02-15-2018, 10:30 PM
Apparently Kill-A-Watt and other similar devices to measure electricity use are not accurate at low wattages.
Searching for info on how much power "wall wart" transformers use on standby, I ran across this note from the Lawrence Berkeley National Laboratory:
http://standby.lbl.gov/measure.html
"Measuring Standby
Few products indicate their standby power use, so you need a meter to measure it. Unfortunately, few meters have sufficient resolution to measure standby power accurately. These cost over $500.
A few meters are now available for less than $100. Unfortunately their accuracy below a few watts is poor. These are nevertheless indicative of standby power. You can improve accuracy by adding a standard load (such as an incandescent light bulb) into the circuit; then measure the difference in power consumption."
I assume this applies to a Kill-A-Watt. So if you want to measure a small transformer's standby energy use, put a known wattage device like a light bulb on the same circuit, then measure the difference between what the bulb uses and what the Kill-A-Watt shows.
The LBL site also has some interesting charts on standby electrical use by different devices:
http://standby.lbl.gov/summary-chart.html
Good luck.
- Winston
Searching for info on how much power "wall wart" transformers use on standby, I ran across this note from the Lawrence Berkeley National Laboratory:
http://standby.lbl.gov/measure.html
"Measuring Standby
Few products indicate their standby power use, so you need a meter to measure it. Unfortunately, few meters have sufficient resolution to measure standby power accurately. These cost over $500.
A few meters are now available for less than $100. Unfortunately their accuracy below a few watts is poor. These are nevertheless indicative of standby power. You can improve accuracy by adding a standard load (such as an incandescent light bulb) into the circuit; then measure the difference in power consumption."
I assume this applies to a Kill-A-Watt. So if you want to measure a small transformer's standby energy use, put a known wattage device like a light bulb on the same circuit, then measure the difference between what the bulb uses and what the Kill-A-Watt shows.
The LBL site also has some interesting charts on standby electrical use by different devices:
http://standby.lbl.gov/summary-chart.html
Good luck.
- Winston