AC adapter amperage differences - how important?

Hi all,

I have a client whose Sony VAIO laptop has an AC adapter whose cord has been trashed; it's on its way out. It's rated for 19.5v at 4.7 amps.

I happened to remember that in my spare parts bin, I have a bit older Sony VAIO AC adapter, which happens to have the exact same plug, same polarity, and is also rated at 19.5v. However, it's rated for 3.3 amps.

It runs the laptop fine, but I'm a little concerned what the long-term effects might be as opposed to looking for an exact-match adapter. Anybody have any opinions (backed up by electrical experience, hopefully) on this?

 

4.7A means about 50% higher power rating than 3.3A (Volts x Amps = Watts (power). You might get away with 3.3A for a temporary fix provided you are very careful. The 4.7A will give capacity for full CPU and GPU load and charging the battery. 3.3A will struggle to handle 2 of those 3.

So, for a long term solution you need to look for something that is a close match for the Volta and amps.

John

 

Old adapter: 90 watts
New adapter: 65 watts

Depending on what the specs of the laptop are, it may need more than 65 watts.
Sometimes manufacturers give you an adapter with a higher wattage than what you actually need, but not often.
You should really get an adapter that has the same voltage and the amperage matches or is greater to be safe.

 

If you have or can borrow a Energy/Wattage Meter, It will show you how much you might be overloading the 65watt adaptor.

 

65W will work fine. If you use the 90W adapter, the laptop will simply charge the battery faster. If you have a lower wattage power supply, you battery will charge slower. That's it.

 

not a;ways true in the old compaques/HP's a 65W unit will charge the unit but NOT run it on ac power when turned on

 

For reference, the new laptop is a thin-n-light (or subnotebook, if you prefer). Core 2 Duo T2500, 13" display, Geforce 7400 Go graphics. Not a major power consumer.

Currently I need to get a new battery for it. I was figuring I'd offer the client a deal on this adapter since I have it lying around, but I'll go Ebay if it's a real issue.

 

If you run a PSU that has a much lower current rating than the correct one, it means you are going to be pushing it to its limit, and constantly.

It depends of course on how big a difference, and also how conservative the original PSU was, and how hard you are pushing the laptop. So you might get away with it fine.

But if you ARE pushing the PSU to its limit (constantly drawing the maximum it can supply), it means more heat, more chance of failure, more chance of blowing a fuse, more chance of melting/burning etc.

 

On the contrary, is it ok to use an adaptor rated at a higher amperage.
My Toughbook Y4 has a 16V 2.5A stock adpator but the only ones i get here are 16V 4A or 4.5 A ones. Is it safe to use these.

Ive also noticed that some adaptors have an earthing pin (mine does) whereas many others dont. Is this important while choosing a replacement ?

 

Yes, perfectly safe. It means the PSU is over-rated, and will run very cool and hopefully last a long time.

 

How important is the three pin power cable ? The adaptor that came with the laptop has three pins on the power cable but most of the replacement adaptors i find here have just two. Will this make any difference to the operation ?

 

This is not usually important. There's a small chance that with a 2 pin (ungrounded) cable then there can be some floating voltage on metal parts of the computer. This is not dangerous.

There are plenty of places where there's only a 2 pin mains power socket anyway. I prefer the 2 pin PSUs because the mains cable is thinner and lighter. so less travel bulk and weight.

John