ben_sa
Now in 3V
My apologies mate. PM replied to in regards to my order.
Cheers for organising.
Ben
Cheers for organising.
Ben
Stir-Bar bulk buy anyone?
- Thread starter mkstalen
- Start date
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mkstalen
Well-Known Member
Probably final update.
Got 19 people down for the buy. (20 including me...)
Still need to confirm specific orders from 1 people.
Still need addresses from 2 people.
Still need money from 2 people.
Plan is to place the order at lunch time tomorrow.
Got 19 people down for the buy. (20 including me...)
Still need to confirm specific orders from 1 people.
Still need addresses from 2 people.
Still need money from 2 people.
Plan is to place the order at lunch time tomorrow.
Hi Mike:
Sent order to your Paypal email but Paypal on my phone is saying server cannot be reached at this time. Will try from desktop but please let me know of another way to pay. My order is:
3X 20mm bars
1X 30mm bar
2X 50mm bars
Total including postage comes to $40.50
Thanks,
G
Sent order to your Paypal email but Paypal on my phone is saying server cannot be reached at this time. Will try from desktop but please let me know of another way to pay. My order is:
3X 20mm bars
1X 30mm bar
2X 50mm bars
Total including postage comes to $40.50
Thanks,
G
mkstalen
Well-Known Member
Order has been placed.
Will keep everyone updated.
Will keep everyone updated.
mkstalen
Well-Known Member
OK. I've been advised by the CFO that the package has arrived at home. Will make sure everything is there and start the process of packing stuff into envelopes.
Giddy up!
Giddy up!
ben_sa
Now in 3V
Haha likewise! and stick my magnets to my fan... and basically put it all together :lol:robbo5253 said:
mkstalen
Well-Known Member
Just finished sorting and addressing everything thismorning (stupid body clock waking me up at 7am on a weekend). They'll all go in the post box today, so I'm guessing they'l be arriving onwards from Tuesday next week.
Happy stirring!
Happy stirring!
Got mine today, thanks for the putting in all the work, Stienberg! The 35mm bars rock, exactly the right size for my DIY stirplate. For the first time, I've been able to run it up to full speed without throwing off the bar. Now to plan the next beer, so I can get these bad boys to work... 
koots
Well-Known Member
Got mine mate, cheers!
phoenixdigital
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Got mine too. Thanks for organising. Now I need to build or buy a stir plate
25R 3W? Those are some weird specs. What exactly do you need one (or three) for? You might find that sort of thing very hard to come by - if they even exist. Depending on how you set it up, you should be able to throw a resistor in parallel around the pot (provided that you know what connections you need, and know what you're doing, etc) to drop a higher value pot (~500R or 1k are more common) down to 25R. That said, 3W is a huge power requirement for a pot. You're not just throwing that in series with the fan, are you?Golani51 said:
And in response to the question: no. For most electronics gear I can't get at Jaycar, I go to element14. They actually do have 25R pots, but only in 1W (and $17 each...)
You could always just make a simple PWM circuit for speed control. Like this one I posted up a couple of weeks back. Or any other PWM circuit you find in that thread/the internet.
Thanks Hammo:
The 3W is not the big issue but putting the 500 ohm pot is next to useless. It does not turn on the fan until the max point. I understand-perhaps incorrectly- that I have to use a lower resistance pot to get the range of speeds for the fan. All the components Ie power supply,switch, pot and fan are set in series.
What is being done incorrectly? turn on OK but only at full throttle. 500 ohm pot currently in use.
R
The 3W is not the big issue but putting the 500 ohm pot is next to useless. It does not turn on the fan until the max point. I understand-perhaps incorrectly- that I have to use a lower resistance pot to get the range of speeds for the fan. All the components Ie power supply,switch, pot and fan are set in series.
What is being done incorrectly? turn on OK but only at full throttle. 500 ohm pot currently in use.
R
Drew
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It's all about ratios. Your fan might have an effective resistance of say...50 ohms? (not sure). The fan will probably only kick on at voltages above say 8 volts. (Okay I'm throwing a few numbers around without justifying them...so shoot me).
Assuming the above numbers..
The voltage across the fan would drop to 8 volts out of the available 12 when your pot is set at 25 ohms (voltage is proportion to resistance), and your fan would increase speed as the pot goes from 25 ohms -> 0 ohms. Between 25 ohms and 500 ohms the fan would only be getting less than 8 volts, hence won't do anything. So that's why only the last 5% of the dial is working for you.
A 25 ohm pot would vary voltage between 8V and 12V, allowing you to use the whole rotation of the pot. (Again...only valid for my wildly arbitrary numbers! But you get the idea).
