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Shop: North Spore North Spore Mushroom Grow Kits & Cultivation Supplies   Unfolding Nature Unfolding Nature: Being in the Implicate Order

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OfflineFunnyLight
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Re: Magnetic Stirrer Speed Control Help [Re: Fred Teddy]
    #18891044 - 09/25/13 08:28 PM (10 years, 4 months ago)

Well,
At the end of the day I really don't think that thing is pulling 2.5A. Maybe it would if it had a full load - IE free to pull air. But it doesn't.

This also goes to how the 10k pot is working out well. Not much current being drawn.

Anyway,
good to hear it's working OP! now spin away, spin spin spin!!!!

WUuahahahah!


--------------------
The most powerful drive through the ascent of man, is pleasure in his own skill.
J. Bronowski

Home of delicious "Psychedelic Nyotaimori".
Thanks Lemmingp for that.

:mushroom2::grin::mushroom2:


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OfflineRogerRabbitM
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Re: Magnetic Stirrer Speed Control Help [Re: PussyFart]
    #18891405 - 09/25/13 09:52 PM (10 years, 4 months ago)

Quote:

Notahacker420 said:
Quote:

FunnyLight said:
10K seems pretty high. He'll have next to no adjustment range. I it'll act pretty much like an on/off switch. 



I made one with a 50K and it was like an on/off switch, but I still could just barely, and I mean barely control the speed.

In my mind, a 10K would have been perfect, but still might have been too much.




Try 100 ohms maximum.  This will actually give control.  Make sure it can dissipate 24 Watts or so.  If the fan needs 2.5 amps at full speed, it's doubtful a 1 amp power supply will be able to drive it without the voltage dropping too much.  Look for a larger power supply.

Thanks FunnyLight for providing an accurate answer.  I always see these threads and marvel at those who would power a 12 volt DC device with 120 VAC, or use a dimmer to control an AC motor rather than a motor speed controller.
RR


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Download Let's Grow Mushrooms



semper in excretia sumus solim profundum variat

"I've never had a failed experiment.  I've only discovered 10,000 methods which do not work."
Thomas Edison


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Offlinenoiz
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Re: Magnetic Stirrer Speed Control Help [Re: RogerRabbit]
    #18946329 - 10/07/13 07:16 PM (10 years, 4 months ago)

Gets the job done with all my new found knowledge ive got a new design in the works for a bigger one with places for 3 lc's

Thanks for all the help. 

[image][/image]


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OfflineSubspecies
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Re: Magnetic Stirrer Speed Control Help [Re: RogerRabbit]
    #18946611 - 10/07/13 08:14 PM (10 years, 4 months ago)

Quote:

RogerRabbit said:
Make sure it can dissipate 24 Watts or so.




Yes, this seems to have been forgotten in the rest of this thread. I don't understand how they didn't fry the pot at full-load, most are not wire-wound and can only handle a fraction of a watt. The picture of the one posted is 0.25 Watt. Unless they are putting a current limiting resistor in series? Blindly hooking things up in electronics is asking for a fire or worse.

Voltage regulation is the worst way to control a brushless motor. The fans have on board control circuitry, they are not a simple connection like brushed motors. The ICs and supporting circuit will not operate properly at low voltage. You also lose torque and generate heat. Pulse Width Modulation with power transistors/FETs all the way.

If your fan or motor is 2-wire (just a positive and a negative) then you can control it with a 555 timer chip, a couple of diodes, capacitors and resistors,  a (low wattage) pot, and a FET. Search 555 PWM circuit. Its pretty easy. If you don't know what any of these things are, then just buy a DC motor controller from the electronics shop. You can get premade and kits. TheReckoning posted the kind of thing you want. But that is only 6W. The advantage of making your own is that you just use a higher value FET if you need more current(cheap). The rest of the circuit stays the same. Buying a high power output controller will start to cost more.

Oh, and if you need lots of 12V current, old PC PSUs make great power supplies. Mine does 12V 16A and 5V 35A.


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OfflineWolfieNuke
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Re: Magnetic Stirrer Speed Control Help [Re: Subspecies]
    #18947358 - 10/07/13 10:44 PM (10 years, 4 months ago)

+1 to the 555 Timer idea - Probably the safest, and most effective route while still cheap... Only problem is that it a little above most people's knowledge unless they have studied Integrated circuit technology or dabbled in it at least.

What you are doing here works in theory, but has major disadvantages. By placing a resistor in series with the fan reduces the voltage for the fan, but does so by dissipating energy through the resistor - by creating heat. The resistor/potentiometer can only handle so much power before failing - possibly causing damage or injury!

The 555 timer mentioned in an integrated circuit with an oscillator (adjustable clock or timing circuit) that can be adjusted with a potentiometer to control an amplifier (in this case a FET or field effect transistor) acting like a super fast on off switch.

