Potentiometer help

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badlee

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Hi all
I am in the process of getting all the things I need to build my stir plate, but have one big problem; I just CANNOT fing a 25 ohm 3 watt potentiometer.

I have tried ebay and they seem to list hundreds of kinds but not the one I am looking for.
I cannot order from radio shack due to not being in the States.

Is there another kind of potentiometer I could use?
Cheers
 
Oh
And it seems that the switch I have is 6amp 250v.
Is that usable?
 
Thanks very much @NeoBrew. The potentiometer listed on Ebay is on the list.
The amazon item will not ship to Thailand and neither does holland computer.
The one listed on Ebay is $13 for shipping.
I was SOOOO hoping to find a Chinese vendor,because they almost always ship for free.
 
@IslandLizard, I have no idea if that is the correct range. I am just going off what is given in almost all of the "how to" posts.
My fan is 12v
My charger is 9v
What would a PWM be?
 
@ IslandLizard, I could not imagine myself being able to make that PWM. It looks way way way above my head.
 
@ IslandLizard, I could not imagine myself being able to make that PWM. It looks way way way above my head.

That instruction is a bit over the top, it can be simply wired in place, without using a PCB/board. I understand it's not for everyone.

BTW, that switch is plenty fine, you're dealing with small voltages and currents here. :)
 
Thank you for the switch info.
If I should decide to not go for the potentiometer,would it be ok with just a plug in and switch on option?
 
Thank you for the switch info.
If I should decide to not go for the potentiometer,would it be ok with just a plug in and switch on option?

You'll likely need some form of speed control to slow it down from max. A simple resistor could work, but the right value would need to be found experimentally. A potentiometer allows for infinite control, as long as the value is correct for the fan/power supply system. If most users say 20-25 ohm is fine, then chances are it is.
 
That item looks like a fantastic option. If you can get that, I would use that.

In the event you can't get that one, you can use a couple of resisters to effectively "convert" a potentiometer to another value range for this application. See the website here for a quick and dirty explanation:
http://www.diystompboxes.com/analogalchemy/emh/emh.html

So, if you only have a larger Pot than you need, you can "downconvert" with a little more electronics. This is what I ended up doing with my stir plate. I do a little electronics work and was just using "parts on hand", so I had to do some creative thinking to give me the right range to work with the fan I had.
 
I could not order that one exactly,but got one from another vendor for ten pence less.
It is in the post now and I am super excited
 
The item I ordered arrived a few days ago.
Could somebody please help me out with how to wire it up?
Compnents other than the PWM are; fan,charger and three pronged rocker on/off switch.

Looks like a nice unit! I assume by "charger" you mean the DC power supply you are using. I also assume your three prong on/off switch is actually a single pole double throw switch. So, two pins connected in either position, but they should switch between which two are connected.

Wire one lead of your power supply to the Power- pin on your PWM device. Usually the "negative", but either will work. Wire the "positive" lead to your switch. Wire the switch pin for "on" (the one that connects to the pin with your power supply) to the Power+ pin on your PWM device. Hook the fan to the Motor+ and Motor- leads on the PWM device. That should be it.

If your fan spins the wrong way from what you want, reverse the leads.
 

How so what? If you are responding to my last post, reversing the leads could damage the fan. Most DC fans are brush less and have electronics to make the motor work. That's why they have a red and black leads. If you reverse the leads it will probably fry it. If its turning the wrong way flip it over and it will be turning the other way.
 
Hi all
I am in the process of getting all the things I need to build my stir plate, but have one big problem; I just CANNOT fing a 25 ohm 3 watt potentiometer.

I have tried ebay and they seem to list hundreds of kinds but not the one I am looking for.
I cannot order from radio shack due to not being in the States.

Is there another kind of potentiometer I could use?
Cheers

Might be late in the day but you are making life trickier than it needs to be I think.

Simple solution.

Just a thought. Best of luck.
 
How so what? If you are responding to my last post, reversing the leads could damage the fan. Most DC fans are brush less and have electronics to make the motor work. That's why they have a red and black leads. If you reverse the leads it will probably fry it. If its turning the wrong way flip it over and it will be turning the other way.

Sorry dude, I thought you were being "funny" and were telling me to flip the bloody fan over :confused:
 
She is up and running!
I had to wait so long due to my stirbar not arriving from China.
She needs a few tweeks,but I am as proud as can be.
In fact,I got it up and running in the office on Friday afternoon.
There was not one person able to work out of facination!

View attachment 1457854907650.jpg
 

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