through ;)
 
I was happy to learn that you could use the motor brake, but I can't figure out why I want to. It's more cost and complexity and I don't know why I need the mill to stop instantly - hardly any of them do that. The VFD should stop it a little faster than coasting, anyway. I was also thinking about having to go around back and manually releasing the brake every time I want to rotate the spindle by hand.

This project could easily escalate to the point that trading up for a Bridgeport would be a good idea. Anything beyond the KISS principle is out of place with this equipment. Lipstick on a pig.

So far it looks feasible. I'll need to make a bushing for the motor sheave (24mm to 7/8), disable the motor brake and attach the line in and out wires to the VFD. The Teco unit already has the variable speed pot and the motor mounts are the same. That should do it. No additional switches, relays, pots, etc.
 
You could wire the brake into a kill switch. For most applications a VFD will stop the motor fast enough.

If you crash and the spindle picks up the workpiece having a kill switch that locks the motor brake and kills VFD power would be a good thing.
 
"You could wire the brake into a kill switch."


That seems to be the case. Once ya run a separate 220V line with relay to the brake coil, the VFD can do anything it can do for a "regular" motor.
 
The VFD should stop it a little faster than coasting, anyway.
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+1

A drive (without any braking resistors) will stop the motor quickly when the motor speed is very slow ... if the motor is running at 1/10 of full speed (114 rpm @ 6 HZ) the stop is instant. That allows tapping with instant reverse, a very nice feature of VFD control for a drill press.

As motor speed is increased, stopping time increases as well. Same applies if you add heavy tooling (which is rarely the case while drilling or tapping). Stops are still quick at 2/10 speed (228 rpm @ 12 Hz), but are noticeably slow running much above that. Play with the decel setting & you'll find a number that works most of the time, worst thing being that too fast a decel will fault the drive & you'll have to reset the drive - no big deal.

vfd1-2.jpg


vfd2-2.jpg


The red "mushroom" switch is the E-stop or kill switch. Mount one where it's easy to hit when things start flying & crashing :crackup: That's about the only time you'll need it, unless you get a shirt sleeve or glove hung up in the tool. Since none of us ever wear gloves around machinery, that shouldn't be an issue ...
 
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olephart said:
Nice setup. Do you need extra resistors for the E-stop?
Click to expand...

Nothing extra for the E-stop. The E-stop is really a "logic" signal to the VFD controller - think of it as the "enable" signal. You can program/design so that it is normally open or normally closed - very easy to do.

You can even have more than one, having then wired in series, so that either all of them have to be closed/open for the machine to run (I did that already in my mill VFD conversion). That is also how I am going to wire my lathe, so make sure that all of the safety interconnect/switches are still active/working when I do the VFD conversion, plus I am (at least right now) planning to add an E-stop on the carriage itself for redundancy.

It will be a great/fun project if I "ever" get the time to start :devil:
 
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