DC brush motor speed control

[Art_H]

I have an elec water pump that I want to modulate water flow. (ie. pump RPM)

-DC brush motor
-12-14v
-12A max
-no reverse or braking required

From all I have gathered so far, PWM looks like the best method so far.

I am looking for direction on some good circuits, and where to look.

Or if there is a more efficient method etc.

Thanks

Art

[ante]

Hi Art,

Here is a good example: http://www3.telus.net/chemelec/Projects/PWM/PWM.htm

[Art_H]

Thanks Ante, that link looks pretty good.

The pump is supposed to flow 35 gal @ 5.8A. 12v

What  kind of current spike can I expect on start-up?

And can I use the PWM at a lower draw initialy to cancel some of the higher spike?

Art

[ante]

Hi Art,

The current at startup is hard to predict, it depends on the load and the setting of the speed (PWM) and also the inertia of the pump. You can use the PWM control to “softstart” but if the motor is stalled or the inertia of the pump is very high the motor might get damaged. The distance and elevation of the pumping decides to some degree how much load the motor has on startup (from a deep well or just horizontally). Some pumps are stubborn at startup like a rubber impeller type and requires a good kick to get started. Shovel pumps are much easier to get going and there are a few other types like membrane, gear and ring pumps with different characteristics. You have to make some tests and measure the current and make sure the temperature of the motor and the electronics stays at a decent level. It might be wise the start at half speed (not lower) and se how it works out, if it starts running effortless try a lower setting and so on.