Laptop AC Adaptors...

[[email protected]]

I've always wondered why laptop AC adaptors are so bulky. I mean
laptops are meant to be mobile and compact and light right? Anyhow, I
came across this article where this guy made a hack to a tiny AC
adaptor an successfully used it for his 16V laptop.

http://www.fixup.net/tips/aps.htm

Can anyone explain why the 16V limit and is there any way I can get 19V
and perhaps 3amps?

 

[[email protected]]

The reasons are simple, and based on standards established by UL:

1. Electrocution hazard

2. Fire hazard

UL largely impacts only items run at 115-Volts or higher, not low
voltages. Hence, UL approval is only needed for the "Wall Wart" itself
and not for the balance of the device to which it is connected.

Harry C.

 

[DaveM]

I've always wondered why laptop AC adaptors are so bulky. I mean
laptops are meant to be mobile and compact and light right? Anyhow, I
came across this article where this guy made a hack to a tiny AC
adaptor an successfully used it for his 16V laptop.

http://www.fixup.net/tips/aps.htm

Can anyone explain why the 16V limit and is there any way I can get 19V
and perhaps 3amps?

There was another thread in the past few days that asked essentially the
same question about a desktop PC power supply. The answer here is the same
as in the orther thread.. . and that is the design of the power supply
itself is the limiting factor. The PSU was designed to perform within
certain limits. Those limits are imposed by the design and construction of
certain components in the PSU, the most obvious being the transformer (yes,
even switchers have a transformer). The turns ratio on the transformer says
that for a certain voltage imposed on the primary, you're only going to get
a secondary voltage that's set by the number of turns on the secondary.
Sometimes there may be enough "headroom" in the design to get just a little
more out, but not much more. And if you push it to the limits, you're
risking the possibility of destroying the unit and/or causing fire.
I guess you're like a lot of others on the newsgroups that want to get
something for nothing. If a PSU is designed to put out 30 watts, there's no
way you can make it give you 60 watts without major redesign and component
changes... making it much more expensive than just buying the appropriate
unit for the job you want to do.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

[w_tom]

Other factors must be part of the laptop power supply
including galvanic isolation that provides computers with
protection from destructive transients, EMI/RFI filtering,
current limiting, and other human safety functions. Properly
designed power supplies do more than just provide voltage.
How to get power supplies at lower cost? Forget to include
those many necessary functions; to market to bean counter
types.

 

[H. Dziardziel]

I've always wondered why laptop AC adaptors are so bulky. I mean
laptops are meant to be mobile and compact and light right? Anyhow, I
came across this article where this guy made a hack to a tiny AC
adaptor an successfully used it for his 16V laptop.

http://www.fixup.net/tips/aps.htm

Can anyone explain why the 16V limit and is there any way I can get 19V
and perhaps 3amps?

Old ones are bulky, the new actually quite small but there is a
limit. For example, that 16V at 3A means that perhaps, even with
today's efficient switching circuits, as much as 10 watts more
(loss) as heat must be dissipated by the adaptor.

That can get pretty hot if a small totally sealed unit just
causally thrown and perhaps covered up somewhere. That heat is
not only destructive to components,and perhaps to humans, it's
running at 100-240V internally so must be safe at temperature
while being handled, plugged and unplugged casually.

In addition to safety, 16V is a good design trade off, reasonable
power using small connector contact area for the current,
electronics are nothing special, 12V auto battery compatability,
pack construction and cell count. is reasonable but I'm not sure
if that was a question too?

 

[Mike Berger]

"successfully" used it, meaning he hasn't destroyed
anything with it yet. He's using very marginal
components and recommending disabling safety circuitry.
I wouldn't power anything with that.

 

[[email protected]]

There was another thread in the past few days that asked essentially the
same question about a desktop PC power supply. The answer here is the same
as in the orther thread.. . and that is the design of the power supply
itself is the limiting factor. The PSU was designed to perform within
certain limits. Those limits are imposed by the design and construction of
certain components in the PSU, the most obvious being the transformer (yes,
even switchers have a transformer). The turns ratio on the transformer says
that for a certain voltage imposed on the primary, you're only going to get
a secondary voltage that's set by the number of turns on the secondary.
Sometimes there may be enough "headroom" in the design to get just a little
more out, but not much more. And if you push it to the limits, you're
risking the possibility of destroying the unit and/or causing fire.
I guess you're like a lot of others on the newsgroups that want to get
something for nothing. If a PSU is designed to put out 30 watts, there's no
way you can make it give you 60 watts without major redesign and component
changes... making it much more expensive than just buying the appropriate
unit for the job you want to do.

I don't want something for nothing man. If a more compact PSU is
feasible at a higher cost, I'll buy it
But it seems most replies are saying it can't be done. Safely.

 

[Michael Black]

I don't want something for nothing man. If a more compact PSU is
feasible at a higher cost, I'll buy it
But it seems most replies are saying it can't be done. Safely.

No, the issue is that the web article started with a certain power supply.

Pick something else to begin with, and you get your "something for nothing".

A few years ago, I got a Mac Powerbook 1400C for forty bucks at a community
group sale. Actually, they were auctioning it and a few other items and I
assumed it was a much earlier Mac but kept bidding because of the group.
I was quite surprised how late a model it was, and then realized
one reason it must have been offered up was that there was no AC
adaptor. I put it aside, and when I finally found information on
the jack used for the AC adaptor, and the power requirements, powering
it up was easy. It needed a 24VDC supply. I set out to build one
with a transformer, but somehow I thought of the inkjet printers that
I'd brough home after finding them in the garbage. First one I opened
had a switching supply that put out 24V. I hooked it up and it
was fine.

Hence, if you need a higher voltage, then you need to look further
rather than try to adapt a supply that has limits built into its design.

Indeed, time after time we see people asking about using computer power
supplies for general purpose bench supplies, and that is often the wrong
choice. The supplies are meant to supply a lot of current, and a lot
of experimentation does not need high current, so then the person has
to deal with load the supply down just to get it to run.

But other consumer items, like those inkjets, have switching supplies
that aren't intended for such high current. And they are either designed
for use without a load, or precisely because they are for relatively low
current a simple load will be fine. In a number of the inkjets I've
stripped, the power supply is on a separate board, making it really easy
to make use of in other applications. You can find them in other things,
VCRs come to mind though I've not checked voltages on the units I've
seen, though by the time they went to switching supplies they tended to
include them on the one board that has the rest of the circuitry.

Michael