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Pc Fan, Re-wire Molex To 12v?

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iralosavic

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My PC fan is powered by a HD adaptor/transformer, which allows for a molex connection at the DC side. The molex pins are currently wired to 5v 2a and the fan torque is insufficient to spin at the desired speed with the necessary magnetic connection to the stir-bar.

Will crossing the wires over (which the cable suggests will be 12v 2a) provide more torque/power and will the fan survive the extra voltage?



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Wolfy

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I'm surprised that your fan is wired to the 5v rail, AFIK most computer fans are 12V.
What does the info sticker on the fan say?
 

iralosavic

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I'm surprised that your fan is wired to the 5v rail, AFIK most computer fans are 12V.
What does the info sticker on the fan say?
I'm using an adaptor that is fan 3 pin to molex, which is wired as 5v. The power supply female molex has a diagram showing how to connect at either 5v or 12v and the way that the adaptor cable is wired is to 5v from what I can tell (as it only fits in one way).

As for the fan power it says it is 12v .3a.

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iralosavic

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Thanks, Wolfy. I re-wired it and the 12v rail has made a significant difference to the fan-speed and power/torque. I have tested it out in 5L with yellow dye, cous cous and breadcrumbs (as above) and it is more than suffiicent.

I have a basic fan speed controlling pot and the wiring was loose, so I had to strip it and re-wire it. Now the potentiometer is only on/off, kicks in about 3/4 the way around. What have I done wrong?!
 

iralosavic

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Oh, I tried re-wiring the pot in the reverse manner and it made no difference. I'm wondering if the solder has bridged the terminals or something, not that I can see that as being the case.
 

Truman42

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Oh, I tried re-wiring the pot in the reverse manner and it made no difference. I'm wondering if the solder has bridged the terminals or something, not that I can see that as being the case.
The resistance in your pot is too high. If its coming on at 3/4 then take 3/4 of the resistance off your pots value and thats what you need.

So if your pot is 100 ohms, 3/4 of this is 75 ohms, so 100-75 = 25 ohms. You need a 25 ohm pot, (generally I think this is what most people use for these)
 

iralosavic

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The resistance in your pot is too high. If its coming on at 3/4 then take 3/4 of the resistance off your pots value and thats what you need.

So if your pot is 100 ohms, 3/4 of this is 75 ohms, so 100-75 = 25 ohms. You need a 25 ohm pot, (generally I think this is what most people use for these)

Thanks for that, Truman. The funny thing is that it worked before the wires went loose and I meddled with it! It's also a fan speed controller designed to work with PC fans, which is what I'm using...
 

Truman42

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Oh okay thats a little different then if it worked fine at 5 volts.

Its strange because if you doubled your voltage you really need to increase your resistance. Not decrease it.
If it worked ok at 5 volts then it should work better at 12 volts with more range on your pot.

Double check your wiring and check your pot with a meter as you may have burnt it out with the voltage increase so that only the last 1/4 of the track is still in tact.

Can you post a wiring diagram?
 

iralosavic

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Oh okay thats a little different then if it worked fine at 5 volts.

Its strange because if you doubled your voltage you really need to increase your resistance. Not decrease it.
If it worked ok at 5 volts then it should work better at 12 volts with more range on your pot.

Double check your wiring and check your pot with a meter as you may have burnt it out with the voltage increase so that only the last 1/4 of the track is still in tact.

Can you post a wiring diagram?

It didn't come with a wiring diagram :/ I also re-wired it when still operating it on 5v and it started playing up before I switched it to 12v... I did double check the wiring a few times... I started to suspect that the terminals had too much solder on them and that the connections weren't clean enough. But I don't understand electronics enough to know if that would make any difference...

The strange thing is... before wiring them up, I (accidentally - it was an awkward game!) bridged the two exposed wires together and touched them on the mounting panel (for the back of a PC) and it started to spin the fan!
 

Truman42

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I meant post a wiring diagram of how you wired it.
 

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