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Author Topic: Doubling voltage of two 9V batteries in series? [OR high voltage]  (Read 1014 times)
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Hello everybody..
I'm trying to charge some capacitors two a voltage of about 36 volts. I intend to do this by connecting two 9V batteries in series and then using a voltage doubler to double that voltage..
so I should get 9 * 2 *2 = 36 Volts.
However,  voltage doubler will not work with a DC supply, so I believe I'll have to generate an AC signal from the DC output of the two batteries in series.
How do I achieve this?
I don't have much experience with electronics.. I assume one would have to use an oscillator circuit?

If there is a better way to achieve the same thing, I'd appreciate any suggestions..
thanks.
« Last Edit: October 01, 2011, 11:08:10 am by mahela007 » Logged

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If there is a better way to achieve the same thing, I'd appreciate any suggestions
Four 9V batteries in series?
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You could use a circuit called a charge pump:

http://en.wikipedia.org/wiki/Charge_pump

The References section of the above link has some good links to additional information.

For lower voltages, devices like the TC7660 can be used to double 5V to 10V, for example, but 36V is too high for all the devices I know of. You may have to build it out of discrete components.

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Four 9V batteries in series?

 smiley-wink I though of that.. but I don't want to have to buy sets of 4 9V batteries all the time. Also, the other way gives me an opportunity to learn more about electronics.

@RuggesCircuits

Thanks. I read the wikipedia article you referred to. So .. how do I build one?
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I though of that.. but I don't want to have to buy sets of 4 9V batteries all the time.

You will probably be buying sets of 2 9v batterys 2x+ times as often than using 4 in series. There is no free ride.   smiley-wink
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ok..
Erm, while we are on the same subject, would it be possible to construct a very high voltage capacitor charger (about 400V) with 9V batteries as the power source? Camera capacitor chargers do this but is it possible to build them out of discrete components? (for a reasonable price)

PS> Yes..I'm trying to build a coil gun  smiley-lol and disposable cameras aren't available where I live.
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Trying to run a coil gun from 9V batteries is going to have you running to the shop for new batteries every 5 nano seconds, if it will ever work.

9 V batteries are about the worst of all batteries when it comes to hw much juice they actually hold.
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If disposable cameras are not available where you live then you could possibly obtain a shoe-mounted flashgun and dismantle it to get the relevant circuitry.  Alternatively some wireless door bells contain strobe lights for use by deaf people; again these are a possible source of low-to-high DC voltage converters.  If you know nothing about electronics, starting by building dc converters is a big leap into the unknown.

With a couple of transistors, 4 resistors, a couple of capacitors, a small  230 to 9 volt transformer and a bridge rectifier you can certainly build a good simple high voltage DC power unit.  Not only will you learn a lot but you also stand the chance of wasting components when the dreaded magic smoke leaks out.
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Assuming your project includes an Arduino, you can set a PWM output pin to 50% i.e. analogWrite(128), then you don't need an oscillator, just a couple of transistors to buffer the signal. See attached. You won't quite get 36v from this arrangement because you'll lose around 4 * 0.7v in the diodes and the transistors, so more like 33v.

I would have suggested a 555 timer as the oscillator, but they are limited to 16v supply voltage.



* Scan 32.JPG (59.63 KB, 1653x1165 - viewed 15 times.)
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If you know nothing about electronics, starting by building dc converters is a big leap into the unknown.

Actually, I would say playing with high voltage while knowing nothing about electronics is good way to take a short trip to the morgue.

mahela007 - before you go down this road for building your coil gun, I strongly suggest you learn more about electronics first - then start studying (but not playing with) high voltage. High voltage electrical and electronic circuits are not toys to be played with. They require care, respect, and understanding, and even then you still might get injured.

As far as a coil gun is concerned, try building a "low-voltage" version first. I built a real simple one a long time ago using nothing more than 12 volts, some doorbell wire, a piece of wood and some tacks. Start at that level, then learn how to build an automatic switching system for the coils using the Arduino (honestly, one could do it without an Arduino - but the programmability option will open up some interesting opportunities you wouldn't have otherwise to "tune" the acceleration of the projectile).

Such a low voltage coil gun, properly tuned, should be able to shoot your projectile more than a few feet; heck, even my simple shade-tree electrician "coilgun" could launch my "projectile" (a cut-off nail) about 6 feet (and I only had 5 or 6 coils, and they weren't very big).

Once you have that perfected, you'll have the basics for the main triggering system for a larger, higher-voltage coil gun - and a better understanding of the control electronics, and perhaps (if you studied along the way), an appreciation for the dangers and complexities of high-voltage systems, and how to properly construct and experiment so that you don't die along the way.
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Ok.. so the 9V battery option is out.

With a couple of transistors, 4 resistors, a couple of capacitors, a small  230 to 9 volt transformer and a bridge rectifier you can certainly build a good simple high voltage DC power unit.  Not only will you learn a lot but you also stand the chance of wasting components when the dreaded magic smoke leaks out.
I assume that would involve using the transformer 'backwards".. i.e as a step-up transformer?

If you know nothing about electronics, starting by building dc converters is a big leap into the unknown.

Actually, I would say playing with high voltage while knowing nothing about electronics is good way to take a short trip to the morgue.

mahela007 - before you go down this road for building your coil gun, I strongly suggest you learn more about electronics first - then start studying (but not playing with) high voltage. High voltage electrical and electronic circuits are not toys to be played with. They require care, respect, and understanding, and even then you still might get injured.

As far as a coil gun is concerned, try building a "low-voltage" version first. I built a real simple one a long time ago using nothing more than 12 volts, some doorbell wire, a piece of wood and some tacks. Start at that level, then learn how to build an automatic switching system for the coils using the Arduino (honestly, one could do it without an Arduino - but the programmability option will open up some interesting opportunities you wouldn't have otherwise to "tune" the acceleration of the projectile).

Such a low voltage coil gun, properly tuned, should be able to shoot your projectile more than a few feet; heck, even my simple shade-tree electrician "coilgun" could launch my "projectile" (a cut-off nail) about 6 feet (and I only had 5 or 6 coils, and they weren't very big).

Once you have that perfected, you'll have the basics for the main triggering system for a larger, higher-voltage coil gun - and a better understanding of the control electronics, and perhaps (if you studied along the way), an appreciation for the dangers and complexities of high-voltage systems, and how to properly construct and experiment so that you don't die along the way.
You're probably right.. So I'll stick to a moderate voltage for now. Once it works, I'll start improving it for higher voltage..
I have a 20V power supply but I believe 20V is a bit too low.. so I'm going to double that. (40 Volts isn't very dangerous, is it? )
Again, I'm going to have to ask you guys for the appropriate circuit..  smiley-lol


BTW: Could you send me a private message with some more details about your coilgun? (to avoid cluttering up this thread) I want to compare it against my design..
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