Tight Arse Stir Plate

[goodbrew]

OK how the hell do I wire these things up. I think I blew up the pot by wiring it up wrong as there was a flash and smoke coming from the pot. The problem I have is I know nothing about electronics. So when I go back tomorrow do I just ask for a "PWM" instead of another "POT"? If so or not how do I wire them up?
I have 2 wires coming from the power source, they go to a on/off switch, one wire to the middle pole and the other to a side pole. Then what? from the centre pole of the switch to the cetre pole of the POT and from the empty switch pole to a side pole on the POT? Then from the middle pole to the fan and the empty pole on the pot to the fan?
This is not easy for me.

Steve

SJW, think of the wiring as a circle, take one wire from your power pack and go to the centre post of your switch, then from the other post on your switch go to the centre post of your pot, then attach one wire from your fan to one of the outer posts of your pot, and finally join the second wire of your fan to the second wire on your power pack. I've recently made one myself using a 1kohm pot from jaycar which does the job really well, doesnt even get warm when you slow it right down.

cheers

 

[SJW]

OK it works great, but it does not work :huh: Well its all wired up and works great except for the little light on the switch, it does not come on now when it live, but dont care.
The problem I have is the stir bars appear to either attract or repell depending on which way they are orientated. So if I fill a flask with water and get the bar pointing the right way when I turn up the power it spins once or twice then gets thrown to the outside of the flask. I am using 4 (2 each side) of those little rare earth magnets, so should I be trying to get the fan/magnets closer to the top of the box or have I bought the wrong stirres. I got 2 a 40 and a 60mm long and one has a band in the middle.

 

[pokolbinguy]

What are you using as a power supply there SJW?

 

[schooey]

I tried at first with those liddle iddy biddy magnets, even when I put all four of them together (two on either side, and all on top of the fan) they weren't strong enough to keep the bar centred. I had to go for the next size up.

 

[lagers44]

That's one of my quesations SJW.

When positioning the magnets which way around do they go ? One north up & one south up , or both the same way ?

I'm guessing it's one up one down ( guessing the stir bar is N & S ) to lock the stirbar to the magnets so it spins with them ?
If i'm correct then that may be SJW's problem his magnets could be both the same way repelling the bar.

Lagers

edit: finish the sentence before sending.

 

[PostModern]

OK how the hell do I wire these things up. I think I blew up the pot by wiring it up wrong as there was a flash and smoke coming from the pot. The problem I have is I know nothing about electronics.

This is why LC called the sales guy at Jaycar an idiot. You ~can~ wire a pot in series with a fan and a power supply and it ~will~ change the speed of the fan until it fails. Pots aren't meant to handle 5W loads. You probably got a .25W pot which eventually did what an overloaded component will do - which is let out the "magic smoke" that makes it work. Once the smoke is out, you can't stuff it back in.

 

[SJW]

All is well now. Just took a bit of practice. I have the two magnets doubled up and once I get the bar centred I just need to ramp it up slowly then back it off once it gets going. I had it going for a couple of hours going so slow you could see the bar spinning and it did not heat up the pot. Its a 500ohm, 3w pot. But even running at an optimal speed its near flat out anyway, but not quite.
Thanks for all your help again, any reason why the light is not coming on when its live?

What are you using as a power supply there SJW?

A 12v phone charger I picked up for $2 at a junk sale.


Steve

 

[newguy]

When positioning the magnets which way around do they go ? One north up & one south up , or both the same way ?

One N, the other S. That way the N and S of the stir bar will each be attracted to a magnet on the fan and the stir bar will have a stronger hold.

 

[kabooby]

any reason why the light is not coming on when its live?

At a guess you may have blown the globe when you connected up the power supply wrong.

Kabooby

 

[LethalCorpse]

It's a 0.5W pot, not 3W, as PoMo said, it's not designed for a 5-10W load, but then you've ignored that one already.

The light on the switch doesn't come on because it's wired up incorrectly, or because you wired it incorrectly before and blew it up. There are two wires coming from the PSU, a positive and a negative. The positive is red, or the middle wire if it's a coaxial cable. The back of the switch is labelled 'Supply, Load and Earth'. The positive from the supply goes to the "supply" pin on the switch. The negative from the supply goes to the "earth" pin on the switch. The load pin goes to the middle of the pot. Then one side of the pot goes to the positive (red) wire of the fan. The negative wire of the fan goes to the earth on the switch (same as the negative of the supply).

And all of that will still fail.

 

[Screwtop]

All is well now. Just took a bit of practice. I have the two magnets doubled up and once I get the bar centred I just need to ramp it up slowly then back it off once it gets going. I had it going for a couple of hours going so slow you could see the bar spinning and it did not heat up the pot. Its a 500ohm, 3w pot. But even running at an optimal speed its near flat out anyway, but not quite.
Thanks for all your help again, any reason why the light is not coming on when its live?



