# Confused about wiring fans in series or parallel and how they draw power?

#### NewShockerGuy

##### Gawd
I'm not undestanding this as far as wiring my fans up.

I have 3 fans that I want to run off a solar panel that is putting out 5watts of power and is rated at 12v. The raw output of the solar panel is up to 21v and when I hook a load up to it, IE: A fan it significantly drops down in voltage...

My problem is this. When the solar panel is putting out 19v of power when I hook one single 120mm fan up to it, it drops the voltage down to about 6-7v that I can read from my multimeter.

So I figured if I wire two 120mm fans in parallel but the problem is that the solar panel doesn't even spin the fans.

IF however I wire the two 120mm fans in series with each other.. postivie to negative, then postive to positive wire on the solar panel and ground to ground I see that the panel then drops down to around 14-15 volts...

If I wire 3 fans in series then the voltage goes to about 17v.... and they all spin.

So I guess my question is why does the voltage increase and all the fans work when wired in series rather than parallel?

I know when you wire batteries in series, you increase the voltage but keep the same AH, and then when you wire them in parallel the voltage stays the same but the AH increases... So in terms of fans wired in series and parallel I guess I'm confused about how they draw power.

I thought by wiring the fans in series it would lower the voltage of the solar panel to around 12v's but it didn't and the solar panel put out around 16-17v to the fans, which is going to be too much in the long run I think and make them die faster...etc. Just wondering what I can do to get the fans to run at 12v and bring the panel down in voltage a little bit.

Thanks,
-Nigel

If you wire it in parallel, then each is tapping into the source independently so each will draw the full 12v power. I am assuming maybe wrongly that each of your fans are 12v power consumers. Anyways, the source is 21v total. If each fan draws 12v, then all three equals 36v.

If you draw it in series, then it is a trickle down economics effects where one device uses what it needs and passes the remaining power along. So it has to start out at a higher voltage in order to compansate for the last remaining fan. By the time the reducing voltage hits the last fan, it should be equal to 12v!? hehe

I am just guessing so just something to think about.

I just took two fans that are wired directly to 5v. Unfortunately, they are in parallel so each fan is getting 2.5v if I am not mistaken. Very weak.

What I did was separated each and gave each its own source of approximately 8v so now each is about 3 times stronger.

My problem is this. When the solar panel is putting out 19v of power when I hook one single 120mm fan up to it, it drops the voltage down to about 6-7v that I can read from my multimeter.

The output resistance of the solar panel is not zero. So if the fan draws 100mA, that means the output resistance of the panel is 19v-7v/100mA = 120 ohms

IF however I wire the two 120mm fans in series with each other.. postivie to negative, then postive to positive wire on the solar panel and ground to ground I see that the panel then drops down to around 14-15 volts...

If the output resistance and each fan is 100ohm, and they are in series, it is a voltage divider and each would get a third of the voltage. So 7V dropped from the panel leaves 14V for each fan, 7V the first, 7V the second- with constant current.

If I wire 3 fans in series then the voltage goes to about 17v.... and they all spin.
Same as above

So I guess my question is why does the voltage increase and all the fans work when wired in series rather than parallel?
I say in parallel they are drawing too much current and so the rail is dropping from the output resistance of the solar panel.

Just wondering what I can do to get the fans to run at 12v and bring the panel down in voltage a little bit.

Use an LDO with enough output current for all the fans you need.