New here, need help please.

Need help with a project? Trying to find a component? Post any general technical questions here.
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Daz69
Posts: 4
Joined: Thu Dec 08, 2016 6:58 pm

New here, need help please.

Post by Daz69 » Thu Dec 08, 2016 7:45 pm

Evening all.

My first post here, so Hi to you all.
I need a little help if you can? I've done a few small electronic projects over the years, but I am not experienced, more of a "tinkerer with stuff".
I've made a magnetic stirrer for mixing my own E-liquid for vaping. These stirrers are readily available for around £100+, however I've seen quite a few on YouTube where others have made their own. However, most of these just use a switch, potentiometer and the fan. However there are a couple that use the LM317T regulator, and from what I read it takes a lot of heat from what would just be suffered by the potentiometer. So, from this I found some schematic diagrams using the LM317T which I followed.

The parts used are:

12v LED rocker switch
1k ohm linear potentiometer
LM317T 1.5A 3 Terminal Adjustable Voltage Regulator
0.1uf 330 ohm Tantulam cap.
1uf Eleectrolytic cap
330 ohm resistor
12v 550Mah computer fan.

I'm using a 12v 500Mah power adaptor to power it.

It's wired as thus: From the switch, the live and ground have the 0.1uf cap across them. The ground goes to the middle terminal of the pot, and the live goes to V-IN on the chip. The left terminal of the pot goes to the 330 ohm resistor and to the ADJ on the chip.
The V-OUT has the remaining leg of the 330 ohm resistor, and heads off to the live terminal of the fan. There is a 1uf cap across the live and ground of the fan wires. The fan ground goes to common ground.
The problem I have, is that there is only 5.5v going to the fan, and the pot only works on the last half of it's rotation.

Basically, the fan has 2 rare earth magnets glued to the hub, and this sits just underneath the lid of the project box. I place a laboratory style glass beaker on the lid, put a magnetic stir bar in, add my liquid ingredients for my vape liquid, and turn on the box power, and turn the potentiometer to begin the stir.

This is where I am confused, however I believe that the issue lies with the 330 ohm resistor. I know the output of my power adaptor is only 500Mah, and the fan states that it uses 550Mah, but I read that this shouldn't be a problem if kept within 100Mah either way. Is the resistor the problem, and if so, what size should I use, if at all?

Many thanks
Daz

David
Posts: 217
Joined: Sun Oct 04, 2015 6:18 pm

Re: New here, need help please.

Post by David » Fri Dec 09, 2016 12:34 pm

The LM317 develops an internal reference voltage (Vref) of about 1.25V between the Vout and ADJ terminals. The voltage at the output is (to a first approximation) Vref X (1 + pot value / fixed resistor value). With the fixed resistor of 330 ohms, and a pot of 1k you will get a max voltage of 1.25 X 1+ 1000/330 - i.e. near enough to the voltage you measured. You need to play around with the values of the pot and/or the fixed resistor. Hope this helps.

Daz69
Posts: 4
Joined: Thu Dec 08, 2016 6:58 pm

Re: New here, need help please.

Post by Daz69 » Fri Dec 09, 2016 3:32 pm

Thanks David.

As I thought then, I need to try a smaller resistor. Am I right in thinking that unlike wire gauge which gets thinner as the number goes higher, resistance is lessened as the number of the resistor gets lower, i.e 150 ohm is lower than the 330 that I'm using?
Sorry if I've asked a numpty question, but as I said, I just tinker with bits and have little knowledge. probably why I only play with 12v instead of 240v :D :D

Thanks again!

Daz

David
Posts: 217
Joined: Sun Oct 04, 2015 6:18 pm

Re: New here, need help please.

Post by David » Fri Dec 09, 2016 7:09 pm

Answer - yes. You could also try leaving the fixed resistor at 330 ohms, and using a 10k pot.

Daz69
Posts: 4
Joined: Thu Dec 08, 2016 6:58 pm

Re: New here, need help please.

Post by Daz69 » Fri Dec 09, 2016 11:01 pm

Yes, that would be a lot easier than disassembling everything and then de-soldering the board lol :)

Thanks Dave, you've been a star. Much appreciated fella.

Daz

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