Capacitive step-down transformer ...

[TinselKoala]

It's how you double the effective working voltage rating. Say you have one 330 uF cap with a rating of 200 V, but your circuit might be making spikes above that voltage and you don't want to puncture your dielectric. So you put two caps in series: This doubles the working voltage but, of course, halves the total capacitance. So you put two series strings in parallel, as in the circuit diagram above. 4 identical caps, series-parallel == the same capacitance but at twice the working voltage...so the arrangement can hold 4 times the energy of a single 330 uF cap without fear of puncture. Energy on a cap goes as the square of voltage: E= (CV^2)/2

It's a common technique: stacking caps in various ways to fulfill a voltage and or capacitance requirement. With good quality, identical, capacitors it usually works out well...if you have the physical room. Of course, a single cap of the correct rating and type would probably have lower overall losses and ESR and self-inductance than a bank of sub-capacitors, and this might be important to a particular design. But series-parallel cap banks are capable of great tricks: See Marx Bank for example.

[FatBird]

All he is doing is using capacitors as NON HEATING resistors to drop the wall voltage down to what he wants.

Xc = 1/2 Pi F C      (Reciprocal of  6.28  x  Freq  x  Capacitance)

The Caps MUST BE AC Rated, like Microwave Oven Caps, Electric Motor Caps, etc.  Electric Motor Caps might be best because they have the highest capacitance.

So he just connects different caps in series & parallel to get the right impedance, which gives him the right voltage at his fuell cell.

In fact, WHY EVEN USE A RECTIFIER?  H2O Cells work GREAT on AC too.

VERY CLEVER IDEA!!  Because the circuit presents a capacitive reactance, his home Electric Meter is probably reading less than he is really using!!!

CAUTION:  This type of circuit can present a Dangerous Shock Hazard because there isn't any Isolation from the Wall Voltage.  BE CAREFUL!

.

[BEP]

You are using these capacitor networks in an A.C. application.

You have three options:

1. Wear protective goggles when power is applied.
2. Connect the series strings of capacitors so the polarities oppose. i.e., connect the negative poles together and use the positive poles for ALL other connections. Plus, follow rule #1.
3. Toss a coin. Without understanding how these things actually work it may work for a while without exploding. It may not.


The only electrolytic capacitors designed for use in A.C. circuits, without exploding, either use design that prevents the erosion of the dielectric during reverse polarity charges -or- is actually two, or multiples of two, electrolytic capacitors in one can connect as in #2 above.

Be safe.

BTW: If you use the series circuit to step voltage down, it isn't a Capacitor Transformer. It is a Capacitive Voltage Divider and an excellent tool under common use.

[DeepCut]

Thanks Tinsel, FB and BEP

BTW, i'm not using it from the wall, i'm using it to stepdown output from my little induction generator, which is putting out 200-250V at about .030 amps.


Thanks again for help,

Gary.

[TinselKoala]

Heh...BEP is totally right, I didn't even consider that someone might use a polarized electrolytic capacitor in this kind of application. For AC from the wall you would definitely want to use oil-paper types, the big cans with no polarity markings. The photo above appears to show some polarized electrolytics (the small bundle)....be very careful.
Speaking as one who has blown up many capacitors over the years, I can tell you that even a small electrolytic can explode violently when given a strong reverse pulse. The can flies off like a bullet and the foil inside unrolls like a party favor, and if your eyeball happens to be in the way....ouch.

I try to select cap working voltages at least twice the anticipated peak circuit voltage. Depending on the total capacity, a puncture can be serious, or not so much. That is, if you short-circuit 30 mA at 220 V, (no capacitance) that's no big deal. But if a single 100 uF cap in a 10,000 uF parallel bank shorts while the bank is charged to 220 V with that same power supply... stand well back.