tezcatlipoca
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- Aug 20, 2014
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This is a write up on the recent stir plate build I did. Please reply if you have any ideas on how to improve this design. In order to minimize the length of this thread, please dont reply just to tell me what a good job it is. Im very pleased with the way it turned out.
I wanted to have two stir plates in one because Im aware that they burn out quickly. I would have bought one, but I was deterred after reading reviews on expensive stir plate units. Many said theirs stopped working, anywhere from one week of use, to 9 months of use. I didnt find any reviews that raved about theirs working after a couple years of creating starters. So, two stir plates would give you the option to make huge starters(up to 4 liters) and it would allow the opportunity to switch stir plates should one fail.
It makes sense that stir plates dont last that long. As far as I know, most operate on spinning disks(computer fans) with magnets attached to create a steadily moving magnetic field that manipulates the stir bar. These fans are built for relatively low load(moving air) and were meant to be operated at 12VDC. The amp ratings on fans state how much current it draws when it is running at max rpm. The fan I used for this build reads 0.37A. At max rpm, with a 1L flask, the fan draws about 0.4A. With a 2L flask, it can draw up to 0.5A. Not only does the magnets weight add to the load, but also the stir bar and moving water are loads on the fan. I do not believe that the extra heat from this increase in current is the biggest problem. That being said, if I do not get good life expectancy from the fans I used, I will try to use something besides a computer fan. I have a metal 120V fan in my cold box and its done well. I could hook that up to a variable AC speed control box, but that would be a more expensive project to be undertaken when this one fails. Im also aware of a 12VDC, 1.95A metal 120mm fan that might be useful for this project as well. Metal fans are heavier, so they are already built to withstand more load. Perhaps, a metal fan would not notice as much the load of the moving water.
Many people used a potentiometer to drop voltage across the fan. When its turned all the way down, the fan will get about 1VDC and not move. As it increases, it will provide all 12VDC to the fan and it will run at max speed. The only problem is the fan will not start turning until about 8-9VDC. You will lose a lot of control this way. A better method is to use a simple and cheap pwm(pulse width modulator) speed controller. This will switch the 12VDC on and off very quickly. If the knob is set to a slow speed, the controller has more off time than on time. If the knob is set to a fast speed, the controller has more on time than off time. By changing this duty cycle, the controller can control the fan speed.
I also wanted to use a see through case, so you can really see whats happening. This will prevent wondering if the fan is still turning with a murky flask of yeast.
From my first prototype, I didnt use a switch before the controller. My controller fried eventually. After looking at it, it appears to have suffered from high currents. It was rated for 5A and I measured the max current of the fan to be 0.5A. I think there was a surge of current either from plugging in the power supply or starting the fan. Therefore, I now have a switch in my design(was going to add it later for independent stir plate control). It appears as though my fan used with the damaged pwm controller was also damaged. Next, I will probe currents when the fan is starting up. If a motor is stopped or moving slowly, it will draw the most current, so this could have been the culprit. Ill test this in the future. Ok, onto directions to imitate my build!
Parts List
Multimeter(used to diagnose problems, discontinuities, failed parts)
2X - Cooler Master fan 120mm sleeve bearing(blue led really makes flasks look great; I didnt notice a red led option when I first ordered)
5 minute Epoxy(Home Depot)
2X - 1.75 washer(measured outside to outside)
2X - 12V, 10A PWM Speed Controller
4X - N52 Magnets1/2x1/8
2X - 12VDC switch(Radioshack with LED to indicate power)
12VDC, 5A power supply
Clear Acrylic Display Case, 13X5.5X5(HobbyLobby Model Car Section)
Wire Strippers/Snippers
Soldering kit/supplies(must be semi-experienced in soldering or be willing to practice on first build)
Drill and various drill bits
various nuts, bolts, neoprene washers, and metal washers
Various braided wires used to transfer power
Wire connectors for switches
Solderless breadboard jumper wires
Optional:
Heat shrink tubing with heat gun
I honestly had most of everything handy, except display case, speed controllers, and the 5A power supply. I had other 12V ones, but they didnt seem strong enough for long-term use.
DO NOT WORK ON LIVE CIRCUITS!! Well, unless you are testing with a multimeter; still be cautious then! The first job is to connect the power supply to the switches. Slice off the very end of the power supply(opposite of wall end). Here we have a red wire and a black wire. Since we want a dual-stir plate, we will need to solder or use connectors to create two red wires and two black wires. I simply cut two red braided wires and soldered them both to the existing red wire. Do this for the black wire, too. Afterwards, I used heat shrink tubing to insulate the wires and make it look nice. Electrical tape is sufficient here after soldering the wires.