Whilst I don't know any disadvantages to using a pot (I've read - uses more energy, and the pots die out sooner or later??) using PWM is more sophisticated. PWM works by delivering many small pulses at full power to the fan. And indeed you can buy a PWM circuit for $6 on ebay. That's what I did.
http://www.ebay.com.au/itm/400506553335?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Assuming the above numbers..
The voltage across the fan would drop to 8 volts out of the available 12 when your pot is set at 25 ohms (voltage is proportion to resistance), and your fan would increase speed as the pot goes from 25 ohms -> 0 ohms. Between 25 ohms and 500 ohms the fan would only be getting less than 8 volts, hence won't do anything. So that's why only the last 5% of the dial is working for you.
A 25 ohm pot would vary voltage between 8V and 12V, allowing you to use the whole rotation of the pot. (Again...only valid for my wildly arbitrary numbers! But you get the idea).
Whilst I don't know any disadvantages to using a pot (I've read - uses more energy, and the pots die out sooner or later??) using PWM is more sophisticated. PWM works by delivering many small pulses at full power to the fan. And indeed you can buy a PWM circuit for $6 on ebay. That's what I did.
http://www.ebay.com.au/itm/400506553335?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
The issue lies in what happens to the power. Drew is more or less right about the ratios, and resistance of the pot & armature resistance of the fan.
Here's the situation: we have a fan, that runs of voltage V1 (I assume it's a computer fan --> V1 = 12V). We want to control the speed of this fan. To do this, we must change the voltage drop across the fan. There are two main ways to do this:
1. Change the total resistance of the circuit. We do this by putting a variable resistor (potentiometer, rheostat, etc) in series with the fan. What this does is introduce a second voltage drop in the circuit (V2). This limits the voltage available for the fan (V1 = 12 - V2). This is simple enough, but has a few drawbacks. Mainly, that this second voltage drop (V2) is dissipating power. How does it do this? Heat. Wasted energy. Plus, the component needs to be able to withstand that heat (25R pot dropping 6V needs to dissipate nearly 1.5W of heat...)
2. Change the voltage running to the fan. There are a few ways to do this (variable voltage regulator, DC-DC converter, PWM...) all with pros and cons. Pretty much, PWM is our best bet here. Basically, we run the fan at full voltage, but turn it on and off quickly enough, that the fan pretty much sees an "average" voltage across it. By changing the proportion of on-time to off-time (duty cycle), we control what that "average" voltage is. The benefit of this (particularly when combined with mosfet drive, as my circuit does) is that when the fan is on, it's on, when it's off, its off. The amount of energy drawn by the circuit is roughly proportional to the duty cycle. There is negligible component heating, so virtually no wasted (heat) energy. And you get the whole voltage control range (0-12V) without having to worry too much about pot value (or power rating).
If I've lost you (or me) above, basically: PWM is the best. You'll get better control, more efficient operation, better component life and lower component cost. That ebay linked controller looks good enough. Or if you prefer to build it yourself, the one I linked before is a good option (the one I designed and made), but there are plenty of others out there if you want to look around. I had most of my components already, so it didn't even cost the $7 or so I listed for components...
Here's the situation: we have a fan, that runs of voltage V1 (I assume it's a computer fan --> V1 = 12V). We want to control the speed of this fan. To do this, we must change the voltage drop across the fan. There are two main ways to do this:
1. Change the total resistance of the circuit. We do this by putting a variable resistor (potentiometer, rheostat, etc) in series with the fan. What this does is introduce a second voltage drop in the circuit (V2). This limits the voltage available for the fan (V1 = 12 - V2). This is simple enough, but has a few drawbacks. Mainly, that this second voltage drop (V2) is dissipating power. How does it do this? Heat. Wasted energy. Plus, the component needs to be able to withstand that heat (25R pot dropping 6V needs to dissipate nearly 1.5W of heat...)
2. Change the voltage running to the fan. There are a few ways to do this (variable voltage regulator, DC-DC converter, PWM...) all with pros and cons. Pretty much, PWM is our best bet here. Basically, we run the fan at full voltage, but turn it on and off quickly enough, that the fan pretty much sees an "average" voltage across it. By changing the proportion of on-time to off-time (duty cycle), we control what that "average" voltage is. The benefit of this (particularly when combined with mosfet drive, as my circuit does) is that when the fan is on, it's on, when it's off, its off. The amount of energy drawn by the circuit is roughly proportional to the duty cycle. There is negligible component heating, so virtually no wasted (heat) energy. And you get the whole voltage control range (0-12V) without having to worry too much about pot value (or power rating).
If I've lost you (or me) above, basically: PWM is the best. You'll get better control, more efficient operation, better component life and lower component cost. That ebay linked controller looks good enough. Or if you prefer to build it yourself, the one I linked before is a good option (the one I designed and made), but there are plenty of others out there if you want to look around. I had most of my components already, so it didn't even cost the $7 or so I listed for components...
