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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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Unread postAuthor: Thrilla » Sun Jul 22, 2007 5:29 am

Marco321 wrote: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.


I have to say it really depends on the school and courses taken, at my school, we have ppl going into some serious sound studio stuff and created a really awesome studio in the school as a project. Yet my grade 11 physics teacher doesn't even know how my air conditioner works lol...
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Unread postAuthor: Scotty » Sun Jul 22, 2007 5:54 am

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[/quote]

ooooooooooooooooooooooohhhhhhhhhhhhhhhhoooooooooooooohhhhhhhhh.

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Unread postAuthor: VH_man » Sun Jul 22, 2007 10:53 am

haha. heare heare

i would use the voltage regulator. i used one on my robot once. it used 2 12V Lead-Acid batteries (2AH!!!!) and i needed full power for my drive motors, but halph of that for the rest of my electronics and servo's. too bad the electronics crapped out on me because i was too stupid to realize 2 amps was enough to fry them completely........... i should have used a fuse.....

i reccomend it highly. just get ready to solder.......
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Unread postAuthor: jimmy101 » Sun Jul 22, 2007 2:26 pm

Jumpin Jehosaphat wrote:To reduce voltage, you use a step down transformer.

Nope. A transformer won't do anything to step down the voltage of a battery, which is a DC source. Transformers don't work with DC, only AC.
("Switched DC" is really an AC signal not a DC.)

The easiest way to step down the voltage is with a pair of resistors or a potentiometer (variable resistor). It is called a "voltage divider". Cheap, simple but very inefficient if you want to take significant amounts of power at the lowered voltage.

A variation of the voltage divider is to use the device (the stungun) as one of the two resistors in the divider. Mush simpler and considerably more efficient way to use the batteries power. So, you just wire a resistor in series between the battery and the stun gun. If the stungun draws say 0.1A (WAG) and has an internal resistance of 10 ohms. (Another WAG but the primary coil of the step-up transformer is probably in the range of a couple ohms to a few tens of ohms.) So, a ~10 ohm resistor in series will cut the voltage supplied to the stun gun in half. Total power dissipated by the resistor ~0.1 watt, since power=(resistance)*(current)<sup>2</sup>. The most common resistors are rated for 1/4 watt so you should be OK.

Simply wire a candidate resistor between the battery and the battery contacts of the stun gun. Connect a voltage meter across the stungun's battery contacts. Hit the "fire" button on the stungun and note the voltage reading. If the voltage is still too high use a larger valued resistor. The tricky part will be finding the correct resistor value without frying another stun gun.

Thilla there is no such thing as a "... the 3 legged transistor, it turns excess voltage into heat, and has its own amp ratings" that does what you describe. I think you mean a voltage regulator IC (which looks like a power transistor.)

The voltage regulator approach suggested by singularity is probably the best way to go.
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Unread postAuthor: Thrilla » Sun Jul 22, 2007 10:12 pm

oops my bad lol :lol:
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Unread postAuthor: dongfang » Mon Jul 23, 2007 3:21 pm

Hey,

To convert a DC voltage to another lower voltage is easy. Just a resistor, or a transistorized regulator circuit .. or one of many other devices.

To increase DC voltage is harder. You will need a coil, possibly as a transformer. But it's not really hard. There are ICs that contain most of the circuit on the market; you have to add a coil or transformer, a transistor and some simple stuff.
The gadget that plugs into a car's cigarette lighter to give a laptop 18-19 volts is an example.

Regards
Soren
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Unread postAuthor: Spedy » Mon Jul 23, 2007 3:42 pm

A good way to drop voltage is a bunch of diodes, each one in series will eat 1 volt. so it would be like
9v
(-) Battery (+) _________________________________ + to circuit---
|
| - 1v- 1v - 1v
|__Diode___Diode__Diode___________________ 6 volts - to circuit---



Hope this helps :)
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Unread postAuthor: paaiyan » Mon Jul 23, 2007 5:46 pm

Here's a <a href="http://www.sciencebuddies.org/mentoring/project_ideas/Elec_p027.shtml">link</a> to a site that has a pretty good how-to for induction coils. After looking it over I think I'm going to make one, seems pretty easy really.

