Which Rheostat to get

[370forlife]

I need something to adjust the voltage for a 12v 172mm nidec fan for the side of my computer. It uses about 2A at full load. It also dosen't change RPM from 10.5 to 18V, but runs down to 7V.

So my question is, do I have to get a rheostat rated at 12v, or does the voltage not matter? Same with wattage, should I get one as close to 24w as possible, or does that not matter? And finally, what should I get Ohm wise?

[Wizard]

Re: Which Rheostat to get

Get a buck voltage regulator anything you can get from junk circuit that has it on the circuit board and cut a island of it, and find the voltage setup divider on that and tap into it with a pot resistor to adjust voltage up and down.

Plenty of datasheets on the buck regulator ICs that drives a FET into a inductor.

Cheers, Wizard

[370forlife]

Re: Which Rheostat to get

Hmmm, it seems these fans aren't that good and running on lower voltages.

They are said to run down to 7V, but run at 3400rpm at 10.5-18v. I ran it on a 8V 4A charger I found, and it was basically the same noise/cfm (240)

I think I will just go with a switch for on/off action. If this thing is going to run 24/7 in my room with the little change in noise/rpm at lower voltages, I will just wire it to run when I need it to.

[Krankshaft]

Re: Which Rheostat to get

Here is an even simpler solution.

Wire up an LM317T variable voltage regulator before the fan. You simply set up a resistive divider (2 resistors) on the control pin have one standard resistor and one POT. The divider controls the output of the regulator and hte POT makes it variable.

There you go a cheap linear variable power supply.

The LM317T is a very common adjustable voltage regulator and can be found at any Ratshack.

If noise is a concern in the future when purchasing fans look at the DBA or decibel rating this is especially important when ordering online.

The CFM is also important depending one how much air you need to move. Of course in most cases more CFM = more noise.

[Wizard]

Re: Which Rheostat to get

LM317 is dandy if wattage is low and I do used one to set my fans to 6V and current was not so high (around 10W to 20W depending on some fans.) total But driving at high amps and you get extra heat to rid of. Uh huh...that what I prefer switching regulator for this if high currents is involved.

Cheers, Wizard

[KeriJane]

Re: Which Rheostat to get

Hi 370!

You could just ante up for a Zalman FanMate
http://www.newegg.com/Product/Produc...82E16835118217

That's just a little controller already built for you in a nice housing with wires and everything.

1001 uses! Well, OK, mostly it just makes fans go fast or slow.

You can also get 3 different fan speeds out of a 4-wire molex... 5v, 12v and 7v (red to yellow)

Have Fun!
Keri

[370forlife]

Re: Which Rheostat to get

Hi 370!

You could just ante up for a Zalman FanMate
http://www.newegg.com/Product/Produc...82E16835118217

That's just a little controller already built for you in a nice housing with wires and everything.

1001 uses! Well, OK, mostly it just makes fans go fast or slow.

You can also get 3 different fan speeds out of a 4-wire molex... 5v, 12v and 7v (red to yellow)

Have Fun!
Keri

I have a zalman fan mate that came with my zalman gpu cooler on my old 8600gt. Works great for the little 92mm delta fan that only uses .1A.

This fan uses about 2A continuously, it would fry it immediately.

[Krankshaft]

Re: Which Rheostat to get

2 amps geez what kind of monster fan do you have?

Provide a link to a pic if you can I wanna see what a 2 amp fan looks like.

The fans I use (Panaflos) 80mm draw between 120 ma (low CFM) to 160 ma (high CFM) .

[370forlife]

Re: Which Rheostat to get

2 amps geez what kind of monster fan do you have?

Provide a link to a pic if you can I wanna see what a 2 amp fan looks like.

The fans I use (Panaflos) 80mm draw between 120 ma (low CFM) to 160 ma (high CFM) .

Its a nidec ta600dc, model A34453-33

240cfm, 3350rpm 172mm x 172mm x 51mm

http://www.nidec.com/ta600dcr/ta600dcr.htm

Open the pdf for more information, and look for model A34453

[bgavin]

Re: Which Rheostat to get

You can also get 3 different fan speeds out of a 4-wire molex... 5v, 12v and 7v (red to yellow)

I routinely change the plug wiring from 12v to 5v on my case fans.

I refuse to use the 7v, which connects a Hot to another Hot.
I understand it works, but that is way out of my comfort zone.

The Zalman fan mate is ultra cheap and works very well.
I bought one for a test device, but do not leave it in the circuit.
There is no pass-through setting on the Zalman. It is also dropping a bit of voltage.

[PM650]

Re: Which Rheostat to get

Perhaps one of these?

http://cgi.ebay.com/6A-Step-Down-Swi...3A1%7C294%3A50
http://cgi.ebay.com/6A-Step-Down-Swi...3A1%7C294%3A50
http://cgi.ebay.com/6A-Step-Down-Swi...3A1%7C294%3A50

[EGuevarae]

Re: Which Rheostat to get

Hi 370!

You could just ante up for a Zalman FanMate
http://www.newegg.com/Product/Produc...82E16835118217

That's just a little controller already built for you in a nice housing with wires and everything.

1001 uses! Well, OK, mostly it just makes fans go fast or slow.

You can also get 3 different fan speeds out of a 4-wire molex... 5v, 12v and 7v (red to yellow)

Have Fun!
Keri

Keri, can you explain this?
I'm no electronics Guru, and the only explanation I can find is the 7v come from the differential of potential (12v-5v=7v). Is that true? And how is it wired? (+)->12v (-) -> 5v?
I ask this because if a project I have on an xBox 360, and I have seen the "7v" fan solution more than once.
I was suggested to use a similar setup like the one discussed here, but due to space constrains, the 7v sounds more viable.
Thanks in advance.

