OK to leave AC adapter plugged into wall outlet?



#20

A question for you electronics guys. For my HP65, I leave the AC adapter plugged into the wall all the time. 99.999% of the time the calculator is not attached. Will this damage the adapter in any way?


#21

Don, the only action is magnetizing current for the transformer, there should be no other effect. Sam EE


#22

"Wall-warts" continue to draw power (at an admittedly low level) even when not connected to a device to be charged. This can cost you a bit more for your electric bill... Our Electric Company guy advises unplugging when not in use, for energy conservation. They also produce heat which, if not rated for continuous use, might be hazardous. I don't know any other reasons for cause to worry.


#23

Quote:
"Wall-warts" continue to draw power (at an admittedly low level) even when not connected to a device to be charged. This can cost you a bit more for your electric bill... Our Electric Company guy advises unplugging when not in use, for energy conservation. They also produce heat which, if not rated for continuous use, might be hazardous. I don't know any other reasons for cause to worry.

There is not a single plug-pack ("wall-wart") ever approved (and all units sold should be type approved) that is not designed for continuous operation, load or no load.
They also have a built-in thermal fuse in the windings to prevent overheating, but if you are talking about an old adapter that may not be the case.
No-load power draw is very low (like 1-2W), so you save very little by disconnecting it, but you can do the calcs yourself and see how much it costs. I'd disconnect it though, just as a matter of course.

Dave.

Edited: 19 Mar 2008, 4:04 p.m.


#24

Quote:
No-load power draw is very low (like 1-2W), so you save very little by disconnecting it, but you can do the calcs yourself and see how much it costs. I'd disconnect it though, just as a matter of course.

At the electricity rates we pay here, each Watt of continuous power consumption works out to very close to $1 per year:

$0.12/kWh x 24 h/d x 365 d/y = $1051/kWy = $1.05/W/year

Stefan


#25

Quote:


At the electricity rates we pay here, each Watt of continuous power consumption works out to very close to $1 per year:

$0.12/kWh x 24 h/d x 365 d/y = $1051/kWy = $1.05/W/year


Basically the same here in Australia, except I pay a 5 cent surcharge on top of that for guaranteed 100% wind energy.
$1/year isn't much, so if it's more convenient to leave it on then by all means do that.
Although I'm somewhat of a greenie, so I'd recommend leaving it off!
I try to have my stuff connected to convenient power switches, so I can switch off entire banks of things when not being used. Like the main entertainment system for instance.

Dave.

#26

Quote:
There is not a single plug-pack ("wall-wart") ever approved (and all units sold should be type approved) that is not designed for continuous operation, load or no load.
They also have a built-in thermal fuse in the windings to prevent overheating, but if you are talking about an old adapter that may not be the case.

On paper, yes. We bought a bunch of cheap chinese made rechargeable drills at work. In every single one the plug-pack melted. Two of them even tripped the 20A breaker they were on. I don't really worry about any old adapters I have, but I never leave new ones plugged in unattended. It's all the same cheap crap made by the lowest bidder.

#27

Whoever imported them should be responsible for ensuring that they meet the safety codes of your country. Cheap Chinese chargers that melt might be legal in China, but they certainly aren't here in Canada.

I assume they tripped the breaker after they melted, presumably due to a short circuit developing?

Stefan


#28

Quote:
Whoever imported them should be responsible for ensuring that they meet the safety codes of your country. Cheap Chinese chargers that melt might be legal in China, but they certainly aren't here in Canada.

They aren't legal here in Australia either.
Heavy penalties exist for those who import them, and people do get prosecuted.

Dave.

#29

Hello!

Quote:
Will this damage the adapter in any way?

It could: First, it will be above ambient temperature all the time due to losses in the transformer, even when it does not supply current to anything. This dries out the capacitors quicker than necessary.

Second, the voltage across rectifiers and capacitors is higher without load, again consuming the capacitors faster than necessary. Small voltage surges (if these occur in your grid) may bring some componetes to their maximum volatge tolerance.

And third (even if environmentalism is still frowned upon and ridiculed even by some educated persons): Imagine 100 Million households keeping ten such chargers (calculator, notebook computers, mobile phones, toys, ...) plugged in all the time each. Even if every idling charger consumes only one Watt (and the old ones take much more than this), a very large coal- or oil-fired powerplant wastes fuel and pollutes _our_ air for absolutely nothing.

Greetings, Max


#30

Does the HP-65's wall wart have capacitors in it? The adapter that came with several of my HP accessories and my 71 seems to be nothing but a transformer, putting out 8VAC, not DC, having no rectifiers or capacitors in it.

