Power Factor Of A March Pump

[MartinS]

Does anyone happen to know the typical power factor of a March 809? I have no easy way of measuring it myself, as my oscilloscope is a 20+yo, single-channel pile of cr*p.

This post suggests a power factor of 0.75, but I can't find anything backing that up. Can anyone collaborate that figure?

 

[razz]

How do you work out the power factor Martin ?

 

[newguy]

If you can insert a small series resistor into the power leads you can probe the current drawn by the pump. If you can simultaneously examine current & voltage while the pump is running with an oscilloscope, the power factor is the cosine of the phase angle between the voltage & current.

If I still had access to my former place-of-work's equipment I could measure the PF quite easily. Now it isn't so easy.

 

[MartinS]

How do you work out the power factor Martin ?

It's really a question for the EEs (Sorry, I probably should have put that in the title). I can't quite remember the exact value (it's been a while since I've done this stuff), but I think it is the integral of the instantaneous power divided by the product of rms voltage and rms current. It can also be approximated from the phase shift of the current relative to the voltage.

 

[razz]

Thanks Martin, clear as mud ! :lol:

 

[Hutch]

It's really a question for the EEs (Sorry, I probably should have put that in the title). I can't quite remember the exact value (it's been a while since I've done this stuff), but I think it is the integral of the instantaneous power divided by the product of rms voltage and rms current. It can also be approximated from the phase shift of the current relative to the voltage.

Hi Martin,

I can't give you a specific answer, but you can easily measure the PF using a power-meter from Jaycar.
I bought one of these to measure power around the house, and it is surprisingly accurate, and it also gives the power-factor, RMS voltage, current, total kWh, price, etc.

If you like, I can make this measurement for you tonight (I have a March pump)?

Hope this helps.
Hutch.

 

[Phrak]

The power meters are great, but there's questions around the accuracy of the PF measurement:
http://www.dansdata.com/quickshot041.htm

Martin, I understand PF, but I don't understand WHY you're particularly interested in the PF on the March Pump. Are you charged by VA instead of kWh? Running from a UPS or generator? Current-limited?

Tim

 

[MartinS]

I can't give you a specific answer, but you can easily measure the PF using a power-meter from Jaycar.

Ahh - excellent! I have one of those, but didn't realise it could do power factor. Thanks! I'll take a measurement tonight, and post it here for the benefit of Google (I'm sure I'm not the only one who has searched for this over the years).

 

[Screwtop]

Does anyone happen to know the typical power factor of a March 809?

One question...............Why :blink:

 

[Offline]

.... (I'm sure I'm not the only one who has searched for this over the years).

actually you might be.

 

[MartinS]

One question...............Why :blink:

It's a somewhat important number for interfacing with control circuitry, which I'm toying with at the moment.

 

[Hutch]

The power meters are great, but there's questions around the accuracy of the PF measurement:
http://www.dansdata.com/quickshot041.htm

Martin, I understand PF, but I don't understand WHY you're particularly interested in the PF on the March Pump. Are you charged by VA instead of kWh? Running from a UPS or generator? Current-limited?

Tim

Interesting Phrak, and thanks for letting us know - although the review would suggest that the PF measurement is more accurate for inductive loads, as is the case for the March pump.
I've certainly noticed it dip well below 100 with certain inductive loads attached (say transformer/wall-warts with no load).
I guess it would be a bit much to expect it to give an accurate PF estimate for only $30!

Martin - I'd expect the PF to vary depending on the "mechanical load" you subject your March-pump to (ie. shutting off the outlet).
Let us know what you find.

 

[mesa]

I'm with Hutch,
I'd expect the power factor to vary too much depending on the load to make it meaningful.

Are you doing something funky like generating your own sine wave to control the speed of the pump or something? If your that serious about it though I'd probably hook up a shunt resistor as newguy said and measure the power factor during operation and adjust your sine wave generator accordingly. That way you can even detect a failure to prime the pump correctly and presumably work out both flow rate and resitance and detect a stuck sparge or whatever you are doing.

