230Volt Fan running at 120 volt
 

I was wondering if running a 230 volt fan would run at 120 vlots
this Comair rotron model PT77B3 is the fan in question...
Will it run? or just burn up?

not a good idea

doubt it'd spin up

get a transformer or tap your house's 230v lines

I don't want to run it full speed...
It is probly over 50db that is why i was wondering if i could run it at 1/2 voltage... 1/2 the speed... half the volume?
duno that is why I'm posing the question here

If i find one that runs at 120Volts..
how do i run it slower so it isn't as loud...
or is that someting you can only do on DC fans?

a dimmer switch may work

efficent it will not be

a lot of 240v fans won't spin at 120v, although some will - very slowly. You're better off getting a 120V fan and running it at reduced voltage.
You can use a Variac or variable transformer to crank the AC voltage up and down and control the AC fan speed that way. I've seen variable transformers for $50 at Fry's that would be great for fan speed control. Fan speed is not linearly related to the AC voltage by the way, it drops off fairly quickly as you drop the voltage.

You can also use a fixed transformer, which is what I use on the desk fans I have placed under tables. Fry's had a 40VA transformer with 120/208/240 volt primary and a 24V secondary. I wired it up as an autotransformer with the 208V primary winding connected to the 120V AC wall. This gave me ~69V on the 120V primary tap on which I stacked the 24V secondary winding adding another 14V (not 24V since the 208V primary is only running on 120V) giving me a total of ~83V. This is pretty much ideal for the fans I have so they run almost silent at the lowest of their 3 speed settings. I put the whole thing in a little box with a switch to select the 83V or 120V and made a small extension cord out of it all.

mad hacker....

get 2 delta 120 by 38mm fans and be done with it... 120v ac is not fun stuff to play with. especially high currents of it....

MadHacker: Big is beautiful (allways wanted that printed on my underwear).
http://www.comairrotron.com/details_...artNumberID=52
Pretty much the same as the one you suggest, but 115 Volts instead. Any reason You don´t wan´t / can´t get the 115 Volt fan?
regards
Mikael S.

you don't really want to do this.

Speed of AC fans are meant to depend on frequency, not voltage

Fans use shaded pole motors, they don't run at exactly the line frequency but have a certain amount of slip. The shaded pole design is a tradeoff of efficiency for easy startup and higher starting/ low rpm torque. There is no problem running AC fan motors undervoltage, it's done all the time. Ever seen a ceiling fan speed control? Using a transformer does the same thing, just gets rid of the buzz.

I'mm looking on ebay at getting 5 New Surplus Comair Rotron Patriot Cooling Fans for $30.
that is a great deal... i need 4 of them for my external rad box(started thread this thread) i want to make.
the reason i want to under volt it is obvios... to LOUD..
at 220 volts it would be 54.3db, at 230 volts it is 57.5db.
at 110 volts 30db? not a clue how i would calculate how loud it would be nor how much air it will move... don't think the graph would be linear.

Cool! If you put the fans on the bottom you won't need casters for the external box - you can just move it around on the hover cushion :)
On a more serious note, I've had good luck controlling the speed of 115VAC motorized impellers (AFAIK also shaded pole motors) with fan speed controllers from Edmund. They're just under $5.
Bob

Good call on this. I have been thinking of other motors, like those used in pumps.

I emailed the seller of the item...
he said
To buy or not to buy.... (Shakespeare at the quill shop)
I guess the worst case would be the fans overheats and burns the entire apartmnet complex down...
doesn't sound to bad...
and the price is right...
time to ponder...

Ceiling fan motors do not use different voltages to change speed. They use specially designed AC motors that allow only 2 - 4 running speeds. These running speeds are all related to the frequency of the AC voltage.

...true, but there are variable fan controlers

The only way to have a continuous (wide range) variable speed AC motor (not the 2 to 4 speed version) is to use a VFD (Variable FREQUENCY Drive). This can be done electronically by converting AC voltage to DC, and then converting the DC back to AC at different frequencies (at the motors rated AC voltage) to drive the AC motor.

