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Old 02-06-2012, 08:09 PM   #1
jfsp
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Default Peristaltic pump: flow control

Simple question : How would you control the flow of a DIY peristaltic pump when you don't want to run it at max speed ? I see 3 choices :

1) regulate/reduce the voltage to get lower speeds (would that work with an AC motor or would I just loose torque?)

2) run at full voltage, but pulse the current (x times per seconds)

3) run at full voltage, full current (max speed), but take breaks every z seconds (for example, run 5 seconds, stop for 5 seconds ...)

Lets assume stepped motors are not an option.


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Old 02-07-2012, 01:46 PM   #2
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Quote:
Originally Posted by jfsp View Post
Simple question : How would you control the flow of a DIY peristaltic pump when you don't want to run it at max speed ? I see 3 choices :

1) regulate/reduce the voltage to get lower speeds (would that work with an AC motor or would I just loose torque?)

2) run at full voltage, but pulse the current (x times per seconds)

3) run at full voltage, full current (max speed), but take breaks every z seconds (for example, run 5 seconds, stop for 5 seconds ...)

Lets assume stepped motors are not an option.
4) Variable frequency drive. This is how AC operated motors in industrial applications have their speed modulated. Instead of changing the voltage, you change the frequency of the electricity from its usual 60Hz to something else. That changes the rate of rotation of the motor. These are generally used on 3-phase motors.

Looks like automationdirect.com can put you in a 1/4HP VFD for $100.


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Old 02-07-2012, 01:49 PM   #3
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Originally Posted by bdjohns1 View Post
Looks like automationdirect.com can put you in a 1/4HP VFD for $100.
Probably not a viable option, since DIY pumps are typically done to avoid shelling out $150 for a ready-made pump.
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Old 02-07-2012, 04:57 PM   #4
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Look into a router speed control. I think it's more of a pwm and pulses the power. I used one to control the speed of a fan before and worked pretty good. Harbor freight has one for I think $20.
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Old 02-07-2012, 11:43 PM   #5
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I tore apart an old treadmill and am using the controller and motor from that to build mine. The motors are usually 90-120 volt DC and all the controls are already there for the speed control. Only cost me $10 on craigslist for the whole thing. The controllers are usually PWM's IIRC so there isn't any loss of torque like you would get using a rheostat. I'll hopefully have mine built in a couple of weeks and then post some pictures.
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Old 02-08-2012, 12:37 AM   #6
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another option for an AC motor is this little device that hooks on to any standard SSR. Supposedly it is better than frequency control for some motors that might otherwise overheat with that kind of control.

like $40: http://www.nuwaveproducts.com/ssrman-1p.htm


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