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How do you reduce battery voltage?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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How do you reduce battery voltage?

Unread postAuthor: Mr. Gopher Killer » Sat Jul 21, 2007 9:17 pm

I have ben building an combustion cannon that uses a cordless ryobe drill handle and rechargeable battery. The problem is the batteries for the ryobe go anywere from 18-21 volts depending on how good there charged. For running a fan it is not really a problem because it is good up to 15 volts and i don't run it that long any ways, but for stun guns the 18 volt battery is way to powerful. I have just fried two stun guns with about 10 shots. I was wondering if there would be an easy way to bring the voltage coming from the battery down to 9volts so it wouldn't fry a stun gun?
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Unread postAuthor: Jumpin Jehosaphat » Sat Jul 21, 2007 9:22 pm

To reduce voltage, you use a step down transformer.
This is the same sort of device used in AC adapters. One using the exact voltages you want may not be commercially available. You may be able to make one on your own, I've never done it so I can't explain how. Your best bet would be to just use a proper battery in the first place.
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Unread postAuthor: Thrilla » Sat Jul 21, 2007 9:52 pm

Use a transistor, they sell all sorts of different voltage/amperage ones at any big electronic stores. It's a small chip, I've used one to reduce 9v to 5v for charging USB devices.
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Unread postAuthor: Marco321 » Sat Jul 21, 2007 9:54 pm

You could try to use some resistors. But it is basically impossible to lower DC voltage.
You could scrap the stun gun and make an induction coil, so you don't have to fiddle with the voltage, they take any DC voltage and make a nice spark.
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Unread postAuthor: Mr. Gopher Killer » Sat Jul 21, 2007 10:01 pm

How do you make an induction coil i have never heard of anyone using one befor?
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Unread postAuthor: VH_man » Sat Jul 21, 2007 10:08 pm

basically, its a little coil that you pulse 12 volts through

with a HUGE coil wrapped aorund it. this creates a huge amperage drop but an amazing voltage spike, making a spark!

yay. i know alot of old TV's have them in them, im not sure what they exactly are however. if youre making your own, make it as precise as possible. (no meshed wires, each winding right next to the previous winding...)
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Unread postAuthor: Marco321 » Sat Jul 21, 2007 10:24 pm

We use them at school, its very amazing. It basically a step-up transformer, since a transformer needs AC current to work, you need to simulate it if you use DC. Use a doorbell, get the hammer thing that hits the bell, connect a current to it, then to the coil. This creates a moving magnetic field which will generate your sparks. But be very careful, it will be very painful if you shock yourself.
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Unread postAuthor: iPaintball » Sat Jul 21, 2007 10:30 pm

TVs use flyback transformers. They are a little more complicated to use because the need to operate at high frequencies to function properly, so yuo need to make a driver circuit. An easier method be an ignition coil. When DC voltage is supplied then removed, like VH said, It creates an amperage drop, but a tremendous voltage spike to be stored. This voltage can be used to create a spark. When they are operating at high frequencies, the produce a constant arc.
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Unread postAuthor: singularity » Sat Jul 21, 2007 10:37 pm

why not just use a voltage reg, you can buy them at radio shack the two most common are the lm7805 (a 5v regulator) and the lm7812 (a 12v regulator) they should only cost a dollar or two and are incredibly simple to wire up. there is also an adjustable reg, i dont know the part number off hand but im thinking its a lm317 its slightly more complicated to wire but still considered a simple circuit.

and for your information it is very easy to lower DC voltage
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Unread postAuthor: Marco321 » Sat Jul 21, 2007 10:47 pm

and for your information it is very easy to lower DC voltage


How might you do that? we learned in physics that its very hard.

why not just use a voltage reg, you can buy them at radio shack the two most common are the lm7805 (a 5v regulator) and the lm7812 (a 12v regulator) they should only cost a dollar or two and are incredibly simple to wire up. there is also an adjustable reg, i dont know the part number off hand but im thinking its a lm317 its slightly more complicated to wire but still considered a simple circuit.


Do these plug into the wall?
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Unread postAuthor: singularity » Sat Jul 21, 2007 11:19 pm

VOLTAGE REGULATORS they are small 3 pin ICs that are dirt cheap can get then at almost any electronics shop (radio shack) they do not plug into the wall you have three pins V in GND and V out basically you put any voltage slightly above the voltage the reg is set to and below 34v and you get clean regulated DC voltage out (for example in a 12v reg you could put any where between 14-34V DC in and you would always get 12V DC out). and it is very easy to lower DC voltage it can be done with a pulse generator (ne555) a transistor and a capacitor, but it is more cost effective to use a reg

ps- i assume your in 9th grade (going into 10th soon) correct? you have learned nothing in school at school all they give you is a taste so you figure out what you like so you can study it more deeply later in life. i am in 10th grade and i can tell you sitting in school hasn't done anything other than slow me down i mean i have built co2 lasers, hover crafts, remote detonators, em accelerators, hv arc generators, cannons, programed micro controller, rebuilt a car, built computers, i can bypass any blocking software, gain access to passwords, i have made assorted explosive compounds, and i can literally fix anything i can find... and thats only scratching the surface
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Unread postAuthor: Thrilla » Sun Jul 22, 2007 12:25 am

singularity wrote:ps- i assume your in 9th grade (going into 10th soon) correct? you have learned nothing in school at school all they give you is a taste so you figure out what you like so you can study it more deeply later in life. i am in 10th grade and i can tell you sitting in school hasn't done anything other than slow me down i mean i have built co2 lasers, hover crafts, remote detonators, em accelerators, hv arc generators, cannons, programed micro controller, rebuilt a car, built computers, i can bypass any blocking software, gain access to passwords, i have made assorted explosive compounds, and i can literally fix anything i can find... and thats only scratching the surface


lol partially agreed, school has a lot of useless stuff, but there are useful info that's hard to obtain through google :wink: Upon assumption that you built your project through plans widely available, try building something entirely new :idea: I'm working on two inventions from ground zero lol, using the stuff i've learned in school.

So yea... I wouldn't just say school slows you down, it only slows you down if you let it hehehe. (ie. I bulid air conditioners in metalshop during physics class)


Anyway, back on topic:
The easiest way: the 3 legged transistor, it turns excess voltage into heat, and has its own amp ratings
The efficient way: hook up some rechargable 1.2v batteries to make 9v.
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Unread postAuthor: Mr. Gopher Killer » Sun Jul 22, 2007 12:45 am

so i could put a voltage reg on the positive wire from the battery to the positive on the stun gun and then put the negitive wire from the stun gun to the negitive on the battery?
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Unread postAuthor: Thrilla » Sun Jul 22, 2007 2:29 am

Here's a link to someone's iPod charger that reduces voltage from 6v to 5v, you can use the diagram and equation in there, the rest is just different component ratings.

Be sure to put a heatsink on the chip if it gets too hot, like stated before, they burn extra voltages in the form of heat.

http://www.reuk.co.uk/print.php?article=Solar-iPod-Charger.htm
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Unread postAuthor: Marco321 » Sun Jul 22, 2007 4:36 am

Hey
I had no idea about that stuff from school. I'm in Year 12 physics in Aus which is the last year of school. We were basically told only way to change DC voltage is to convert to AC and use a transformer. Come to the think of it i have come across one of the things you are talking about, i used it to invert a DC current, no idea why i didn't remember lol.

But yeah, school does only just scratch the surface.
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