A question for you electrical gurus

sailcruiser · Nov 7, 2011

Hi Jim I'm far from a guru but I had a thought. Does your laptop have a DC plug available? Most laptops are DC and the brick AC to DC. So rather than convert DC to AC via inverter then back to DC which takes power in itself just go straight DC? SC

hero4theday · Nov 7, 2011

Sailcruiser is right. Computers run on dc. You can all ways check with you laptop mfg to find out if one is availble or you may be able to find a after market one. I know, didn't really answer your question but something to think about.

dparilla · Nov 7, 2011

Brookstones and sky mall almost always have 12 volt laptop adapters available.

AtlanticAl · Nov 7, 2011

doehunter said:
I just bought a couple more toys for the boat.
1st on the list is a Black and Decker 100/500w power inverter.
2nd. is a Ryobi 12v cordless drill kit with charger and 2 Nicad batteries.
Charging the drill batteries should be no issue. Now for the real reason for the big inverter.

I'm hoping to be able to bring my laptop on the boat mostly for watching movies at night, but obviously it could have many other uses as well.
Now my laptop is a battery hog so I can't watch a whole movie without plugging in. The power supply that came with it is huge.
One thing I don't know is will it actually pull what the power supply has on the label? I'm thinking not but I don't know how much less to expect.
So assuming worst case at full load, here it is.
The power supply label says, input 100-240V~2.25A 50-60hz.

output 19V- 9.5A
If I try to calculate my amp draw at 12V. Do I just do :
115X2.25=258 A then:
258/12=21.5 A for a 21.5 amp draw at full load on my batteries???
If that's correct, I may not bother.
I really need a smaller less power hungry computer but for now that's what I have. On the other hand it's really cool. 17 inch screen and 4, Harmon Kardon speakers. It has the best sound I've ever heard on a laptop!
Jim

Firstly, why didnt you buy a power cord for your laptop, that plugs into the cigarette lighter?
Secondly, as the volts go up, the amps come down, a 120 volt, 100 watt lightbulb will draw, 100 divided by 120 volts, equaling about .9 amps, a 20 or so watt cabin light on 12 volts, will draw closer to 2 amps, your inverter supplies 500 watts, 110 volts, which is about 4.5 amps, way more than enough to power a laptop, but it dosent mean the input is 4.5 amps, at twelve volts, to get 500 watts, your draw would be 41 amps, (that is of course at maximum power, a car alternator would output fifty to seventy amps, so you could use that inverter, with just a car engine running, and invertor secured to the battery terminals (it will blow the cigarette lighter fuse,when you put load on it) Anyway, your laptop will only requre between 40 and 80 watts, so even at full use watching a movie, if you got it up to 80 watts, you would draw about six amps, that is a huge invertor, i have a 120 watt, and i had a 400, but that one.

Kestle · Nov 7, 2011

BIG POINT...some laptops and many land-designed electronics do not handle the modified sine wave output of cheap inverters. The pure sine wave inverters are always better to buy if you can't find a DC connector.

Jeff

Robspan · Nov 8, 2011

igo has an adapter that has both a 110v and 12v adapter. I have it and it works great on my boat and in the car. Be sure that whatever adapter you get has the correct wattage: 19v x 9.5a = 180.5 watts. That's a lot.

Also, I've read that some cordless chargers don't work well with modified sine wave inverters. Check the instructions on your Ryobi.

Sumner · Nov 8, 2011

doehunter said:
......The battery in the laptop is only 14.4 volts, so it seems that the power supply wouldn't actually output 19.5 @ 9.5A ???

I could at this point still take the inverter back, and look for one that doesn't have the modified sine wave like Robspan has. Or , back off of taking the computer on board...

A car battery is 12 volts, but your charging system puts out over 14 volts. You need a higher voltage than what a battery is to charge it. The power supply is "capable" of 9.5 amps. Hopefully your laptop doesn't need that many amps to charge and run.

The others are right our computers run on 12 volts and 5 volts if you look at the outputs of the internal power supplys. There again if the battery is 12 or 14 then the computer will have a clean 12 volts to work with. Some of the notebooks and other computers can run on 12 volts, but won't be able to charge the batteries, which could be ok if you don't need to charge their battery.

The computer I built...

http://purplesagetradingpost.com/sumner/macgregor-navigation/Compter-Nav-index.html

... uses the same chip set that is in a lot of notebooks, but the motorboard has a number of serial ports along with USB ports. The serial ports come in handy running SeaClear and connecting to the handheld GPS. The computer itself uses less than 1 amp, the monitor also uses less than 1 amp also and the hard drive uses some when being accessed, about 2 amps total. When running the Wifi radio it goes up to a little less than 3 amps.

