NerdKits - electronics education for a digital generation

You are not logged in. [log in]

NEW: Learning electronics? Ask your questions on the new Electronics Questions & Answers site hosted by CircuitLab.

Everything Else » Power Regulation/Conversion Efficiency and Switching Voltage Regulators...

August 24, 2013
by JimFrederickson
JimFrederickson's Avatar

I have talked about "Power Regulation Efficiency" before, but now I have
been paying a little closer attention.

In that past I have seen numerous articles that talked about "unplugging
Wall Adapters when not in use".

Normally I just ignored those things. My power consumption was pretty
low, and since they didn't supply "any data what-so-ever" to back their
statement I was more tempted to believe they were just people spouting off
about things they didn't really know about. (I like data and reasons...)

One thing I have always done was to make sure that the Wall Adapters that
I used were Switching Type. (Thinking that was "good enough"...)

Well now that I am "Off-Grid" at 1 location and technology and my
expertise have reached a point where things I have thought about forever
can be implemented.

The result is I am paying alot more attention.

Cases in point:

Device Rating       Plugged-in      In-use  
12vdc 1.5a          20 watts        24 watts  
12vdc 1.5a          20 watts        34 watts  
19vdc 2.0a          40 watts        45 watts

(I do have more examples, and all of the above are across multiple
devices, and are all newer Adapters.)

NOTE: The 19vdc Adapters were for powering Notebook Computers
If the Computer was charging the Watts went to 90 on an empty charge and
scaled down to 60 and then finally back to the 45 watts. (Which made some
sense.)

So it turns out these things are ALOT less efficient than I had thought.
(Even though I wasn't necessarily expecting too much in efficiency.) I was
expecting, just thinking about it without getting the numbers, that there
would be something around a 30-40% overage of Watts Used compared to Watts
Delivered. Watts Used being a multiple of Watts Delivered, rather than a
sub-multiple percentage increase, was quite a shock!

Interestingly ALL of my USB-Power Wall Adapters are EXTREMELY EFFICIENT,
despite that they are some of the cheapest ones that I have. (They range
from 5vdc with 500ma to 2.0a output current.)

I have purchased a couple of different Switching Voltage Regulators and
have found that, for DC-to-DC, they "can be" much more efficient than
their linear counterparts. (Although they cannot currently completely
replace their linear counter-parts.)

Has anyone else used Switching Voltage Regulators?
Which ones have you found to work well?
("working well" could be subjective for cost, efficiency and/or ease of use.)
What about making efficient Power Supplies to convert from AC to DC?

August 24, 2013
by Rick_S
Rick_S's Avatar

I've used the LM2575S-5 with a video switching project for one of the machines at work. The machine utilizes 24VDC I/O for the machine control so I needed a regulator that would handle dropping that down to 5V without heat issues. I purchased small boards with the regulator, coil and some supplimental circuitry on eBay and they worked great (Once I found out they needed a 100uf cap on the output). Didn't even warm up, and have been running the video switcher for several months now without issue.

Rick

August 24, 2013
by BobaMosfet
BobaMosfet's Avatar

JimFrederickson-

It's always worth questioning assumptions. Can you tell us how you measured the draw for each the power-adapters you measured, please?

BM

August 24, 2013
by JimFrederickson
JimFrederickson's Avatar

BobaMosfet -

All of the AC Adapters were measured using at least 2, and sometimes 3, different methods.

1 - AC Wired through my multimeter
2 - Off of the meter on a DC-AC Inverter
3 - Using a Kill-a-Watt Meter

I think the actual values may be a little "off", but I am very confident that the
general results are correct. (Those being that "alot" of Wall Adapters use substantial
power just being plugged in but not actually powering anything.)

Being "Off-Grid" at the moment there is also the anecdotal data of the amount of time
that the batteries are lasting, as well as the actual battery voltage over tens of
hours depending on what I have plugged in.

August 26, 2013
by BobaMosfet
BobaMosfet's Avatar

JimFrederickson--

Thank you. Wasn't questioning the work (FYI). Was just curious what you'd done to test it 'in circuit' with a load.

I admit, you've got me interested in examining this sort of thing as well now. I agree, your findings are counterintuitive, and frankly, I would think power adapters would be better at this stage of the game.

BM

August 26, 2013
by BobaMosfet
BobaMosfet's Avatar

JimFrederickson,

I guess one of the things I found shocking was that in all cases, they were using more watts than they are rated for (just using the PIE formula).

BM

August 26, 2013
by JimFrederickson
JimFrederickson's Avatar

Knowing how something has been tested is always a good idea.
I didn't take any offense or slight.

The PIE Formula?

P = IV?
(I am guessing you are using "E" instead of "V"?)

In any case...

I was confused a bit as far as the Wall Adapters using "more than their rated output".

Then it occurred to me, that it is "their rated output".

I have satisfied myself with the conclusion that the "rated output" is just that. It
is what Wall Adapters are rated at delivering and NOT what they are rated to use. ("What is needed to deliver that amount of power.)

What I had expected to find though was some "fractional percentage increase of
delivered power" in order to produce that power.

As mentioned...