You can also convert the AC to DC and use a DC motor. This is what variable speed AC hand drills do.

well i thought about it... I should buy...
buy a transformer...
i think the fan may run to slowly.
will have to do some math and assume a linear graph,,,
at least it may give me a rough idea what the voltage i will need...

VFD's are not the only way to have a variable speed motor. You can also do the job with varying the AC voltage on a shaded pole motor. The drawback is the efficiency and torque of the motor decrease as the rate of slip increases (rotation rate vs the line frequency). However in the case of fans and pumps the load also decreases with rpm and this is not a problem. The drop in efficiency means there is more self heating in the motor, but this is cancelled out by the fact that as the voltage drops, so does the total power into the motor. The method is not usually used in industry because of cost reasons or the need to maximize efficiency.

I suggest you go get a cheap variable transformer and plug a fan into it. You'll find that you can smoothly control rpm from 0 all the way up to max speed. The motor doesn't overheat nor are their any other problems with using this method.

So... this is the "right" technique for shaded pole motors in general?
Maybe it's time for me to re-test some of the AC motorized impellers I couldn't get to run quietly enough. Did you mean something like this - or are there cheaper-yet variable transformers that'd work?

If you are looking for big fans here's an alternative
http://www.allelectronics.com/cgi-bi...180&type=store

I bought one of these beasts and at 12V the thing is running about 2300 rpm, pulls about 0.5Amps and blows like a hurricane, even at 5v it's still spinning at 850rpm and putting out a nice breeze. It runs down to about 4.4V
It's also 2" deep so it handles back pressure better than small fans. It will just fit on the back of a Chenbro SR104 Genie case (you have to mount the fan externally to avoid some of the internal sheetmetal structure). An interesting alternative for only $15.

Yep, that'll work. I've seen some at Fry's for as low as $50, you can also go on ebay and do a search for variable transformer and get 20-30 hits. Some pretty good prices there. You can also get ones that have taps so you can hook it up to 120V and it will put out 0-240V so you can play with 240v equipment, which I've found pretty handy in the past. Some on ebay for $30 that'll do that. They are pretty robust, usually the only time they go bad is when somebody shorts it out and fries a winding.

thanks for all the info...
but having to buy a variable transformer on top of the cost of the fans offset the value of the deal to much...

ferdb the link on the pabst 6.75" fan seems almost perfect for my neads... thank you...
but this fan 24 VDC 6.75" FALCON® FAN for $14 looks like a better deal...
300cfm at 57dBa instead of the Papst 133.3 cfm at 61dBA
both run at 12-24 volts... so a computer power supply will be great.(have a few to spare)
also the fan has 3 wires... I wonder what the 3'rd wire is for...
now if i could find this in a 12 volt variety.. it would be perfect.
I already have a 4 channel fan bus that could handle the watage of each fan....

The CFM info for the Papst 6424H on that page is not correct, it's a 280CFM fan.
Here's the data sheet
http://www.ebmpapst.us/allpdfs/6400%2EPDF

Looking at the data sheets it seems like the papst handles backpressure a little better, the Comair is probably quieter. How they'll work in your application though is just sort of guessing. At $14-$15 you might as well buy one of each and see how they work for you. They're both fun ;-)

If you really want to get a 12V version you can buy them retail, but they're expensive. The papst runs about $100. Here's some links for retail fans
http://dkc3.digikey.com/PDF/T043/1298-1303.pdf
Scroll through this or...
http://www.mouser.com/catalog/619/1161.pdf
just keep clicking on the next button on the bottom of the page to see all the pages.

I can't argue with the price...
What I'm curios about is how loud will they be at 12 volts?
How much air will it move?
Unless I mange to find 12 volt versions before I get paid…
looks like the pabst fans are the one…