Converting cheap AC buzz box to DC

[mike 109444]

If they are polarized then you are talking DC. Not sure what is going on in that pic but if you are connecting across the DC out put of the rectifier then caps will need to be connected correct way round (think like a battery)

 

[633Squadron]

I'd also consider adding in a couple of high voltage zener diodes, to reduce the back EMF.

 

[dbach]

Ok, a little update to the project.
Finally the schottky diodes have arrived.
Here some photos of the project. On the last 2 pictures you see the reactor.
Still I'm waiting for the 100V 120000uF capacitor from China.

 

[mike 109444]

Have you used (or do you need to) the white heat transfer compound as used on processor chips ?
Do yo have a link for the large capacitor ?
ps looking goo so far

 

[dbach]

Here is the link on Ebay for the huge capacitor, I hope it will work
http://www.ebay.co.uk/itm/171708504458?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT.

Yes I had some thermal paste from my last processor change, so I have used it, but I think it's not absolutely necessary.
I don't know it's good or bad, today i have tried the rectifier, the open circuit runs on 42.V AC and 39.8 V on the DC side.

 

[dbach]

Hello, the project makes progress - only one stupid question.
The AC voltage in the open circuit is 42.6V, DC 39.8 on DC side as described above.
Now I have connected 4 thin film caps 0.5uF, 600V DC no polarity, as shown in the schematics.
Choke and output cap is still not fitted.
Now I'm a little nervous, because the DC voltage in the open circuit has gone up to 75V.
Why? And what will happen to my 100V 120000uF Cap?

 

[vince01]

Hi, its been a very long time since i taught myself electronics, about 45yrs lol, but none the less the theory is still the same, the why, a full wave bridge rectifier creates DC, but its what you would call very course DC, if you were to look at the DC via an oscilloscope you would see what you would call spurious emissions, the unwanted components from the AC input, these spurious emissions are collected by the smoothing capacitors and stored, which in turn gives an imposed voltage, a higher voltage than the applied voltage. As you will know, a true DC voltage from say a battery would have a completely flat line with no spurious, but because the bridge is supplied via an AC input which is sinusoidal, the bridge cannot fully create the flat line of DC, and hence the spurious output.
This higher voltage could well damage the capacitor in the final part of the circuit, so simply fit one exceeding the higher voltage being created, hope this helps.

 

[dbach]

BIG PROBLEM, CAPACITOR TO BIG OR WRONG?

Hi, its been a very long time since i taught myself electronics, about 45yrs lol, but none the less the theory is still the same, the why, a full wave bridge rectifier creates DC, but its what you would call very course DC, if you were to look at the DC via an oscilloscope you would see what you would call spurious emissions, the unwanted components from the AC input, these spurious emissions are collected by the smoothing capacitors and stored, which in turn gives an imposed voltage, a higher voltage than the applied voltage. As you will know, a true DC voltage from say a battery would have a completely flat line with no spurious, but because the bridge is supplied via an AC input which is sinusoidal, the bridge cannot fully create the flat line of DC, and hence the spurious output.
This higher voltage could well damage the capacitor in the final part of the circuit, so simply fit one exceeding the higher voltage being created, hope this helps.

Thank you very much for your detailed answer. So that's the reason I can read on the output side DC and as well AC voltage?
Today the big capacitor 100V / 120000uF has arrived.
I have connected it and tried a weld bed. It's only splattering, no welding possible. Disconnecting the cap and everything seems to be fine so far.