RE: [CAD_CAM_EDM_DRO] Re: Transformer sizing?

When you talk of Volt-Amps, realize that a transformer's output current is
determined by the wire size. Volt-Amps will change, depending on the input
voltage to the transformer. Assume that you have a transformer rated at 220
volts input and 100 volts output has an output rating of 100 volt amps. The
secondary should be capable of supplying 1 amp. If you run this transformer
from a variac so that the output is only 50 volts, you can still only expect
it to deliver 1 amp, so the Volt-Amp rating drops to 50 Volt-Amps.

-- Carol & Jerry Jankura
Strongsville, Ohio
So many toys, so little time....

|-----Original Message-----
|From: sleyed [mailto:Sleyed@...]
|Sent: Tuesday, January 22, 2002 11:12 PM
|To: CAD_CAM_EDM_DRO@yahoogroups.com
|Subject: [CAD_CAM_EDM_DRO] Re: Transformer sizing?
|
|
|Hello JV,
| I can explain a bit on this subject and I'm sure others can
|explain more. A good book on the basics of electrical principles for
|the sake of reference is a big plus too.
| Not to sound flipant but, there is a lot of stuff between the
|transformer and the stepper motor that can be even more confusing.
|
|To be helpful,
| Transformers are rated in VA which is the same as Watts(Volts *
|Amps).
| Average draw means just that. Add up all of the loads in like
|terms, calculate an average duty factor for each. Same for the peak
|and add 25-30% just to stay safe.
| The 67% you mention is an upper limit to the intended max load you
|plan on having it drive. Let's say you you have a 10 va(Watts)
|transformer on hand. Your max load would be 6.7 Watts. This way it
|will last longer and never be loaded to it's limit, preventing
|damaging heat build up taking into consideration the peak beyond the
|67% at whatever duration. It is a minor cush factor. Circuit
|protection will also be in the upper part of this region. No sense in
|being too foolish.
| It can be a balancing act when it comes to over/under rating. I
|would relate this as to how tightly the smoke in them is wrapped.
|Go to the big side of reasonable if funds permit.
|
|DC
|
|
|--- In CAD_CAM_EDM_DRO@y..., "jvbsa" <s8in@g...> wrote:
|> Hi, I am just beginning my journey into CNC and would like some
|info
|> or links regarding transformers sizing for stepper motors (constant
|> current supply).
|>
|> I am confused regarding the real operating VA requirement for
|> transformers, Average current draw and peak, etc.
|>
|> I have seen the figure of 67% mentioned. Is this for one winding or
|> for both.
|>
|> Kindly point me in the right direction.
|>
|> Many thanks
|>
|> JV
|
|
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