How a laptop charger works

[Davidh373]

Hello all,
I was just wondering how a laptop charger works. I have recently moved my laptop upstairs for a media center in my room. I close the lid and use an external monitor, leaving the power button mostly inaccessible without unplugging everything, including speakers, an external HDD, and may other accessories. I've been putting it to sleep as of late for convenience.

Alright, onto my real question. Does a laptop charger use the same amount of power all the time? I've been tempted to unplug it every night to save on utilities, but if it works more like a traditional computer PSU, and it fluctuates in power consumption it isn't a big issue. So overall will it be better to unplug it every night and let it sleep away some power to let it charge the next time it's used, or does it not use much power once the battery is charged.

Just in case this is relevant, I have a MacBook Pro Santa Rosa.

 

[Aluvus]

If there is no load on the supply, it is using very little power - a few watts. It would still be slightly better to unplug it, but not enough to really matter.

 

[Davidh373]

If there is no load on the supply, it is using very little power - a few watts. It would still be slightly better to unplug it, but not enough to really matter.

Just out of curiosity, is this true of most modern chargers? For things such as cell phones and handheld gaming devices?

 

[theevilsharpie]

Hello all,
I was just wondering how a laptop charger works.

Very carefully :hmm:

Just out of curiosity, is this true of most modern chargers? For things such as cell phones and handheld gaming devices?

Yes. A power supply is a power supply. If it doesn't have a load to power, it's not going to be using any power. Unless it's also a space heater

 

[VirtualLarry]

Yes. A power supply is a power supply. If it doesn't have a load to power, it's not going to be using any power. Unless it's also a space heater

No, it depends if it is a switching power supply, or a linear.

OP, feel the weight of the power brick. Is it really heavy, or is it kind of light? If it's light, then it's a switching PSU (most laptop bricks are). If it's really heavy, it's a linear, and it will take the full wattage all the time.

 

[Davidh373]

well what are we talking when we say "light" and "heavy"? 0.5 lbs compared to 2? I would say it's pretty light though. At least average for a laptop charger.

I found this page with a description.

http://www.google.com/products/cata...og_result&ct=result&resnum=1&ved=0CCoQ8wIwAA#

 

[fffblackmage]

A lot of the old "wall warts" are heavy because they have a large transformer in them. These are linear power supplies. They're notorious for leeching power if you leave them attached to the wall outlet, even if the device it's supposed to be powering is off.

Many of the newer ones are switching and use much smaller transformers. These are lighter in weight and more "green," as they don't leech power like the linear power supplies (or, at least, not nearly as much).

I'd say you're fine leaving the laptop charger plugged in.

 

[Davidh373]

A lot of the old "wall warts" are heavy because they have a large transformer in them. These are linear power supplies. They're notorious for leeching power if you leave them attached to the wall outlet, even if the device it's supposed to be powering is off.

Many of the newer ones are switching and use much smaller transformers. These are lighter in weight and more "green," as they don't leech power like the linear power supplies (or, at least, not nearly as much).

I'd say you're fine leaving the laptop charger plugged in.

Thanks, and I think I know what you mean by heavy. You guys are talking about the ones you used to see in the 90's that pretty much weighed 5 lbs. Thank you for all your help guys.

 

[SparkyJJO]

No, it depends if it is a switching power supply, or a linear.

OP, feel the weight of the power brick. Is it really heavy, or is it kind of light? If it's light, then it's a switching PSU (most laptop bricks are). If it's really heavy, it's a linear, and it will take the full wattage all the time.

Not entirely true.

The old linear ones will drain some power, yes, but not the full amount. I've tested this

Also, you can be 99.999% sure a laptop power adapter is the switching type - if it wasn't, it would be one very inefficient lead weight brick to haul around lol.

 

[Rubycon]

Not entirely true.

The old linear ones will drain some power, yes, but not the full amount. I've tested this

Also, you can be 99.999% sure a laptop power adapter is the switching type - if it wasn't, it would be one very inefficient lead weight brick to haul around lol.

Correct - the old bricks have higher core losses and poor power factor (not a big deal for residential customers) whereas SMPS' sip power when lightly loaded. Some feature a standby mode where power input is <1W.

 

[SparkyJJO]

I got curious about cell phone chargers. You may have heard about how you should unplug them because if you don't you are wasting all kinds of electricity and that's bad for your wallet and bad for the planet and yadda yadda... Well, I tested the ones I have here for my old phone and my current phone. Hm. It didn't even hit anywhere close to even a watt.

So, for kicks, I did some math, and found it is 5 cents or less per month (depending on your $/kWhr rate) to leave a cell phone charger plugged in 24/7. Mine costs me about a penny and a half.

 

[fffblackmage]

I think most (if not all) cell phone chargers are now switching mode PSUs. I'm not sure how much power those linear PSUs leech, but they dissipate enough power, while powering nothing, to remain quite warm to the touch.