Standby power measurement - Page 1
Forum section: electronics / projects

author: quarks
author_rank: Frequent Contributor
timestamp: January 25, 2015, 05:23:24 pm
content: Today I made some measurements to find the lowest power consumption gear I can measure.Here are some results (see picture)Left side is Samsung (7mW + 40mW) and right side is Nokia (25mW + 115mW).Not bad at all, but the top Ansmann AES1 really is below my capabilities and looks like to be (as advertised) "Zero 0 Watt Technology".My guess is, it must be way under 100µW.Besides this, I used VAC measurement with some of my handheld DMMs (Fluke + Gossen) as a load and most showed around 5mW (as expected with 10 MOhm Input impedance at 230VAC).Just for fun I also tried my benchtop DMMs and was quite surprised to see 50mW (=> only 1 MOhm input impedance). So far I never realized this and I would like to know if there is a good reason for that. Does anyone know why the "better" gear has lower impedance?thanksquarks

author: quarks
author_rank: Frequent Contributor
timestamp: February 06, 2015, 07:07:15 pm
content: I do not know if anyone is interested, but here is an update.I have build a measurement adapter for my "reference" power meter and experimented with higher Shunt values.AES1 measured with 100 Ohm shunt: reading is "Zero"but with a 1k Ohm shunt I get a reading of about 2µW.I am really amazed by this "Zero 0 Watt Technology" from Ansmann!For further investigations, I ordered some high value resistors and will build reference loads and try to find out how accurate low values can be measured.

author: eneuro
author_rank: Super Contributor
timestamp: February 06, 2015, 08:35:14 pm
content: Quote from: quarks on February 06, 2015, 07:07:15 pmIt could be interesting teardown suspect, while I wonder what they used as mains switchAnother question is how many hours this thing have to work ... to give us back investment to buy this thing + shipment costs, while it is not available for free, so we have to pay for those"zero 0 watts"

author: quarks
author_rank: Frequent Contributor
timestamp: February 07, 2015, 07:50:49 am
content: Hello eneuro,thanks for your reply.Probably my english is not good enough, because I unfortunately do not really understand what your point is.Measuring power (W, VA, var, PF...) correctly is challenging. Especially really low stanby power is not an easy task and needs special care. When you measure Volts and Amps at the same time you always have a systematic errors you have to take care of. I.e. the voltmeter itself will add (in my case) up to 50 mW if you do not watch out.Byequarks

author: mij59
author_rank: Frequent Contributor
timestamp: February 07, 2015, 08:19:35 am
content: In the Netherlands one Watt of standby power will cost about 2 Euro's per year.Best way to safe money is to unplug.

author: dom0
author_rank: Super Contributor
timestamp: February 07, 2015, 07:20:30 pm
content: You also just can't multiply RMS voltage and RMS current to calculate power consumption. Result of Urms * Irms is apparent power, not true power...

author: rr100
author_rank: Frequent Contributor
timestamp: February 08, 2015, 05:33:46 am
content: Yes, you can't just multiply V and I RMS you need to integrate the product of instant V and I.The first thing I can think of (and used the trick quite a few times) is just to have a relay that feeds part of the circuit via a pair of normally open contacts going over itself. I don't know how common trick would be but I've used a few times and is what I think of reflexively.

author: SeanB
author_rank: Super Contributor
timestamp: February 08, 2015, 07:33:10 am
content: Quote from: eneuro on February 06, 2015, 08:35:14 pmCould be as simple as a latching relay and a supercap charged during operation so there is energy stored to close the switch when needed. As it is a time switch it will hold enough charge to operate when the on time is reached and then use a small transformer or capacitive dropper to recharge the supercap ( or a 2-3 cell NimH cell pack) during on time.This was done on true off delay relays to open the contacts of a bistable relay when the power was removed, using internally a 6 cell button cell pack of NiCd batteries. You just needed a minimum power on time of 30 seconds to charge the pack up somewhat, and it had a simple charge circuit if the power was applied long term that limited current to the C/20 continuous charge rate.

author: rr100
author_rank: Frequent Contributor
timestamp: February 08, 2015, 08:23:44 am
content: Maybe I don't understand what this thing does but why would it need to store any energy while it's off?Edit: to clarify: for me it looks to be just a timer that goes from on->off. I assume we're talking about the power consumption when is off, otherwise it clearly isn't microwatts, I see a LED there (or maybe that is active only when setting it up?).

author: quarks
author_rank: Frequent Contributor
timestamp: February 08, 2015, 09:56:34 am
content: Maybe I was not clear what this is all about.I am mainly interested in accuracy and in finding out where the limit of my gear is.And accurate very low standby power measurement is very challenging.Therefore I looked for a device with the lowest standby consumption I have and the 7mW was the lowest I could find in my pile of DUTs until I tried the Ansmann.BTWThe Ansmann AES1 is just a timer which I use to charge my tablet. I use it because I do not like that many vendors of mobile devices (maily those where you cannot change the battery) seem to overcharge the internal battery by purpose, so the device is kind of "programmed" to fail after the warranty.The AES1 itself was/is not subject of my interest, but was the first device I was not able to measure with any of my power meters, therefore it suddenly became very interesting to me.I hope this clears things up.

author: SeanB
author_rank: Super Contributor
timestamp: February 08, 2015, 10:10:33 am
content: True, if it is a time switch that only switches off then all it needs is a trigger coil to switch a power switch off, with the user pressing the button to reset it back on. Was used on Grundig TV sets to have a true zero power option, with the only thing being you needed to press the button on the TV to turn it on.On this I assume it is only using the switch to connect mains to a controller with a relay ( probably bistable) to power on the output and then it simply times out to pop the relay off using the energy stored in a capacitor. After relay of there is nothing connected to the mains, so it only draws a very small capacitive power between the internal wires and relay contacts.

author: dom0
author_rank: Super Contributor
timestamp: February 08, 2015, 10:15:40 am
content: Yeah, if it's indeed "zero power" you'll only ever measure leakage currents... which is challenging, too

author: eneuro
author_rank: Super Contributor
timestamp: February 08, 2015, 12:18:41 pm
content: Of course power measurement of such small power consumption might be challenging, however useless, while amount of energy which such devices can save in our electricity bill is qestionable and people can save much more money if they drive his car not at 130km/h but 100 km/h and lower while power required is function of speed to power of three than investing in such devices like this crappy looking "zero 0 wat" whatever marketing name it hasIdea of timeout operation is also stupid, while one day in the hurry one can forget that this dummy thing will disconnect some important equipment and we can lost a lot of money