For now, I will only focus on one stir plate, since the other one follows very similar instructions. I fed one of the red power supply wires to the supply side of my switch. The black power supply wire went to the earth side of the switch. The other red wire is intended to go to the other switch, while the black wire needs to go to the pwm controller(negative power side). In order to have two controllers, you will need to jump this black power wire from one pwm controller to the other, but this isnt a problem as the slots accommodate two wires. There needs to be a red jumper wire going from the load connector of the switch to the positive power on the pwm controller. From here, use the breadboard jumpers to run power from the motor + and on the controllers to the fan. For my fan, the middle connector needs to be red, and one outside one must be black. However, you can change the configuration on the fan wires until it starts working. The extra wire on the fan is used for speed reporting of the fan. Now, you should have a working fan as long as the power is plugged in, switch is on, and controller knob is turned up.
With this complete, it is time to epoxy the washer onto the fan. The washer serves two purposes: it semi-isolates the magnets from the DC motor(if the magnets are placed directly onto the fans, they will not allow the motor to turn) and it allows you to reposition the magnets before using epoxy to permanently place them down. Personally, I will leave the magnets just sitting on the washer. It seems sufficient and you could reposition them later is you switched stir bar sizes. It is important to get the washer as close to center as possible, so there is minimal vibrations, wear on fan, and a steady rotating magnetic field. Mix the epoxy on a paper plate and place a healthy dose on the washer. Place this on the fan and try to center it best you can. After it dries a little but it still pliable, you can turn the fan on to see if you have a winner. This can take a hundred different tries, so be patient! Ive found its easier to center if the fan is upside down against a surface, washer on bottom side. Then, you can move the fan slightly and monitor the small edge of the washer becoming uniform on all sides. If you cannot do it before the epoxy hardens, take the washer off, let it harden, and then try again. I can say it gets easier with practice. Second one I made took me about a minute to get it more centered than my first fan.
After the washer is on, let it set according to the epoxy instructions. Then, you can mount two round magnets onto the washer. Do not let the magnets bang together, they will shatter. Slide carefully to get them apart easily. Also, the polarity on the two magnets must be opposite. You want to be able to place a stir bar over the two magnets and the bar is attracted to both sides of the washer at once. You want to mount it to where they are on the outsides of the washer and are symmetric. Magnet placement has everything to do with throwing stir bars(mine havent ever done this) and probably chatter from stir bars(mine chatter at max speeds). I am still adjusting magnet placement to attempt to reduce chatter, just because. Of course, for yeast starters it is not necessary to pull a vortex all the way down to the bottom. Even a small dimple in the top part is indication that the yeast at the bottom are being stirred.
The washer placement is the most difficult part. I will mostly leave it up to you on how to mount the pieces inside the case. Each fan can be hung from the top of the case on each side with four bolts. My 120 mm fan is big enough that the bolts allow 2L flasks to sit in between them. I also used neoprene washers for vibration reduction and regular washers to equally space the fan from the case. You want the magnets as close to the case as possible without the chance of rubbing when you set the heaviest flask on it you plan to use. Also, beware that the stir bar has the power to lift the fan up if the magnets are too close. If you fan wont move when a flask is on, most likely your fan is too close.
I personally desoldered the potentiometer(knob) on the speed controller so I could more conveniently mount it, but this isnt necessary. My knob pulled off and behind it, there was a nut that might could support the entire board if you mounted it towards the bottom of the case. I also have the power supply loosely inside the bottom of the case. I drilled a hole at the bottom end of the case to run the power wire out, so the case can close with the power cord going through. I also drilled holes to mount the fans, to mount the controllers, switches, and knob of potentiometers. Even after all those holes, it seems the structural integrity of the display case is still holding. I was able to drill through my acrylic case very easily(even ¾ holes). Do not get a glass case!
Most of the bolts I used were #6 or #8. I would just bring the pieces with you to the hardware store after you figure out how you will lay things out. Whenever I get another big washer, Ill take a video of attaching it to another fan I have. That way, Ill have a back up for when one goes out.
I also made this convenient amazon wish list for people wanting exact links to most of the parts.
http://amzn.com/w/1BFF3DQ9WPSMA
Below is a video of the working prototype. It still has the damaged fan on the other side. It seems that it doesnt move as fast, so Im thinking the fan windings might have reached too high of a temperature.
