Measuring power consumption/draw of mobile devices using a multimeter

[SymphonyX7]

Does anyone know how to measure a mobile device's power consumption or power draw with a multimeter without tapping onto the battery terminals?

I've been reading some reviews of mobile devices on Notebookcheck.com and I've always wondered how they measured the power consumption of devices that have a sealed battery, like tablets and some smartphones. They stated that they use a Voltcraft VC940 multimeter to get the readings, but where they actually tap to measure it, I don't know.

Take this review for instance that they made of a tablet: http://www.notebookcheck.net/Review-Acer-Iconia-A1-830-Tablet.114552.0.html

In Anandtech's recent review of the Galaxy S5, they also posted power consumption/draw measurements of several devices, some of which have sealed batteries. They didn't mention how they got their measurements, but I assume their method isn't any different from Notebookcheck's.

 

[TuxDave]

What about at the charging pin?

 

[teejee]

What about at the charging pin?

I think that only gives you the charging current, the power for the device is probably drawn from the battery even when battery is full.

 

[TuxDave]

I think that only gives you the charging current, the power for the device is probably drawn from the battery even when battery is full.

Well if you think about it, I'm sure the equation is:

Power dissipated = power delivered from the battery = power to charge the battery + heat

And batteries are only slightly warm so maybe the heat term is small?

 

[SymphonyX7]

Apparently no one has any idea how they actually do this. Trade secret perhaps?

Technically, it's also possible to measure draw from the charging pin. The problem is the rate of charge provided by the charger isn't always constant.

 

[randomactsoftech]

First of all you would need to be a bit more specific. Are you looking for how much power it consumes performing specific tasks (ie. web browsing vs. playing music) or are you looking for an average of how much it consumes during normal use. Theoretically if you wanted to know an average you can find out voltage and mAh of the battery online. you should be able to fully charge the device, time how long it takes to die and then let basic algebra do the rest. I think the only way to get current for specific tasks would be to open it up, remove the battery and put a meter between the battery terminal and the device. if your using an apple device... Godspeed.

 

[SymphonyX7]

First of all you would need to be a bit more specific.

Specific of what exactly? Regardless whether the device is on load or not, I just want to know how how they get their measurements using a voltmeter/multimeter when the battery is sealed. That simple.

If you read it again, I'm not looking for computations of power consumption inferred from data provided by the built-in power management IC of the device.

 

[jjsbasmt]

Almost impossible to do when phone is on since it is always pinging cell sites, and since the sites talk to the phone and adjust the phones RF power output as the phone moves around and conditions change in the topography, atmosphere, and distance form the cell tower, it would very difficult to determine and any moment the amount of power the phone is using from the battery. Randomactsoftech is on the right track however.

 

[SymphonyX7]

Almost impossible to do when phone is on since it is always pinging cell sites, and since the sites talk to the phone and adjust the phones RF power output as the phone moves around and conditions change in the topography, atmosphere, and distance form the cell tower, it would very difficult to determine and any moment the amount of power the phone is using from the battery. Randomactsoftech is on the right track however.

Again, since when did varying consumption values matter? That's off topic. Besides, if the radio's power draw is a concern since it's difficult to create a completely controlled test environment for it, just put it in airplane mode.

The point is this: How the hell are they measuring the device's power draw with external equipment like voltmeters/multimeters when they don't have access to the battery terminals of the device (smartphone or tablet with sealed battery)?

 

[Belegost]

Again, since when did varying consumption values matter? That's off topic. Besides, if the radio's power draw is a concern since it's difficult to create a completely controlled test environment for it, just put it in airplane mode.

The point is this: How the hell are they measuring the device's power draw with external equipment like voltmeters/multimeters when they don't have access to the battery terminals of the device (smartphone or tablet with sealed battery)?

Who claims to be doing so?

Where I work to do power draw tests the battery is removed, and test leads attached to the battery connection to the mainboard, the leads are passed outside the device, usually through holes drilled in the casing, or notches at a seam, and then an ammeter can be put in line before hooking up to a bench power supply.

 

[SymphonyX7]

Who claims to be doing so?

Notebookcheck.com. Every tablet or smartphone they review has power consumption/power draw readings in addition to the usual battery rundown tests you see in every other review. They state that they use a Voltcraft VC940 multimeter to get the readings.

Where I work to do power draw tests the battery is removed, and test leads attached to the battery connection to the mainboard, the leads are passed outside the device, usually through holes drilled in the casing, or notches at a seam, and then an ammeter can be put in line before hooking up to a bench power supply.

This is essentially what I mean, minus the drilling and whatnot. I assume they don't pry open the devices with sealed batteries just to get the readings. It's a huge waste. So I'm very curious as to how else they could possibly get the readings with external equipment.

 

[randomactsoftech]

Obviously it is impossible to know exactly how that particular website gets their info but I have a few theories about the process in general.

1) Alot of a devices power info is published by the manufactures when a device is released. There is also some info that a reputable website could get directly from the manufacture if they requested it.
2) I would imagine that the software an some of the devices have been hacked to get readings from the battery (assuming a device was built in a way that that information could be gathered)
3) I think that some websites do in fact crack open the battery compartment and run test by hooking up a multimeter to the leads.

I assume they don't pry open the devices with sealed batteries just to get the readings. It's a huge waste. So I'm very curious as to how else they could possibly get the readings with external equipment.

Your not wrong when you say it would be a waste (environmentally). However, to imply that it would be not financially beneficial would be wrong. Notebookcheck.com has a google page rank of 4 (which is fairly high) and over 2 million external back links to their site. I dont know the specific monthly traffic they get but I bet its enough to make them more money than most of us make in a year just off of the 3 or 4 advertisements on their main page. That makes a pretty good case for them to spend $100 - $1500 on a device just to take it apart and test the battery..... I know thats what I would do if I were them!