Need help converting from D cell batteries to 12v

[Tim A]

I have this fan:

http://www.coleman.com/product/cool.../2000009115?contextCategory=5850#.T3PKLxB5mSM

I like the fan because it works and magnetically attaches to my tent's windows. I'm tired of buying D batteries. It takes 6 D cells and burns through them faster than I like.

Can I convert this fan to 12v? I can't find the spec but I assume the operating voltage is around 9v (batteries in series) I'd prefer something like an inline resistor and male cigarette dapter vs a bulky DC power supply. Unable to find the correct google search term. Are there any other factors i need to consider? Thanks in advance for any help.

Tim

 

[wrcsixeight]

Those brushed motors draw a lot more current than brushless motors.

Here is a product which will work for you:

http://www.powerstream.com/dc6.htm


My recommendation is getting a 12 volt computer 'muffin' fan and figuring a way to attach it to your tent's screen.

My favorite by far is the Silverstone fm 121.

http://www.amazon.com/SilverStone-FM121-Control-Designs-120X120X25mm/dp/B000BWEIFU



It is adjustable speed 33 to 110 cfm and anywhere in between. Nearly silent to pretty loud. Under 0.1 amps to a little over 0.4 amps.

A regular sized starting battery could power one of these at full speed for 4 days assuming it was the only load and not fall much below 50% state of charge.

 

[Tim A]

wrcsixeight, thanks for the advice and the link to products. I'm going to try and find out how much current my fan pulls. Excellent idea with the PC fan, never thought of that!

 

[Tim A]

Found this:

http://www.amazon.com/Medela-Volt-L...s=baby-products&ie=UTF8&qid=1333022686&sr=1-1

According to description, it is meant to power a 9v breast pump off a 12v input.

 

[wrcsixeight]

Do note that most disposable cell batteries list 1.5 volts but really are in the 1.6 to 1.7 volt range when new, and when at the point of replacement are in the 1.35v range.

So a dc to dc converter putting out 9 volts exactly will not turn the fan as fast as 6 fresh D cells will. Whether this is a factor or not for you is something to consider. There is also the fact that DC to dc converters are not 100% efficient.

Radio shack also has ciggy plugs with different output voltages and assorted barrel pins. I used to use on one of my MP3 players, but while charging and listening to music, there was a loud background hum that was less apparent with other 5 volt dc sources.

I'd buy the silverstone before the breast pump 9 volt source for nearly the same price. No conversion losses, and the fan at any speed but full is pretty darn quiet, and moves a lot of air.

 

[Tim A]

Noticed on the fan unit, the input from the external battery pack is labeled 9V, 15W. So the fan's current draw should be about 1.67A, right? However, when I test for current coming out of the external battery pack, I'm seeing 5 amps!

wrcsixeight, can I run down my test procedure for you? (digital multimeter) I've got the black lead plugged into "COMM" and the red lead plugged into "10A". I'm inserting the red probe into the battery pack's male plug (center conductor) and the black probe to the outer conductor. The meter reads 5.XX amps. That seems wrong (high) to me.

When testing VDC, I've got the red lead plugged into the volts/ohms socket and black lead to "COMM". Same thing, test across center and outer conductor and get about 9VDC, so that looks good.

Both current and voltage tests were performed with the high speed/low speed switch set to "high". The switch is on the external battery pack. I get lower voltage/lower current readings when the switch is set to "low".

I'm not ready to give up on this fan yet...I love the magnetic attachment! Thanks.

 

[wrcsixeight]

5 amps does seem very high for that fan. I am not sure your test procedure is right or not. DMM's vary somewhat, and I admit to owning a cheapo Harbor freight Cen tech, and I cannot even get it to read amps, though my older one did, but it read completely different than a Fluke Multi meter.

I know the amp draw on my devices because I have a battery monitor. All my current flows through a shunt, and is displayed on the monitor. An extremely handy tool.

How long does a fresh set of D cells last in that fan on high?

 

[Tim A]

OK, my test was flawed. Youtube un-flawed me haha. For volts/ohms etc. you test across the two conductors. For amps, you have to "insert" the meter into the circuit. So I cut one of the wires, stripped both ends and put a lead from my meter on each end. Hooked up the fan, turned on "high", fan was running...that got me .88A on high, which is about what I wanted to see.

