Power Factor Of A March Pump

[MartinS]

Spoke to a controls guy at work today and he said I might be able to get away with putting a 2 or so watt resistor across the motor and that should do the trick. I suppose this is a snubber?

I'd expect you'd need a capacitor in there too, especially given the low power factor of the pump.

I tested the pump again last night with and without load (but primed), and it bounced around between 0.30 and 0.33.

Couldn't use a DC controlled mechanical AC relay as I think they require too much current for what my system could supply, just TTL/CMOS levels (i had a weak power supply too).

Given your weak power supply, this might not work, but did you try driving the relay off your unregulated Vin? An NPN transistor between the relay and ground, and an appropriate base resistor might get you across the line. If you're using CMOS logic, you're never going to be able to drive anything without transistors (4000 series will normally only put out about 1mA at 5V).

 

[rwmingis]

Given your weak power supply, this might not work, but did you try driving the relay off your unregulated Vin? An NPN transistor between the relay and ground, and an appropriate base resistor might get you across the line. If you're using CMOS logic, you're never going to be able to drive anything without transistors (4000 series will normally only put out about 1mA at 5V).

Hi Martin,

Your probably right, for this project i might consider that. I used a very small transformer on the last project as a DC relay wasn't planned so even that would cause a lot of noise on the system, probaby more than the microcontroller would like.

How does this change in power factor (what you expected .75 to .3) affect your design?

Rob

 

[MartinS]

How does this change in power factor (what you expected .75 to .3) affect your design?

It pretty much rules out doing any solid state stuff for me. The whole reason for going solid state was to keep the element driver and pump driver the same, but I just don't have the knowledge to design a snubber that will work in both applications (A simple RC snubber with enough capacitance to correct the power factor on the pump would screw up the element). I could just leave the snubber components off in the element driver, but the more I think about it, the more sense a mechanical relay makes. Mechanical relays have the added advantage that they don't need any heat management.

Power isn't usually a problem for me, either. I almost always over-engineer my power supplies.

 

[Ducatiboy stu]

I do remember calculating PF using a dual trace CRO....


But...I would have to deep into the shed and find find my tech notes from 20Yrs ago....and yes..i still have them...

 

[Screwtop]

I do remember calculating PF using a dual trace CRO....


But...I would have to deep into the shed and find find my tech notes from 20Yrs ago....and yes..i still have them...

Threw mine out when they gave me a desk job :lol: