3 Stage Voltage Multiplier

[Alphabetical]

I am building a portable high voltage (around 350VDC) source, and I need to know what values of capacitors and diodes should I use. I plan on using a DC to AC inverter of around 500 watts (for a high ceiling) and the output directly into the voltage multiplier. A 3 stage Voltage Multiplier should generate around 360VDC if I am correct, and this will be sufficient. However, I need to know what kind of diodes and capacitors to use.

Would this Diagram of a voltage multiplier be correct but without the last set of Diodes/Capacitors?
**broken link removed**

 

[colin55]

What frequency are you using?

 

[Alphabetical]

60Hz, straight from the DC-AC converter.

 

[Sceadwian]

The capacitors in particular and the diodes in that kind of voltage multiplier are under incredible stress under load, what's your desired output power?

 

[Alphabetical]

The capacitors in particular and the diodes in that kind of voltage multiplier are under incredible stress under load, what's your desired output power?

What would be reasonable? Perhaps 250ma?

For the Diodes, I would want something like 400VDC and a few amps? As for the capacitors, If you give me a general idea of what kind of capacitance I will need, it would be greatly appreciated.

 

[Speakerguy]

A 3 stage Voltage Multiplier should generate around 360VDC if I am correct,

Sorry, this is wrong. 120VAC is about 170VDC when rectified/filtered. So two stages would be ~340VDC, three stages would be ~510V.

Personally I would just find an isolation style voltage transformer with dual primaries and dual secondaries. Use the primaries in parallel, and the secondaries in series to get 240VAC. Then use a bridge rectifier to full wave rectify this, and then your bulk filter caps. This will get you around 340VDC. The capacitors in this arrangement will be much, much smaller than in the voltage multiplier circuit for the same current. This is because the ripple current frequency will be 4x that of the ripple current in a voltage doubler setup.

 

[Sceadwian]

340-540V DC under no or extrmely light loads, draw any current from it and it will quickly equalize to the normal VAC expected, especially from a multi stage voltage booster. You want a few amps, I don't think voltage multipliers like this are really a good idea because the ripple currents the capacitors undergo is WAY above what normal capacitors can be expected to give. You're better off using a proper transformer, I doubt any capacitive solution would survive under those loads unless you used something like motor run capacitors, and a single one of those is going to be bigger than the transformer required.

 

[Alphabetical]

Your idea is excellent, although I cannot find a transformer with a price I can afford, nor are they parallel. A 2 stage voltage multiplier will have to do, unless we can find a cheap xformer.

 

[Sceadwian]

Alphabetical, you missed an important part of my post. The capacitors required for that much current are going to be motor run capacitors and are going to be larger and cost MORE than the transformer that does the same thing in the first place. We're not talking bulk cheap power supply filter caps here, they'll be essentially passing 100% ripple current under heavy load. Most caps simply aren't designed for that. The ones that are are overbuilt and cost more because of it.

You said 250ma rating for the caps, and then stated a few amps for the diodes, which doesn't make sense because the caps will be passing every bit of current that goes through the multiplier.

 

[Alphabetical]

What could I do then? Any other way to go from 12VDC (from a SLA battery) to voltages upwards of 400VDC?

 

[Sceadwian]

Find an appropriate transformer. Voltage multipliers handle load changes HORRIBLY bad anyways especially with any increased number of stages.

 

[Alphabetical]

What about a DC DC boost converter?

 

[Sceadwian]

Again, probably as or more expensive than a transformer for that power level. Why do you think power inverters like UPS's still tend to use transformers? They're damn good at what they do =) Exactly how much current do you need on the high voltage side?

 

[Alphabetical]

I dont think I even need that much current. Less than 50ma, as I need the voltage, not the current.

 

[Sceadwian]

Then why are you worried about cost so much? All you need is a transformer with a 3-1 turns ratio, and 450 volt rated insulation, it only needs to be rated for about 20VA for that output current. It's not gonna be big. You could probably wind it yourself if you have a transformer core to work with. You could rewind just about an 20-30VA core with the proper insulated wire at the right turns ratio.

 

[Alphabetical]

What if I built a inverter (DC to AC) and built it for 360ish VAC?

 

[Alphabetical]

Found this:
Oatley Electronics
I could use that and configure it for 240VAC.

Anyways though, what values for the capacitors and diodes for the voltage multiplier? I can build the kit for the end product, but experiment with the voltage multiplier.

 

[Alphabetical]

I think that kit would be the best way to go. All I need is a 240VAC to 8V-0-8V transformer.

EDIT: Forget the kit, I will buy a 12vdc to 240vac inverter, that way it is already built and working.

 

[Alphabetical]

Found this:
**broken link removed**

Would this be a good choice?

 

[JeffreyHLewis]

Please note that when deriving higher voltages, the application will dictate the type of power supply design. Voltage doubler /tripler...etc, are commonly seen used for high impedance usually capacitive loaded circuits.(the last generation CRT high voltage supplies were hybrid doubler-flyback driven) Applications like photomultiplier tubs, Avalanche Pin Photodiode bias or image intensifier drive, all have high voltage requirements with minimal average current draw. The voltage doubler circuit will "fall on it's nose" when you load it too heavily and the instantaneous current capacity is limited to the components used and the operating frequency. Please check your maximum load current and select the proper design topology for your power supply. This will save you lots of headaches later on.
As Sceadwian has indicated above, there are many designs available to acheive your goal at a minimal cost with best performance.