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Old 01-15-2012, 07:33 PM   #1
ahave
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Default [Video] Dual Purpose PWM Project: Stir Plate & PWM Controller

I am calling this project 'done' despite a few glitches. I had a need for a stir plate and also a PWM controller w/SSR for an electric heater (electric smoker for now, HLT down down the road)

Inside the box is a hand-built power supply and 555 timer circuit providing the PWM signal. The selector switch has two purposes:
1) Select the output: When the box is in stir plate mode the SSR will not be active and vice versa.

2) Select the cycle time: The switch will select which capacitors the 555 circuit will use which allows for longer hold times so not to burn out the SSR.

The adjustment knob controls the duty cycle (?), going from near 100% ON to somewhere around 50% ON. The knob provides the same ratio in both modes.

Video shows the box in action w/ a 7/8" stir bar and lamp.


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Old 01-15-2012, 09:41 PM   #2
stlbeer
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Genius!

Nice job.


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Old 01-26-2013, 06:04 PM   #3
fc36
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Any chance we can get schematics or build info?
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Old 02-16-2013, 12:55 AM   #4
ahave
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well, unfortunately I don't really have a schematic. I kinda built it ad hoc, without a circuit design other than what I put together in my head. It uses the standard 555 timer PWM circuit with the exception that one of the capacitors is tied to a double pole, double throw switch. The double pole switch allows me to toggle between different capacitors and at the same time toggle the output of the 555 circuit.

For example: When the switch is in position A, I use a cap appropriate for stir fan control and the other leg is tied to the output of the 555 circuit powers the fan. When the switch is in position B, I use a cap appropriate for heat stick control and the other leg is tied to a SSR controling the 15A 110V line out the back.

I also built my own bridge rectifier powersupply to power everything. Totally not worth it considering you can pick up wallworts pretty easy and for much much cheaper than what it cost me to piece it together.

If you are still interested I can try and put together a schematic of the design.
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Old 02-16-2013, 01:19 AM   #5
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Thats brilliant!

I'm interested in a schematic as well.
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Old 09-17-2013, 04:21 PM   #6
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Quote:
Originally Posted by ahave View Post
well, unfortunately I don't really have a schematic. I kinda built it ad hoc, without a circuit design other than what I put together in my head. It uses the standard 555 timer PWM circuit with the exception that one of the capacitors is tied to a double pole, double throw switch. The double pole switch allows me to toggle between different capacitors and at the same time toggle the output of the 555 circuit.

For example: When the switch is in position A, I use a cap appropriate for stir fan control and the other leg is tied to the output of the 555 circuit powers the fan. When the switch is in position B, I use a cap appropriate for heat stick control and the other leg is tied to a SSR controling the 15A 110V line out the back.

I also built my own bridge rectifier powersupply to power everything. Totally not worth it considering you can pick up wallworts pretty easy and for much much cheaper than what it cost me to piece it together.

If you are still interested I can try and put together a schematic of the design.
Resurrect, yes, please provide us with a schematic. I'm re-interested in this as a side project to my eBIAB that I have planned. It might be nice to utilize the PWM that I already built for my second stirplate to also potentially control a 5500W Camco element with an SSR. I don't need you to draw a perfect diagram, but a back-of-the-envelope drawing would be a great help.


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