EDIT: It appears that if you took out the vibrator apparatus, you could make the project easier, but you'd only get a spark when it turned on or off. SO you could take that out and make it a much easier project, or leave it in and get a whole bunch of really big sparks, really fast.
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Unread postAuthor: Mr. Gopher Killer » Mon Jul 23, 2007 9:44 pm

man you guys are awsome! I am not to great when it comes electronics but i am learning a lot from reasurching all of your guys different methods. It looks like the voltage reg is the best way to bring down the voltage but it also looks like the hardest to hook up correctly. I like the doide way because it looks easy. I am disappointed right know because none of the radio shacks were I live carry any electronics parts, all they have is tv supplies or helo kitty ipods. I think i will just have to order them off there web site.
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 4:23 pm

Mr. Gopher plans to reduce the voltage of his battery to half of what it is intended to be used for, it seems like anything you try to do will get too hot after a few uses. I think the best thing to do would be to just purchase a rechargeable 9v battery. I'm not super sure about this, but wouldn't current be what fries a circuit in most cases rather than voltage? It seems to me that even at a lowered voltage he runs the risk of frying his circuit, if not starting a fire.
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Unread postAuthor: singularity » Thu Jul 26, 2007 4:33 pm

but the voltage reg can only source one amp in most cases and when voltage is reduced current is also reduced if the wiring is keep the same (remember ohms law?)for example if i have wires that have 100ohms resistance (100 ohms is way higher than what a normal wire would have but its just an example) if i put 18 volts into those wires the maximum amps i could get out of them would be 180mA now if i put 9 volts into the same wires i could only get 90mA. current=voltage/resistance, besides that circuit has some form of current limitation in it and if the same voltage is supplied the same amps will also be supplied due to the nature of the circuit
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Unread postAuthor: iknowmy3tables » Thu Jul 26, 2007 5:02 pm

you need an inverter, and then a transformer, I sudjest using multiple weaker batteries and wiring only a part to that component

fun fact: the military makes their own custom batteries that have two 12 volts inside, the socket on the out side has several holes so depending on the arrangement of the pins on the accessory's plug
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 5:11 pm

singularity wrote:but the voltage reg can only source one amp in most cases and when voltage is reduced current is also reduced if the wiring is keep the same (remember ohms law?)for example if i have wires that have 100ohms resistance (100 ohms is way higher than what a normal wire would have but its just an example) if i put 18 volts into those wires the maximum amps i could get out of them would be 180mA now if i put 9 volts into the same wires i could only get 90mA. current=voltage/resistance, besides that circuit has some form of current limitation in it and if the same voltage is supplied the same amps will also be supplied due to the nature of the circuit


Ugh, electronics can get so confusing. I'm just saying he should be careful, even if the current is reduced along with the voltage, one or the other may end up being too high for the circuit in the end. I don't see a reason to mess with batteries anyways it can be dangerous and it will doubtfully be efficient.
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Unread postAuthor: paaiyan » Thu Jul 26, 2007 5:15 pm

Jumpin Jehosaphat wrote:
singularity wrote:but the voltage reg can only source one amp in most cases and when voltage is reduced current is also reduced if the wiring is keep the same (remember ohms law?)for example if i have wires that have 100ohms resistance (100 ohms is way higher than what a normal wire would have but its just an example) if i put 18 volts into those wires the maximum amps i could get out of them would be 180mA now if i put 9 volts into the same wires i could only get 90mA. current=voltage/resistance, besides that circuit has some form of current limitation in it and if the same voltage is supplied the same amps will also be supplied due to the nature of the circuit


Ugh, electronics can get so confusing. I'm just saying he should be careful, even if the current is reduced along with the voltage, one or the other may end up being too high for the circuit in the end. I don't see a reason to mess with batteries anyways it can be dangerous and it will doubtfully be efficient.


Look guys. It's electricity. Electricity kills things. Be careful, end of story.
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Unread postAuthor: Jumpin Jehosaphat » Thu Jul 26, 2007 5:19 pm

Yay! Somebody gets what I'm trying to say.
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