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fast cap bank charger

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josh1234

Wed Aug 01 2012, 12:31PM

Registered Member #5969 Joined: Mon Jul 30 2012, 09:27PM
Location: ringwood
Posts: 14

could i use a simple 12vdc to 240vac inverter and then rectify the output to make a fast cap bank charger you could make a high power output 150w in a small package

blackgrunge

Wed Aug 01 2012, 04:58PM

Registered Member #1889 Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55

It depends on voltage you want to charge the capacitor bank at. The caps I was using for my design were rated for 450v so I was charging them to ~360v off of 120v mains power. So obviously if you need to charge your caps at above ~240v you would need some sort of voltage multiplying rectifier. If you're trying to charge your caps at 240vdc then at 150w you need diodes in your rectifier rated for at least 240v and ~1amp.

I assume if you need to use an inverter then you are trying to charge you cap bank with a car battery which I would advise against since the more you deplete the battery the lower the voltage is going to be unless you use a car battery voltage regulator (which are ~$20). Honestly, you would be much better off charging your cap bank off of mains power with a step up or step down transformer it's much simpler and much cheaper (no inverter and no voltage regulator).

Ben Solon

Wed Aug 01 2012, 06:02PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

Or if you are trying to be semi portable, a smps dcdc converter is a much better option. A couple hundred watts is easily acomplished without a bulky inverter, and the best part is that it can be regulated to the volt.

Yanom

Thu Aug 02 2012, 06:56PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

I built a CW circuit that gives me ~300v and ~600v outputs from the 120VAC wall socket.

josh1234

Thu Aug 02 2012, 06:59PM

Registered Member #5969 Joined: Mon Jul 30 2012, 09:27PM
Location: ringwood
Posts: 14

do you have any circuit diagrams for a good smps dc/dc converter that i could use to charge a cap bank

DerAlbi

Fri Aug 03 2012, 07:16AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Hi guys

I am currently thinking about designing a microcontroller based SMPS in fullbridge configuration. I try to get 600W out of 24V. Target voltage is about 400V. With this Voltage i use a stepdown topology to charge the Capacitor with constant _Power_, This should ease the controll of the fullbridge due to constant load operation and should charge any capbank in no time

But: building an efficient topology is very hard! I would like to utilize Zero Voltage Switching, however this is not easyly done with microcontroller since sensing the voltage transition is not easy.

if someone would love to help... this would be a goog community project

Harry

Fri Aug 03 2012, 09:02AM

Registered Member #4081 Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139

Try the ZVS (Mazzili) driver, it's very efficient and powerful. You'll have to wind your own transformer though round a ferrite core.

Forty

Fri Aug 03 2012, 02:25PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

to answer your question: Yes. that should work.
rectified 240ac will give you a peak dc voltage of about 340v, so as long as your caps are rated higher than that you should be alright.

I couldn't find any dc-dc converters that gave 300+ volts(from a =< 24v input) at a decent power.

The mazilli circuit does make a powerful charger but it requires some sort of regulation and auto turn off (something I haven't quite found a reliable method for) if you don't want to watch the voltage and shut it off manually

blackgrunge

Fri Aug 03 2012, 03:40PM

Registered Member #1889 Joined: Mon Dec 29 2008, 07:36AM
Location:
Posts: 55

To be honest, it's just not practical to charge off of a 12v or even 24v dc source. At 300w were talking about 12.5 amps @ 24v or 25amps @ 12v input and to build a non-commercial dc-dc converter at those sort of power levels is going to expensive and difficult to construct. Plus you have the problem of constructing heat sinks to dissipate the heat generated by the switching

I guess it boils down to how bad you want to charge off of a battery. There are commercial options out there (for instance at lowes) for a ~300w DC-AC converter that you could then rectify+mulitply (depending on need) the output of that.

If you're wanting a circuit schematic that charges a capacitor bank from a battery you're going to be hard pressed to find a cookie cutter example out there. What your wanting is a very unique application of a boost converter. You haven't really given us what voltage you want to charge your cap bank to so there's only a limited amount of help we can provide with such limited information.

ConKbot of Doom

Fri Aug 03 2012, 09:00PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

On candlepowerforums, Ive seen someone steal the ~300VDC bus from an inverter to power a ballast that required a similar DC voltage to run a short arc (maybe UHP) bulb off of a battery.

It all depends on the inverter though. Some push/pull a modified sine wave at 12v right into a chunky transformer, some use a DC/DC to get an appropriate bus voltage and output the 120/240VAC directly from the AC line. (PWMed and filtered for pure sine, stepped and minimal filtering for modified sine)

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