Laptop AC Adaptors...

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.

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

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

  1. Electrocution hazard

  1. 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.

Reply to
hhc314

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!!!

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Dave M
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Reply to
DaveM

Reply to
w_tom

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?

Reply to
H. Dziardziel

Reply to
Mike Berger

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.

Reply to
rivest

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

Reply to
Michael Black

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