[ame]https://www.youtube.com/watch?v=p4cNZtsSmQk[/ame]
I wanted to have two stir plates in one because Im aware that they burn out quickly. I would have bought one, but I was deterred after reading reviews on expensive stir plate units. Many said theirs stopped working, anywhere from one week of use, to 9 months of use. I didnt find any reviews that raved about theirs working after a couple years of creating starters. So, two stir plates would give you the option to make huge starters(up to 4 liters) and it would allow the opportunity to switch stir plates should one fail.
It makes sense that stir plates dont last that long. As far as I know, most operate on spinning disks(computer fans) with magnets attached to create a steadily moving magnetic field that manipulates the stir bar. These fans are built for relatively low load(moving air) and were meant to be operated at 12VDC. The amp ratings on fans state how much current it draws when it is running at max rpm. The fan I used for this build reads 0.37A. At max rpm, with a 1L flask, the fan draws about 0.4A. With a 2L flask, it can draw up to 0.5A. Not only does the magnets weight add to the load, but also the stir bar and moving water are loads on the fan. I do not believe that the extra heat from this increase in current is the biggest problem. That being said, if I do not get good life expectancy from the fans I used, I will try to use something besides a computer fan. I have a metal 120V fan in my cold box and its done well. I could hook that up to a variable AC speed control box, but that would be a more expensive project to be undertaken when this one fails. Im also aware of a 12VDC, 1.95A metal 120mm fan that might be useful for this project as well. Metal fans are heavier, so they are already built to withstand more load. Perhaps, a metal fan would not notice as much the load of the moving water.
Many people used a potentiometer to drop voltage across the fan. When its turned all the way down, the fan will get about 1VDC and not move. As it increases, it will provide all 12VDC to the fan and it will run at max speed. The only problem is the fan will not start turning until about 8-9VDC. You will lose a lot of control this way. A better method is to use a simple and cheap pwm(pulse width modulator) speed controller. This will switch the 12VDC on and off very quickly. If the knob is set to a slow speed, the controller has more off time than on time. If the knob is set to a fast speed, the controller has more on time than off time. By changing this duty cycle, the controller can control the fan speed.
I also wanted to use a see through case, so you can really see whats happening. This will prevent wondering if the fan is still turning with a murky flask of yeast.
From my first prototype, I didnt use a switch before the controller. My controller fried eventually. After looking at it, it appears to have suffered from high currents. It was rated for 5A and I measured the max current of the fan to be 0.5A. I think there was a surge of current either from plugging in the power supply or starting the fan. Therefore, I now have a switch in my design(was going to add it later for independent stir plate control). It appears as though my fan used with the damaged pwm controller was also damaged. Next, I will probe currents when the fan is starting up. If a motor is stopped or moving slowly, it will draw the most current, so this could have been the culprit. Ill test this in the future. Ok, onto directions to imitate my build!
Parts List
Multimeter(used to diagnose problems, discontinuities, failed parts)
2X - Cooler Master fan 120mm sleeve bearing(blue led really makes flasks look great; I didnt notice a red led option when I first ordered)
5 minute Epoxy(Home Depot)
2X - 1.75 washer(measured outside to outside)
2X - 12V, 10A PWM Speed Controller
4X - N52 Magnets1/2x1/8
2X - 12VDC switch(Radioshack with LED to indicate power)
12VDC, 5A power supply
Clear Acrylic Display Case, 13X5.5X5(HobbyLobby Model Car Section)
Wire Strippers/Snippers
Soldering kit/supplies(must be semi-experienced in soldering or be willing to practice on first build)
Drill and various drill bits
various nuts, bolts, neoprene washers, and metal washers
Various braided wires used to transfer power
Wire connectors for switches
Solderless breadboard jumper wires
Optional:
Heat shrink tubing with heat gun
I honestly had most of everything handy, except display case, speed controllers, and the 5A power supply. I had other 12V ones, but they didnt seem strong enough for long-term use.
DO NOT WORK ON LIVE CIRCUITS!! Well, unless you are testing with a multimeter; still be cautious then! The first job is to connect the power supply to the switches. Slice off the very end of the power supply(opposite of wall end). Here we have a red wire and a black wire. Since we want a dual-stir plate, we will need to solder or use connectors to create two red wires and two black wires. I simply cut two red braided wires and soldered them both to the existing red wire. Do this for the black wire, too. Afterwards, I used heat shrink tubing to insulate the wires and make it look nice. Electrical tape is sufficient here after soldering the wires.
