Stirplate build

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Whitey70

Whitey70

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Ok, so I dont have much of a clue about electrical wiring, I wanted to build a stirplate, read a few threads on here & on the internet.

Amazaingly I got it to work......sort of.

Heres the break down.
120mm 12vdc .35A brushless cpu fan
Cell charger (writing is so small I cany make out anything about it) for smart phone
10,000 ohm potentiometer
Project enclosure
HDD magnets (harvested from 3HDD)

At first, connect black to black & red to red between charger and fan. Fan spun, but not execisivley fast imo. Generated plenty of air movement, but didnt seem to have balls.

Then connect all to the pot, after some fiddling figured out how to get it to work.

Put one magnet on fan, it attached, figured Id play with it before gluing it.

Mounted to lid of enclosure with small rubber grommits (+- 1/8") between lid and fan, plenty of room to spin free.

Put lid onto enclosure, dropped 1" stirbar in 1000ml flask fill of water, it centered on magnet, turned pot gradually up, started to spin. I could see from the get go that there wasnt enough momentum. After 1 min there was a very small vortex forming, but nothing more. Figured Id try a 2000ml flask.....nothing, did start to smell burning plastic tho.

So which component(s) are all wrong?

Any advice would be appreciated.
TIA

:)
 
Well, your speed problem is because your smartphone charger is only supplying 5v (almost all smartphones charge on 5vdc, so they can charge off of a USB port).

Not sure where the burning plastic came from. If you're drawing 0.35A through the pot, it's going to be dissipating almost half a watt (most 100k pots have a "Full on" resistance of 4 ohms or so). So if the pot wasn't spec'd for at least that much it might be burning up. It might also put out enough heat to burn the plastic around it. It's hard to say.
 
You can pick up used chargers at places like Salvation Army and Goodwill stores cheap!
Get a magnifying glass so you can read that tiny writing, I use one all the time!

a 12 v model, even a 9 will probably get you want you need.
You don't need a huge vortex, you're only keeping your yeast in suspension.
 
The smell was coming from the fan, I think. At one point I had stacked two hdd magnets then put them on the fan. I think between the mass of the magnets and force they generated, it was probably too much for the answer.
 
Oi Vey:drunk:

So I went to the Shacks and bought a cool power adapter that can run from 3v to 12v. Thinking I'd solved my woes, I crawled back into my cave, hooked it all up and whamo it worked......for a second. Then I saw flashing lights in the pot, and wisps of smoke wafting out of the pot. Then, the pot didn't work, that is to say the fan was spinning like a banshee despite manipulating the pot.

Figuring that I'd killed the pot, I went back to the Shack, got another 10k pot, and hooked it up. This sorta worked until I twisted the twisty and the light show started up, complete with the smoke special effects.

I mean it sorta works, when I turn it down the fan sits still with an aggravated twitch, kinda like I how I feel when I drink a Monster BFC,

Since the power source upgrade, I can see that the fan has way more balls than I thought it had......question is, what now? Higher resistance pot? Lower resistance pot?
 
UPDATE! Just looked closer at the power adapter, says it's an AC-DC adapter, with one of those funky multi adapter connections at the end......will cutting off that multi adapter return the thing to an AC only source? if so, what's the impact to a DC fan and the pot?
 
Buy a rheostat. turn the voltage all the way up on the adapter. Wire it it up and you should be fine. I just built one myself. Put a switch inline to power it on and off.
And yes cut the metal end off. Connect the hot side to the rheostat and the neutral from the fan and adapter together. Then take the hot write from the fan and connect it to the other side of the rheostat. Plug it in. should d work
 
Whitey70 said:
UPDATE! Just looked closer at the power adapter, says it's an AC-DC adapter, with one of those funky multi adapter connections at the end......will cutting off that multi adapter return the thing to an AC only source? if so, what's the impact to a DC fan and the pot?
Click to expand...

AC plug into the wall - everything coming out of the wires is DC. no problem with the adapter.

you've probably wired the potentiometer wrong. Only one wire goes to the pot, the other is a direct connect to the fan. The fan's other wire will connect to another side of the pot. Many of them have 3 legs, you'll have to figure out what works, but nothing should smoke it, since it's only one 'side' of the current, not both.

wiring1.gif
 
Whitey70 said:
Oi Vey:drunk:

So I went to the Shacks and bought a cool power adapter that can run from 3v to 12v. Thinking I'd solved my woes, I crawled back into my cave, hooked it all up and whamo it worked......for a second. Then I saw flashing lights in the pot, and wisps of smoke wafting out of the pot. Then, the pot didn't work, that is to say the fan was spinning like a banshee despite manipulating the pot.

