Why 13A fuse in laptop AC plug?

I was just looking for a few spare plug leads for my NP8170 AC adapter and noticed that the plug that came with it has a 13A fuse in it. The general consensus is that a 13A fuse should only be used for very high drain devices and that for a laptop a 5A should suffice. Since the lead that came with the actual laptop from the manufacturer has a 13A fuse, I assume there is a reason for it.

Anyone else given this any thought?

 

My first thought is to understand 'general consensus'.

 

A 5A 'slow-blow' fuse or a 13A 'instant-blow' fuse is alright for me. As long as it is rated at less than the 15A a typical home/office circuit is designed for.

Think of it like this: the 13A fuse will allow your notebook to fully use the power from the adaptor even for transients of 1000's of a second, where the 5A fuse may limit what total power your notebook can sustain (over time).

 

P = U x I
12V x 13A = 156W

Because the adapter can output 156W before the fuse goes? If you put a 5A fuse it would only support a laptop that draw 60W?

Doesn`t matter what electric circuit from the outlet the adapter is connected to though since the only current that goes through the adapter is what the laptop draw

 

Cloudfire,

If I'm not mistaken, the laptop has a 220W adaptor.

I am also assuming that the fuse is between the wall and the adaptor, not the adaptor and the notebook.

 

Well the conversion to amps is a bit strange for some products. I see Ohms law being a bit strange in some cases, like solar panels and such, so yeah it could very well support 220W too.

But ok, a fuse on a plug. Never heard about it before. Is it the fuse for the home circuit or the laptop? Well nevermind me. To confused to give any help

 

No strange/confused conversion to amps - at least, not if the manufacturer is speaking English.

Ohms law is a law because it is invariable too.

I could still be wrong here... but that is what a quick search on google gets (220W adaptor for the NP8170 notebook).

 

It sounds like the OP is on the UK and he is talking about the 13A fuse in the plug that mates with a wall socket. A 13A fuse on a consumer notebook is certainly not a good idea, as the socket can supply over 2.8Kw of power before that sucker will blow. That's enough to smoke a lot of things! I'd change that to a 2A slow blow.

- Tim

 

Well DOH I found out what is wrong with my example. The AC adapter gives out secondary voltage of 20V.
Which means the adapter/plug/whatever fuse he is talking about, supports up to 20V x 13A = 260W

But then again, if it is a fuse which is part of the electric net in the house, the 20V example is wrong. Once again, I`m confused. Hence my nickname "clueless moron". Im out. Goodnight lol

 

no... its on the input side... which is 120/240v...


120v X 13a = 1.5Kw

 

Yep, I am in the UK and I forget that tha USA areas do not use any fuses in plugs.

I saw much debate online concerning the use of a 13A fuse in plugs for laptops and computers. Some suggested it was a good idea to cope with spikes or surges from initial boot up but the vast majority agree that it is a very bad idea.

 

Maybe 13A fuses were cheaper. If you wanted you could easily swap it for a 5A fuse and it would work just the same.

When it comes down to it, fuses are there to prevent fires and to stop you from shorting out the whole house. The fact that they might protect the device they're being used on isn't the main concern. In these situations, a 13A fuse should work just as well.

 

But don't people have circuit breakers in their homes?

 

They do, but do you only use your notebook in your house? It's there to protect the PSU, but as I said earlier, a 13A fuse at 220V is enough to do some serious damage, without the fuse even blowing....

- Tim

 

If it is an instant blow fuse, it will protect from a short from the adaptor or the notebook. ...While letting the adaptor/notebook have all the power it needs without artificially limiting it.

It is not meant to be 'protection' from any other possibility - just from a short.

And, I wouldn't be surprised if your notebook (fully decked out...) wouldn't use that kind of power (transiently...) when pushed to the max.

 

The fuse should be there to protect the cable coming from the plug. If an overload occurs (not a short), which draws more than the cables current capacity, there is a danger the cable will melt or catch on fire. Sure, the adapter could use a lower rated cable but for the UK 13A mains cables are standard.

The adapter should have it's own protection, much lower than 13A and not be relying on the fuse in the plug.

 

OK, lets get this straight. A notebook is NEVER going to pull 13 amps on the mains side. Even at 110V that would still require the notebook to pull 1.4KW from the adapter. You could run five high end gaming laptops on that kind of power without a single problem.

 

It's not about how much the adapter will pull (although technically a fault could cause a draw of more than 13A) but about how much the mains cable (flex) can handle. I wouldn't be surprised if the OP has a standard UK lead which can be used universally on many appliances and therefore produced at a low cost.


FYI ring mains in the UK can be typically higher than 13A so to use lower cost flex with lower rating current requires a fuse and as stated before the adapter should have it's own internal protection on the input.

 

I'm a HVAC engineer so this might be BS in relation to portable appliances. When I size a fuse for a piece of equipment, it is based on the cable size; so as to prevent the cable melting. If the euipment itself needs to have seperate protection then we install a thermal overload or a secondary fuse(in this case, possibly built into the transformer).

Like I say, take this with a pinch of salt, I have no idea of standards for portable appliances.

 

2.8KW of transient power? ROTLF

 

Yeah, you can rotfl, but you obviously don't know how electical circuits can work.