Laptop power

[cpedw]

I've just bought what seems like the answer to my prayers. A power supply for laptops which goes direct from 12 V to 15, 16, 18, 19 or 20 V at 3.5A or 22, 24 V at 2.9A. All for £19.99 from Maplin (code N59AC).
I suppose it's not 100% efficient since it takes up to 8A at 12V but it's very small and neat and comes with a selection of connectors.
Well, I'm impressed anyway.

Derek

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[davel]

No reason to believe it's not efficient.
I build a convertor for my PC from a few components. The output voltage is determined by the value of one of the reisitors. It's highly efficient and I'm certain that the same principles will be emplyed in the Maplin device. The 8 amp reference will almost certainly be referring to the maximum current that can be drawn from it rather than the typical consumption.

<hr width=100% size=1>Dave L.

 

[Trevor_swfyc]

They also do an inverter 12v - 240v max 150 watts for the same money. I purchased one last week to do some soldering on the boat, worked very well, no problems. I see no reason why this could not be used to run a laptop and it would be useful to recharge a handheld radio. The item charged must have a charger adapter, something to do with applying an inductive load rather than a resistive. It will not run a 60 watt bulb due the high resistive load on start up but it will run an economy bulb 9 watt eq to 60 watt which would supply emergency light on mains failure.

Trevor

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[William_H]

Hello Davel and others. Forgive me for rattling on it's winter here and I am missing sailing terribly.
It depends a lot on whether you need to increase your 12 volts to your reqirement often 18 volts for laptop. This requires that the DC be switched to AC transformed to a higher voltage then rectified a sample of the output being used to vary the switching on ration to give an exact regulated voltage. In terms of watts in to watts out they tend to be in the range 60 to 90% efficient.
The regulator you built I am guessing is a linear regulator which can only reduce the voltage. It uses a transistor as a resistor to drop the voltage to the output with a feedback sample of the output to adjust the regulating transistor. The whole thing can be built into a single silicon chip. As for efficiency the current out must be same as current in while the voltage out is lower than volts in the power diffe4rence being dissipated in heat. If you wanted 3 volts out from 12 volts then 9 volts must be dissipated in heat and efficiency would be rated as very low ie for 1 amp drain you would put 12 watts in to get 3 watts out and efficiency of 25%
A variation for voltage reduction and regulation switches the current off and on rapidly into an inductor the output is rectified and again a sample regulates the on ratio of the switch. This device can deliver more output current than is taken from 12 volt battery if the voltage reduction is large. The power in is still more than the power out and efficiency again is 60 to90% Most 24 to 12 volt converters for high current are this type.
regards will

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[davel]

Hi Will,
The unit I built was a "step-up" converter based on a switching regulator (the resistor I was referring to controls the feedback voltage and hence the regulated output). This is about 90% efficient (much better than running an inverter to convert 12v dc to 230 v ac then using a transformer to step back down to 15v dc) and only cost a few pounds in component costs.
I believe the Maplin unit referred to at the top of the thread is based on the same principles since it clearly provides a "step-up" conversion. There's no reason why it can't be built to the price quoted.


<hr width=100% size=1>Dave L.

 

[Sybarite]

Is there anybody out there who could translate this thread into English for me - preferably limited metaphorically speaking to two syllables or less so that that such techno-free participants such as myself can understand a concern which I also have?

John

ie can I and if so how can I use my laptop on board?

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[chriscallender]

I'll have a go - there are two ways that you can power your laptop from the boat's batteries

- the first is to buy a gizzmo that gives you mains power from the boat batteries. Then just plug your normal laptop power adapter (the one you would use at home or office) into it and away you go

- the second is to buy this Maplin gadget that doesn't go through the intermediate stage of making mains power, but converts the output of the boats batteries to something that the laptop can use directly

Benefit of approach 1 is that you can use the same box of tricks to power most mains electrical equipment you might want to use on board (as long as it doesn't overload it, your 2 bar electic fire isn't going to work!).

Benefit of the second approach is that it might be more efficient (thats what most of the discussion was on) so you might not drain the battery so much when you're running the laptop.


Hopefully that was techno-free enough.

Chris


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