Figuring that I'd killed the pot, I went back to the Shack, got another 10k pot, and hooked it up. This sorta worked until I twisted the twisty and the light show started up, complete with the smoke special effects.

I mean it sorta works, when I turn it down the fan sits still with an aggravated twitch, kinda like I how I feel when I drink a Monster BFC,

Since the power source upgrade, I can see that the fan has way more balls than I thought it had......question is, what now? Higher resistance pot? Lower resistance pot?
Click to expand...

You just burned out a second pot - the one you are choosing can not handle the current being drawn by the fan motor.
 
@bob1006, haven't tried it yet, I was having a minor epiphany upon seeing the diagram. :)

thargrav. What 'size' pot should I be getting? From my snooping around the net, most folks use a Radio Shack special, I've seen folks us 25 ohms pots. These were 10,000 ohms.

what spec should I be looking at?
 
25 ohms is fine but it's not the ohms that's getting you - it's the wattage. You need a rheostat which is a higher wattage type of pot.
 
Those muffin fans really don't draw much wattage - like a nightlight - 4-8 watts

Correct the wiring and then if you can't get the motor to respond to the pot appropriately, you'll have to change the pot -
 
Use a simple lm317 circuit. Stirstarters has a good DIY.
 
Note that if your pot/rheostat has three prongs than the power in (from your wall wart) is usually the middle post, then you use one of the outer ones to wire in the fan. Depending on what side you wire the fan to will result in what way you turn up/down the fan speed.

I add them to mine, too, but if your magnets are strong enough and placed properly then the stir plate should still work without the rheostat.
 
Well, folks. I'd like to take this opportunity to thank each of you for your kindness and helpfulness. Special shout out to Hang Glider, that picture of yours is what worked the magic.

Right now, I'm doing trials with the plate, I have a 2000ml flask with cleaner in it, swirling a way at 9v, I'm going to let it run over night, and see how it does.

Once again, thanks so much to all of you
 
thargrav said:
25 ohms is fine but it's not the ohms that's getting you - it's the wattage. You need a rheostat which is a higher wattage type of pot.
Click to expand...

Hang Glider said:
Those muffin fans really don't draw much wattage - like a nightlight - 4-8 watts

Correct the wiring and then if you can't get the motor to respond to the pot appropriately, you'll have to change the pot -
Click to expand...

Rheostats on ebay look rather huge and pricy, while the potentiometers I see seem to stop about 2 watts. I have an old 120VAC dimmer switch lying around. It was paid for years ago, so I don't care if it's overkill. Would this be safe, and would it work for a 12VDC fan?
 
The quick answer is "no" and for 2 reasons.

1. Your line power is 60 Hz AC and the voltage crosses zero 120 times a second. A 120 VAC dimmer switch works by delaying when the voltage "starts back up" after crossing. This causes a non-sine wave that could damage the power supply.

2. Your 12 VDC power supply is regulated. And assuming you don't turn it into a crispy critter it will work hard to maintain or regulate its 12 VDC output at 12 volts.

In regards to wattage - assuming your fan draws .2 amps, it's total wattage is 2.4 watts. But a fan with a rheostat or potentiometer in series draws far less and a 1 watt, 100 ohm to 300 ohm should be fine. I mentioned rheostat earlier because I know without a doubt that a rheostat would work fine.
 
thargrav said:
the quick answer is "no" and for 2 reasons.

1. Your line power is 60 hz ac and the voltage crosses zero 120 times a second. A 120 vac dimmer switch works by delaying when the voltage "starts back up" after crossing. This causes a non-sine wave that could damage the power supply.

2. Your 12 vdc power supply is regulated. And assuming you don't turn it into a crispy critter it will work hard to maintain or regulate its 12 vdc output at 12 volts.

In regards to wattage - assuming your fan draws .2 amps, it's total wattage is 2.4 watts. But a fan with a rheostat or potentiometer in series draws far less and a 1 watt, 100 ohm to 300 ohm should be fine. I mentioned rheostat earlier because i know without a doubt that a rheostat would work fine.
Click to expand...

+1
 
ThreeDogsNE said:
Rheostats on ebay look rather huge and pricy, while the potentiometers I see seem to stop about 2 watts. I have an old 120VAC dimmer switch lying around. It was paid for years ago, so I don't care if it's overkill. Would this be safe, and would it work for a 12VDC fan?
Click to expand...

I got my rheostat at Radio Shack, and it was only a few dollars..
 

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