I'm typing this right now on that computer. I take it out of the boat and to the house. I needed to keep the 12 volt start battery charged for the Endeavour, so brought it home and it is under the desk with a charger on it and the computer and monitor right now are running off of the battery here in the house. I was tired of transferring files from the home computer to the laptop to the boat computer. Now most of what I use is on the boat computer which I'll use at home, on the Mac or on the Endeavour. It is backed up on a portable USB harddrive and also onto the house computer.

The power supply I used in the computer will operate on 6 volts to 25 volts and put out the 12 and 5 volt outputs the computer needs. So I have no problems if the batteries drop under 12 volts like when the outboard is starting or the voltage goes over 14 volts while the batteries are charging. We have 12 volt batteries in our cars and boats, but the voltage is hardly ever exactly 12 volts.

On the inverter we bought the ...

...one above and it is a 'pure' sine wave and we have had no problems charging the power tool batteries and the camera batteries with it. It will run other items also, but for Ruth's laptop we have a DC to DC converter that does use somewhat less energy vs. running her computer off of the inverter.

You can get the above inverter on Amazon...

http://www.amazon.com/Wagan-EL2200-Elite-Watt-Inverter/dp/B003INJ3VI

...right now for about $60, we paid I think about $75. I'd recommend it to someone looking for a lower wattage inverter. We don't need more as everything else on the boat is 12 volts.

Like you said with your amp meter you will know what the laptop uses,

Sum

Our Endeavour 37

Our Trips to Utah, Idaho, Canada, Florida

Our MacGregor S Pages

Mac-Venture Links

dvideohd · Nov 8, 2011

are there...

chargers for battery packs used in Power Tools that would do the job? since there are some power tools running 18-24V packs, then that might work....

--jr

monkeybars · Nov 8, 2011

just try it in your driveway before going out to sail.if theres not enough power your computer won't function right but it won't hurt it as long as your not over voltage anything in the 9-14V range should work fine. I power a 26" sony flatscreen lcd tv and a dvd player all on 200W inverter with no problems.

njwtech · Nov 8, 2011

The others are right. Converting DC to AC so that you can convert back to DC is highly inefficient and will convert a large percentage of the input power into heat instead of running the laptop. I won't speak to the issue of charging the cordless drill, but the most efficient way to run your laptop is with a DC-DC power supply - specifically a "switching" power supply, because it will need to convert the 12-14V power from your battery up to approximately 18-19V that most laptops require. Switching power supplies are far more efficient and generally have less losses due to heat than other types of supply, and they are particularly good at taking the voltage up the few volts necessary to run the laptop. Do a search online for "switching laptop power supply" and you should find something that will be as efficient as you can get.

As for the inverter - I think they are better used in a car than on a boat unless you have a way of charging up your battery easily.

njwtech · Nov 8, 2011

ray carlson said:
if theres not enough power your computer won't function right but it won't hurt it as long as your not over voltage anything in the 9-14V range should work fine.

I respectfully disagree. Under-voltage can also do damage - particularly in a laptop. The condition is called "brown-out" in the electronics design field. Some processors handle it ok - some don't. Other components also may or may not handle a brown-out intelligently. We try to program our particular hardware to shut down if the voltage reaches a critical level, but not everyone does this or does it properly. IMHO to be safe always use the design voltage and polarity for the job.

shipwreck66 · Nov 8, 2011

I have an isolated Group 31 battery hooked to a 750watt inverter and I run everything, all houseplugs are hot. TV, fans, minifridge, laptop, plenty of power.

Sumner · Nov 8, 2011

If you mainly want to watch movies Ruth bought a small DVD player that runs...

... on 110 or on 9-12 volts with a car plug. It is a GPX® PD931 9" portable DVD player and cost $60 at the Alco discount store here in town and uses 1.5 amps at 12 volts.

Something like that might be the simple way out until you get a computer with less draw. Nice having the amp meter for checks like this

,

Sum

Our Endeavour 37

Our Trips to Utah, Idaho, Canada, Florida

Our MacGregor S Pages

Mac-Venture Links

Kestle · Nov 8, 2011

We use an portable DVD player too. BTW, most have outputs that can be patched into monitors.

Jeff

A question for you electrical gurus

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