DC Spindle motor

[Phooey]

Hey,

I'm new to this, only machine time spent at school CNC shop-
I have a Bridgeport (series II) in the garage now, not up and running yet. It's in good shape mechanically, good ways and very clean, but i haven't started it up. Its been looking like my best option is to run 240 from the house (there to supply the dryer) and get a VFD for the spindle (while also totally replaceing the BOSS6 contoller even if it does work), but what about DC? Im looking at a 1.25HP 180VDC motor and speed controll with 120V input at surpluscenter.com,
(about 200 bucks together) what do you guys think? Has anyone here done this? not sure what to do with this thing but i'm excited and want to see some chips soon! Thanks,

Phooey

[Al_The_Man]

Unless it was a high quality DC motor and controller, I personaly would prefer the VFD route.
Al.

[Phooey]

how high a quality do you have in mind? The obvious advantage here would be no need for new wiring in any place i might move to (save maybe a larger breaker)- but if your thinking it wouldn't be reliable that could certainly be a huge problem. so long as its rated for continuous duty, is there a reason quality would be a bigger concern with a DC motor than with any off-the-shelf 3 phase?

Phooey

[Halfnutz]

For whatever reason, I am not sure of the technical details, but there is not a direct correlation between DC motor HP ratings and AC HP ratings. There is also a difference between single and three phase AC ratings.

You would need a very large and very highly rated DC motor to go neck to neck with that three phase AC motor in the bridgeport. I dont know exactly what would compare, but it would be much more powerfull than the 1-2.5 HP treadmill duty DC motors at SurplusCenter. Ive got a couple different models of them, and they just wouldn't be up to par in my oppinion.

If you have the option, stick with the existing American 3 phase motor that came in the mill and get a VFD and a converter. I am no expert, but from what Ive seen I think you would be much better off that way than trying to change over to a DC set-up.

(The obove comments are the authors and do not represent the oppinions of CNCZone or it's management.)

[Al_The_Man]

Originally Posted by Phooey how high a quality do you have in mind? The obvious advantage here would be no need for new wiring in any place i might move to (save maybe a larger breaker)- but if your thinking it wouldn't be reliable that could certainly be a huge problem. so long as its rated for continuous duty, is there a reason quality would be a bigger concern with a DC motor than with any off-the-shelf 3 phase? Phooey

The reason I mentioned the quality of the DC motor is if it was a DC only, i.e. Permanent magnet motor then it Might be worth while, but if it is a series connected AC/DC motor, definately its not the way to go, A DC series wound motor has a higher top end rpm, but the speed regulation is very poor, varies with load etc.
But to get comparable true DC permanent magnet motor performance down to low rpm using a 3ph motor and VFD requires a quality VFD unit.
Al.

[roonster71]

check this out! a bp with dc spindle motor

http://truetex.com/dcdrv.htm

[Phooey]

This is really cool (thanks for the link Roonster), It seems to be working pretty well for him. do you think there is any reason not to scale this up a bit for the series II (2HP)? Main question, unless there are other objections- would you agree with him that you can use a lower rated motor than the origonal? it does make sence, if really heavy cuts are infrequent enough that it stays cool. i'm looking at this:
http://surpluscenter.com/item.asp?UI...tname=electric
of cource i'd put a heat sink and fan on the speed controll SCRs.
Thanks for all your quick help guys,

Phooey

[Al_The_Man]

The motor you show is 180v so you will need to run the drive on the 230v setting to get top rpm, otherwise with an SCR drive you just get a max of line voltage out on 120vac.
Al.

[Phooey]

i think i could use a transformer for less than a hundred dollars to get it up to 240 input, they are allot cheaper than a phase converter and of cource the input needed is one phase- what do you think? - but we are up to so many new parts (new motor, controll, and a transformer) that it might be cheaper at this point to keep the three phase motor and run the dryer line out to the garage like others have done- I still think it would be really sweet to have everything 120 input though, if its possible. Realistically, i've been looking at my finances and if i am just going to upgrade everything at the same time (stepper drivers, computer, software, spindle motor and everything) I can't do it for almost two months, which gives me plenty of time to think about it. I'll be looking for more motor options to solve this problem. There was a thread here about using a treadmill motor, but it doesn't look like that project was ever finished so there is no final performance information and, as halfnutz mentioned, I just don't have faith in those motors, they aren't continuous duty anyway. i'll be poking around for a good deal on a <=120VDC motor with better performance than those.

[roonster71]

I just adapted my xlo 602 mill to a dc spindle drive i used a 90v pac sci 1 hp motor
just got it running tonight!!! and im not shure if i like it or not? the original motor was 3phase 1750ish rpm 1.5 hp, and the dc motor is 90v 3000ish rpm 1 hp it it has the speed i like but the torqe i think is lacking maybe a 180vdc would be better? but it is nice to have it all working without having to rewire the house. i still have to play with the speed controll it has a tourqe setting ???