[370forlife]

Re: Which Rheostat to get

xbox 360's already have thermally controlled fans.

If anything I would want a mod to make the fans at 100% all the time.

[EGuevarae]

Re: Which Rheostat to get

xbox 360's already have thermally controlled fans.

If anything I would want a mod to make the fans at 100% all the time.

That's the idea. A fan running all the time. 5v is not enough, 12v is too noisy. 7v should be in the middle, so that's why I asked.
I guess I'll start a new thread.

[Toasty]

Re: Which Rheostat to get

@eguevarae -
Use diodes in series rated at 2x - 3x the fan current. Each one will drop 0.7v. Just keep adding until you're happy with the noise level. You can also add a switch to bypass them and run at full power when needed. Easy and CHEAP!

Toast

Edit - or a multi-position switch to pick a number of speeds.

[EGuevarae]

Re: Which Rheostat to get

@eguevarae -
Use diodes in series rated at 2x - 3x the fan current. Each one will drop 0.7v. Just keep adding until you're happy with the noise level. You can also add a switch to bypass them and run at full power when needed. Easy and CHEAP!

Toast

Edit - or a multi-position switch to pick a number of speeds.

I just did that to another unit brought to me yesterday - I don't know why I am now the "It's broken, please fix it" guy from the apartments complex I live. Anyway, I took this and your suggestion as a model. This is not the console but the switch looks the same, but no window on our 360.



The switch was taken from a ThermalTake fan kit. It has three speeds, but it does not use diodes. It has three resistors inside. I guess they limit voltage, right?
It was a cheaper (we had it already), cleaner and better looking solution.

I will give the diodes a try on the other system, or one of the others that I'll come across
Thanks, Toasty.

[Toasty]

Re: Which Rheostat to get

Just make sure those resistors don't overheat. Resistors are okay when used to vary the voltage on the 3 wire fans, yellow wire. The full 12 volts is applied (black & red wires) and circuitry in the fan follows the applied voltage on the yellow lead to vary the speed. It is very low current on the yellow lead, hence the tiny resistors, 1/8 or 1/4 watt.

Using resistors on a 2 lead fan requires much higher wattage resistors, typically several watts or more. They also need to be located in an area with enough airflow to permit them to dissipate the heat they generate. A stalled or dirty/clogged fan will burn them out.

A 12 volt fan rated at 0.25 amp will need a 2-3 watt resistor. A 5 watt allows a good safety margin. Ceramic or film type only, no carbon resistors due to the potential fire hazard. Approximately 24 ohms would give you around 8 volts. 33 ohms for about 7 volts.

Here's the diode voltage divider schematic.

Toast

[EGuevarae]

Re: Which Rheostat to get

Just make sure those resistors don't overheat. Resistors are okay when used to vary the voltage on the 3 wire fans, yellow wire. The full 12 volts is applied (black & red wires) and circuitry in the fan follows the applied voltage on the yellow lead to vary the speed. It is very low current on the yellow lead, hence the tiny resistors, 1/8 or 1/4 watt.

Using resistors on a 2 lead fan requires much higher wattage resistors, typically several watts or more. They also need to be located in an area with enough airflow to permit them to dissipate the heat they generate. A stalled or dirty/clogged fan will burn them out.

A 12 volt fan rated at 0.25 amp will need a 2-3 watt resistor. A 5 watt allows a good safety margin. Ceramic or film type only, no carbon resistors due to the potential fire hazard. Approximately 24 ohms would give you around 8 volts. 33 ohms for about 7 volts.

Here's the diode voltage divider schematic.

Toast

They were not carbon type. The three resistors were white squares (ceramic, right). The thing was rated for a huge fan which ran off from 12v for an AMD CPU. I didn't check the wattage on those, but as they were for 12v I tought they will be fine. I didn't take into consideration the (great amount of ) heat inside the 360 once closed.
I will recheck on this.
Thanks again, Toasty !

[KeriJane]

Re: Which Rheostat to get

Keri, can you explain this?
I'm no electronics Guru, and the only explanation I can find is the 7v come from the differential of potential (12v-5v=7v). Is that true? And how is it wired? (+)->12v (-) -> 5v?

Hi Eguevarae

That's right, it's the difference in potential from the +12v to the +5v, with the +5v (red) used as negative and the +12v (yellow) used as positive.

I first came across this on an exhaust fan in an original Antec Aria.
It came wired this way and was the topic of discussion in an early Aria review.

There was a little controversy about possible detrimental effects to the PSU. It never affected mine badly and the PSU was that proprietary 300w Antec thing stuffed with Fuhyjju. Surprisingly, the PSU lasted for years even after the fan in question went all noisy and got replaced. For all I know, it still works.

Since then I've used the 7v option occasionally but only with relatively small fans operating on reasonably powerful PSUs. I would be hesitant to try it on a small PSU as I lack the knowledge to predict the effects on the PSU.


Have fun,
Keri

[EGuevarae]

Re: Which Rheostat to get

Hi Eguevarae

That's right, it's the difference in potential from the +12v to the +5v, with the +5v (red) used as negative and the +12v (yellow) used as positive.

I first came across this on an exhaust fan in an original Antec Aria.
It came wired this way and was the topic of discussion in an early Aria review.

There was a little controversy about possible detrimental effects to the PSU. It never affected mine badly and the PSU was that proprietary 300w Antec thing stuffed with Fuhyjju. Surprisingly, the PSU lasted for years even after the fan in question went all noisy and got replaced. For all I know, it still works.

Since then I've used the 7v option occasionally but only with relatively small fans operating on reasonably powerful PSUs. I would be hesitant to try it on a small PSU as I lack the knowledge to predict the effects on the PSU.


Have fun,
Keri

Thanks, Keri.