How do you control voltage?

Question

I want to control the amount of volts i am using for my science fair...for example if I want a constant 45 volts how would I do that? is there A device I can conect to like 6 9volt batteries that would allow a constant output of 45 volts? please include the names of any devices and the websites where they can be found....thx

Answer 1

It's called a voltage regulator. 45V is an already difficult voltage to deal with. While not lethal, it can already hurt you if you touch it. Few electronic circuits operated on 45V or more will tolerate abuse, so you have to be careful and also have a few spares of your parts, just in case.

I would probably use three 15V regulators in series, i.e. two 9V batteries plus a 15V regulator like the 7815 to make stable 15V and then use three of these circuits in series.

http://www.onsemi.com/pub/Collateral/MC7800-D.PDF

Don't forget the capacitors on input and output! They are important.

And keep in mind that the regulator has a quiescent current which will drain your batteries even while you are not using it! A typical 9V battery will have 200mAh or so. With the regulator needing roughly 5mA, it will be empty in roughly 40 hours!

Answer 2

You can connect six 9V batteries (properly) in series to get 45 volts. Keep in mind that the maximum current from a 9 Volt battery (or a string of them in series) is only a few tenths of an ampere.

You can also buy an AC-to-DC converter, more commonly known as a, "power supply". 48Volt DC power supplies are common. You might even get one on the surplus market for under US$50. Google "surplus electronics" and search the various online stores.

You could also make your own 40 Volt DC power supply, but it sounds like you'll have enough on your hands with the rest of the science fair project, itself.

Good luck.

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Answer 3

As a previous responder suggested, it would be helpful to know if you need the 45 volts as a power supply (and how much current do you expect to need) or a voltage "reference" where current requirements might be lower.

In any case, if you don't need it to be a super accurate reference, you can use a small three terminal regulator and "float" it on a zener diode of the correct voltage to get to 45 volts (i.e. if you use say a 12 volt regulator, then you'd need a zener of around 33 volts). Look up "series regulator" or "series pass" regulator for more info.

Answer 4

Voltage adds when sources are connected in series. For example, if you need 6 volts, you can connect four 1.5 volt batteries in series. If you don't know what a series connection is you can read about it here http://en.wikipedia.org/wiki/Series_circuits#Series_circuits
I think it would be best to ask a science teacher for a DC power supply that you plug in and can adjust. I'm sure they have one somewhere in the school.

Answer 5

you can use a resistance or a varible resistance.
you have to check de voltage with a multimeter, you say that it need to be 45 volts, well, in you dont have a voltage source, conect batteries in series put the variable resistance and measure the ouput, you can change resistance of the variable resistance until you have 45 volts.
good luck!

Answer 6

Although it probably doesn't help you, at least as far as your question is concerened, I must point out that a previous correspondent's "the maximum current from a 9 Volt battery (or a string of them in series) is only a few tenths of an ampere" is utter rubbish.

Answer 7

well I could probably help you out, but I'm gonna need some more details. Why do you need exactly 45 volts and why does it have to be constant?

Answer 8

They make a variable voltage transformer, which would be much more reliable than trusting batteries to last. Radio Shack used to sell them, but I'm sure you could find something similar online.

Answer 9

It is a resistor; I = V/R , so in effect both.