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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 09-01-2008
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How to power laptop

We have a 120 volt charger for our laptop but I would like to be able to charge up without going through an inverter. It seems very inefficient to jack the 12VDC up to 120VAC with an inverter and then use a transformer to change back to 20VDC or whatever the laptop needs. Does anyone know of a gizmo that converts directly from 12VDC to 20VDC?
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Old 09-01-2008
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You might be able to look on ebay and find a charger that plugs into a 12v outlet for your laptop.
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Old 09-01-2008
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Kensington and Targus have several models of adapters to power your Laptop from a Cigar lighter. The one I have now a Toshiba wont work because no adapter is made..
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Targus | Mobile Power Store They can help

Last edited by P424; 09-01-2008 at 01:53 PM.
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Old 09-01-2008
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DC/DC converter

I have a Kensington 70 Watt power adapter that I use both aboard and in my minivan to power my Dell D610 and my Dell ATG.

(similar Kensington unit)

The removable Tips are unwieldy, but I think it's more efficient than using an inverter and AC/DC adapter. I must have the tip that only powers, but does not charge, the computer.

I am considering adding a couple of storage batteries in a space near compression post on my Ranger 33 as a second bank to dedicate exclusively to ships computers. When I have my cell phone and PC and anchor someplace with a strong Sprint PCS signal (Fort Townsend State Park has five bars of signal at the mooring buoys !) it's just like I'm at the office. Except I'm smiling every morning.
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Old 09-01-2008
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I am completely unimpressed with the DC power supplies I have seen. They are very expensive, and the universal ones are cheaply made (in spite of their costs!) Cigarette lighter plugs are notoriously unreliable and can be a fire hazard. To make matters worse, in the process of stepping up the DC voltage (very similar to how a inverter works) a very large amount of RF noise is generated. Don't waste your money unless you can verify a specific model works in the marine environment or the store has a good return policy. I find that a quality marine hard-wired inverter with a standard laptop AC adapter is the most reliable. The inverter should have a bonding lug so that it's chassis can be appropriately grounded. It should also be shielded to prevent RF noise. My inverter draws 2-3 amps when powering my laptop. This seems quite reasonable and is certainly no more, maybe even .5amps less than the $90 DC DC adapter that I ended up donating to the dumpster after it almost caught on fire offshore.
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Old 09-01-2008
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My grumble on this: Why do the new laptops run on such odd DC voltages? I've got an antique IBM Thinkpad that is happy as a lark running directly off the 12 volt system.

My newer Compaq wants to see 18.something volts. Oh, well.

I'd simply run an inverter and be done with it. As to the quality of 'universal' power supplies, I wouldn't touch one with a stick. They aren't regulating the various voltages, they're putting a big dropping resistor in series with the output of the bridge to change the voltage out. Naturally, that means that the current is also going to be down. They certainly aren't worth what you have to pay for them.
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Old 09-02-2008
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Quote:
Originally Posted by johnpen2000 View Post
We have a 120 volt charger for our laptop but I would like to be able to charge up without going through an inverter. It seems very inefficient to jack the 12VDC up to 120VAC with an inverter and then use a transformer to change back to 20VDC or whatever the laptop needs. Does anyone know of a gizmo that converts directly from 12VDC to 20VDC?
Speaking as an electrician, there are a couple of different circuits you could use to step up 12v dc to 20v. Im not sure how happy your insurance company would be about you installing a homebuilt rig on your boat, but if you were happy about the laptop being fairly static it is totally do-able.
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Old 09-02-2008
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A small inverter will do the job more efficiently than a big inverter, but will put out a considerable amount of electrical noise.
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Old 09-02-2008
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Thanks all

I really appreciate all the response. It seems that just using a small inverter (which is what I have been doing) is probably the most practical way for me to go for now. It still irks me though, from an efficiency standpoint. Seems like an opportunity for some electronic engineer/entrepreneur to look at.
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