Power Adapter for Laptop

[Jack O'Brien]

Just got my first laptop and plan to get some navigation software that uses the free electronic charts from NOAA.

The old board had a thread which included mention of a "DC Transformer" which I questioned because I was unaware such things existed. And somebody said they got a very inexpensive DC to DC transformer for their laptop. Now I need one so I don't have to run an inverter to supply AC for the computer's AC to DC wall adapter.

The Dell AC adapter output is rated at 19.5 VDC and 90 watts. I want to plug into a Dell Inspiron 1100/1150 Notebook computer.

I found some that cost $120. Anybody have a better source? TIA.

[Tony D-26X_SusieQ]

There are a lot of low output inverter devices out designed for running your laptop in your car. They run around $20-$30 and should do what you are wanting to do without a lot of draw on your battery. I have a 150 watt inverter I use for mine. This also allows me to run some low powered appliances i.e.: stereo, tv etc.. Stay away from the large inverters. They are expensive and will suck a battery dry in a very short time.

[Chip Hindes]

I looked at the same thing for my Dell laptop. From an efficiency and simplicity standpoint, it seems to make sense to use a transformer to go from 12VDC to 19.5VDC directly, and not bother with the 120AC in between. However, I was concerned about what a voltage spike on the 12VDC line might do to the computer. I like the idea of having that big computer power supply in between to better isolate the computer from power line glitches. Besides, the DC to AC inverter can be used for other stuff; small battery charger (no not the type that charges the house battery, that would indeed be stupid) Dremel, blender, etc...

I admit this whole approach may be misguided, but I decided to go with a good sized inverter, and got a Xantrex 600 from Defender for $80. It turns out it needs a fuse and some heavy duty wiring which will drive the cost up by another $50 or so, so be aware when you're purchasing.

Stay away from the large inverters. They are expensive and will suck a battery dry in a very short time.

Don't know if you were around way back when, but if you could review my previous posts on this matter you'd know you were "preaching to the choir." I'm well aware of the consequences; heck, even if you ran only the computer alone, and it drew a constant 90W, you'd kill your 65 amp hour battery (below 50% charge) in less than four hours, and it would take over three hours of running the outboard at fairly high speed to charge it back up. I intend to use all those 600W very rarely, and not for very long.

You can blender (300W) a pretty decent margarita in under two minutes

[jmdefino]

I thought I'd throw in a couple of notes on this.

There are no DC to DC transformers per se. Transformers will only pass AC. There are miniature DC to DC switching power supplies that will effectively change the DC voltage. I use one on my laptop for the plane and when on the boat.

Chip, most of the filtering in that computer supply is on the AC side. And, that inverter generates plenty of hash on the AC line. The bulk of the DC filtering is in the computer. This includes the laptop battery which acts as a large capacitor.

It is much more efficient to use the DC to DC supply over the inverte - supply method. However, the DC to DC supplies are not cheap where as the small inverters are. If you use the inverter method for this need, get a small one. It will be more efficient for this application.

[Don T]

Hello:
I was looking at this same thing and I have a question. Why do I have to use the 20v input? The battery pack for my laptop is 8.4v. I was planning to use one of my old battery packs to wire a simple regulator and power the thing directly. I suppose my only consideration would be the speed of the computer operating in "power conservation" mode.

Has anyone tried this approach?

My home computer's power supply provides + - 12v and +- 5v DC. Surely the lap top uses the same since it is a requirement of CPUs and motherboards. Those voltages could easily be regulated and filtered direct from the boat batteries.

Transformers require AC to operate. Any time you want to increase DC voltage you have to convert to AC first. On the other hand, the AC power adapter for your laptop is a standard switching power supply which converts the 120v 60hz AC down to a DC voltage before converting it back to AC at 1khz (so they can use a light weight efficient transformer). Depending on the voltage of the internal DC you may be able to connect the 12v DC supply there and bypass the 120v transformer. It may be as simple as opening it up and installing the connector and wires. If you connect to the AC poles of the rectifier it won't even matter what polarity the incoming DC is. Now that I think of it, I have some extra supplies laying around here, I may give this a try.

[jmdefino]

Don, I did that once with an older Toshiba I had. It was a simple battery and it worked well. Most of the newer computer batteries are "smart batteries" with multiple connections. You may have more difficulty with the newer computers.

[Dimitri-2000X-Tampa]

I have a 12V microwave in my galley and it doesn't run right unless I use both batteries and keep the voltage up with the engine running. I used to use a 120V blender (via inverter) on my former boat and it was the same story. The blender motor wouldn't start under load without the alternator running (big alternator on a diesel inboard). I expect the 12V blenders are better (and $$$) but probably also require quite a jolt to get started crunching ice.

I wouldn't use these kinds of appliances when overnighting in an anchorage and trying to conserve power for more important things, but the family sure loves their microwave popcorn when we are daysailing or overnighting with shore power

[Jack O'Brien]

Specs for my Dell Inspiron 1150 say only:
14.1" Display Panel with Backlight (typical): 5.2 W
Battery: 14.8 VDC (either 4300mAH or optional 6450 mAH)
AC Adapter Input: 100 to 240 VAC, 1.5A (max), 50 to 60 Hz
AC Adapter Output: 5.62 A (max at 4-second pulse), 4.62 Continuous
Output Power: 90 W standard
Rated Output Voltage: 19.5 VDC

I presume the higher output voltage of the adapter versus the battery is to allow charging of the Li-ion battery.

Whether the laptop would run on a direct feed from a 12 VDC house battery I don't know but, I would not try this without advice from somebody more computer savvy than I.

I do have both a 300 W and a 1000 W inverters available. Got 210 AH of house/starting battery and 105 AH of standby battery.

The Suzi DF 50 charging coil puts out 216 W at some unspecified RPM. Some part of that is used by the engine.

Looks like I'll just use the 300 W inverter unless I find a reasonably priced DC to DC "Transformer" with the right specs. (Either AC or pulsating DC can be transformed conventionally. I don't know what modern, solid-state electronics can do.)