Re: [CAD_CAM_EDM_DRO] Lose A Few Volts

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