Phantom loads

Some progress in tracking down my phantom loads! I had a shot at this a few months ago using the Fluksometer but I found for low power loads (like everything off) the update rate was very low. Also I had to arrange inverters and batteries to power the Fluksometer and my Wifi/DSL while I was testing which was messy.

Anyway I purchased a true RMS clamp type ammeter that can measure the current on individual circuits, as long as you can get to one conductor (doesn't works on pairs). This works OK but I am measuring at the bottom of its 400A range, so not very accurate.

So I turned everything off at the power points, and used the clamp to measure the power going into the house at the fuse box while I switched off each breaker. I found that the phantom current was still 0.5A, all through breaker for "circuit #1" (which goes to power points in the house).

Thats 120W, or 2.9kWh a day! I can account for most of my other power (e.g. nerd equipment) that is on all of the time.

So need to work out what's hooked up the circuit #1.

Then the wife came home so electricity was needed again and I had to stop. It appears that my alarm is part of the problem, thats about 0.2A. However it may have been charging it's battery after a house power down, so need to check that again.

- David

drowe67's picture

Another disturbing thought - My PV system generates an average of 8 kWh/day year round, or 4 kWh/day in Winter. So this phantom load is sucking 75% of my PV electricity in Winter. AAAAAAAHHHHHHHHH!

drowe67's picture

OK I think my phantom loads were actually poor power factor switch mode laptop supplies!

Quiet house today so I switched everything off and went back to the fuse box and tried switching off the "circuit 1" breaker. Once again I could see about 0.3A (bit less than the other day) going through this breaker.

Rest of the house was drawing 0.1A total, which I could accept (e.g. security lights, alarm, oven clock, cordless phone, several TVs switched off)

Then I traced the circuit I current to some laptop power supplies (without laptops). Using my power-mate lite (plug-in energy measuring gadget) I discovered the laptop power supplies were drawing 1W of real power but 17VA. So I think this reactive current was being measured by my AC clamp ammeter and the Flukso. When I removed the laptop power supplies the phantom power on circuit 1 went away.

My nerd equipment is another 24 hour load, and it also has many switch mode power supplies. So I powered this from a battery for a few hours (via a 12V to 240V inverter) so I could run the Flukso. Finally - on the Flukso graphs I saw my house at 40W or lower household power measurements from the Flusko. I even went under Bart's line - just for a moment :-)

So I think my phantom loads are actually the Flukso reading high on my laptop chargers and my nerd equipment. I also run some other inductive loads, like the EV chargers and a pool pump.

The clamp ammeter was useful for measuring my nerd equipment, as I could measure the DC current being drawn from the 12V battery feeding the inverter, bypassing any reactive power issues. The inverter is no doubt losing some power, but this gave me an upper bound for my nerd equipment of 36W.

I'll try to reduce this over the next few days by running multiple 12V boxes from one switch mode supply.

I am also wondering if a single 12V switch mode power supply working harder will have a better power factor than many power supplies just ticking over.

- David

drowe67's picture

Today I tried replacing 4 12V power supplies (a mixture of older transformer style and new switch mode) with one switch mode supply. I soldered up a cable with 4 2.1mm DC plugs on it.

Worked OK, but the power consumed didn't drop much as measured on my plug in power meter (just 2W less). The Flukso readings do seem to have dropped a little, I think because the power factor may have improved by using just one supply instead of four.

I also found that my TV when off has 17VA with just 1W real power.

- David

icarus75's picture

Hi David,

That's some very nice research into your phantom loads! I did some calculations based on the readings from your power mate:
phi = acos(1W/17VA) = 87° which is indeed a quasi reactive load.
Assuming a pure capacitive load we get:

So most likely there's a 1uF cap sitting in front of the switch mode power supply. Connected to the mains without actually powering a device they will indeed have a terrible power factor and cause a current clamp to overestimate real power consumption.


drowe67's picture

Thanks Bart for those interesting calculations. BTW I am not sure if the 17VA load was inductive or capacitive. I imagine the switch mode PS in the TV was just "idling" compared to it's normal 150W power consumption when on. So very low duty cycle pulse feeding into a large inductor. Or perhaps it's a second, auxilary power supply designed just for standby mode.

After putting 4 of my nerd equipment loads on one switching 12V power supply I have seen a significant decrease in the Flukso readings for my house (like 100W drop in the minimum overnight). I think this is because we have one load with a better power factor compared to 4 loads with very poor power factors, as the power supplies were not working very hard. Not saving any real power obviously, but it's nice to reduce the phantom part of the reading.



icarus75's picture

Here's an interesting article shedding some light on a switched-mode power supply's power factor:

"Power factor is an important measurement for two main reasons. First, an overall power factor of less than 1 means that an electricity supplier has to provide more generating capacity than actually is required.

For example, consider an office building drawing 200 A at 400 V. The supply transformer and backup UPS must be rated at 200 A × 400 V = 80 kVA. But if the power factor of the loads is only 0.6, then only 80 kVA × 0.6 = 48 kVA of real power are being consumed. In other words, if the power factor were 1, the supply capacity (transformers, cables, switchgear, UPS) could be considerably smaller.

Secondly, the current waveform distortion that contributes to reduced power factor is a cause of voltage waveform distortion and overheating in the neutral cables of three-phase systems. Primarily for this reason, international standards such as IEC 61000-3-2 have been established to control current waveform distortion by introducing limits for the amplitude of current harmonics.

To comply with these standards, designers use circuits that force the current waveform to be near sinusoidal and in-phase with the voltage. These circuits are known as power-factor correction circuits.

Remember that power-factor correction circuits are not perfect, sometimes only providing a power factor close to 1 when the power supply is at or near rated full load. Since power supplies often are derated in use, power-factor measurements must be made on the equipment under test (EUT) across a range of working conditions."

I installed a switch between the socket and my nerd equipment to switch off the power-supply units of my computers, printer, soldering iron, oscilloscope and lamps. Even if they only draw reactive current when idling, causing no impact on household consumption money-wise, they still unnecessarily load the grid.

pirlouwi's picture

Silly question: the energy counter installed by my Electrical company, is it measuring reactive power as well as active power?

icarus75's picture

Residential users are only charged based on active energy consumption.

fl177's picture

To add some perspective: in our home and offices, i measure about 3.7% reactive consumption.

3 years ago i had installed an additional kWh meter ( Carlo Gavazzi EM23DIN ) that measures both active and reactive electricity consumption. We have some TL- fluorescent lamps (with capacitor compensation) and some inductive loads, mainly 2 central heating pumps, washing machine pump motor etc...
Over the course of the last 3 years, i measured 38464 kWh active and 1409 kvarh reactive consumption or 3.7% . We don't get charged for the 3.7 % reactive part, but the electricity company has to generate and transport it. I have allready done a campaign to lower the reactve part (e.g. by replacing old capacitors).

icarus75's picture

Which capacitors are you replacing then? The ones in the TL-fluorescent lamps?

fl177's picture

yes, the building and TL-lamps date from around 1975. After 35 years or so a lot of capacitors had dried out and i had to replace them.