Underpowering a Cooling Fan

[Bones]

I can't imagine this not being answered on the internet, so I'm presuming my failure to find the answer thus far is probably because I'm not using the correct terminology.

Anyway, I'm debating whether to cool my MH-C9000 with a fan when I'm charging at it's highest output, but I want to direct the air into the bottom vents so it cools the components rather than the cells.

I also want to airflow to be comparatively subdued, and I've found that I can accomplish this by powering a 12 volt computer cooling fan with a 5 volt power supply.

Accordingly, I would like to know if this could cause a safety risk or cook either component?

If it matters, the 5 volt power supplies' output is rated at 2.0 amperes.

 

[clintb]

Undervolting fans is something commonly done in the PC world to quiet the fans. Check out silentpcreview.com for details; I've never done it. Also, if memory serves correctly, under-volting a 12V to 5V might require a fan that can handle that low of a starting voltage.

 

[Black Rose]

This is something I would like to do as well.

This past weekend I was charging some Rayovac Hybrid C & D cells with the C9000 at 1500 mA.
The heat smell from the charger itself was quite noticeable.

 

[Lite_me]

I've been running a couple of 12v 80mm PC fans on ~5v power packs for several yrs now. They sit on top of a couple of DVRs helping with airflow to keep them cool. No problems.

My tall Antec PC case houses stacked 80mm fans in the front, as well as in the back. I have the 4 12v fans fed with the 2 leads connected to the 12v & 5v rails ultimately feeding them ~7v to reduce their speed. Link... Link2...

They run so much quieter this way. The 4 of them @ 12v were very annoying and unnecessary, actually... speed wise. Now, they provide adequate airflow without the noise. I've had no problems running 2 boxes like this.


There is always some risk involved when doing something like this, so be aware. The PC case thing is somewhat OT but still related to under-powering 12v fans and my experiences. Just a word of caution for anyone who may wanna give this a try.

 

[Kestrel]

The heat smell from the charger itself was quite noticeable.

"I love the smell of Napalm in the morning. It smells like ... victory."

 

[HKJ]

I also want to airflow to be comparatively subdued, and I've found that I can accomplish this by powering a 12 volt computer cooling fan with a 5 volt power supply.

The only problem is if you fan starts reliable on 5 volt, some fans requires 7 volt to start.
You can also buy a low noise, slow running fan, then you can run it directly on 12 volt.

A common way to reduce voltage to a fan is to put a couple of diodes in series with the 12 volt supply (a diode is 0.6 volt). Or you can get a circuit that supplies 12 volt on startup, then reduces the voltage.

 

[Bones]

Many thanks for the comprehensive replies.

With undervolting the newest term in my lexicon, I am now comfortable with utilizing the 5 volt power supply after also verifying the fan still seems to start very reliably.

I must admit that it never occurred to me to try undervolting as way to control the air flow, I just didn't have a 12 volt power supply I was willing to dedicate to this task.

Now, I don't have to go shopping for another power supply and my airflow dilema is resolved.

Cool.

 

[TakeTheActive]

I...My tall Antec PC case houses stacked 80mm fans in the front, as well as in the back. I have the 4 12v fans fed with the 2 leads connected to the 12v & 5v rails ultimately feeding them ~7v to reduce their speed. Link... Link2...

They run so much quieter this way. The 4 of them @ 12v were very annoying and unnecessary, actually... speed wise. Now, they provide adequate airflow without the noise...

If you're running a Windows OS *AND* your motherboard supports it, take a look into programs like 'SpeedFan'.

I have my CPU and case fans tied to my CPU temperature (and my case fans are also tied to my HDDs temperatures). When the CPU is cool / idling, my fans run at ~35% (about 5% above stall speed, IIRC). When the CPU is hot / working, my fans gradually increase up to 100%.

Provides for quiet operation most of the time while also allowing for maximum cooling when necessary.

 

[Illum]

Anyway, I'm debating whether to cool my MH-C9000 with a fan when I'm charging at it's highest output, but I want to direct the air into the bottom vents so it cools the components rather than the cells.

hmm...From the way your application sounds, you don't need to move air in a large area, have you considered a blower type fan?


Since fans draw very little current, usually under 200ma...wiring in linearly a potentiometer isn't a bad idea either

 

[Mjolnir]

I have all 4 of my computer case's 120mm intake fans hooked up to a rheostat type fan controller, which has dials that adjust the speed by changing the voltage. The fans themselves also have 3-way switches on them, so I can limit them that way as well. One of my other PCs has an 80mm fan that is attached to another fan controller like THIS one. It you get something like that then you will be able to control the fan no matter what minimum voltage is required to run it.

 

[Bones]

Here's the undervolted fan ready to run, it's going to be especially nice not to have to listen to it whine away at 6000 rpm:

I was going purchase the appropriate end and connect the power supply directly to the fan, but then it ocurred to me that if I spliced into the power supply instead, I could still use the USB hub I intended to rob for the power supply.

Now, I can cool my MH-C9000 and utilize the USB hub to experiment with my nifty new Eneloop charger and mobile booster:

-

 

[VidPro]

Undervolting fans is something commonly done in the PC world to quiet the fans. Check out silentpcreview.com for details; I've never done it. Also, if memory serves correctly, under-volting a 12V to 5V might require a fan that can handle that low of a starting voltage.

from what i found most slower fans wont startup at 5V but will at 7V, i had to hand crank them to get them going, like silentx and stealth types.
but
high-speed high power fans like tornadoes, and other harsh sounding high-rpm type fans that take more power to run, will startup at only 5v.
then
some fans have microcontrollers in them, like the thermally adjustable fans, they use PWM to slow down and speed up, they are also likly to kick up and start running at lower voltages, because the microcontroller will pulse the fan, which can get it moving, without a manuel spinning.

even if it doesnt get turning, the ammount of power going in, at the 5v cant really cause any burnup problems, because there isnt enough total power hitting them at 5v.

 

[Illum]

-

Plugging an UPS into itself are we?
Yes...a continuous self charging device:nana:

The only problem is if you fan starts reliable on 5 volt, some fans requires 7 volt to start.

For some fans, its the static friction they have to overcome before it starts spinning, once awhile for those kinds of fans I'd manually give it a twirl

 

[Bones]

Plugging an UPS into itself are we?
Yes...a continuous self charging device:nana:
...

Not quite Illum, that's an owner modified version of the charger in its I (heart) Eneloops mode:

Here's an image of it in continous charging, or closed circle, mode:

Its contemplate the universe (infinity) mode, also known as its navel gazing mode:

And, just to show it's more practical side, it's hanging or carry strap mode, which it will only enter while closed to keep the cells from falling out:

I'm sure there's many more, but I'm only at page 22 of the manual...

 

[Illum]

 

[Kestrel]

+1, good one. :thumbsup:

 

[VidPro]

the perpetual power picture performance. :thumbsup: