Electronic question

[PhL0aTeR]

I have 2 PC fans rated 12vDC @ 130ma

I'm trying to use on of these type of power supplies to power it



What specs does this power supply need to have?

I'm thinking 12vDC and at least 260ma, right?

If i had an AC adapter of the same specs, (12v 300ma) what would that do?

[Foolds]

should just have extra load encase you need it

[King Nothing]

You should be fine.

[rforsythe]

AC won't work on a DC motor, but otherwise you're good.

[Filo]

I'm thinking 12vDC and at least 260ma, right?

If i had an AC adapter of the same specs, (12v 300ma) what would that do?

I am not an electrical engineer, but I play.... oops, yes I am.

Your first guess above is right - 12VDC and at least 260mA. You are better off being conservative and overdoing it on the current rating. It won't cost anymore and it will give you room for the power supply or the fan ratings to be off, plus will lower the stress on the system if you turn it on and off frequently.

For the second question - I assume you mean you have a 12VAC 300mA supply? If that is the case then there are a few things that may happen when you hook up a DC motor to an AC line. First, the motor won't turn. The DC motor has a commutator which won't work with an AC voltage. Another possibility is that the motor will smoke or catch fire. It might not happen, but video tape it if you chose to hook them up together. The most likely thing that will happen is that the motor will present a much lower impedance to the power supply than the supply is expecting and you will have a blown fuse (if it is fused) or a blown power supply transformer. If the motor tries to pull enough current, you may just end up with a tripped breaker. Either way, never connect an AC motor or power supply to a DC power supply or motor. It won't work the way you want it to.

[King Nothing]

AC won't work on a DC motor, but otherwise you're good.

Oops! Missed that vital point right there.

[Scer]

Not sure if you were going to run both fans in series, but even if you did then you would still be fine. Still with a little bit to spare actually.

series on seria

Edit: Aren't those plug DC transformers??

Also, from what I remember I think the fan would work very erratic when you try to use AC current. But I would ditto on video taping it for scientific evidence of course

[Filo]

Not sure if you were going to run both fans in series, but even if you did then you would still be fine. Still with a little bit to spare actually.

series on seria

Ooops, careful there Oscar. You won't be able to run them in series (from the electrical point of view). If you put them in series (+12 V to red on motor 1, black on motor 1 to red on motor 2, black on motor 2 to gnd) they will have the same current through them, but different voltages. If they are both exactly the same, they will each have only 6 volts supply and they won't work right in some way. Put them in parallel (+12V to red on both, black on both to gnd) and they will each have 12V supply and will pull approximately 1/2 of the total load current.

[PhL0aTeR]

AC won't work on a DC motor, but otherwise you're good.

Define "wont work"..... this is actually a post hookup question, i did hook the AC adapter to the DC fans, they spun, but it didnt seem like they were operating at 100% efficiency....

I am not an electrical engineer, but I play.... oops, yes I am.

Your first guess above is right - 12VDC and at least 260mA. You are better off being conservative and overdoing it on the current rating. It won't cost anymore and it will give you room for the power supply or the fan ratings to be off, plus will lower the stress on the system if you turn it on and off frequently.

For the second question - I assume you mean you have a 12VAC 300mA supply? If that is the case then there are a few things that may happen when you hook up a DC motor to an AC line. First, the motor won't turn. The DC motor has a commutator which won't work with an AC voltage. Another possibility is that the motor will smoke or catch fire. It might not happen, but video tape it if you chose to hook them up together. The most likely thing that will happen is that the motor will present a much lower impedance to the power supply than the supply is expecting and you will have a blown fuse (if it is fused) or a blown power supply transformer. If the motor tries to pull enough current, you may just end up with a tripped breaker. Either way, never connect an AC motor or power supply to a DC power supply or motor. It won't work the way you want it to.

As said above, the 2 fans did turn, it was after the hookup that i realized the power source i had was AC and not DC, but i would venture to say i let it run for about a min or two once, then another min or two another time before i realized something didnt "add up"

Not sure if you were going to run both fans in series, but even if you did then you would still be fine. Still with a little bit to spare actually.

series on seria

Edit: Aren't those plug DC transformers??

Also, from what I remember I think the fan would work very erratic when you try to use AC current. But I would ditto on video taping it for scientific evidence of course

Sorry, no video, but it did work, and i cant really tell if the fans are running at a constant speed, the only thing of note is it seemed that they are running slow, but without a way to check RPMs im lost. FWIW i bought them because the guy said 75CFM, website specs say 50CFM, so im wondering if the fans being capable of moving less air are actually what has got me thinking they ran "slow"

So bottom line is, id be better of using a 12vDC power rated at 300ma or so?

[Scer]

Good eye Adam! I was thinking parallel but said series. I graduate and forget the small stuff. =P

I am thinking this would be the ideal situation but hey I have thought worse things.

think on thinkas

Ooops, careful there Oscar. You won't be able to run them in series (from the electrical point of view). If you put them in series (+12 V to red on motor 1, black on motor 1 to red on motor 2, black on motor 2 to gnd) they will have the same current through them, but different voltages. If they are both exactly the same, they will each have only 6 volts supply and they won't work right in some way. Put them in parallel (+12V to red on both, black on both to gnd) and they will each have 12V supply and will pull approximately 1/2 of the total load current.

[Filo]

Define "wont work"..... this is actually a post hookup question, i did hook the AC adapter to the DC fans, they spun, but it didnt seem like they were operating at 100% efficiency....



