Saturday, June 14, 2014

Cell Phone Charging and Power Usage.

One of the comments on this blog made me start wondering about the little parasitic devices we have all over the house.  I've always assumed that they drew so little power they wouldn't matter when compared to to the kilowatt guzzling motors and heating elements we have in the larger appliances.  One little device that annoys me is the cell phone charger.  Every time the phone gets to a full charge it tells me to unplug the charger to save energy.  Sheesh, leave me alone, let me worry about how much power I'm using.

However, the commenter said his measuring device recorded 15 watts for several of his devices.  If I can confirm that, I may have to think about doing something since I have a bunch of them around the house.  So, I'll take on an annoyance and see what the power usage really is for my cell phone charger.

This little phone sucks 12 watts when it first starts out, so I need a really good wall wart that can supply over two amps to get the quickest charge.  Since I used the 'genuine' Samsung charger for this test, I let the phone drain down to (approximately) the same point and tried one of those 'Samsung' chargers that are available on Ebay.

Don't let the scale confuse you, this charger never gets over 1 watt.  Since my granularity (using this monitor device) is 1 watt, it could have gone a little higher or lower and still read this way, so I plugged in an amp meter in series and watched a while and it didn't ever go over 500 mA.  It doesn't have the stair steps of the real Samsung charger and took much longer ( less than an hour compared to over 2.5).  It looks like buying a real brand name may result in much, much better performance.  However, how the heck do you tell if it's really from the manufacturer?  Both of them are labeled 'Samsung' and they are the same form factor.  The ratings on the side are the same, so how do us folk out here in the world tell the difference?

I don't have an answer to this, and I'm certainly not going to buy a few hundred different ones and try them out.  I'm seriously thinking about making a load to test these things before I try to depend on them for anything.  If they fail the test, I'll do some serious complaining to the supplier.  The other thing I'm thinking about is putting together a power supply that will give me 5V at three amps reliably.  This would be useful to see how the charge characteristics of the phone look when it has enough current available.

Just for fun, I weighed each of them.  The real Samsung charger weighed 37 grams and the other one came in at 25 grams.  The real one has 12 grams more stuff in it, or thicker plastic.  Since I plan on using the fake for other things, I'm not going to dismantle it ... yet.  But here's a picture of the two of them:

The fake is the black one.  

Just to let you folk know though, there are two differences between them. 1. The real one has a UL certification on it, the fake doesn't.  That's really easy to overcome, they simply add another certification stamp to it.  2. The fake says 5.0 volt at 2 amp, and the real one says 5.3 volt at 2 amp.  Once again, that's easy to overcome.  I've already mentioned the weight, but no supplier tells you the weight of the device.

Anyway, I started this as an investigation into parasitic power and wound up researching chargers and their capabilities.  Sigh.  At any rate, let the buyer beware.


  1. This is a subject close to my heart - both fake wall warts, and parasitic power.
    1. fake stuff. If I've just bought a new phone for several hundred $, I'm not going to trust a $5 fake supply to charge it. I've had a genuine charger go wrong and toast my phone, which was easy to prove. Luckily.
    2. Parasitic power. There are (international?) standards for wall warts. In the latest standard a small <20W one must use <0.5W when plugged in. However, this doesn't apply to things like dish washers and washing machines etc. Old branded phone chargers are great for home made projects around the house, but watch out as the older transformer ones have a high power wastage - I have one that consumes 5W to supply 1W. I recently replaced the transformer in my garage door opener which took 11W with a switch mode one that takes 1W.
    Always make sure the power monitor you're using looks at the power factor or you'll get mis-leading readings.
    It is estimated that the amount of power wasted by wall warts and the like in the UK is just slightly more than the new nuclear power station to be built at Hinkley point. Makes you think.

  2. With the fake wall warts, the standards don't apply. They just slap a sticker on it and it looks like it was certified. Every charger I've tried so far has a power factor in the high 90% range. We're totally on our own with these devices.

    As I've said in a number of posts, I'm not an environmentalist, I'm a pragmatist. Around my house, I chase down the big wasters and see if there is something I can do about it. I don't use a lot less power, but I pay a whole lot less for it than my neighbors. Thus, an 11 watt wall wart would go right out with the trash, or be scavenged for useful parts.

    I gotta go check the power usage on my garage door opener now.

  3. My comment on PF was to do with the measuring equipment, rather than the actual figure; as domestic customers, we're billed in W, so a PF of 0.1 makes no difference to our bill, but it sure annoys the power company who have to deal with the reactive power in the network (which costs them err us money) The waveform distortion caused by the switching PSU causes us all a bit of grief too.
    While you're checking the garage door openers, look at the electric gates, burglar alarm, etc. I'm a little shocked at how bad some transformers are made now; my gates had a 200W toroid that took about 15W - I replaced it initially with an old one I had lying around which took 4W, then used a small wall wart just to power the electronics (<1W) which switches in the main one as required.
    Typically, if I have a 20W 24/7 load, it costs me around £20 ($30) per year, but I don't have your exotic tariffs (yet) By going around the house, I managed to get our base load from around £100/year to around £11.
    But as you say, you have to be pragmatic.

  4. I'll never be able to get it as low as you do. Here in AZ, I have to run ceiling fans 24/7 in a couple of rooms and those things use 45W each. So, I may be able to keep it around 200W or so, but something as low as 20W is out of reach.

  5. I'd think 200W is pretty low in America. It's estimated that the uk average standby is around 300W, so that's £300/year ($450) It's often the low power things that build up and cost the money.

  6. Regarding fake power supplies... I don't know if you've ever checked out this guy's website, he goes to insane depths checking out consumer power adapters.

    Ken Shirriff's blog

  7. I had not seen that. What I'm beginning to think is that I should build myself a 10 amp at 5V power supply and put some usb ports on it for my devices. Just plug them in and let them charge up. Then, I can have a central place and only one supply to worry about. Sure, when I travel, I might have problems of some kind, but I won't have to be worrying about the supply I'm using.

    Let's see, there's a lot of laptop supplies out there, maybe ...

  8. Hello, this Samsung USB charger is purchased in store, not on Ebay, it is original or fake ?


    1. There's no reliable way to tell by just looking. There's two things you can do to get some assurance that you have a good charger. First is to weigh it. I mentioned the weight I found above and I'm sure it's because there's more stuff in the Samsung charger. The other way is to get one of those little devices that measures the current from a USB port. They cost a couple of bucks and will tell you if it's providing the current you need.

      However, the Samsung store online is good about providing real Samsung equipment, so I think you're OK.