Note: damage to your meter could occur when testing for current, pay attention to the different jacks on your meter, there are one or two specific jacks for measuring current.

Not sure exactly on the D cell battery life. One set will last no more than 16 hrs on high, which is the way we used them at night when sleeping in the camper shell. The RTT shouldn't be quite as stuffy. I have about a month before I need this fan project completed so I will try to find a "dimmer" switch that will allow me to adjust the speed of the fan from the tent.

 

[Tim A]

For a fan speed "dimmer" switch: could I use something like this? I know the specs are off (12v vs. 9v), but if all it's doing is limiting current, then I'm wondering if this will do the job.

http://www.amazon.com/Ledwholesaler...1_fkmr1_2?ie=UTF8&qid=1333104857&sr=8-2-fkmr1

My max current is 1.5A, limited by the 9v adapter I chose.

 

[wrcsixeight]

The first product I posted in this thread will work as a speed control. The issue is you must try not to allow more than 9 volts into the fan motor. It will spin faster and shorten it's life. I am not sure the light dimmer switches will work as envisioned. Some might slow the fans, but draw the same amount of current as if it was turning full speed. This is really outside my knowledge of electricity.

I have a similar ciggy plug with adjustable output voltage and have run fans on it. The fans I tried needed 6 volts to start turning, and 4.5 volts to keep turning after that. 4.5 volts initially was not enough to start the fan spinning, and I imagine that they would burn up if fed 4.5 volts for very long without turning. The current consumed by the fans on this adjustable regulator was linear with input voltage. Since I have 200 watts of solar, my battery voltage spends the better part of the day in the high 13's to low 15's. This adjustable regulator never allowed more than 12.4 volts even when the battery was up at 14.8. The fans moved so much more air at 14.8 compared to 12.4. Perhaps your 9 volt fan will not mind the 12.8 volts of your battery too much.

I do not use that adjustable regulator anymore. The Silverstone fans fm 121 are so superior to anything else I have tried. They simply move the most air for the least current consumption and noise produced. I have one as an exhaust fan on my roof. It has been running continuously for 3.5years. The biggest fault of the fan is when it needs to be cleaned. I use a lot of rubbing alcohol and q tips and time to clean the 9 blades. But I also cook daily under this fan, so it gets a big workout.

But with my windshield and side window screens up, and my fans running, the interior temps of my van do not exceed ambient temps until late afternoon when ambient temps drop. It is always strange to open a closed vehicle that has been baking in the sun, and find the interior no hotter, perhaps even cooler than ambient air temps.

 

[Tim A]

wrcsixeight, thanks for all your inputs on this!

How does adjusting voltage change fan speed? Not questioning, just curious. Reduce voltage, increase current/fan speed?

Turns out I can't use the LED dimmer linked above since it's dims the LEDs by sending pulses, and that's not what I want for a fan. (thanks to EE's at my work)

Ordered the 12v-9v breast pump adapter. Yes, by the time I'm done, I'll have a lot of cash invested in this fan. I think it's worth not to have to worry about D batteries anymore.

 

[4RunAmok]

I'd have purchased the computer fan, and then went to Michael's (craft store) and picked up 8 rare earth magnets and 4 small flat plastic containers to fit the outside magnets into, and glue the other 4 magnets to the fan, and now I have a magnetically attached, brushless DC powered fan that I could still power with the D battery power pack if I wanted because the fan will still move plenty of air under 9 volts.

 

[wrcsixeight]

How does adjusting voltage change fan speed?

Voltage is like electrical pressure. Think of it like a garden hose spicket. Barely turn it on and 3 volts are dripping from the end of the hose. Crank it fully open and 12 volts are shooting out the end of the hose. Not an exact analogy, but close enough.

 

[Tim A]

Got the 9v adapter in...works fine off 12v power. Current is up from .9a (D batteries) to 1.1a

Will probably give it an overnight test before deciding if I need a high/low switch. I might also give the computer fan a try too, thanks guys.