As said above, the 2 fans did turn, it was after the hookup that i realized the power source i had was AC and not DC, but i would venture to say i let it run for about a min or two once, then another min or two another time before i realized something didnt "add up"



Sorry, no video, but it did work, and i cant really tell if the fans are running at a constant speed, the only thing of note is it seemed that they are running slow, but without a way to check RPMs im lost. FWIW i bought them because the guy said 75CFM, website specs say 50CFM, so im wondering if the fans being capable of moving less air are actually what has got me thinking they ran "slow"

So bottom line is, id be better of using a 12vDC power rated at 300ma or so?

You can check the speed. Get an adjustable timing light and strobe it until it syncs. I would say they will not be running at a constant speed. You may also be scoring your commutators, so you will shorten your fan life. Also, with an AC input on a DC motor, your torque is going to vary with your input voltage, so you should get a pulsed output. At 60Hz you aren't going to see this because the inertia of the fan blades is going to act like a low pass filter and smooth out the pulses. You are not doing your motor or power supply any favors by keeping them hooked up.

Bottom line, yes you would be better with a DC PS. Or, if you want to get all Mister Physics, you can go to Radio Shack and get a full wave rectifier, rectify your 12V output (which will get you 6VDC), filter it, put it through a charge pump (using some switches, caps, and diodes) and pump it back up to 12V. But that is only something a geek would do.

[PhL0aTeR]

I should have added this to the first equation, but with DC i see polarity.... when i hooked this AC adapter up, i was told that the white stripe is hot, and to connect it to the red wires on the fans, then the black wires from the fans connect to the solid black on the adapter. what is the case with the DC adapters, if my guess is correct i would say that if i hooked it up one way it would spin one way, and reverse it, will it spin the other way? In that case should i be worried about the polarity of the DC adapter that im looking to purchase?

[Filo]

what is the case with the DC adapters, if my guess is correct i would say that if i hooked it up one way it would spin one way, and reverse it, will it spin the other way? In that case should i be worried about the polarity of the DC adapter that im looking to purchase?

It depends on how fancy the fan is. If it is just a plain motor then hooking it up backwards will just cause it to spin backwards. If they put some electronics in there to make sure it spins only one way in its application, then it won't spin backwards, and may hurt the fan to hook it up backwards. If they have an electrolytic capacitor in the fan (looks like a little metal can with blue or orange plastic around it) it will go POP if you hook up the DC backwards. As long as you don't have a connection from line ground to your DC ground, the polarity of the power supply isn't really going to matter. You will have to hook up the power supply to the fan through some sort of wiring harness - just make sure your more positive voltage goes to the red wire. This assumes you aren't going to be grounding the fan to a chassis ground that is set by another power supply BTW. If you want to be sure of no problems, get the correct polarity.

[PhL0aTeR]

It depends on how fancy the fan is. If it is just a plain motor then hooking it up backwards will just cause it to spin backwards. If they put some electronics in there to make sure it spins only one way in its application, then it won't spin backwards, and may hurt the fan to hook it up backwards. If they have an electrolytic capacitor in the fan (looks like a little metal can with blue or orange plastic around it) it will go POP if you hook up the DC backwards. As long as you don't have a connection from line ground to your DC ground, the polarity of the power supply isn't really going to matter. You will have to hook up the power supply to the fan through some sort of wiring harness - just make sure your more positive voltage goes to the red wire. This assumes you aren't going to be grounding the fan to a chassis ground that is set by another power supply BTW. If you want to be sure of no problems, get the correct polarity.

fuck....

these 2 fans are going inside of a cabinet that houses some other electronics.... it gets fairly hot and i hate just leaving the doors open when i have everything running so i wanted to hook up a couple 120mm PC fans mounted to the side of the cabinet to exhaust the hot air.... i guess if the fans wont work the way i have them mounted to the cabinet, ill just unscrew them and turn them around....

how do i know what the polarity is of these fans?

http://www.masscool.com/masscool/Product.aspx?ID=257

[Scer]

The power wire plug ins probably only go in one way. Just figure which lead the red one goes to and that's the positive.

lead on leadas

[PhL0aTeR]

The power wire plug ins probably only go in one way. Just figure which lead the red one goes to and that's the positive.

lead on leadas

wha? the end is of no use to me, or leads, those get hacked off and soldered/heatshrink...

[Scer]

Yeah... like filo was saying. the white stripped one on the DC plug is your positive and so is the red going into the fan. White stripped to red and black to solid.

match on matchas

[Filo]

fuck....

these 2 fans are going inside of a cabinet that houses some other electronics.... it gets fairly hot and i hate just leaving the doors open when i have everything running so i wanted to hook up a couple 120mm PC fans mounted to the side of the cabinet to exhaust the hot air.... i guess if the fans wont work the way i have them mounted to the cabinet, ill just unscrew them and turn them around....

how do i know what the polarity is of these fans?

http://www.masscool.com/masscool/Product.aspx?ID=257

The power wire plug ins probably only go in one way. Just figure which lead the red one goes to and that's the positive.

lead on leadas

Your DC PS will have 2 wires but probably not the same connector that fan has. If you want to get really sexy, you can get one of those terminal wiring blocks that people use for model trains or telephones. Hook up the fan red leads to one connector and the blacks to another. Check your power supply polarity with a voltmeter. Hook the high side to red, low side to black and you are good to go.