Re: [CAD_CAM_EDM_DRO] Stepper Power Supply. Question about Voltage

kaynrc wrote:

> Hello
>
> I am just getting around to selecting some transformers to build
> sparate little power supplies for Dan Mauch's 5 amp boards, and each
> transformer is rated at 26 VAC, 5 amps. I plugged one in, and read it
> at 29.2 VAC, which is fine by me.
>
> Then I connected the bridge rectifier and got a surprise, which is a
> reading of 26 VDC. I had not yet hooked up the 10,000uf, 50 VDC
> capacitor. Because the VAC is supposed to be higher than the VAC (by
> a factor of 1.41) I expected the DC voltage to be higher, around 35
> to 39 VDC. Again, it might be important that I did not attach the big
> cap yet.

Yes, the cap is important. Without it, the meter is just averaging the
rectified sine wave, which still has big peaks and valleys. With the
cap, it will hold the peak voltage.

> So, what's going on? Will I notice a voltage increase when I add the
> capacitor?

Yes.

> Why is my DC voltage so low just taken right off the
> rectifier, since it's only suppose to consume around 1.7V?

Because the meter avarages the waveform.

> Is the
> transformer perhaps too small to supply proper voltage?

Probably not.

> And last,
> these 521 oz-in motors that I got from Camtronics (and the circuit
> boards) can run up to 40VDC, so am I simply going to operating slower
> with somewhere around 25 to 30 VDC? Noticably slower?

No. You need the cap to provide a steady voltage, and it will be about
1.4 x what you have seen so far, or about 36 Volts.

Jon