Re: power supply

The Triac/ dimmer approach does not sound like a good idea to me for
voltage limiting.

If the Triac fires in quadrant 1or 3 of the AC wave form you will
still see the full AC mains voltage on the transformer . You are now
relying on the fact that the Triac is limiting the "effective power"
of the AC wave form. This works only because the coil resistance and
circuit components limit the peak current in the secondary charging
the bulk capacitor.

For a steady load you can achieve a current balance that works well
enough but the motor controls are dynamic. As soon as the drives
revert to a regenerative braking the current draw drops or reverses.
This will allow the bulk capacitor to charge to full voltage very
quickly as it is being helped by both the AC input and regenerative
energy.

Limiting the Triac to the falling edge of the cycle Quadrants 2 and
4 is possible but now your peak current capacity will be very low as
the "effective" power to the bulk capacitor is well under 50% max.

I think this approach will cause problems without a very wide safety
margin.

Brian
BSP

--- In CAD_CAM_EDM_DRO@y..., "Mike Snodgrass" <snarf@s...> wrote:
> On my ongoing search to use easily available and cheap solutions...
I have several step down transformers that I would like to use as
power supplies. The problem is that after inputing 120V I get 82V
output after filtering and rectifying. 2V over the threshhold of my
drive. I installed a easily available light dimmer in the input and
after applying load I can precisly control voltage. These units are
rated at 600W, the thyristor in the unit can be paralled to give
more current or use a heavier one designed for router speed control.
I also mounted a cheap VOM in the circuit to monitor voltage.
>
>
> [Non-text portions of this message have been removed]