Smaller Solar Panels

[unbusted67]

...right but the wattage will change with the voltage so you would be solving for x an y at the same time

ie. Watts (x)=16volts x Amps(y)

We know neither watts nor amps at 16V. We only know the wattage at @ 110VAC right? At least I am assuming that that is what the Panasonic spec sheet was going off of

Or is the wattage a constant regardless of voltage?

I will not be using an inverter, just the DC/DC brick.

[hellosailor]

"Or is the wattage a constant regardless of voltage?"
Pretty much so. If the computer draws 100 watts, it will draw the same 100 watts regardless of how you juggle the source voltage and amperage. Reality is never quite that simple, because for "simple" wall art type power supplies (not computer grade supplies) the voltage is not tightly regulated and as the load draws more amperage, the transformer saturates and the voltage supplied drops. So a "12 volt" wall wart may put out 17v under no load.
Then there's some efficiency and conversion issues, volts times amps is technically called "VoltAmps" today and isn't necessarily the same as Watts for all purposes.
But for the work we're doing here, yeah, the wattage will be pretty close to being a constant. Any type of power supply or convertor typically runs 90-95% efficiency IF it is well designed AND it is operating under full load, so a rule of thumb is that each "box" will eat 10% of the supply power. Which is one reason why using a direct dc-to-dc converter "should" save about 10% of power consumption, compared to using a 110V invertor and then down-converting with the laptop's normal power brick.

The fine points do matter, but here, it is enough to quote Chairman Mao: "Black cat, white cat, all same. Catch mice."

Since the laptop's own AC power brick is rated around 16V 2.5A, that's 40 watts. Your dc-to-dc convertor may be optimized for that kind of low load, or more likely it is at least a 75W capacity so it will lose a little efficiency running at 40W or less. No real way to tell without measuring it, and since the Kill-A-Watt only works on AC lines...that won't help you here, you'd need to use an ammeter in the DC line.

And then again, that 40W load probably means "run the computer and charge the battery at the same time, with some intermittent drive use". 40W sounds light for a notebook, more like a netbook? Or an older machine with a small screen and economical processor?

[Masquerade]

This might sound like a really dumb suggestion but I think most laptops run off 12 volts from the power supply. Eliminate the power supply and the inverter and you should save a bit.
Colin

[Masquerade]

Oh... all it means is creating a new plug connection...

[surfmachine]

I have a evinrude, OMC, yachtwin 8hp and it puts out 4 amps DC.

[Not Sure]

It seems to me that it is cheaper and easier (both in use and to repair) to simply keep the laptop at AC and use a small (and easily replaced) pure sine wave inverter for the laptop (and more small inverters for other appliances where needed). When docked the laptop runs on AC (filtered through an inexpensive/sacrificial UPS), and when on boat power alone it uses the small sine wave inverter. The house batteries are charged by a small generator and augmented by a solar panel when away from the dock AC. For a small vessel this combination is hard to beat, as the individual components are easily replaced and readily available if/when they fail, and the small loss in efficiency is well worth the price of avoiding a convoluted DC/DC setup using difficult to locate and difficult to replace components, the failure of any of which renders the devices unusable. KISS.

My chartplotter/netbook's power consumption is 19v, 1.5A, 30 watt, as stated on the brick. 30 watts certainly seems minimalistic to me for an onboard computer, (as opposed to the 19v, 6.15A used by the P4 laptop. Ouch!).

[Sailmonkey]

By a clamp on ammeter that is capable of reading dc current. You can put over any wire on the boat and tell how many amps each is producing or consuming......

Craftsman Digital Clamp-On Ammeter

[hellosailor]

DC current for $60?! I may have to buy one of those on general principal, they used to be AC-only till you hit at least the $200 point. Still...For $20-25 a plain multimeter with an in-line 10A ammeter function would do this job.