Edited: 19 Mar 2008, 5:12 p.m. after one or more responses were posted


#31

Quote:
Does the HP-65's wall wart have capacitors in it?

The Museum says Yes! http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=390

-Jonathan

#32

A 82001A with no load at 120V 60hz supply is 10.5 ma AC true RMS. That works out to 1.8 watts...


#33

While you may express current in RMS , in this case it is almost all reactive or inductive lagging current. It does not compute into watts. As to the capacitor life, it is likely designed for power supply use and can lose it's forming coating if left disused for several months. It should be powered at least regularly. Sam


#34

Quote:
It does not compute into watts

I disagree. You say it "is almost all reactive or inductive lagging current" but power is being consumed none the less. How do I know? It gets hot. Period. Work is being done. If I added to my previous post and said the power factor was 1.0, would you still disagree the dissipation was 1.8 watts?

I will not dispute the fact that it isn't exactly 1.8 watts but it isn't zero either. Meanwhile, my watthour meter on the side of the house continues to spin...


#35

Just a note.

The adaptor for my HP-67, which is now about 28 years old, has never experienced any problems after having been "plugged in" for long periods of time without the calc being attached.

tm


#36

Thanks Trent and everyone. My hp65 adapter has also been plugged in for a long time, and I was just wondering if that could harm it. Sounds like probably not, but I may just unplug it when not in use just to be safe (and avoid lightning problems).

#37

You say:

Quote:
If I added to my previous post and said the power factor was 1.0, would you still disagree the dissipation was 1.8 watts?

Is the power factor in fact 1.0? How did you measure it? Why would you add that to your previous post if you didn't know? Do you think that designnut is just guessing that the current is almost all reactive?

Of course, if the power factor is 1.0, then the power dissipation would be 1.26 watts (not 1.8) watts.

But it is extremely unlikely that an unloaded adapter would present a 1.0 power factor load to the line, because what they contain is a small transformer, and sometimes a rectifier/regulator. The no-load power consumption is almost all hysteresis and eddy current loss in the transformer core (especially if there is no rectifier/bleeder or regulator).

You can't determine true power consumed (and power factor) by just measuring the current consumption of a load and multiplying by the applied voltage; this only gives the apparent power (see http://en.wikipedia.org/wiki/Power_factor). You need a true wattmeter such as the Kill-a-Watt, a handy low-cost device that is readily available; you can find multiple vendors on the web. But the Kill-a-Watt won't suffice to make suitable measurements of these kind of adapters because the power they consume when unloaded is usually less than 1 watt and the Kill-a-Watt doesn't have the necessary resolution.

However, having been in the business of designing transformers for a while, I have an electrodynamometer wattmeter specifically designed to measure the true power consumed by very low power factor loads. In other words, it's designed to accurately measure core loss of transformers. The power consumed by an unloaded adapter will be almost all core loss, even if the adapter has an internal rectifier and capacitor (but no bleeder resistor or regulator).

I measured (unloaded) the adapter that came with my HP-71, which has no internal rectifier, and found the following:

Current drawn from a 120 volt line is 20 mA.
True power consumed is .30 watts.

The product of 20 mA and 120 volts is 2.4 and it might be thought that this means the adapter is consuming 2.4 watts, but in fact it is only consuming about 12% of that amount (a power factor of .125).

I also measured (unloaded) the adapter that came with my HP-45 and got the following results:

Current drawn from the 120 volt line is 28.6 mA.
True power consumed is .7 watt.

The HP calculator adapters are quite low idle power consumption because they are only called on to supply a very small power in use and have a very small transformer.

In contrast, the wall wart that came with a Radio Shack battery charger draws 22 mA when unloaded, but consumes a true power of 1.2 watts. Its rated load is .5 amp at 12 volts, much more than the calculator adapters. It has a larger transformer and hence greater core loss. In a properly designed transformer, the core loss should be just about proportional to the volume (and therefore, weight) of iron.


#38

No, of course I don't know the PF and I doubt designut does either. Thats really not the issue. My statement was simply bait to see if someone else wanted to explain that in the world of AC and non-resistive loads that amps x volts != watts until you know the PF.

This was also the reason I mentioned my watthour meter was spinning. You explained better than I could. Thank you.

You also measured *real* power consumption for the adapters, something I could not do with my limited tools. Real numbers are better than speculation... thank you for the effort.

Edited: 20 Mar 2008, 8:46 a.m.


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