What a Difference an Inverter Makes

[Roger Long]

Since I don't have refrigeration and my electrical loads are modest, the largest draw on my boat seems to be the laptop computer. When I'm anchored out, which is most of the time, and spending a lot of time online, the battery monitor goes down pretty quickly. I either have to run under power or idle the engine (which I hate to do) every other day if I don't ration my computer use.

I've been running the laptop with a 150 watt, plug in, inverter from West Marine. I just got Universal Car DC Adaptor, 15-24 volts, 6A, 90W which comes with a set of plugs that automatically set it to the right voltage when plugged in. It has an LED display to confirm the voltage.

Plugging the computer into my old set up with a CD running, I see about 2.45 amps on the battery monitor with everything else on the boat turned off. It fluctuates a bit according to what the computer is doing.

Plugging in the new adaptor, I only see about 1.6 amps on the monitor. The computer battery is fully charged since I've had it connected to shore power AC for my time here but it's pretty clear that the conversion penalty of the inverter is substantial.

This device should pay for itself in fuel and wear and tear on the engine eventually.

Http://www.BattDepot.com
Part No: ACUNV90CR
$56.99

I'll have to confess, because I was thinking "computer" instead of "boat" I didn't think to check if SBO has such a thing. It looks like a good piece of boat equipment. With 8 different adapters, it should run almost anything that needs 11-15V DC and less than 6 amps.

 

[Don S/V ILLusion]

Roger
Is the new thingy you replaced a 150w inverter with simply a smaller inverter or is it something else?

 

[FourPoints]

I think he replaced the inverter with a dc power supply for his laptop....

 

[Roger Long]

Is the new thingy you replaced a 150w inverter with simply a smaller inverter or is it something else?

Old: Inverter plugged into boat 12 volt socket, laptop AC power supply plugged into inverter.

New: Aftermarket car adapter plugged directly into boat 12 volt socket. It steps the voltage up to the 16 volts the computer needs, duplicating the output of the AC power supply.

Voltage is not stepped up to 110 AC and then back down to 16 volts DC in the new setup. That's where the inefficiency is, or was.

 

[Don S/V ILLusion]

Got it, the title confused me
Thanks

 

[Binnacle Bat]

Old: Inverter plugged into boat 12 volt socket, laptop AC power supply plugged into inverter.

New: Aftermarket car adapter plugged directly into boat 12 volt socket. It steps the voltage up to the 16 volts the computer needs, duplicating the output of the AC power supply.

Voltage is not stepped up to 110 AC and then back down to 16 volts DC in the new setup. That's where the inefficiency is, or was.

I'm not an electrical engineer, but I think there is still an inverter involved. My understanding is that you cannot 'step up' DC with a transformer, so the DC current would have to be converted to AC (not necessarily 60 Hz), run through a transformer and then converted back to to DC. That's not to say that your new gizmo may not be much more efficient that the Waste Marine unit, which probably has far more capacity needed than your laptop requires.

Allan

 

[JohnShannon]

Here is one way to do it

http://cds.linear.com/docs/en/datasheet/3780ff.pdf

Uses an inductor to pump the 12V to 16V if thats what you want.

 

[Roger Long]

but I think there is still an inverter involved.

I'm not an electrical engineer either but I think you are probably right. However, the DC power supply doesn't have to step the voltage all the way up to 110 and manufacture an approximation of the sine wave that will let small AC motors like shavers work. It only need to make AC at 12 volts and then step it up and rectify it. Thus the significant increase in efficiency.

 

[Maine Sail]

I'm not an electrical engineer either but I think you are probably right. However, the DC power supply doesn't have to step the voltage all the way up to 110 and manufacture an approximation of the sine wave that will let small AC motors like shavers work. It only need to make AC at 12 volts and then step it up and rectify it. Thus the significant increase in efficiency.

Actually it is a DC to Dc boost converter. The computer already runs on DC not AC.. The AC wall wort only converted AC 120V to DC 16V.

So on a boat, via an inverter, you go DC to AC and back to DC again a very inefficient conversion with lots of waste heat.

With a 12V power supply you go DC to DC with only a slight bump in voltage required, which can be done quite efficiently....

That said the draw on your computer, even with a charged battery, seems very, very low?

Most I see are at a bare minimum of .5A, and depending upon SOC and software running they can suck as much as 5A - 7A..

Computers are one of the biggest "stealth" energy hogs we have on boats. Newer ones are more efficient but they all suck a lot more current than people assume they do, especially if run through an inverter. Over 24 hours some of them can rival the consumption of a 12V refrigeration system....

 

[Buck420]

Add a reasonably priced, flexible, solar panel, that you can put on deck when you're anchored, and stow (rolled up), when tied up or underway, and you would further reduce engine charging needs.

 

[WayneH]

My laptop with a DC/DC plug runs about 2amps when charged and 5amps while charging the battery. Bigger draw than the refrigerator. That's on an analog meter so I can't say if it's running 1.95 or 2.45amps.

 

[Stu Jackson]

Model question

Roger, I clicked the link. You gave a model #, but not the manufacturer?

 

[Roger Long]

That said the draw on your computer, even with a charged battery, seems very, very low?

It's a small computer, SONY Vaio laptop on the small side. You might have also read my post before I discovered a typo in the amps.