Re: Voltage Regulators or Diodes to drop voltage?

This seems to be a case where the best and most reliable solution (and probably the cheapest) is low tech. All the high tech ways are costly and introduce more parts. Keep it simple and take some turns off the secondary of the transformer. When finished don't wrap it up with duct tape, plastic doesn't handle heat real well. Get some cotton tape from a motor rewinding shop or from an automotive electrician and use that. (You could even reliably use some cotton bandage). When its wrapped up and tied tightly just paint it with shellac flakes dissolved in alcohol overnight.

Regards
Bob Thomas

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "abbylynx <abbylynx@y...>" <abbylynx@y...> wrote:
> Hi again,
>
> Well, my linear power supply is working well. Too well in fact..
> after the bridge recifier and capacitor, it's pumping out 38 volts.
> This would be fine, only that the maximum voltage limit on my driver
> board is 35V. Aaah!
>
> Anyway, I need to drop off about 4V or so, just to be safe. Any
> advice? I know I could just open the transformer and start taking
> windings of the secondary, but (A) it's tedious as hell, (B) it's
> probably defeats the isolation (my duct-taped result would certainly
> not be as isolated as the original) and (C) ... it's just plain not a
> good idea.
>
> So I was wondering about other avenues? I'd heard someone talking
> about using Diodes to drop the voltage on the line? What diodes do
> you use for this and how many? (I can no longer find the message).. I
> have some diodes around, but they're all meek li'l 1AMP ones, they'd
> certainly become a small short-lived heating element on the 7AMP
> power supply.
>
> Also, what about voltage regulators? I know they don't make anything
> above the 7805 and 7812 (no 7824).. but I know there are variable
> ones available where you can set the output voltage with a resistor.
> Again, looking on the web I've only been able to find some meek li'l
> 1.5ampers - which'll no doubt be carbon-toasties(tm) by the time my
> steppers have vamped it. A voltage regulator would seem good - since
> it might just save the driver board in the event of the AC power
> supply jumping up a few volts in a surge etc.
>
> Any advice welcome!
> Thanks. :)