Re: [CAD_CAM_EDM_DRO] Voltage Regulators or Diodes to drop voltage?

Three volts too high on an Unregulated 35 Volt supply ! If your final electronics cannot tolerate any more than 35 Volts, then that's where your problem is.
No one should run electronics on 35 Volt unregulated supply IF it only tolerates 35 Volts, bad practice, and will cause problems.

Assuming you are in the USA. Assume a AC supply of 110-115 Volts.
and if you "tweak" for 35 Volts DC output (I assume under full load ) Come to think about it.... 3 Volts swing on an unregulated supplies doing 7 Amps from full load to light load is good.... !
Then a small change in Input Supply and you are back to square one....
I think power companies are allowed to deliver your AC with +- 10% variations.

Anyway, if you are determined to tweak it, you can try the following...

Did you wind the transformer ?

If there is still space you can add windings to the secondary equal to 2-3 Volts and connect that extra winding in Anti Phase.
In the "old days" this was called "bucking" turns or similar.
That will Subtract the extra Voltage.
These extra windings can be wound on top of or outside the existing windings. When I say outside I don't mean around the
iron core, I mean on the bobbin where the other windings are.
As you only require 2-3 Volts I expect it will only take a few turns and it may be quicker to thread them by hand.

Diodes in series will work, you mentioned 7 Amps . That means 7A * 3V = 21 Watts !

Regulators are fine but 7 Amp 35 Volts Linear versions are few and far between, you could build your own using discreet components or spend half your life building a switch mode PSU.

If you did wind the transformer, in future add some taps in the primary to allow for small adjustments. You may have seen these on commercial transformers
with extra primary winding/s (not tap) just for that reason.

My final advice is : Don't run critical electronics so near to maximum voltage on unregulated supplies.....

Best regards
Hans W




"abbylynx " 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. :)
>
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