 

[MartinS]

Martin, I understand PF, but I don't understand WHY you're particularly interested in the PF on the March Pump. Are you charged by VA instead of kWh? Running from a UPS or generator? Current-limited?

Sorry, I missed this question earlier. I want to switch the pump with a triac, and want to know how much snubbing I'll need.

 

[MartinS]

Are you doing something funky like generating your own sine wave to control the speed of the pump or something?

No, and for the record, March says you shouldn't do that. I'm just doing simple on/off control without wanting to mechanically switch the mains, but since phase control is discouraged by March, I don't want the switch to play silly buggers when it should be turning it off.

 

[rwmingis]

No, and for the record, March says you shouldn't do that. I'm just doing simple on/off control without wanting to mechanically switch the mains, but since phase control is discouraged by March, I don't want the switch to play silly buggers when it should be turning it off.

Hi Martin, am looking to do the same thing. I was going to just switch my march pump using a zero crossing SSR. I found out the hard way that these don't work too well on refrigerators due to the starting circuits that they have, however I thought they would be okay for low power pumps since they're zero crossing. Incidentally I was able to fix my problem by having the SSR control a mechanical 240v relay which then switched the fridge on.

Is there any inherit problem with this idea?

 

[MartinS]

Hi Martin, am looking to do the same thing. I was going to just switch my march pump using a zero crossing SSR. I found out the hard way that these don't work too well on refrigerators due to the starting circuits that they have, however I thought they would be okay for low power pumps since they're zero crossing. Incidentally I was able to fix my problem by having the SSR control a mechanical 240v relay which then switched the fridge on.

Is there any inherit problem with this idea?

I wouldn't think the zero-crossing is too important unless you're planning on PWMing it. If you have a zero-crossing SSR firing a 240v relay, I'd expect you'd be losing the advantage of the zero-crossing anyway. The relay is going to take a few ms to switch, and you're going to be back to square one - possibly worse if the engage and release times of the relay are 5ms or 15ms for example (in which case it will always fire at the worst possible time).

The simplest solution for switching a pump (assuming you don't have any other requirements) is to go the mechanical route. Get a relay with a low voltage DC trigger. You only switch it a few times in a session, so you don't need to worry about transients.

Back to my original question, I just popped home to test this, and tried running the pump dry for a few seconds (naughty me, I know): The Jaycar power meter read 0.30 power factor... That's nasty! If that's right, then an SSR is unlikely to work without external snubbing.

I might go the mechanical route myself now, but for simplicity, I was hoping to use the same circuit to duty cycle my element.

 

[newguy]

I might go the mechanical route myself now, but for simplicity, I was hoping to use the same circuit to duty cycle my element.

I use an SSR for my heating element in my HERMS, and a relay to switch my pump and the element in my HLT. I struggled with the same issues as you currently are when I designed my system. The only critical component (when it comes to frequent switching) is whatever is driving the heating element. Everything else can be comfortably switched with a relay.

 

[MartinS]

I use an SSR for my heating element in my HERMS, and a relay to switch my pump and the element in my HLT. I struggled with the same issues as you currently are when I designed my system. The only critical component (when it comes to frequent switching) is whatever is driving the heating element. Everything else can be comfortably switched with a relay.

Yeah - that's the way I'm thinking, but the OCD/modular-design part of my brain is going to be scarred forever.

 

[rwmingis]

I wouldn't think the zero-crossing is too important unless you're planning on PWMing it. If you have a zero-crossing SSR firing a 240v relay, I'd expect you'd be losing the advantage of the zero-crossing anyway. The relay is going to take a few ms to switch, and you're going to be back to square one - possibly worse if the engage and release times of the relay are 5ms or 15ms for example (in which case it will always fire at the worst possible time).

You're right about that, mechanical should do nicely except for the control power requirements. 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). 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?

On the other project, I had no trouble running the mechanical relay off the SSR. I suppose the relay on the coil is not a heavily inductive load.

Cheers

Rob