# Noob question, 12v fan on multiple 9v batt

#### Dosmastr

Joined Jul 3, 2020
17
Hi Everyone,

I'm trying to rig up some small to 12v blower fans on my 2yo's bike helmet. Running them off a 9v batt isn't moving much air... I know one can double the pathways to cut the current in half... Is there a way I can rig up 4 9v in series to get 36v, and then split that through 3 fans (12v each).

I couldn't find any charge pump that took 9v and put out 12v.

Suggestions solicited!

#### jpanhalt

Joined Jan 18, 2008
11,088
9-V batteries won't last very long due to their low capacity. You'll probably have better luck with 3 or 4 rechargeable lithium ion batteries in series and fans in parallel. Or, just run a plug from the propulsion battery(s). Like pilots, your child will have to plug in his headset.

#### Dosmastr

Joined Jul 3, 2020
17
Yeah I got some alkaline 9v just for proof of concept, I'll get some li ion rechargeable ones if I can make this pan out.

Running the 36v source in parallel will drop the current but won't the whole circuit still be at 36v?

I would just run 2 fans off the 4 Batts while using resistance to bring it down to 12v but does the resistance just sink/waste the power?

No battery on propulsion yet, just a balance bike but a power wheels might be in the cards for Christmas!

#### Audioguru again

Joined Oct 21, 2019
2,998
A series resistance wastes battery power by heating the resistor. You do not want more heat.
Lithium batteries might explode or catch on fire in an accident!

#### jpanhalt

Joined Jan 18, 2008
11,088
I was not referring to the fans in parallel on 36V. That will likely burnt them out. What I meant was that 3 or 4 lithium-ion batteries in series will give at least 12 volt or more (depending on the chemistry).

#### Audioguru again

Joined Oct 21, 2019
2,998
The motors on the fans produce heat and the batteries also produce heat.
Carrying the weight of fans and batteries also produces heat.

#### Tonyr1084

Joined Sep 24, 2015
5,865
HERE are some 5 volt fans.

Keep in mind that moving air requires power. As much power as you supply you'll move that much air. A 9V battery isn't powerful. Back in my high school days we called that common 9V battery a "Transistor" battery. Not because it had transistors, but because it had the voltage needed to switch them on. They were never intended to be a source of high power. If you want to move more air you're going to need more power.

#### Audioguru again

Joined Oct 21, 2019
2,998
Put a huge solar panel on top of the kid's helmet to power the fans.
Oh, maybe a pretty big windmill can power the fans?

#### Tonyr1084

Joined Sep 24, 2015
5,865
Put a huge solar panel on top of the kid's helmet to power the fans.
Oh, maybe a pretty big windmill can power the fans?
NOOOOH! Put a functioning air scoop. The faster he pedals the cooler his brain.

OK, sorry. We're getting a little silly. Has to do with CV19 and being sequestered in my basement.

#### Dosmastr

Joined Jul 3, 2020
17
HERE are some 5 volt fans.

Keep in mind that moving air requires power. As much power as you supply you'll move that much air. A 9V battery isn't powerful. Back in my high school days we called that common 9V battery a "Transistor" battery. Not because it had transistors, but because it had the voltage needed to switch them on. They were never intended to be a source of high power. If you want to move more air you're going to need more power.
Im with you, but since the plan was using a 9v or 2 or 3 I got 12v blower fans, they are only 40mm
https://www.amazon.com/gp/aw/d/B079BMX2S6?psc=1&ref=ppx_pop_mob_b_asin_title

#### Dosmastr

Joined Jul 3, 2020
17
If only the laws of physics allowed voltage to be split like current...

#### Audioguru again

Joined Oct 21, 2019
2,998
Since Amazon and their sellers know nothing about electrical products there is not one word about electric current or noise level.
The high speed fans will probably scream like a remote controlled drone up close.

#### Dosmastr

Joined Jul 3, 2020
17
Since Amazon and their sellers know nothing about electrical products there is not one word about electric current or noise level.
The high speed fans will probably scream like a remote controlled drone up close.
Yeah the blower doesn't say Even on the side how many amps it pulls.
It doesn't make much noise at all but I'm running at it only 3/4 voltage, That said I just ran 18v across it and it was still reasonably quiet though who knows how long lived it would be

#### Dosmastr

Joined Jul 3, 2020
17
Pardon my ignorance here but running at 18v at 200 mA scale on my DMM, it's reading 1.1 for current...
And 0.6 same scale at 9v

1.1mA seems too low is it 11mA?

#### Dosmastr

Joined Jul 3, 2020
17
Oh whoops, trying to measure amps in circuit meant for 2 Batts I shorted one, 50mA, 46. 43. 41. $hit!! (Pulls plug!) Running 2 9v in series about 10min later it's at 17v and 5 min later down at 16.75. Golly I though I'd get a couple hours on a full set at least! Thread Starter #### Dosmastr Joined Jul 3, 2020 17 Oh whoops, trying to measure amps in circuit meant for 2 Batts I shorted one, 50mA, 46. 43. 41.$hit!! (Pulls plug!)

Running 2 9v in series about 10min later it's at 17v and 5 min later down at 16.75. Golly I though I'd get a couple hours on a full set at least!

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#### djsfantasi

Joined Apr 11, 2010
7,633
Oh whoops, trying to measure amps in circuit meant for 2 Batts I shorted one, 50mA, 46. 43. 41. \$hit!! (Pulls plug!)

Running 2 9v in series about 10min later it's at 17v and 5 min later down at 16.75. Golly I though I'd get a couple hours on a full set at least!
That’s the point @jpanhalt made in post #2. And others. A 9VDC battery has very little capacity. They were meant to be used in low current applications.

#### jpanhalt

Joined Jan 18, 2008
11,088
According to this source, a 9 V alkaline battery can provide a maximum of 310 mAh at a 100 mA discharge rate. At 500 mA, the capacity drops to 170 mAh. A common lithium-ion will provide 2100 mAh or more. Also running 12-V fans at 18 volts will take more current. Put your batteries in series to get the voltage you need; put the fans in parallel.

#### Tonyr1084

Joined Sep 24, 2015
5,865
Since Amazon and their sellers know nothing about electrical products there is not one word about electric current or noise level.
The high speed fans will probably scream like a remote controlled drone up close.
I just poked that out there. The reviews complain of noise. Yeah, they're probably junk. But the point is that there are 3.3 volt fans, 5V fans, (probably 9V), 12V and higher available somewhere.

#### Tonyr1084

Joined Sep 24, 2015
5,865
I'm trying to rig up some small to 12v blower fans on my 2yo's bike helmet.
Hate to tell you this, but it looks like your two year old needs a shave.