A 12v phone charger I picked up for $2 at a junk sale.


Steve

Steve I glued a length of acrylic strip across the fan so I could position the magnets further out, that seemed to help with the positioning problem.

It's a 0.5W pot, not 3W, as PoMo said, it's not designed for a 5-10W load, but then you've ignored that one already.

Don't see a problem, he's using a phone charger.

 

[LethalCorpse]

Don't see that as a problem if he's using a phone charger.

Makes no difference whether he's using a phone charger, a car battery, or a 40A heavy duty benchtop supply. 12V is 12V, the current is determined by the fan and the pot, and for most of its deflection, the pot will need to handle well over 0.5W.

You said earlier there's no need to overdesign this. That's true, but there's also no need to underdesign it, which is what a series pot is. A simple linear regulator circuit is a minimum design, with an off-the-shelf fan controller being appropriate for those that lack the expertise to hook up a regulator. As SJW has demonstrated, if you can't wire up a regulator circuit you may not be able to wire up a pot either, so simplifying it to the point of inadequacy doesn't necessarily make it any easier, and certainly doesn't make it better.

 

[SJW]

Makes no difference whether he's using a phone charger, a car battery, or a 40A heavy duty benchtop supply. 12V is 12V, the current is determined by the fan and the pot, and for most of its deflection, the pot will need to handle well over 0.5W.

You said earlier there's no need to overdesign this. That's true, but there's also no need to underdesign it, which is what a series pot is. A simple linear regulator circuit is a minimum design, with an off-the-shelf fan controller being appropriate for those that lack the expertise to hook up a regulator. As SJW has demonstrated, if you can't wire up a regulator circuit you may not be able to wire up a pot either, so simplifying it to the point of inadequacy doesn't necessarily make it any easier, and certainly doesn't make it better.

I guess that fact is it works and even if I only get a couple of years out of it $2.25 for a new pot still puts it in the Tight Arse Stir Plate catagory. I appears that heaps of people use the pots with no problems. If it does blow I will try the 500ohm 3w Wirewound jobs that Goathearder uses.
The light still works so I wil double check my wiring when I get home.

 

[PostModern]

I haven't read the whole thread, but an LM317, a resistor, a bit of experiment board and the off-cuts of your resistor for tracks is all you need. Piss easy to wire up. I did one for a 120mm fan controller a couple years ago. Took about 5 mins (plus soldering iron warmup time) to assemble. I believe it still works. I might pull it out, dust it off and make a TASP myself.

 

[schooey]

If you want to do it really tight arse and crudely, you dont even need the board. Just solder the resistor to the LM 317, and the other to the wiring and put some heatshrink over it, and yep, its a 5 min job

 

[Benniee]

Earlier in this thread there was a few people who got their magnets from old hard drives. Does anyone have any pics of this?

Benniee

 

[PostModern]

If you want to do it really tight arse and crudely, you dont even need the board. Just solder the resistor to the LM 317, and the other to the wiring and put some heatshrink over it, and yep, its a 5 min job

I screwed my LM317 to an appropriate heatsink with thermal compound and everything. Not quite as fussy as LC, but gettin' there

Earlier in this thread there was a few people who got their magnets from old hard drives. Does anyone have any pics of this?

Benniee

About halfway down this page http://www.dansdata.com/magnets.htm
Further down that page is a really cool liquid called Ferrofluid. Like magnetic motor oil!

 

[LethalCorpse]

For the more adventurous, here is a simple PWM circuit using a 555 timer. <$5 worth of parts.

 

[Screwtop]

Makes no difference whether he's using a phone charger, a car battery, or a 40A heavy duty benchtop supply. 12V is 12V, the current is determined by the fan and the pot, and for most of its deflection, the pot will need to handle well over 0.5W.

You said earlier there's no need to overdesign this. That's true, but there's also no need to underdesign it, which is what a series pot is. A simple linear regulator circuit is a minimum design, with an off-the-shelf fan controller being appropriate for those that lack the expertise to hook up a regulator. As SJW has demonstrated, if you can't wire up a regulator circuit you may not be able to wire up a pot either, so simplifying it to the point of inadequacy doesn't necessarily make it any easier, and certainly doesn't make it better.

Do the math - Voltage (12V) total series resistance (max 50K + typically 160) therefore Current and Power = 2 fifths of **** all

 

[hockadays]

Lethal,

I've seen the circuit diagram but have you got any pictures of how to wire it up. You could call it the "Lethal method". Ps excuse me if you already have as I haven't looked back over this thread for a few weeks.

cheers