To start, I have very little knowledge of electronics so bear with me please. I'm trying to build a ferrofluid sculpture, my plan is to place an electromagnet, something like this,

http://www.ebay.com/itm/20mm-12V-25...184?pt=LH_DefaultDomain_0&hash=item2c93443a70

Now my question is, can i hook up a computer fan controller and use a dc power source to power this?

 

I would use a simple linear supply even just a bridge is all you need, you also usually need to do a reverse pulse to demag whatever you are lifting is a light object it can stay attached.
Max.

 

DC 12 Volts 0.25 Amp so I don't see why not. Any power source 12 VDC capable of the load should work. My guess is this is just an electro magnet. Why the fan controller though? My guess is you plan to modulate the magnet?That said I agree with Max in that you could build a small linear supply or even a 1 Amp 12 Volt DC wall wart.

Ron

 

yes i want to control the strength to see what kind of different effects/shapes i can get. However you completely lost me on the explenation.

 

yes i want to control the strength to see what kind of different effects/shapes i can get. However you completely lost me on the explenation.

OK, sorry if I lost you, looking back at your original post:

Now my question is, can i hook up a computer fan controller and use a dc power source to power this?

The DC power source isn't a problem, what I am curious about is the use of a computer fan speed controller. Your magnet when 12 VDC is applied draws about 250mA (1/4 Amp). The strength of a magnet like this is based on amp turns and in keeping it simple the more current flowing through the magnet's coil, the greater the magnetic field it creates (the stronger it is). Computer fan speed controllers work by using PWM (Pulse Width Modulation) they don't vary the current to the fan but turn the fan On and Off at a very fast (pulsed) rate. When On the fan sees full voltage and current and when Off there is no voltage or current. Thus the fan is "pulsed" On and Off. I am just not sure how that will work out with an electro magnet? I never gave it much thought. We would be pulsing the magnet coil rather than increasing and decreasing the field strength by changing the current. Maybe another forum member has some thoughts?

Ron

 

Ah I'm following slightly now haha. Well thats what someone suggested a while back and since then nobody (until now) had a better idea. So yes, i need some way, preferably a turn dial, to control the force of the electromagnet. Is there anything on the market that might have that effect or is it something that would have to be custom built?

 

My wild guess is that you may be able to " freeze " a glob about ping-pong ball size. Interesting experament.
An old fashon rheostat would fill the bill- like Ohmite Model K, 100 ohm, 1 A max. If you were in Tucson I would loan it to you. Or use a power darlington transistor, ( or MOSFET ), heat sink & 5k pot. You'll need a DC power source , about 15V @ 1.5 A.

 

Ah I'm following slightly now haha. Well thats what someone suggested a while back and since then nobody (until now) had a better idea. So yes, i need some way, preferably a turn dial, to control the force of the electromagnet. Is there anything on the market that might have that effect or is it something that would have to be custom built?

I would give it a try with the fan speed controller. I never tried the process but saw some cool videos of it. I have over the years worked with some large magnetic particle inspection machines using Magnaflux Powder Florescent Magnetic Particle Liquids which was interesting. Yes, there are adjustable current supplies and yes there are units one can build but for starters a fan speed controller is relatively inexpensive so I would see how it works out before getting into more complex or expensive current supplies.

Ron

 

I'm not trying to "freeze" I'm going to attach a series of odd shaped metal objects that i can transfer the magnifying effect to and see what kinds of different sculptures i can come up with.

 

I figured as much cost wise, but if the electromagnet bases its gauss off current and a fan controller won't change current aren't i kind of SOL from the start?

 

You could buy a few 10 ohm, 1 watt resestors and connect them in series then put the string in series with power supply & magnet. Use two clip-leads to selectivley short or un short out resistors.

 

is there no such thing as a variable dc current controller?

 

is there no such thing as a variable dc current controller?

There are power supplies out there that offer both adjustable voltage and current like this one which is relatively cheap. A Google of "adjustable current source" will bring up dozens of hits including some roll your own drawings of circuits using regulators like the LM317 for example. Your current linked to magnet draws very little current at 1/4 Amp but if you get into this with future projects and larger magnets it's good to plan ahead. So anyway you can build or buy depending on what you want and how comfortable you are buying a pile of parts and building.

Also, I have no idea as to the quality or reliability of the cheap stuff pouring in from China.

Ron

 

is there no such thing as a variable dc current controller?

A Variac followed by a bridge rectifier.
Max.

 

What about hooking up a rheostat? Right now I'm not too concerned about reliability or going bigger, i just have a bowl of ferrofluid sitting on my shelf and have for some time. Just figured it was time to do something with it and this is what i came up with.

 

Speaking of rheostats, I just saw an ad for a 200 ohm, 25 watt, Cat# RHE-200 @ US $ 4.95 from All Electronics, CA USA.

 

Depending on how quickly the ferrofluid responds to changing fields, the PWM control might work just fine.

PWM position control of solenoid valves, for example, can be quite effective, and produce results equivalent to current control. The mass and friction in the valve system prevent it from responding to high frequencies, so it moves in relation to the average current, which is the max current times the pwm duty cycle.

If a $5 part works, that definitely sounds like the way to go for now, but if you want to scale up later or add external control from a computer or uc, I imagine PWM would work well, as long as the pwm frequency was high enough (1kHz has worked well in my valve experiments, but I don't know how ferrofluid response would compare.)

 

So another dumb question I'm sure. Just had a thought about this, if i place an electro lift magnet under say an 1/8th sheet of plexi and an iron object on top for the ferro fluid to attach to, will the magnetic field "jump" or will the two have to physically touch?

 

Magnetic fields jump, but not very well. An eighth of an inch should work well enough on ferrofluid.

Why not just grab a refrigerator magnet and play with it?

 

Why not just grab a refrigerator magnet and play with it?

Or a scrap yard crane lift magnet, 100amps @ 240vdc
Max.