Inverter or DC-to-DC for laptop, etc.? - Page 3 - SailNet Community

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  #21  
Old 10-28-2009
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Colin,

You are correct that your voltage range is important. If you look into your specific model laptop, you can usually find that range and see how sensitive it is. Most 12V appliances can run on anything from 12V (80% discharged, no load) to 14.8V(highest charging voltage that I am aware of).

DC to DC converters generally use an inductor to change the voltage and should be able to do step up or step down.

Unfortunately, I have no experience with the iGo but it sounds like an interesting product. I think what this really comes down to is what is available on the market that meets your needs for a reasonable price, no what is technically feasible.

The comment about LED lights is smart. A GE90 which is very common on boats draws about 1amp and if you run even one for 5 hours a day, that is 5amp hours which adds up if you get a couple of lights.
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Thanks for tip about the LED lights. These were definitely on my list of upgrades, but I hadn't got around to asking that question, yet.
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Looks like the internal battery for my laptop is 10.8V 4.8A. Don't know if I'm enough of an energy miser to hot wire it, though, yet. For now, I think I'll see what efficiency a converter has and call it good enough if it's not too far off.
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Quote:
Originally Posted by Bene505 View Post
I could say more about this method of using the battery case, or even design something that would work if there's enough interest.

.
Im all ears..
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If you cut the wire on your laptop electrical cord between the converter brick and the laptop, you will find two stranded wires, one wrapped around the other. My laptop is rated at 19 volts. I'm guessing if I hooked the wires up to a 12 volt and 6 volt battery in series, the laptop would run perfectly fine.

I'm not going to try it with the laptop I currently use, but if I have more time and motivation I might try it on one of the old laptops I have lying around.

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The power supplies used for laptops are called switchers, as are the DC to DC converters. Inverters are also properly called switchers, because they use the same technology too.

All of them work this way: You start with DC. If the source is AC you rectify it with diodes to get DC. Then you change it to high frequency AC (20 KHz to 300 Khz) by using transistor switches. High frequency AC makes transformers and filter capacitors hugely more efficient, and really tiny. So you can step the high frequency AC up or down to any voltage you want. Now if you want DC you just rectify it into DC and you are done. If you want AC you change it to high voltage DC and then use a second switcher to create 60 Hz AC.

You might wonder why the inverter does a double conve plsersion. The reason is that if you did it in one step (like they did in the old days) you needed a huge heavy inefficient transformer, and great big filter capacitors to handle the ripple. I worked at a plant where they made switcher power supplies. They had a transformer there rated for 200 amps output at 24 volts. It operated at 20 KHz. It was the size of an orange, the output conductors were 4/0 copper about 3/8" in diameter!

Now of course if you plug in your laptop power supply to the AC inverter you've got the whole conversion process going again! On the plus side is that all this conversion provides lots of isolation to the laptop from vlotage swings on the ships batteries. But it does waste power, especially if the inverter is much bigger than the load.

So if you can beat the possible reliability issues a multi device DC to DC converter for charging the laptop, cell phone, handheld GPS etc. would be the most efficient setup.

Gary H. Lucas
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Mas que sorte marujo !! I always had Toshibas before, and used Taurus DC-DC converter for use on car, boat and airplane. Stored at boat for 2 years and never had a problem. I suppose iGo has the same approach,so I believe it is a great product too. I also think DC-DC is more efficient than going DC-AC-DC, but since I use Mac today, there is no of-the-shelf option for me, and I assure you it is less efficient now ....
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