If you can read a simple design schematic and solder, I would recommend this solution.


Edited by WolfieNuke (10/07/13 10:55 PM)


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OfflineFunnyLight
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Re: Magnetic Stirrer Speed Control Help [Re: WolfieNuke]
    #18948759 - 10/08/13 09:46 AM (10 years, 4 months ago)

Quote:

FunnyLight said:
Couple of things going on here.

First, the main idea is that you want to adjust the voltage going into your DC Brushless Fan (fancy name for a fan with a nice motor). Adjusting the voltage being fed to a motor will ultimately adjust it's speed.

That fan looks like it's pretty beefy. It has "12v, 2.50A" specs on it. Which means, that it CAN pull about 2.50Amps of current at 12v. And that 12v is DC, not AC. This means you do NOT want to use that little dimmer switch Pestilence listed above.

Looking at the power supply (or wall wart) it's listed at 12v and 1.0A. This means that it will provide the correct voltage of 12v DC, but it may not be able to provide enough current. So a bigger supply, MIGHT be needed, but not necessarily. It's worth a shot to try to get it all hooked up.

The best way to control the speed of the fan would be to hook up your power supply to a voltage regulator, like this one. Then run that regulated, or stepped down voltage to the fan.

This might seem complicated and daunting, but in reality it's not. People naturally feel very uneasy messing with electricity.





While I do not mention the power dissipation, I did recommend the best way to control the speed of the fan. And for a brushless motor, adjusting the input voltage is by far the best way to control the speed. I do not understand how you can say that adjusting the voltage will cause a loss in torque and generate heat?

Sending a chopped up PWM signal as the input voltage to a brushless motor is an absolutely terrible way to go about this. This would be fine for a BRUSHED motor, that acts as a simple resistors for the most part. A brushless motor is much more complex with the the control scheme and will not enjoy intermittent power pulses.

The current rating on the fan is listed as 2.50A. This will be a maximum. So if that fan is in an open enviroment sucking air from one side of a board to another, it MIGHT pull 2.50A. You close off both sides of the fan blades and it takes away all load of air movement. Reducing the power requirement to what is only needed to spin the blades, this should be quite low.

Combine the reduced load, with the low RPM requirements of a magnetic spinner and you've greatly reduced your load. Now there is load implied to the fan via the magnetic coupling of the spinner, but it is likely much less then the fan blades pulling air.

Whatever the case, he's got this working. If it works for the long term, that is yet to be seen. The best option, and a pretty slick one if running multiple spinners would be to get a single 12v Power Supply then split that off to an Adjustable Voltage Regulator for each individual fan/spinner.  Or if you feel adventurous wire up a simple LM317 Regulator.

But if your stuff works, then it works. If it works forever as is, you got lucky :wink:


--------------------
The most powerful drive through the ascent of man, is pleasure in his own skill.
J. Bronowski

Home of delicious "Psychedelic Nyotaimori".
Thanks Lemmingp for that.

:mushroom2::grin::mushroom2:


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Offlinenoiz
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Re: Magnetic Stirrer Speed Control Help [Re: FunnyLight]
    #18948871 - 10/08/13 10:13 AM (10 years, 4 months ago)

Loving all the info in this thread. I will make the next one right but as for this one its like we say at work "if it barely works its not getting fixed". I realized this way isnt the best or safest so im going to keep a very close eye on it until I build a proper one.

Thanks for the info it will not go unused.


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OfflineFunnyLight
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Re: Magnetic Stirrer Speed Control Help [Re: noiz]
    #18948926 - 10/08/13 10:29 AM (10 years, 4 months ago)

Hey man, as long as that potentiometer doesn't feel too warm, and you don't get some sudden power surge I very much doubt that things will end up in a catastrophic failure/fire. Things will just quit working. Probably the wall wart first.

Not saying disregard all caution here, but no need to prep everything in a fire proof room for this scale of electrical shenanigins.

My opinion, and I'm sure others will say it's wrong.


--------------------
The most powerful drive through the ascent of man, is pleasure in his own skill.
J. Bronowski

Home of delicious "Psychedelic Nyotaimori".
Thanks Lemmingp for that.

:mushroom2::grin::mushroom2:


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Offlinenoiz
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Registered: 08/20/13
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Re: Magnetic Stirrer Speed Control Help [Re: FunnyLight]
    #18948974 - 10/08/13 10:45 AM (10 years, 4 months ago)

Thanks the other day I saw the recent comments and had it running for a while to test out a new stir bar I bought so I let it run for some time with my eye on it. After like 10 min I turned it off and nothing was warm but im still going to use with caution dont wanna burn my girls new house down...


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