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Electricity Question

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Oct 8, 2006
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Electricity Question

12V and 3 loads

connected like

Load 3 <- Load 2 <- Load 1 +12V - Load 2
Load 3

So load 2 and 3 are connected the the (-) battery side
Load 1 is connected in series to the other 3 and the only connected to the positive side

What is the volt each load will get?
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a) You'll have to describe the loads better than you are, because RLC of the components, and any other drops are relevant;

b) I'm not sure exactly what your topology is; could you draw something in Paint and post it please.

c) What exactly is "12V"? A specific waveform? AC? DC? Do you want steady-state response, impulse response, what?

d) If the load is a 'battery', what is its internal resistance? (@ operating temperature) Or do you want it modelled as an 'ideal' battery?
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well it will be actually 19Vs and the loads are 12v Fans (the ones used in computers)

I was hoping to get atleast 8-9V for each without going out and buying resistors

2 worked well but its the 3rd i want to add it...
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Why don't you draw a picture of what you're trying to? I have absolutely no idea what your circuit looks like, and your description is brutal.
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killoverme wrote: I don't know i just want the 8-12V anyone know a way without connection resistors?
Any other nameplate data on those fans???

I really wouldn't advise the series configuration. You'd want to go with something like a LM341-12 (or some other part that's good for more than 500mA). Because if, for whatever reason, the rotor locks on one of the fans, you'll be exposing the other fans to the full 19V, which would also cause problems. Also, you could protect paralleled branches of the circuit with individual fuses.
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didn't think of that... so get resistors? lol. or capacitors...

its 12V 0.25A
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killoverme wrote: didn't think of that... so get resistors? lol. or capacitors...

its 12V 0.25A
Just use LM341-12's then -- they can handle 250mA no problem (prolly won't even need heatsinking). And forget the series/parallel stuff; just use a regulator for each fan.

Where does 19V come from anyways???
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where can i get LM341-12 in Toronto and how much are they average and how do u connect them
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killoverme wrote: where can i get LM341-12 in Toronto and how much are they average and how do u connect them
You'd have to look at the datasheet, but Vregs have 3 pins; Vin, Vref, and Vout.

Vref, you'd tie to your system ground. Vin, you'd connect to your source, and Vref you'd connect to your load.
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The question still stands: where is the 19V coming from? I thought it's a 12V source.
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its a laptop power supply adapter thingy.

I was using 12V as an example for easy division
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pitz wrote: You'd have to look at the datasheet, but Vregs have 3 pins; Vin, Vref, and Vout.

Vref, you'd tie to your system ground. Vin, you'd connect to your source, and Vref you'd connect to your load.
where can i get them though, resistors seem easier to get.
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killoverme wrote: where can i get them though, resistors seem easier to get.
No ideal, although any electronics supplier worth his salt should be able to obtain and sell you National Semi parts without any difficulty.
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Since the OP does not seem to be very knowledgeable about electronics, I would suggest getting resistors. Off the top of my head I would get 100 ohm variable resistors, that would allow you to tune the resistance so each fan gets the voltage you want. Get larger variable resistors and not the dinky ones since you might need to pass a few hundred millamps through them. I am guessing that a 100 ohm variable resistor rated for 1 watt is enough.

Also you can use diodes instead of resistors, each diode chews up about 0.7v regardless of current. If you need 9v you can put 4 diodes in series with the 12v and get about 9.2v. I think a 1n4002 would be good, they are dirt cheap, widely available and should be rated for about an amp.
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The problem with 100 ohm resistors is that they'll probably just burn out if you use the 1/4 Watt variant.
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toalan wrote: Since the OP does not seem to be very knowledgeable about electronics, I would suggest getting resistors. Off the top of my head I would get 100 ohm variable resistors, that would allow you to tune the resistance so each fan gets the voltage you want. Get larger variable resistors and not the dinky ones since you might need to pass a few hundred millamps through them. I am guessing that a 100 ohm variable resistor rated for 1 watt is enough.

Also you can use diodes instead of resistors, each diode chews up about 0.7v regardless of current. If you need 9v you can put 4 diodes in series with the 12v and get about 9.2v. I think a 1n4002 would be good, they are dirt cheap, widely available and should be rated for about an amp.
drain it with diodes eh lol didn't think of that.

We'll i figured i could actually do wiht 4 fans after all. wireless adaprter gets hot. too =/

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