Re: [CAD_CAM_EDM_DRO] Re: Motor calculations? Help!

Lance Hopper wrote:

>Hello,
> I've been talking to the guy myself trying to help him out. He's
>already bought 200V 40A Rutex drives as I understand. Now he's
>trying to figure out the PS.
>
>

Ah, OK, that sounds like the best course.

> The original drives were fed 120 3ph from the secondaries of a
>2.5kva 3ph transformer as he describes via his electrical schematics.
>He was trying to see if the stock 3ph transformer (has delta and Y
>wiring configurations, he has the schematics, maybe he should post)
>could take ~220 1ph (all he has available) and output ~120 1ph that
>could be rectified and used for the Rutex drives. I doubted that it
>would work and be dangerous/stupid to try, but what do I know.
>
>

Is there any way to use a 3ph transformer for 1ph in and 1ph out?

No, it really will not work well on single phase. Where did this thing get
120 V 3-phase power? That is an extremely odd voltage. 208 and 230 V
L-L is the most common low-voltage 3-phase supply in the US. Or, is this
120 V line-neutral voltage? That would normally be termed 208 V 3-phase,
as the line-line voltage is how it is usually measured.

> Is there any way to use a 3ph transformer for 1ph in and 1ph out?
>What if he used a phase converter and ran 220 3ph to the primary,
>then just ditched one of the 120 3ph legs to get 120 1ph to be
>rectified/filtered for the Rutex drives? Any safe/smart workarounds
>on this?
>

The best way to go, I think, would be to use a 240:120 V step-down
transformer
rated for 2.5 KVA at that voltage. (If you can't find one with that
exact rating,
you could use a 480:240 V 5 KVA transformer at half input voltage.)
With a 240 V output with a center tap, and using 2 diodes, you can get
170 V DC, which may be acceptable to the Rutex drives. (I'm being cautious
here, because the Rutex's 200 V rating is apparently the actual rated
voltage
of the transistors. So, I don't know if the 200 V Rutex drive can
actually be
run off 170 V DC without problems. It is probably best to ask Rutex about
that. If necessary, one can get tapped autotransformers to adjust the
voltage down somewhat.

Jon

>
> Otherwise, he's going to have some $ into some large kva
>transformers for the X/Y and Z servos.
>
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" <cnc4me@g...>
>wrote:
>
>
>>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>
>>
>>
>wrote:
>
>
>>>cnc_4_me wrote:
>>>
>>>
>>>
>>>>Jon, I do not see this the same way you do. Don't you think the
>>>>continuous current rating is more important than the peak
>>>>
>>>>
>current
>
>
>>>>rating? 28 Kg-Cm / 2.44 Kg-Cm/Amp = 11.5 amps, a gecko would
>>>>
>>>>
>>still
>>
>>
>>>>have plenty of reserve. 20 amp limit would still give 49 Kg-Cm.
>>>>
>>>>
>I
>
>
>>>>wish i had one of these motors for my Z axis.
>>>>
>>>>
>>>>
>>>>
>>>What's the peak rating for, if you never can get closer than 20%
>>>
>>>
>of
>
>
>>it?
>>
>>
>>>I might be worried that you might not be able to break static
>>>
>>>
>>friction on
>>
>>
>>>the table with 20 A. What is the leadscrew pitch, and is the
>>>
>>>
>screw
>
>
>>directly
>>
>>
>>>driven by the motor, or is there a belt reduction?
>>>
>>>What horsepower and spindle taper does the machine have?
>>>
>>>Jon
>>>
>>>
>>From what I understand from reading these forums is that any force
>>much greater than continuous rating isn't to usable, maybe for a
>>fraction of a second for fast acceleration. Maybe if he adjusts
>>acceleration so it does not snap your eyeballs it would be ok.
>>
>>49 Kg-Cm is about 47 lb-in. Nothing to sneeze at.
>>
>>
>>I guess what I am getting at is I would not try to discourage this
>>guy and say it will not work. I think it is very likely it will
>>work with slower acceleration and with 30% less speed on X and Y
>>because of voltage restrictions with Gecko drives. Rutex would
>>
>>
>give
>
>
>>him full speed and slightly higher acceleration.
>>
>>
>>Wally
>>
>>
>
>
>
>
>
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