Re: Lose A Few Volts

Hi Jon,

Thanks very much!
I understand the diodes, but haven't ever used a transformer
wired like that. I do see people discussing it, but never
paid much attention as I thought it was for more commercial
type applications.

I made a sketch and put it here...
http://www.flickr.com/photos/26361144@N00/

I'm thinking I understand your directions, but something
doesn't look quite right. If you get a chance to look, I'd
be grateful.

Thanks again for the info.
John

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> John Hansford wrote:
>
> >Hi All,
> >I'm using a 48v torroid transformer...67.2 VDC.
> >Using 3V 3A unipolar nema23 from Hobbycnc on Gecko G202's
> >Wired bipolar, series.
> >2.8 amps to the motors.
> >
> >So far all is well, But i'd like to lose about 8 Volts.
> >Reason is the motors run at 150 degrees. I'd like to get
> >them down to around 130. I'm just more comfortable with them being
> >a little cooler. I'll drop the current down to around 2.2
> >
> >Can i just put a few diodes on the transformer and lose the
> >8 or so volts? Is there a better way?
> >
> >
> >
> Putting some power diodes after the rectifier bridge will drop about
> 0.67 V per diode. You don't want to put the diodes between the
capacitor
> and the Gecko drives as there are circumstances where energy can be
> returned from the drive, and you want the main cap to be able to absorb
> that.
>
> The only other way to do it is with a buck transformer in series
with the
> transformer primary. You want to drop about 12% of your voltage. With
> a 120 V main supply, that would be 14.4 V. Well, if you put a 12.6 V
> filament
> transformer in as a bucking transformer, that would drop 10.5%, and
get your
> output down to about 60 V.
>
> Wire the primary of the filament transformer acoss the incoming line.
> One side of the filament transformer's secondary goes to one side of
the
> line, the
> other side goes to one of you main power supply transformer's primary
> connections. The other main xfrmr's wires goes to the other side of
the
> line.
> So, the filament transformer is in series with one side of the main
> transformer's
> primary. Depending on the phase of the windings, this will either
> increase or
> decrease the line voltage by 10.5% If it goes up, you need to swap the
> filament
> transformer's secondary wires. The secondary of the filament
> transformer needs
> to be rated for the highest current the main transformer's primary will
> draw.
> So, a very small transformer can handle this job.
>
> Jon
>