For now, I will only focus on one stir plate, since the other one follows very similar instructions. I fed one of the red power supply wires to the supply side of my switch. The black power supply wire went to the earth side of the switch. The other red wire is intended to go to the other switch, while the black wire needs to go to the pwm controller(negative power side). In order to have two controllers, you will need to jump this black power wire from one pwm controller to the other, but this isnt a problem as the slots accommodate two wires. There needs to be a red jumper wire going from the load connector of the switch to the positive power on the pwm controller. From here, use the breadboard jumpers to run power from the motor + and on the controllers to the fan. For my fan, the middle connector needs to be red, and one outside one must be black. However, you can change the configuration on the fan wires until it starts working. The extra wire on the fan is used for speed reporting of the fan. Now, you should have a working fan as long as the power is plugged in, switch is on, and controller knob is turned up.
With this complete, it is time to epoxy the washer onto the fan. The washer serves two purposes: it semi-isolates the magnets from the DC motor(if the magnets are placed directly onto the fans, they will not allow the motor to turn) and it allows you to reposition the magnets before using epoxy to permanently place them down. Personally, I will leave the magnets just sitting on the washer. It seems sufficient and you could reposition them later is you switched stir bar sizes. It is important to get the washer as close to center as possible, so there is minimal vibrations, wear on fan, and a steady rotating magnetic field. Mix the epoxy on a paper plate and place a healthy dose on the washer. Place this on the fan and try to center it best you can. After it dries a little but it still pliable, you can turn the fan on to see if you have a winner. This can take a hundred different tries, so be patient! Ive found its easier to center if the fan is upside down against a surface, washer on bottom side. Then, you can move the fan slightly and monitor the small edge of the washer becoming uniform on all sides. If you cannot do it before the epoxy hardens, take the washer off, let it harden, and then try again. I can say it gets easier with practice. Second one I made took me about a minute to get it more centered than my first fan.
After the washer is on, let it set according to the epoxy instructions. Then, you can mount two round magnets onto the washer. Do not let the magnets bang together, they will shatter. Slide carefully to get them apart easily. Also, the polarity on the two magnets must be opposite. You want to be able to place a stir bar over the two magnets and the bar is attracted to both sides of the washer at once. You want to mount it to where they are on the outsides of the washer and are symmetric. Magnet placement has everything to do with throwing stir bars(mine havent ever done this) and probably chatter from stir bars(mine chatter at max speeds). I am still adjusting magnet placement to attempt to reduce chatter, just because. Of course, for yeast starters it is not necessary to pull a vortex all the way down to the bottom. Even a small dimple in the top part is indication that the yeast at the bottom are being stirred.
The washer placement is the most difficult part. I will mostly leave it up to you on how to mount the pieces inside the case. Each fan can be hung from the top of the case on each side with four bolts. My 120 mm fan is big enough that the bolts allow 2L flasks to sit in between them. I also used neoprene washers for vibration reduction and regular washers to equally space the fan from the case. You want the magnets as close to the case as possible without the chance of rubbing when you set the heaviest flask on it you plan to use. Also, beware that the stir bar has the power to lift the fan up if the magnets are too close. If you fan wont move when a flask is on, most likely your fan is too close.
I personally desoldered the potentiometer(knob) on the speed controller so I could more conveniently mount it, but this isnt necessary. My knob pulled off and behind it, there was a nut that might could support the entire board if you mounted it towards the bottom of the case. I also have the power supply loosely inside the bottom of the case. I drilled a hole at the bottom end of the case to run the power wire out, so the case can close with the power cord going through. I also drilled holes to mount the fans, to mount the controllers, switches, and knob of potentiometers. Even after all those holes, it seems the structural integrity of the display case is still holding. I was able to drill through my acrylic case very easily(even ¾ holes). Do not get a glass case!
Most of the bolts I used were #6 or #8. I would just bring the pieces with you to the hardware store after you figure out how you will lay things out. Whenever I get another big washer, Ill take a video of attaching it to another fan I have. That way, Ill have a back up for when one goes out.
I also made this convenient amazon wish list for people wanting exact links to most of the parts.
http://amzn.com/w/1BFF3DQ9WPSMA
Below is a video of the working prototype. It still has the damaged fan on the other side. It seems that it doesnt move as fast, so Im thinking the fan windings might have reached too high of a temperature.
[ame]https://www.youtube.com/watch?v=p4cNZtsSmQk[/ame]
