installing some small fans..

[S 3/6]

I am going to install a couple of cooling fans inside on of my hotter running 1 gauge locs. Especially with running it outdoors here in AZ, the added air circulation will help keep the circuitry from frying.

So here is my question. I can get very good quality, and inexpensive fans from the local computer store (your basic 12v DC fans) or I can by a much more expensive AC fan.

The loc uses AC power from the tracks, and for the one fan I want to run at all times, I need to tap off the AC power. The question is, what happens if I use a DC fan with AC power? I did an experiment and touched the wires to the track directly and the fan seems to have worked normally (although with a bit of a hum, very quiet however). Will it eventually burn out? or is it just going to make this hum and that's all?

Short version.. can I use a DC fan on an AC power source?

 

[Ray Marinaccio]

I would use a bridge rectifier between the fan and AC track power. It will change the AC to DC.
The Fan may have a diode wired inside the motor so it will only run in one direction and when you conected the AC to it it ran on half the AC wave which would produce a hum.

 

[S 3/6]

Ray, I think that you nailed it, the fans (I have 3) run in one direction only, so I am assuming the AC will not "harm" them.

I have two fans mounted near the motors, which spin up as the motor speeds up, and the 3rd mounted in the electronics bay and is on constantly (being powered by AC).. the hum is minimal and actually contributes to the realistic sound of the loc (which is an electric)..

so my main concern (that the DC fan will burn out fast) is not warranted?

 

[ezdays]

Sam,

The peak AC voltage is alway higher than its RMS (or stated) voltage, so when it's rectified and filtered, it will produce a higher DC voltage, and yes, it will cause the fan to burn out quckly.

I used to make small one-amp power supplies for the security market and basically, they were just a bridge rectifier, a large capacitor and a regulator. You can get a 7812 regulator just about anywhere. Try the Fry's store down on Thunderbird for all you components. If you want the circuit schematic, just ask.

 

[S 3/6]

Hi Don

thanks for that info.. My only concern is space, I don't have much more than 1" by 1/2" to put such a bridge rectifier in. Ideally if I could find a small AC fan that runs on 16v, that would make it simple. The only ones I could find need 110v or 220v which is not at all what I need.

Another option is to just let these burn out every few months or so and replace them as they only cost about $10.

But if Ii could get a small bridge rectifier to install that doesn't require an engineering degree to figure out, that would work too. Do you have any links on the web for such rectifiers?

 

[ezdays]

Sam,

I would need the specs on the fan you are using, (ie: DC volts and current) and I can design you something that can fit when you have the space. I would not count on replacing your fans "every few months", one might last weeks, or minutes or just a few nonoseconds and they will run hot before they go south. The point is, if your fan doesn't require too much current, you can get by with a very simple circuit. 12VDC fans are by far the most popular and easiest to get.

 

[S 3/6]

yup, this one is a 12V DC, and draws about .12 amps.. it's about 50mm square, and made by evercool (they're on the web). There are three wires coming out of it, a plus, a ground, and a signal for speed (yellow, which I trim off as I don't need it)... There is a space about 1.5" tall, and ,1" wide, by .5" thick were I can use velcro to install a rectifier (if you can make it in some kind of smooth housing it would help).. of course I'll be glad to pay you for the parts and your time Don!

Thanks (btw, call my cell if you still have it, we can discuss more)

SAm

 

[ezdays]

Sam,

OK, I've got a 12 volt fan I can play around with and see if I can get it to run properly just with a half-wave rectifier and a regulator. Since you fan is over 100mA, I have to go to the next level which will be 500 mA, but I'm sure I can get it to fit in the space you have.

I still have your cell #, so I'll give you a call in a day or so.

 

[ezdays]

Sam,

I tried my circuit on a .16 amp fan. I used one diode, a large capacitor and a 12 volt regulator, powered from an 18 VAC transformer, and it worked fine. I checked the DC with an oscilloscope and it was clean.(no ripple). The regulator runs a little hot, but I'd expect that. If you mount it near the fan, that should keep it cool.

I'll give you a call tomorrow and maybe you can just stop by the house and pick up the parts. As far as costs go, you owe me a hot dog and drink at the next show (I'm assuming the food wasn't that bad at the snack bar).