ALL of my USB Wall Adapters use very little when just plugged in, plug in a USB Device to get powered and they increase their usage by about that amount.

Note that the set of Wall Adapters being discussed is NOT all of the Wall Adapters
that I own, just the 12 or so that I have being used at the moment. (They tend to
add up... Cell Phone Chargers, USB Power Supplies, External Hard Drive Power
Supplies, Lights, Cameras, Spares, etc...)

My Energizer Battery Chargers are also the same. No batteries to charge, very little
draw, put in batteries a draw.

One thing I thought was "FUNNY" about the Laptop is if, when it is running from the
Wall Adapter, I switch it down to "Power Saver Settings" the "Total AC Watts" actually
goes up!

Now I do know that the "Power Saver Settings" actually do reduce the power necessary
for the Laptop because I do run on batteries frequently and those settings do increase
how long I can run on batteries. (So they are indeed reducing the Laptop Power
Requirements.)

August 26, 2013
by JimFrederickson
JimFrederickson's Avatar

Thanks Rick for that recommendation.

I will add that one to my list to be looked into.

Long ago, well over 1yr, for my projects I switched to "Switching Power Regulators
that are compatible to the 78xx Series for most of my battery operations".

I often use the Murata Switching 78xx Compatible Regulators. I have found them to be
"much more energy efficient" when there is a need to do a "Step Down" of more than 4v.

It is just now that I am becoming much more interested in having power supplies that
are for the purpose of powering Projects in more of an "Installed type Situation"
rather than an "Experimental type of Situation".

So I am looking at more options to see what I can find.

Mostly I need in the range of 1-3amps.

Although, associated with my most recent observances, I do intend on building a
replacement Wall Adapter for My Laptop. I really do, considering it is nearly an
extension of me, need to get it's usage WAY DOWN!

While I often do UNPLUG the Wall Adapter from My Laptop, I have NO DESIRE to
constantly UNPLUG the Wall Adapter from the Wall! It probably won't be anytime
immediately, but sometime...

August 26, 2013
by BobaMosfet
BobaMosfet's Avatar

JimFrederickson-

I've thought about this more, and generally speaking, for any valid results, the measurement can only be done between the wall (aka MAINS) and the adapter. Because in all cases, the adapter is a load. Any load hanging on the adapter will be reflected, and you an use the difference to determine how much the adapter itself uses (quiescent).

MAINS may be line voltage if 'on grid' or battery if 'off'.

If you measure this in any other way, without a load on an adapter, it can be invalid based on the way the way the adapter is designed. Components inside the adapter are chosen based on expected load, and if that load doesn't exist-- it may behave in odd ways (very high voltage and almost no current, for example).

Also, if your 'off grid', is your power a stepped approximation to fake AC, or is it DC? Just something to consider, as this may also have a bearing.

Hope that helps

BM

August 26, 2013
by BobaMosfet
BobaMosfet's Avatar

To clarify, my above remark was obviously not aimed at all adapters, but many behave this way, so it's worth understanding.

BM

August 27, 2013
by JKITSON
JKITSON's Avatar

I am in the process of going total solar. Started about 6 months ago of finding more effeciant pc's & other appliances. Have been able to cut our existing power bill by about $50 per month. I have found the Wall Worts, TV, Direct TV, printers etc do not actually turn off by there remotes. All of these consume power unless unpluged or on switched plug strips.

August 27, 2013
by JimFrederickson
JimFrederickson's Avatar

Hello BobaMosfet and JKITSON

You both seem to be basically "re-iterating my initial observations and points"...

I reread my initial posts, and I think they are accurate, but just to make sure I will
explain more.

I was, am, viewing the "Power Regulation Efficiency" broadly in terms of both "when it
is delivering it's rated power capacity, as well as when it is in standby". (After
even when the load is 0 it is still "Regulating Power"...)

My "expectation" was not that a Wall Adapter "turns off", but that it's power usage
would ALWAYS, obviously, and preferably dramatically, drop when plugged in but not in
use.

What I was/am surprised about is that this "expected obvious drop of power usage
when Plugged in but not in use does not always occur". (Not in use meaning "not
supplying power to a load"...)

Hence my intent to replace all of my Wall Adapters that are not as "Efficient" in
terms of overall-usage as I had expected...

So I was wondering what kind of switching regulators others were using. (I already
have already been using them for DC-DC battery operations, but since I would be greatly
broadening my usage of those parts I thought I would inquire what Switching
Regulators others had used.)

August 27, 2013
by BobaMosfet
BobaMosfet's Avatar

I'm going to test several myself and come back with findings.

BM

September 01, 2013
by JimFrederickson
JimFrederickson's Avatar

Hello BobaMosfet,

I will be really interested to hear what you find...

Hopefully in another 2 weeks I will know more about my schedule and can determine when I
replace a few of the Wall Adapters I have that "are not what I had expected"...

September 05, 2013
by BobaMosfet
BobaMosfet's Avatar

JimFrederickson-

Me, too. I'll post as soon as I can, and have the info gathered. I've got 5 wall adapters of various kinds to test with.

BM

Post a Reply

Please log in to post a reply.

Did you know that a piezoelectric buzzer can be used to play music with your microcontroller? Learn more...