modern vs old wall wart (aka cell phone, ipod, etc. chargers)

[Daox]

I actually checked things out yesterday. The dog fence takes a 12V wall wart and I have no 12V switching type wall warts around. It does only pull 2W continuously, so at most I'd probably get it down to ~1W with a switching supply would be my guess.

I do agree going out and buying a switching type power supply isn't probably worth it to save 1-2W. However, I always seem to have a bunch of these things laying around, so if you can re-purpose them, that is great.

Just for kicks lets calculate what a 2W continuous savings would be.

2W * 24hrs a day = 48Wh / day = .048 kWh / day

.048 * 30 days a month = 1.44 kWh / month

.048 kWh * 365 days a year = 17.52 kWh / year

17 kWh probably costs you around $2 a year. Not horrible energy or cost wise.

[MN Renovator]

Regarding efficiencies with older style linear power supplies, the only way to have a marginally/acceptably efficient one is if the load is not variable and the power supply is designed for that exact level of power output with a little bit of headroom so it doesn't overheat. It will still be less efficient though then a switch-mode supply and it is usually made obvious by the heat that the power supply puts off if you are able to compare both a switch-mode supply and a linear supply putting out the same load.

If the electric fence power supply doesn't pull a ton of power and was well designed for the load, it might be efficient but I have a feeling that the length of wire run would change the characteristics of the load and is possibly worth changing out depending on what a Kill-a-what or similar device says it draws. If it truly is a minimal draw through the outlet, it won't make much sense touching it. It makes more sense to replace supplies that have a higher output or a variable load including devices that sit standby.

My humble '2 cents' opinion. I know someone who works for a company that makes linear supplies for fixed loads such as lighting(high powered LEDs like street lighting and warehouses) and its an engineering feat to make them efficient enough to make sense but my opinion is that they don't especially when it means the supplies are larger and less efficient but in their application, it might not make a big difference to their specific customer when it saves those customers a ton over conventional lighting, especially when they can get a better part of the visible light spectrum versus drab dimmer looking orange HPS lights.

[Daox]

Out of curiosity I did just take a look on Amazon to see what a 12V switching type power supply ran. It is about $5.50 (with shipping). Assuming it would save me 1W (which I am unsure of), it would actually have a payback of roughly 5 years. Just thought I'd mention it. Am I going to order one? Probably not by itself. But, if I remember to add it to my next order I might...

[Piwoslaw]

You can often find power supplies/wall warts at electro-junkyards, thrown out with the wireless phone, answering machine, alarm clock, etc., it was attached to. Some look brand new...

[Rccubed]

There is one drawback to using the switching power-supplies. Whatever the rating on the case is pretty much the max you can do with them. I made a hot wire foam cutter for making toys out of foam and some forms for lost foam casting and the only supplies that were up to the job were the old Transformer type, the switching supplies would simply shut down. Granted this is not something that would lend it's self to that type of design very well any way, but I thought it was worth mentioning that some times the old way is the best way. But I did like the info and I will be changing out most of the other wall-warts I have. My guess is I could save a good deal over a years time, with all the battery chargers for the different types of equipment I have around! Thanks for the article/info!!
Rccubed

[sparkchaser]

Hi DAOX,
I was wondering the same thing, and recently borrowed a Kill-A-Watt from my PUD and did pretty much the same test, with the same conclusions! The new little power supplies that came with my iPhone, iPod, Kindle, and Droid phones all were zero at no load. WOOP!!