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

#### jpanhalt

Joined Jan 18, 2008
11,088
This is the one for dad:

Replaced the CocaCola with batteries for junior.

#### Dosmastr

Joined Jul 3, 2020
17
Yep the batteries lasted an afternoon and are now quite dead.
Golly two Batts add alot of weight!!
Had to reposition them ... It was making the thing front heavy lol

Until now?! Bunch of joker's you all!!

#### Audioguru again

Joined Oct 21, 2019
2,998
I looked at a You Tube test of Amazon vs Duracell "test" of 9V alkaline batteries. The test was a waste of time since the author did not test how long each battery will power a load.

Another proper(?) test said that the Amazon battery was a good choice but maybe Amazon paid them to say that.

#### Dosmastr

Joined Jul 3, 2020
17
Ok, I need more idiot checks here
Leaving Batts in series, 18v ( or probably 16-17 nominal)
If I put the fans in series that will cut current flow (double load right?) And Batts may last longer but fans spin slower

Running parallel will keep both at the same speed but one but kill Batts 2x as fast.

Biggest dumb question of the day, what happens if I run 2 Batts in series but then add ONE more on parallel? The series burns the 3rd batt right?
Am I committing any errors above (aside from this whole fools errand)?

I looked at a You Tube test of Amazon vs Duracell "test" of 9V alkaline batteries. The test was a waste of time since the author did not test how long each battery will power a load.

Another proper(?) test said that the Amazon battery was a good choice but maybe Amazon paid them to say that.
Project Farm on YouTube did a great test of cylinder Batts, but not 9v

#### Audioguru again

Joined Oct 21, 2019
2,998
A 9V battery does not have enough power to drive a 12V fan so its voltage will quickly drop to 7V then slowly drop to 5V for an hour before it is dead.

Two 9V batteries in series driving two fans in series is the same as one battery driving the first fan and the second battery driving the second fan.

Two batteries with the same voltage in parallel will run a fan twice as long as one battery.

Two 9V batteries in series then one 9V battery in parallel will quickly smoke all the batteries.

#### jpanhalt

Joined Jan 18, 2008
11,088
Ok, I need more idiot checks here
Leaving Batts in series, 18v ( or probably 16-17 nominal)
If I put the fans in series that will cut current flow (double load right?) And Batts may last longer but fans spin slower

Running parallel will keep both at the same speed but one but kill Batts 2x as fast.

Biggest dumb question of the day, what happens if I run 2 Batts in series but then add ONE more on parallel? The series burns the 3rd batt right?
Am I committing any errors above (aside from this whole fools errand)?
You seem to be stuck on 9-V batteries. Why? Everyone has told you they will not work.

#### Tonyr1084

Joined Sep 24, 2015
5,865
There are other batteries out there. One such battery is the 18650. However, the batteries have to be properly managed for voltage and charge rate. A short circuit could cause your son's helmet to turn into a barbecue pit. So DON'T use the 18650.

Another solution would be eight D cell batteries (if you insist on 12V fans) in a pack that is mounted on the bike frame. Run a wire with a 1/8 inch plug to connect the helmet to the batteries. But now your 2 year old son has to manage a wire. And damage to the wire is likely.

Another solution would be to get a 12V SLA (Sealed Lead Acid) battery and mount that to the frame. Far more power than the D cell batteries but more expensive. Until you count rechargeablity. Then the SLA becomes far more attractive. But with its higher power density comes the issue of a short circuit either in the helmet or the wire hanging down your son's back. A fuse would solve that issue. AND the SLA can tolerate a greater discharge to its voltage. Still, you don't want to just let it sit without being charged every three months. Lead acid batteries don't like hanging around without being charged. Their plates inside the battery can sulfate, leading to a loss of power.

Finally, you can put batteries and an air blower with a hose attached to the helmet like they do in NASCAR. You've seen the cooling air hoses that attach to their helmet. But now you're talking even more power and cost. I've come a far cry away from what you first proposed. Others will have a different approach, but these are some of the ideas I can come up with.

