[Gllug] Multi-voltage power adaptors

[James Roberts]

On 07/02/11 11:38, Andrew Back wrote:
> On (10:58 07/02/11), dominicwalden at tesco.net wrote:
>> Hi,
>>
>> I recently purchased a Toshiba Satellite 4080XCDT (for £15 bought as shown) without a power adaptor. It didn't power up when someone tested it for me, but I'd need to get my own adaptor in order to diagnose what the problem is.
>>
>> So, I have two options. One is to buy a single voltage power adaptor suited for this laptop (for about £20), or buy a multi-voltage adaptor (I was thinking Maplins unless there are better places, for about £25-30). My question is whether there would be advantage to getting a multi-voltage. It would mean that if the Sat didn't work I could always use it for other laptops (thus I don't waste £20). But, would the single voltage be better 'performance-wise' (I dunno if that would be the right way to put it, I know very little about laptops im afraid), would there be a risk with the multi-voltage of being of it lower quality or behaving weirdly (power surges, not sticking to its designated voltage, etc.)?
>
> I suspect it will ultimately come down to quality. The main consideration
> should be that it's regulated.

...

While agreeing with the general tenor of previous comments, our 
practical experience (of fairly regularly having to source replacement 
external power supplies for laptops) is that as long as one buys a 
respectable make (and Maplin probably just sneaks in) there is very 
little practical difference between single output voltage and switched 
replacement supplies: we have had zero failures of replacements of 
either type over the last ten years.

All else being equal, a switched-voltage external supply will be larger 
than a fixed voltage one supplying the same current, as the inductors 
cannot be optimally targeted at a single voltage/current balance.

But really, there's not a lot in it.

Also, the (nowadays almost always) single voltage supplied is always 
internally modified (by DC/DC conversion) to the necessary voltages for 
the components and batter charging: Li-Ion cells in particular have 
critical voltage and current control requirements not ever (in our 
experience, anyway) provided by the external adaptor, which is best 
though of as a pre-regulator.

Moreover, we have found that with some ranges of laptops (Sony comes to 
mind) the only practical difference between using the proper supply and 
one rated at lower amperage is a much slower charge cycle. I'd never 
recommend this, though, except on very rare occasions and in extremis... 
you don't want either a power supply, or worse, a Li-Ion battery, to 
blow up. Do not try this at home.

MeJ

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