Author Topic: Input voltage tolerance on laptops  (Read 12420 times)

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Offline cybergibbons

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Input voltage tolerance on laptops
« on: July 22, 2011, 10:14:12 pm »
Evening all...

I'm fairly free and easy with laptop power supplies. If the voltage is within ±1V or so, the power available isn't too far wrong (most 120W laptops will work fine for web browsing on a 65W adapter), and the polarity is right, then I'll give it a go. I've never had any problems with Acer, HP, or Dell in doing this. I just use my normal check - "Is it on fire?" - to keep an eye on things.

However, it seems a lot of people don't agree with this and absolutely insist that exactly the right voltage is used. Of course you also get those who insist the "amperage" is the same, mainly due to a lack of understanding. They cite "overcharging batteries" amongst other reasons.

I think that you would have to go a long way out of your way to design a DC-DC converter that couldn't deal with a ±10% input voltage range. I also can't see any way that the battery wouldn't be charged correctly, being behind a converter and then a Li-Ion battery charger.

What are people's experience with this? How far have you pushed the limits when powering a laptop?

 

Online IanB

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Re: Input voltage tolerance on laptops
« Reply #1 on: July 22, 2011, 11:03:35 pm »
I've always used the matching brand of power supply with the laptop (e.g. Dell power brick with Dell laptop).

When I have used an under powered supply on a Dell, the laptop has notified me "the connected power supply does not have sufficient power for full performance--the machine will run in power saving mode at reduced speed" -- or words to that effect, I don't remember precisely.

Another story with a netbook using the in-flight power supply on an airplane. The in-flight magazine said "the power outlet can run a laptop but you cannot charge your battery". Hmmm, I thought...? Anyway, I plugged in the power adapter (it is a tiny low powered one for a netbook) and looked at the power settings in Windows. Lo and behold it said "the machine is powered but the battery is not being charged". Huh?

So I don't know the whole story here (or even the half of it), but there is a degree of intelligence in these laptop power systems.
I'm not an EE--what am I doing here?
 

Offline Psi

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Re: Input voltage tolerance on laptops
« Reply #2 on: July 22, 2011, 11:08:54 pm »
It used to be that the laptops switchmode could handle anything from around 11v to 16v.
The AC powerpack was around 15v but you could also use a cable to your car cigarette lighter and it would run from 12v direct.

Sadly i'm pretty sure all/most modern laptops can't do that, they're just not designed to handle the extra current needed at 11V compared to the 19-22V of an AC adapter.
If you order a car adapter for your modern laptop its a powerpack in itself, designed to take 11-15V and output 19-22V
« Last Edit: July 22, 2011, 11:15:51 pm by Psi »
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Offline Psi

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Re: Input voltage tolerance on laptops
« Reply #3 on: July 22, 2011, 11:14:23 pm »
Another story with a netbook using the in-flight power supply on an airplane. The in-flight magazine said "the power outlet can run a laptop but you cannot charge your battery". Hmmm, I thought...? Anyway, I plugged in the power adapter (it is a tiny low powered one for a netbook) and looked at the power settings in Windows. Lo and behold it said "the machine is powered

Ive found that quite often you can get it to work by plugged the laptop in but not turning it on until the battery is charged. There isn't enough power to run the laptop and charge at the same time. So you need a fully charged battery first, then you can run the laptop for as long as you like.

I guess it depends on the reason; if it cant handle the current of charging+running then you can get away with doing only one at a time, but if the voltage is lower than the charging circuit can use then it's never going to be able to charge.
« Last Edit: July 22, 2011, 11:18:59 pm by Psi »
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Uncle Vernon

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Re: Input voltage tolerance on laptops
« Reply #4 on: July 22, 2011, 11:24:15 pm »
I've always used the matching brand of power supply with the laptop (e.g. Dell power brick with Dell laptop).

When I have used an under powered supply on a Dell, the laptop has notified me "the connected power supply does not have sufficient power for full performance--the machine will run in power saving mode at reduced speed" -- or words to that effect, I don't remember precisely.

Another story with a netbook using the in-flight power supply on an airplane. The in-flight magazine said "the power outlet can run a laptop but you cannot charge your battery". Hmmm, I thought...? Anyway, I plugged in the power adapter (it is a tiny low powered one for a netbook) and looked at the power settings in Windows. Lo and behold it said "the machine is powered but the battery is not being charged". Huh?

So I don't know the whole story here (or even the half of it), but there is a degree of intelligence in these laptop power systems.

Take a look at the Dell plug that centre pin isn't a power connection. It is connects an ID chip (Maxim I do believe) that identifies the supply. Your notebook is reporting a change of or lack of expected ID rather than any supply measurement. The charge circuit won't kick in until the ID requirement is satisfied.  I suspect in some cases the batties may still be slow charged.

The ID chip strategy can be used for good or evil.

http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed

« Last Edit: July 22, 2011, 11:26:58 pm by Uncle Vernon »
 

Offline cybergibbons

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Re: Input voltage tolerance on laptops
« Reply #5 on: July 23, 2011, 07:45:00 am »
It used to be that the laptops switchmode could handle anything from around 11v to 16v.
The AC powerpack was around 15v but you could also use a cable to your car cigarette lighter and it would run from 12v direct.

Sadly i'm pretty sure all/most modern laptops can't do that, they're just not designed to handle the extra current needed at 11V compared to the 19-22V of an AC adapter.
If you order a car adapter for your modern laptop its a powerpack in itself, designed to take 11-15V and output 19-22V

Indeed - my first laptop had 10.2-15.8V as the input range. That was so long ago though that it may have had a linear regulator in it!
 

Offline cybergibbons

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Re: Input voltage tolerance on laptops
« Reply #6 on: July 23, 2011, 08:01:27 am »
Take a look at the Dell plug that centre pin isn't a power connection. It is connects an ID chip (Maxim I do believe) that identifies the supply. Your notebook is reporting a change of or lack of expected ID rather than any supply measurement. The charge circuit won't kick in until the ID requirement is satisfied.  I suspect in some cases the batties may still be slow charged.

The ID chip strategy can be used for good or evil.

http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed

Don't get me started on this. Oh, too late!

My girlfriend has two Dell laptops, one old and one in current use. At work I have two Dell laptops that I regularly use, and most others also have Dell laptop. I also have a pile of 9 adapters, all of which have had the ID chip fail in them. Not one has an issue with the actual power supply.

Each time they fail I need to go through a painful process of spending upwards of an hour on the phone, trying the power supplies in other laptops, flashing BIOS and so on. Eventually they send out a new adapter.

Worse still, their power rating seem to be way off the mark. Load the 90W adapter to 100% and the supply gets so hot it bulge and smells of melting. I've not tried with the 210W beast on one of the mobile workstations, but that gets too hot to touch anyway!

 

Offline hacklordsniper

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Re: Input voltage tolerance on laptops
« Reply #7 on: July 23, 2011, 10:08:04 am »
If the charger has too low power output you will need to remove battery or either charge it when its shut down. I had sucess powering 19 V input laptops from 12 V and they work fine but cant charge the battery.

My main computer ViewSonic VOT120 came with 22 VDC adapter but im running it of 12 VDC from my solar system. The current intake has increased by 50 % but it works like this almost 2 years (altrough heating much more)
Oh, the joy of sending various electronics to silicon heaven
 


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