Wiring helmet fans

[kibosh]

I'm getting ready to orer some stuff from allelectronics.com to wire a pair of fans in my Tusken, but I want to make sure I'm setting things up correctly. I plan on installing a 12VDC fan in the mouth to draw fresh air in, and another 12VDC fan on top to blow hot air out. I plan to power them with 3 9V batteries. I also want to add an on/off toggle switch.

Is this ok so far?

Now, to wire them is where I get confused. I've seen a few posts here about this, but I'm a visual learner. I think I want to wiring everything in series, correct, so I'd have a 24V load and a 27V power source? This is what I'm thinking:



Does this look correct?

On all the toggle switches I've seen, there are three connection posts. Does anything need to be connected to the third one? Do I need to find a switch with only two posts???

Thanks guys. I appreciate your expertise in this matter!

 

[PadawanLearner]

you're going to want to add a resistor to that or I'm pretty sure you'll burn through fans.
Granted, I don't know the specs of your fans...if you do the math you'll see that there's 3 volts unaccounted for. They don't just magically disappear.
You can use the resistor to not only limit the amps through your circuits to whatever is in tolerance for those fans but also take care of the last 3 volts.

I should also mention that you could put the fans in parallel and you'd be able to drop a 9 volt out of that circuit

 

[kibosh]

If the fans were in parallel, my load would be just 12V, correct? With 2 9V batteries, I'd then have an extra 6V though wouldn't I?

 

[stormtrooperguy]

i've always just done 1 9V battery to 1 12V fan. it's a bit underpower but still works fine.

 

[Barking Dragon]

I am running a 9v battery with a 12V fan and it runs just fine aswell. It last me for about 2 hours before it dies. I tried using rechargeable batteries but they just didn't long at all That I found out the hard way

 

[kibosh]

2 hours, huh? Man, I was hoping they'd last longer than that. Once I get my supplies, I'll test the speed with two batteries, and then test with 3 and chck the heat.

Thanks guys!

 

[WookieeGunner]

One small thing. You need to double check the switch, a lot of them will need you to have one wire on the center pin and one on an edge pin. The third wouldn't be used. A little technobabble to help you find a switch. An On/Off switch is called a single pole single throw switch (SPST). This is the typical two pin switch. Flip the switch in one direction, it makes a connection, in the other it doesn't. These are actually harder to find then you think. The more common is a single pole double throw. This is the type you have above. It is your classic A/B switch. They are more commone because all you have to do is not use one pin and you get an On/Off switch. The trick is that there are two major types of this switch, one that has two positions (left and right) and one with three (left, center, and right). You want on that just has two positions.

 

[kibosh]

Good to know! Thanks for the clarification on the switches.

 

[PadawanLearner]

If the fans were in parallel, my load would be just 12V, correct? With 2 9V batteries, I'd then have an extra 6V though wouldn't I?

that is correct. Your resistor would drop the remaining 6 volts. to determine the size of resistor you'd want to look at the tolerance levels for amps for those fans and use a number in there and plug it into V = I * R, or I guess in your case it would be R = V/I
Then you would want to multiple your 6 volts by whatever amperage you decided on to make sure you know the wattage of resistor you would need.

So...let's say it was .02 amps, you would have 6/.02 = 300
The wattage would then be .12
So you would want a resistor of 300 ohm's with a wattage of 120mWatts or greater.
Hope that helps, no it doesn't matter where in the circuit you put the resistor, but I would probably put it inbetween the switch and the fans.