How to do a DC motor on small Milling Machine????

[240GTRZ]

Help Guys,

I just finished rebuilding a Rotex horz/vert small milling machine and both motors need to be replaced. I would like to replace the 1/2 hp motor on horz.shaft and the 1/2 hp motor on the vert. head with some kind of DC setup. Would this be a good idea? I was thinking it would be nice to control the speed without moving the belts around. Here the problem, I know nothing about buying or setup DC drives. Anybody like to give the low down on how to do this with out breaking the bank. ( some secerts would be nice

Dan

[Thrud]

Dan

It can be done, and sometimes quite cheaply. That is if you can find suitable surplus motors, otherwise it may be smarter to stick with AC and get a VFD.

Check past post on this subject - it has been flogged to death.

[240GTRZ]

Thrud,
Thanks for the info! What I would like to know is, what size 3 phase motors I would need to get to replace the ones that are currently being used? The mill head has a 1/2 hp 110v and the horz. has a 1/2hp 110v. So if I understand how to do this, I would buy two 3 phase motors and and a motor drive unit ( what size?) Also, how do I run two motors from one VFD? Only one motor is used at a time? Sorry about these newbie ?'s but I no electrical wiz!!
Thanks, Dan

[Jeff Manuel]

Dart Industries makes a very nice and inexpensive DC controller for fractional HP motors. It is their 125 CK (if I remember correctly) and will easily handle 1/2 hp motors. It is availble rom WW Grainger as 2 M 510. Again I guess at the number and it maybe 3 M 510.They sell it for about $80.00 and I have a local source that sells it for about $65.00. It is a chassis style which means you will have to provide a housing and some AC line fusing but otherwise all is there and it is easy to wire. I have use these for a lot of things with great success.

[chip's]

Dan,
The 3 phase motors you need are the same as the single phase motors you have now and they will have more poop too.
If you use a vfd you don't need any more motors. The drive will run one motor at a time just fine.
I hope this helps, Rick.

[Thrud]

Dan
You would need to get one that is the same frame size as the ones you currently have. This number is stamped on the rating plate.

[240GTRZ]

So,I should get two motors the same hp and frame size to fit the Rotex. What size or type of drive should I get and please keep in mind that I know nothing about these things? Also, should I look for a new one or can I save a little scratch by buying used? Can both motors be wired in to the drive and switched by the drive or would I have to have a plug on the output of the drive and switch the plug to each motor depending on which motor I want to use.
Thanks Guys for the help!!!!
Dan

[chip's]

Dan,
3 phase used motors can be had in most cases without much problem. Check em' over good. If you buy from a motor shop you should be ok. Run it first.
You can install a drum or other switch or a contactor behind the drive to run one motor at a time or use cords and plugs.

[docsteve66]

A few months ago the consenus seemed to be that the vfd must never be operated with no load. I haveelearned a little more than I knew then,and what I havelearned leads me to believe that operating with no load is disasterous to the VFD drivers. So your switching best be done with no power to a motor. And now I have told more than i really know bout vfds> confrimation or rebuttale gents? be kind to a old codger please.
Steve

[Thrud]

Steve
I am of the considered opinion that just as everyone (usually) has an butthole and an opinion (oft intermixed) it is better to be safe than sorry and if one insists on running multiple motors with a single VFD then cut power to said VFD before changed the circuit over to the other motor.

Just as it is possible to yank a card from a computer while it is running - only an idiot or brain dead moron would try it. SO DON'T DO IT WITH POWER APPLIED TO THE VFD!

I would also like to confess to having pulled a card from a live computer in a "blonde moment" - $3000 computer and $2000 card and the only casualty was my shorts.

[This message has been edited by Thrud (edited 01-07-2003).]

[docsteve66]

we all done some dumb ones. Down on Swan Island, 1961, working at a radio staion, 50,000 watts housed in semi trailers, there was a "cage". Inside was the main power supply. A big shorting bar was tied to the cage door intended to drop down and short the final filters capacitors (interlocks were to disconnect the iput power if door opened). Some work was needed inside. Work not finished when time to go on air and we were wroking with (that day anyway) guerillas (actualy cubans abandoned when bay of pigs aborted). Gettin on air was important. By passed the interlocks, tied shorting bar back just in case its holding circuit failed (most like it would be due to my ham handedness). Was piddling along happy as clam in mud. very safe. Every rule violated but safe. Idiot friend (Azor) decided to come help. He openedthe door with me watching. Neither of us remembered that I had tied the shorting bar to the door. Sounded like ashot gun went off, both were dazzled by the flash, Big old diesels roared, operating door flew open, Azor says over and over, don't any one move till we can see. No damage one. But I do think I litterly voided my bladder.

Locked azor in a "relay rack" cabinet where tuning coils were and with his permission, turned the power on. buts that another story. I guess if the risks are acceptable the job is safe.
Steve