On Thursday 01 November 2007, Kirk Wallace wrote:
>On Wed, 2007-10-31 at 20:15 -0600, Jon Elson wrote:
>> Kirk Wallace wrote:
>> > What is the best way to drive a 4hp, 90VDC, 40A spindle motor on a
>> > Hardinge CHNC? Some of the large DC motors I have seen, look like
>> > universal motors which would operate on AC or DC. Does anyone know if
>> > the CHNC spindle motor could work on AC? I'm thinking, a few dimmer
>> > switches in parallel and a stepper to turn the dials ;). I wonder if it
>> > would be cheaper to go with a 3-phase motor and VFD. Thanks.
>>
>> No, these motors are NOT universal motors. You could rectify
>> the mains to drive the motor, but then it would draw 40 A from
>> the line. You should be able to find an SCR drive for this.
>> You can't parallel dimmers, they can't be trusted to give the
>> same pulse width.
>
>I was joking about the dimmers. So far I have found this:
>
>http://www.baldor.com/products/detail.asp?1=1&page=1&catalogonly=1&catalog=B
>C155&product=DC+Controls&family=One+Way%7Cvw%5FDCControls%5FOneWay&voltage=1
>80
>
>but this puts out 180V and I need 90V. Plus it seems that this kind of
>controller does not interface with a computer well at all. It's
>beginning to look like DC lathe spindle drives are a specialty item,
>which means, hard to find and big bucks to buy or repair.
>
>> If it is a standard-frame motor, then you
>> could go the 3-phase and VFD route. That may not give you the
>> range of speeds and torque required.
>
>The newer VFD's are much better with this aren't they?
>
>> If you want smooth,
>> controlled reversing, then you need a DC servo drive. If you
>> don't need a complete 4-quadrant servo drive, then the SCR DC
>> motor drives may be the way to go. Baldor and plenty of others
>> make these, they show up on eBay all the time.
>>
>> Jon
Hey guys, even the lowly board out of a Harbor Freight 47xx8 micromill, except
for the current rating, makes a truly excellent vsc when combined with a
PMDX-106.
This board, with a much larger bridge rectifier replacing its puny 4 amp
device, and about 6 of the mosfets it uses in parallel with smallish current
sharing R's in series with the src's of each of the devices could probably do
that just fine. The speed control is very stiff with this unit, so stiff
that if I'm doing something heavy, I have to rig an ammeter in series with
the motor in order to see how close I am to the 'red line'. Otherwise it
just blows the fuse with no detectable motor slowdown first.
The only problem that I could foresee might be related to this boards ability
to drive that much gate capacitance of the paralleled mosfets and still
achieve good switching speeds. It is something I have not played with
personally, so one might approach this by adding one device at a time &
watching the heating. Running correctly, the mosfets shouldn't heat more
than 10F if screwed to a good heat sink and delivering 50% of their rated
current. In my own case, that would be at least 10 amps, but I didn't yet
replace the puny bridge rectifier either. Mine is currently in a closed
plastic box with the PMDX-106 and has run that way for half a day at a time
without the box getting noticeably warm. The direction relays make as much
heat as the rest of the circuitry.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Rule #1:
The Boss is always right.
Rule #2:
If the Boss is wrong, see Rule #1.
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