If we go back to the D cell batteries - you can put a battery pack on your sons back. That will shorten the wire and keep the weight off the helmet. And if you get rechargeable batteries you can get more for your buck.

In the end, the product you have to engineer MUST NOT endanger your son. There's probably good reason why nobody has designed a helmet with fans. At least I've never heard of such. Putting extra weight on the head leads to more stress on the neck muscles. Putting that weight on a 2 year old's head ? ? ? I don't think I'd do that.

#### Tonyr1084

Joined Sep 24, 2015
5,865
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#### Audioguru again

Joined Oct 21, 2019
2,998
There is a rechargeable fan that goes around the neck of seniors. It is advertised as AC and many stupid seniors think AC means Air Conditioning since the ad says it is cooling.

#### Tonyr1084

Joined Sep 24, 2015
5,865
many stupid seniors think AC means Air Conditioning
So, in this case what does AC actually mean? We know it's not an air CONDITIONER, it would just be a fan. But what sort of fan? And what does AC stand for? Acceptable Cretin? As in Fool and his money?

#### Dosmastr

Joined Jul 3, 2020
17
You seem to be stuck on 9-V batteries. Why? Everyone has told you they will not work.
I don't see anything else which is light enough or small enough or able to sit in sunlight and or have no risk of explosion in a small crash.

I don't see anything else which is light enough or small enough or able to sit in sunlight and or have no risk of explosion in a small crash
Edit, just saw some posts offering options

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#### Dosmastr

Joined Jul 3, 2020
17
It's a lightweight helmet, the 60grams I'm adding arent taking it outside the normal weight range for this market.

Hoping the rechargeables are a little lighter and longer lived so I can series the Batts but parallel the load. It will be a day of playing with DMM and stopwatches

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#### MrChips

Joined Oct 2, 2009
23,248
Solar powered fan.

#### Audioguru again

Joined Oct 21, 2019
2,998
Here are details of an Alkaline 9V battery and a safe common Ni-MH rechargeable 9V battery:

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#### Audioguru again

Joined Oct 21, 2019
2,998
So, in this case what does AC actually mean? We know it's not an air CONDITIONER, it would just be a fan. But what sort of fan? And what does AC stand for? Acceptable Cretin? As in Fool and his money?
The same company produces another portable AC unit. "AC" might stand for Air Cooler.
You fill it with water and turn it on. I think it sprays the water on you and the fan evaporates the water which cools you the same as sweat cools you.

#### MisterBill2

Joined Jan 23, 2018
8,471
OK, I have gone through the posts and there is certainly a lot of ????? going on.
Back to post #1, why does the TS think that a fan is needed for a helmet??
One alternative is a vented helmet to allow a lot of air circulation. The purpose of a helmet is to protect against impacts and with the correct material a lot of holes would still leave a lot of protection in place. The second benefit is that the holes will reduce the weight, and that will reduce the force of any impact. One more thing is that if the toy the 2 year old is riding is unstable enough that tipping is a problem then the plastic should be recycled and get a more stable toy to ride. Just because a product is available does not mean that it is even slightly safe.

#### AnalogKid

Joined Aug 1, 2013
9,186
That looks like a small rotary impeller, not a traditional tubeaxial fan. Can you post a close-up photo of the label? Or a link to the vendor?

Separate from that, a high-efficiency buck regulator circuit (ebay module) will drop 18 V down to 12 V with much less power loss than a resistor, AND give constant fan speed as the batteries deplete and their terminal voltages drop. $1 from China,$5 from US. Where are you located?

ak

#### crutschow

Joined Mar 14, 2008
27,010
That looks like a small rotary impeller, not a traditional tubeaxial fan.
Yes, centrifugal type fans can be more efficient (and quieter) at moving air where there's a low pressure drop.

#### MrChips

Joined Oct 2, 2009
23,248