Had a go at making my own magnetic stirrer, even though I have no knowledge
about circuitry and such and got it working for a minute or two, before something
burnt out (Probably the Potentionmeter I used)

Was wondering if someone in the UK/ROE could possibly hash together a circuit consisting of
some kind of power adapter to a Potentiometer(?) to 4 or 5 used or new computer fans?
I can then glue magnets to the top of each fan and that should function fine as a lab
stirrer.

Honestly, I'd do it myself, but my soldering skills are pants, my eyesight is pants
the lighting in this house is pants and the price of buying a retail one is bordering
on scandalous. Obviously I'll pay money, just not £700 type money.

Cheers
Noel Craig
Belfast.

 

If there's a better way to do it as opposed to computer fans then that's great, whatever works, so long as the amount of power can be variable because a magnetic stirrer typically doesn't work at full pelt, you have to bring the power up gradually, or so it seems. I'm really not at all knowledgeable or qualified to be tinkering with this sort of stuff so was hoping a hobbyist could hash one together for me.

 

Also, if someone wants to hit me with a quote, that would be fab, It could look like the biggest
pile of **** so long as it actually works, I'm happy.

 

Don't bet on it, I don't even know what any of that stuff is tbh. I'd rather pay someone lol.

 

I honestly don't, I haven't had much in the way of exposure to electronics beyond what goes on inside a computer. It actually scares me for the most part. That's why I came here.What I know is that this thing ain't worth £700, that part I do know. I might be stupid on this subject, but I'm not that stupid.

 

I honestly don't, I haven't had much in the way of exposure to electronics beyond what goes on inside a computer. It actually scares me for the most part. That's why I came here.What I know is that this thing ain't worth £700, that part I do know. I might be stupid on this subject, but I'm not that stupid.

Here is an easy solution. Connect 12V DC wall adapter to the screws that say "power" and the motor wires to the two screws that say "motor".

http://www.ebay.com/itm/6V-90V-DC-1...hash=item41ade9cf7d:m:m-xh_8jH5urg6o6OyC_5HHg

 

There's many many magnetic stirrers on ebay for under $100 Aussie dollars..........You mean to tell me you can't find any on ebay ?

You found a magnetic stirrer with 4 or 5 motors to stir 4 or 5 glasses for under $100 on ebay? Aussie Ebay is evidently better than UK Ebay I'm going to assume however that what I outlined in my original post you have either forgotten about.

 

Here is an easy solution. Connect 12V DC wall adapter to the screws that say "power" and the motor wires to the two screws that say "motor".

http://www.ebay.com/itm/6V-90V-DC-1...hash=item41ade9cf7d:m:m-xh_8jH5urg6o6OyC_5HHg

So I grab 4 or 5 computer fans, twist all their wires together, then connect them all into that device and everything will work? If it's that simple, maybe even I could handle that.

 

The way I was originally trying to accomplish this task was considerably more difficult, if someone can confirm above likely to work, I'll go for it and try making myself!

 

Awesome, well, thanks for that. I know the PC Fan idea works for this sorta thing because people make them all the time, neodymium magnets are small, light and emit a strong enough magnetic field, that and the fact that both pc fan and such magnets are as cheap as chips. I'll buy one of these board's and see how it goes, I'll take your advice and check the draw on each fan, don't have any car batteries around but those wall adapter's are cheap as chips too, so blowing them occasionally wont bother me terribly.

I look forward to this

Cheers.

 

So I grab 4 or 5 computer fans, twist all their wires together, then connect them all into that device and everything will work? If it's that simple, maybe even I could handle that.

Try with one fan first.

You may have a problem finding a 12 v wall adapter that can cup ply enough amps to power 4 or 5 PC fans. A wall adapter is generally 350 milliamps (mA) to 2000 mA (2A). The fans should say how many mA each. Add them to get the total.

Also, DO NOT connect that eBay device into the wall power (230 VAC). Get an AC to 12V DC adapter. Best to find one that is 2 amps or so.

 

Just thinking out loud here. Don't computer fans spin much faster than a magnetic stirrer should?

 

Just thinking out loud here. Don't computer fans spin much faster than a magnetic stirrer should?

And wouldn't gluing magnets on the blades unbalance them and ruin the bearings? Not to mention adding to the load, increasing current draw and burn out the motor?

 

Just thinking out loud here. Don't computer fans spin much faster than a magnetic stirrer should?

Yes, in some instances about twice the speed.
The real problem is not the top end speed, since I can lower that using the Potentionmeter but rather
it is the lowest stable speed that is the greatest problem. Magnetic stirrers require a gradual increase
in speed, otherwise the flea / magnet in the jar, will not rotate correctly. Once the flea is rotating, then
it is possible to increase the RPM up to in access of 1000.

 

And wouldn't gluing magnets on the blades unbalance them and ruin the bearings? Not to mention adding to the load, increasing current draw and burn out the motor?

Not necessarily. Neodymium magnets create quite a powerful magnetic field even in small
sizes, I have tested this with a 5mm dia magnet with success. It's also quite possible to
shave the blades down a bit to decrease the weight.

Honestly, it works fine, probably better ways to do it, but for a few pound, it's grand.

 

Yes, in some instances about twice the speed.
The real problem is not the top end speed, since I can lower that using the Potentionmeter but rather
it is the lowest stable speed that is the greatest problem. Magnetic stirrers require a gradual increase
in speed, otherwise the flea / magnet in the jar, will not rotate correctly. Once the flea is rotating, then
it is possible to increase the RPM up to in access of 1000.

That is why the motor speed controller I linked to above will be ideal. A potentiometer will add resistance in series to limit current to control motor speed. The controller I linked shortens the pulses of full power (duty cycle) to control motor speed. Ideally, I should be able to turn this down to 1% of the fan's top speed (1 turn per second or less).

 

That is why the motor speed controller I linked to above will be ideal. A potentiometer will add resistance in series to limit current to control motor speed. The controller I linked shortens the pulses of full power (duty cycle) to control motor speed. Ideally, I should be able to turn this down to 1% of the fan's top speed (1 turn per second or less).

What is the current rating of the fans you have?

 

Gopher, that's really exciting news. I found cheaper alternatives to the one you posted but not sure if they
would do as good a job. I'd have to wait a month to receive them, which is fine, but if the one you posted
is the better option, then I'll buy it.

http://www.ebay.co.uk/itm/331911905340

 

What is the current rating of the fans you have?

The only technical data on them is that they are DC 12V. I used them
in a different project connecting to a little controller running at 3.3V
and they worked fine for weeks on end, even at full pelt.

[Edit]

They only cost £1 each give or take so killing them
is of little concern tbh.

 

If I was doing this I'd start with a different motor. The wiper motor from a car. It rotates at a lower speed and is more controllable. The crank arm that is attached to the motors shaft is ready made to mount the magnet. Even though a wiper motor is a higher amperage motor, that is due to the strain from the wiper linkage, running as a stirrer there would be next to no amp draw after it is turning. A wiper motor and battery charger and you pretty much there, need more than one stirrer? Add another wiper motor. With a little ingenuity you could even make one motor do all four stirrers. (Think radial airplane engine)

Running a computer fan at a much lower voltage, won't it cause it to heat up?