Double Stir Plate Help in the Electronics Required

[MickJ]

Have seen the posts on stirring yeast and said i have a few of those parts laying around, but i allways do my ferments in two so why not a double Stir Plate........
Made the box with some spare silky oak timber and the top is an offcut fibreglass piece from a motorhome builder, it's the white sandwich panel sides ........

Go to Jaycar and ask for, 2 12v on off switches, 2 nice looking knobs please.......
O and 2 speed controls to suit my fans and 12v power supply ??????????
Answer was you tell us which POTENTIOMETERSyou require, there is a formula that is used to work it out !!!!!!!!!!!!!!!!!!!

So being a sheetmetal tradesman in my past life my skills in electrical only go so far......
I'm good with 12v but not this part of Electronics design...
As i look at other posts the only speed control was using voltage selection 5v,9v ..........
Now if i can get the right Potentiometer or a few that work with different power supplies and fan combinations, other builders would know what to buy............

Power supply is Astone HDD case Switching Adapter 100-240v 50/60Hz,0.8A.... output 12.0v 2000ma..............
Both fans are 110 dia DC brushless DC 12v 0.27A..............

So i think the fans are 270ma each, so there is enough power and you could also go up to 1000ma or 1.0A 12 volt fans ...............

Question 1 is, which Potentiometers should i use...
Log single gang 1k 5k 10k 25k 50k 100k 250k 500k 1M
Linear singal gang 500R 1k 5k 10k 25k 50k 100k 250k 500k 1M
Log double gang 10k 50k 100k
Linear double gang 10k 25k 50k 100k

Question 2 would be, if others want to build a stirrer would the Potentiometer be different with other single fan and small 12v ma power supplies..........


Thanks MickJ :doh: :doh: :doh:

[kyranr]

Hi Mick. I'll keep the answer brief without the calculations. Basically Logrithmic pots are used in audio applications as we don't hear in linear steps. You will need a linear pot for smooth voltage adjustment. The lowest value I can see listed is 500R. This will give you a adjustment of between 0.97v and 12v across 1 fan. 0.97v across a 12v fan will be too small to be usable but that is the lowest value pot listed(when the pot is turned right down the fan will not spin). If you choose to reduce the voltage to a fan in this way the torque also dramatically reduces with voltage. Is torque important? If so I would use a 12v motor speed controller. These use PWM (pulse width modulation) which basically turns the power on and off quickly to determine speed. This will maintain most of the torque in the fans. Jaycar sell these as well although they are a lot more expensive than a single pot.
P.S. 0.27A X 12V = 3.24W so the pot would have to have a wattage rating over 3.24W. Most of the "normal" sized pots are only rated at 0.5W

[kyranr]

Actually check Ebay. The have 12v motor speed controllers on there starting a just a few bucks!

[1 2many]

Actually check Ebay. The have 12v motor speed controllers on there starting a just a few bucks!

:text-+1: PWM speed controller is the way to go Speed controller grab something like this and you will be good to go. :handgestures-thumbupleft:

[MickJ]

Thanks
kyranr & 1 2many

"These use PWM (pulse width modulation) which basically turns the power on and off quickly to determine speed. This will maintain most of the torque in the fans."

So have ordered from Hong Kong 3off "Pulse width PWM 12v/24v/36v DC motor speed regulator controller switch 3A" from 1 2many's link.....
Also ordered 2off "Hot DC 1.8v 3v 5v 6v 12v 2A Low Voltage Motor Speed Controller PWM 1803B"

http://www.ebay.com.au/itm/400814660894 ... 1439.l2649

All up $17.03, I also have two fridges with the STC-1000 temperature controllers and will be fitting 12v blower fans in them that i can also control...........

More photos when the projects done....
MickJ

[1 2many]

Good Stuff Mick keep us informed on your progress :handgestures-thumbupleft: