Tight Arse Stir Plate

[Hutch]

Anyone know anywhere in Melbourne city I can get a stir bar?

cheers
johnno

I saw some at G&G the other day, same as the ones you can get from the chem-lab supply joints mentioned on here.
Only one size though.

 

[tk75]

Anyone know anywhere in Melbourne city I can get a stir bar?

cheers
johnno

I'm also wondering if there is a place in the CBD to get some stirbars.

 

[SpillsMostOfIt]

I bought my stuff from here:

http://www.ssapl.com.au/

which is not in the CBD, but they do have every variant of every thing you might ever want and at decent prices. I found them to be very easy to do business with - they're not really set up for over-the-counter sales, but did so happily when I drove out there to pick up stuff I'd previously discussed via email.

 

[Simon W]

- Sanitise some PET 800ml bottles and fill with aforementioned hot wort

Umm, yes, sorry - I'd boil

Get an empty coke bottle and pour in some boiled water to see what happens to PET.
Dunno what temperature is safe for PET, but some experimenting will get you an answer.

 

[KHB]

i need a little help im building my stir plate, i had the power wired up to a switch and then wired up to the pot, but i managed to kill the pot??

I wired it up positive and negative to the pot like the guy in the shop told me. Just wondering if i should of wired it different i really want the swith in the circuit as i have already fitted it to the box cheers ben

 

[crozdog]

i need a little help im building my stir plate, i had the power wired up to a switch and then wired up to the pot, but i managed to kill the pot??

I wired it up positive and negative to the pot like the guy in the shop told me. Just wondering if i should of wired it different i really want the swith in the circuit as i have already fitted it to the box cheers ben

KHB,

the pot should be "in series" with the +ve line on the output side of your power switch (assuming 12v DC here).

 

[KHB]

KHB,

the pot should be "in series" with the +ve line on the output side of your power switch (assuming 12v DC here).

When you say in series what do you mean i had the positive and negative in line from the power outlet to the swith to the pot and to the fan fan wires and pot wires where connected together, i got a bright red light at the pot then smoke.

???????

 

[KHB]

Just thought of this wondering if my power sorce was to much for it??

the output is +5V DC
3000MA

The pot was a 500(cant remember the simble that follows)it looks like an upside down u with legs!

 

[chovain]

Just thought of this wondering if my power sorce was to much for it??

the output is +5V DC
3000MA

The pot was a 500(cant remember the simble that follows)it looks like an upside down u with legs!

Are you sure you didn't have the pot connected directly across the power connector? It sounds like you overloaded it, which can only really happen if you connect it directly across the power, and turn it all the way down. Can you upload a photo of the circuit? It's difficult to solve problems like this without knowing exactly how you've connected things up.

Edit:

i got a bright red light at the pot then smoke.

You let the magic smoke out!

 

[crozdog]

it sounds to me like you were running the pot in parallel with your power supply. The pot therefore carried a lot of current and therefore destructed. There are 2 basic methods of connecting something - in series (which is inline with the current flow), or in parallel which is across the current flow.

The power supply isn't the issue, it will supply the power which is "demanded" by the circuit - if the pot is wired incorrectly there will be a lower resistance path which the power supply will happily push electrons down.


something like this (sorry about the crappy ascii art)
/
+ ----------/ ----------POT----------------------------------------------------Circuit to be controlled-------------------------------- -ve/earth

+ve, switch potentiometer (connect to 1 side & wiper) (don't have details of what you're doing here) -ve

Use the "ohm" scale of a multimeter to measure the resistance of the pot and to confirm the connection. You can get pots where the resistance changes in either a linear or a log manner.

here is a primer on pots http://www.jaycar.com.au/images_uploaded/potprimr.pdf

This primer on ohms law & power will also be useful http://www.jaycar.com.au/images_uploaded/ohmpower.pdf

Edit - added ohms law/power link

 

[KHB]

Are you sure you didn't have the pot connected directly across the power connector? It sounds like you overloaded it, which can only really happen if you connect it directly across the power, and turn it all the way down. Can you upload a photo of the circuit? It's difficult to solve problems like this without knowing exactly how you've connected things up.

Edit:


You let the magic smoke out!

Red is positive Blue is negative sorry bout the crap drawing hopefully this helps

 

[LethalCorpse]

A pot wired inline is the worst way to control a motor's speed. It will fail eventually, particularly at maximum speed (minimum resistance). Most pots are only rated to 0.25W, and a 500ohm pot can handle a max of about 22mA. If you hook up a fan who's normal operating current is 100mA, it will kill the pot at the higher speeds. At lower speeds, the pot can protect itself a bit better, because it's limiting the current, but it's still decidedly inadvisable.
A decent switchmode controller would be ideal, but if you've not played with much electronics, or you don't want to buy an off the shelf fan controller, this is a simple circuit which will do the job, it's three parts which can be bought at Jaycar/DSE and will give a regulated output between 1.25V and 10.5V from a 12V supply. Use a heatsink on the LM317 if your fan draws more than 200mA normally, and don't use it for motors bigger than 1A.

 

[KHB]

The above circuit confuses the hell outta me.

What was wrong with my circuit can anyone explain that

 

[chovain]

Red is positive Blue is negative sorry bout the crap drawing hopefully this helps

That circuit is far to simplistic to do the job, and will let the smoke out any time you turn the pot all the way down.

Your pot is just a resistor that varies from 0 to 500 ohms. Now, when it's at 500 ohms, things will behave kind of sensibly: Some current will go through the pot, while the rest will go through the fan. The fan will spin. As you turn down the pot, more current will go through it, bypassing the fan. When it gets to 0 ohms, it'll short out the power completely.

Now, if you put everything in series (so the power, switch, pot and fan form a "loop"), things will behave slightly better, but it's still not what you want. All the current will flow all the way around the loop every time you turn the power on. At 0 ohms, there will be no voltage drop across the pot, so the fan will get "full power". As you turn the pot up, the resistance will rise, and you'll get a voltage drop across the pot, and power will be taken away from the fan. That's the opposite of what you want, and 500 ohms will never take enough power to completely stop the fan.

There's a good control circuit at http://brewiki.org/StirPlate. It's a little hard to describe how it works, because it uses a semiconductor to regulate the voltage that the fan will receive. If you follow it though, it'll work.

Edit: Beaten to it by LethalCorpse. His circuit is simpler than what I linked to, and will do the job fine.

If you don't understand it, get a friend with a better understanding of electronics to throw it together for you.

 

[LethalCorpse]

Take another look at it, it's as simple as it gets, simpler even than the diagram you posted. It's the same as the circuit mark posted, but I left off the capacitors to make it simple for you, and it should survive without those caps. Just follow the wires - buy an LM317, a 20k pot, and a 2.7k resistor. The left leg of the LM317 is connected to the middle leg of the pot and one end of the resistor. The other end of the resistor is connected to the middle leg of the LM317 and the positive lead on the fan. The left leg on the pot is connected to the negative leads for the power supply and the fan. The right leg of the LM317 is connected to the power supply. That's it.

If you want to add the caps as suggested in the brewiki page, buy a 100n ceramic cap, and a 10u electrolytic cap (you don't have to know what all of these components are or how they work - the folks at Jaycar should be able to find them for you. DSE staff won't know where to look though). Connect the two legs of the ceramic to the two leads of the power supply - doesn't matter which way around. Then connect the two legs of the electrolytic to the two leads of the fan - this one does matter, but there's a stripe to indicate the one that should go to the negative lead. This will make the circuit more stable, and reduce the small risk that pulses will kill the LM317. If you don't use them, and it fails, it's only another few dollars to replace the LM317.

 

[KHB]

Take another look at it, it's as simple as it gets, simpler even than the diagram you posted. It's the same as the circuit mark posted, but I left off the capacitors to make it simple for you, and it should survive without those caps. Just follow the wires - buy an LM317, a 20k pot, and a 2.7k resistor. The left leg of the LM317 is connected to the middle leg of the pot and one end of the resistor. The other end of the resistor is connected to the middle leg of the LM317 and the positive lead on the fan. The left leg on the pot is connected to the negative leads for the power supply and the fan. The right leg of the LM317 is connected to the power supply. That's it.

If you want to add the caps as suggested in the brewiki page, buy a 100n ceramic cap, and a 10u electrolytic cap (you don't have to know what all of these components are or how they work - the folks at Jaycar should be able to find them for you. DSE staff won't know where to look though). Connect the two legs of the ceramic to the two leads of the power supply - doesn't matter which way around. Then connect the two legs of the electrolytic to the two leads of the fan - this one does matter, but there's a stripe to indicate the one that should go to the negative lead. This will make the circuit more stable, and reduce the small risk that pulses will kill the LM317. If you don't use them, and it fails, it's only another few dollars to replace the LM317.

Cool so using the switch i have drawn above where and how would i wire this in i wanna use it i have already cut the hole

 

[chovain]

You should be aware of a couple of things with the LM317 though:
* Jaycar sells LM317 in a few different packages. You want the TO-220 package, aka LM317T. Jaycar's catalogue number is ZV1615 (Ask them for that, and they'll give you the right thing - it looks like a transistor that's been run over by a train).
* These things are more sensitive than components you'd be used to handling. Try not to handle any of the metallic contacts if you can avoid it: A zap of static electricity, even one too small for you to feel, could destroy the LM317.
* The big metal "tab" on the back of the LM317 is electrically connected to the centre pin. Make sure it doesn't touch any other components, or you could get a short. You're probably not going to kill it even if you short it out, but it can get awfully hot if shorted.

 

[LethalCorpse]

I wouldn't worry about static electricity frying an LM317. They're really not that sensitive. Even CMOS components, which most people think you can't go near without a wrist strap and a blessing from a priest, are these days pretty bloody resilient.

Attached is the circuit updated to show the caps, and the switch

 

[KHB]

Take another look at it, it's as simple as it gets, simpler even than the diagram you posted. It's the same as the circuit mark posted, but I left off the capacitors to make it simple for you, and it should survive without those caps. Just follow the wires - buy an LM317, a 20k pot, and a 2.7k resistor. The left leg of the LM317 is connected to the middle leg of the pot and one end of the resistor. The other end of the resistor is connected to the middle leg of the LM317 and the positive lead on the fan. The left leg on the pot is connected to the negative leads for the power supply and the fan. The right leg of the LM317 is connected to the power supply. That's it.

If you want to add the caps as suggested in the brewiki page, buy a 100n ceramic cap, and a 10u electrolytic cap (you don't have to know what all of these components are or how they work - the folks at Jaycar should be able to find them for you. DSE staff won't know where to look though). Connect the two legs of the ceramic to the two leads of the power supply - doesn't matter which way around. Then connect the two legs of the electrolytic to the two leads of the fan - this one does matter, but there's a stripe to indicate the one that should go to the negative lead. This will make the circuit more stable, and reduce the small risk that pulses will kill the LM317. If you don't use them, and it fails, it's only another few dollars to replace the LM317.

Just thought id get someone to check this for me.

Been on jaycar and have product numbers

pot RP7516

 

[KHB]

Take another look at it, it's as simple as it gets, simpler even than the diagram you posted. It's the same as the circuit mark posted, but I left off the capacitors to make it simple for you, and it should survive without those caps. Just follow the wires - buy an LM317, a 20k pot, and a 2.7k resistor. The left leg of the LM317 is connected to the middle leg of the pot and one end of the resistor. The other end of the resistor is connected to the middle leg of the LM317 and the positive lead on the fan. The left leg on the pot is connected to the negative leads for the power supply and the fan. The right leg of the LM317 is connected to the power supply. That's it.

If you want to add the caps as suggested in the brewiki page, buy a 100n ceramic cap, and a 10u electrolytic cap (you don't have to know what all of these components are or how they work - the folks at Jaycar should be able to find them for you. DSE staff won't know where to look though). Connect the two legs of the ceramic to the two leads of the power supply - doesn't matter which way around. Then connect the two legs of the electrolytic to the two leads of the fan - this one does matter, but there's a stripe to indicate the one that should go to the negative lead. This will make the circuit more stable, and reduce the small risk that pulses will kill the LM317. If you don't use them, and it fails, it's only another few dollars to replace the LM317.

Looked on the jaycar website
pot RP7516
2.7K resistor RR0582

Are these the right ones??
Cheers Ben