CrookedChris
Well-Known Member
After getting frustrated with the speed control limitations of brushless computer fans and just feeling uneasy about the lack of robustness in the speed control methods being implemented by the nice people on this forum I decided to go a step further in making my own stir plate.
Don't get me wrong, I don't think there's anything intrinsically wrong or unsafe with the designs I've seen implemented here. It's just that as an anal retentive electrical engineer I wanted finer control from 0 to full speed with no dead bands in the speed control knob and a robust design that will last me forever.
So I've implemented a very simple PWM (pulse width modulation) speed controller with a brushed DC motor (not a fan). My electronics provide ramp-up control, max speed limitation, and protection of the electronics from voltage spikes created by the motor (back EMF spikes). The brushed motor is a little louder than a brushless fan but the noise is dampened by the enclosure and is completely drowned out by the sound of the stir bar when stirring liquid.
I've made mine and it's working great. I haven't put together a schematic drawing or anything yet, just scribbles on scrap napkins and bits of paper. If people on this board are interested in my design I'll put together a schematic, bill of materials, and build instructions and post them to this thread. If no one's interested, I won't waste the time. So if you want to see it, speak up.
Additionally, if any of you guys (or gals) are really interested I would consider putting together ready to assemble kits of parts for sale. I'm not sure what it would cost yet. I'd just take the cost of all the parts (including a professionally manufactured circuit board and stir-bar) and mark it up a bit for my time and effort assembling the kits and dropping them off to be shipped. This option might be cheaper than getting all the parts yourself because of the volume discounts I might be able to get on the parts if enough people are interested.
I'll try to post pictures sometime in the next couple days but mine looks externally like all the others built in a Radio Shack project box. Inside there's a little circuit board and a bit of PVC pipe to hold the motor in place. On the end of the motor's shaft is a small plastic disk to which rare earth magnets are glued.
Also, in case anyone didn't know a small (too small for a 2L starter?) professionally manufactured stir plate can be purchased on-line for less than $90. But what fun is that? Hanna HI 190M Magnetic Stirrer
Don't get me wrong, I don't think there's anything intrinsically wrong or unsafe with the designs I've seen implemented here. It's just that as an anal retentive electrical engineer I wanted finer control from 0 to full speed with no dead bands in the speed control knob and a robust design that will last me forever.
So I've implemented a very simple PWM (pulse width modulation) speed controller with a brushed DC motor (not a fan). My electronics provide ramp-up control, max speed limitation, and protection of the electronics from voltage spikes created by the motor (back EMF spikes). The brushed motor is a little louder than a brushless fan but the noise is dampened by the enclosure and is completely drowned out by the sound of the stir bar when stirring liquid.
I've made mine and it's working great. I haven't put together a schematic drawing or anything yet, just scribbles on scrap napkins and bits of paper. If people on this board are interested in my design I'll put together a schematic, bill of materials, and build instructions and post them to this thread. If no one's interested, I won't waste the time. So if you want to see it, speak up.
Additionally, if any of you guys (or gals) are really interested I would consider putting together ready to assemble kits of parts for sale. I'm not sure what it would cost yet. I'd just take the cost of all the parts (including a professionally manufactured circuit board and stir-bar) and mark it up a bit for my time and effort assembling the kits and dropping them off to be shipped. This option might be cheaper than getting all the parts yourself because of the volume discounts I might be able to get on the parts if enough people are interested.
I'll try to post pictures sometime in the next couple days but mine looks externally like all the others built in a Radio Shack project box. Inside there's a little circuit board and a bit of PVC pipe to hold the motor in place. On the end of the motor's shaft is a small plastic disk to which rare earth magnets are glued.
Also, in case anyone didn't know a small (too small for a 2L starter?) professionally manufactured stir plate can be purchased on-line for less than $90. But what fun is that? Hanna HI 190M Magnetic Stirrer