Need help wiring stir plate

[Sellick]

I realize there have been other threads on this, but after looking at a few I'm still confused. Electronics tend to be an area I always need a bit of guidance on.

For my build, I've pulled an old HDD apart and I'm using the enclosure as my stir plate case because it already has a built-in on/off switch and power supply with plug in. The fact that mine has the power switch already built in is what's confusing me compared to some other builds where a switch is being installed at the same time. I'm not sure if my wiring looks little different because of that or if I've done something wrong.

I installed this potentiometer, which from other builds seemed to be one that worked well. 10k Ohms. Switch rated 3A at 30VDC.

I read up on how to wire a pot and went about it what I believe is the correct way:
Ground from both the old HDD and my new fan to the top terminal.
Power from old HDD to the middle terminal.
Power going to fan from the bottom terminal.

PROBLEM A:
With the enclosure switched on, I turned the pot switch all the way down (fan no longer moving) and noticed that it immediately started glowing on the inside and I could smell burning. I turn the fan back up so that it's moving again and the glowing/burning stops.

PROBLEM B:
When my pot switch is all the way up, it's not spinning as fast as it did when I tested the fan without the pot wired up. Is there too much resistance in my potentiometer? I did a test wiring before I soldered everything and I believe it was running at normal speed, so I'm not sure if I didn't notice at the time or if Problem A fried something which is causing it to run slow now.

Fan is rated for 12V and 0.5A.
Power supply is rated for 12V and up to 2A.

 

[doomy86]

Hi Sellick,

Do you have 3 cables comming from the fan ?

It could be that you connected the speed sensor of the fan.

 

[Sellick]

Hi Sellick,

Do you have 3 cables comming from the fan ?

It could be that you connected the speed sensor of the fan.

If I did that, the fan wouldn't run, would it? The fan does run with the two wires I'm using.

I've also solved the speed issue... I had hooked up the 5v wire in the hdd enclosure instead of the 12v. Switched that today and the fan is running at full speed when powered through the pot. But the moment i turned the speed down, pot started frying again... Think I've burned this out. Gonna go buy another and see if that helps.

 

[day_trippr]

A 10K potentiometer is far from ideal for this application.
Find something closer to 50 ohm @ 3W...

Cheers!

 

[Sellick]

A 10K potentiometer is far from ideal for this application.
Find something closer to 50 ohm @ 3W...

Cheers!

Thanks for chiming in!

Brew day today with a buddy who is a set electrician (very different than an electrician who would wire your house, but he still deals with electrical stuff) so I had him take a look at it. That was what he determined after looking at it. The fan calls for 6 watts, but this pot is rated for closer to a half watt. Ran to radio shack and 3 watts is the highest we could find.

Now I'm confused about how other guys have done their setups with what looks like very similar fans...

 

[Sellick]

Well, my buddy suggested this dimmer here, so we wired it up tonight and the stir plate is now working. Just have to get the fan and magnets attached then replace my stir bar since it doesn't sit centered on the magnets. Seems to be a poorly made stir bar.

 

[audiophool]

Aside from the underrated pot, the wiring is wrong. Ground should be on the top terminal, and + (from the HDD power supply) to the bottom terminal. Power to the fan should come from the middle terminal. The way you have it wired, when you turn down the pot you are shorting out the power supply.

 

[Kent88]

sub'd, carry on

 

[day_trippr]

tbh I saw "10K pot" and didn't bother looking at the pictures.
But, I agree, the wiring is a smoke machine - no matter what pot was used.
There's no good reason to have the ground circuit connected to the potentiometer.

I would put the PS hot wire on one of the outer pot pins, put the fan positive lead on the middle pin (wiper), and air-splice the PS ground to the fan negative lead to complete the circuit...

Cheers!

 

[doomy86]

This is how i built my stir plate, i use diodes as speed control:

http://lukasholenweg.com/2017/03/12/double-stir-plate-with-speed-control/

 

[Sellick]

Alright, finally got this thing all put back together.

Bought this dimmer switch on Amazon. (link here) Pulled it apart and attached it to one of the walls inside the case.

Wiring was really simple at that point.

Love the fact that when it's sitting on the shelf, it just looks like an old HDD.

I also like the fact that the front power button turns it on and off.


Works at a nice range of speeds too. We'll see how well it works with a starter when I get to my next beer that needs one!

Thanks everyone who chimed in.

 

[Sellick]

One thing I should mention...

I got a 1.5" stir bar and was having issues with the magnet when it was a single piece. Once I broke the magnet in half, attached to the washer and got everything centered, the 1.5" stir bar worked brilliantly. Also thought I would need to stack two broken magnets on each side, but one is working just fine.

 

[stz]

My plate is kind of finicky though it looks sweet. I used a spare hammond enclosure, a chinese special ebay PWM DC voltage controller left over from when I bought a bunch of different ones to choose a winner for a pump controller circuit, a 12V dc wall adaptor, some neodymium magnets and an old 12v 800mah motor. The motor is hot glued to a mounting plate which gives me a better height inside the enclosure, the controller is mounted to a board which fits the enclosure with a potentiometer and LED on the front and I've a surface mounted a female socket on the back for the power cord which is the way to turn it on and off. I would have gone with a power switch if I'd had one knocking around which would have surface mounted neatly.

The motor works in the wrong range though, basically the first few percent from off is all I can use, beyond that it spins too fast to hold the bar in place. I went digging in my bits box in an attempt to tune it and added a 3k ohm resistor to the pot which brought me a little more useful range, but still maybe the first 25% is all.

It rocks when I'm doing something like final apparent attenuation though because this doesn't need to be sterile I can use a stack of magnets in place of a stirrer bar and this can handle much higher rpm's.