Masquerade-
That would be a fast way to trash a laptop. Very few of them run on 12V or anything nominally 12V these days. Add that to the fact that "ships power" ranges from about 11V to 14.4V in normal use, while the computer is designed to operate from a tightly regulated specific voltage, and if you don't blow it up right away, you're likely to burn it out in weeks at best.

NotSure-
A pure sine wave inverter used to be damned expensive, hve they really gotten cheap enough to be right for this job? And bear in mind, you'd want to buy a dedicated 50W inverter for the laptop, because using a 100W or (heaven help you) 400W inverter with only a 40W load on it, is terribly inefficient. On top of the double-conversion losses.

[unbusted67]

Originally Posted by hellosailor

40W sounds light for a notebook, more like a netbook? Or an older machine with a small screen and economical processor?

Yes it is a toughbook cf 18

Originally Posted by surfmachine

I have a evinrude, OMC, yachtwin 8hp and it puts out 4 amps DC.

And what are your power requirements like? Do you have a laptop on board, or any other heavy draw items?

Originally Posted by Not Sure

It seems to me that it is cheaper and easier (both in use and to repair) to simply keep the laptop at AC and use a small (and easily replaced) pure sine wave inverter for the laptop (and more small inverters for other appliances where needed). When docked the laptop runs on AC (filtered through an inexpensive/sacrificial UPS), and when on boat power alone it uses the small sine wave inverter. The house batteries are charged by a small generator and augmented by a solar panel when away from the dock AC. For a small vessel this combination is hard to beat, as the individual components are easily replaced and readily available if/when they fail, and the small loss in efficiency is well worth the price of avoiding a convoluted DC/DC setup using difficult to locate and difficult to replace components, the failure of any of which renders the devices unusable. KISS.

I am relying on that added efficiency to even make this feasible.

So judging from the information I have supplied in this thread does it sound like this can work? I filled out West marine's little power budget form and it keeps telling me I will need to run an outboard with a 4 amp alternator for 8 hours a day if I need to have my computer on for 5 and run lights and instruments. Should I plan on a bigger solar array? I was thinking of something in the 20 watt range.

[hellosailor]

"run an outboard with a 4 amp alternator for 8 hours a day" That's nominally 32 amp-hours at 14 volts. A 20-watt solar panel would probably be rated at 16 or 17V so it might be only a 2.5A output. On a bright sunny summer day, you can expect the entire day's output (12 hours) to be equal to four hours at peak rate, i.e. 4 x 2.5 = 10 amp hours from that single 20W panel. You'd need three of those panels according to your estimate for 32 amp hours daily--and that's probably a minimum.

[s/v 'Faith']

Are you using the laptop for navigation? If so you may want to reevaluate. It is not a good option on a small boat (IMHO).

Factor into your E budget the days that are overcast... they can be budgetbusters, and those are the days you may want to sit on the hook and use the laptop for more time.

Also, FWIW, the inverter loss can be quite significant. The "DC to DC" converters are also inverters.... the DC voltage multipliers rely on an oscillator to make the DC to AC, step it up, and then rectify it back to DC. They are more efficient then the alternative because they are purpose specific but there are still losses.

[unbusted67]

Ugh yes I am using it for navigation..or WAS using it for navigation. Looks like i will be getting myself some paper charts. Now I wish I hadn't bought this dang computer. That's what I get for putting the cart before the horse.

Thanks for everyone's help on this. It is a bit of a tedious thread.

[Arranman]

Why not try a SAMSUNG NC10 notebook. With an optional bigger battery pack (ebay) I can get up to 7 hours running out of it with my nav program running. Got mine on a deal via Vodafone and comes with it’s own built in sim card, so can access the internet when in range. Combined with a 30 watt solar panel, a small wind turbine and two 120 amp hour house batteries, this setup worked really well last summer sailing in the west of Scotland.

[unbusted67]

Originally Posted by Arranman

Why not try a SAMSUNG NC10 notebook. With an optional bigger battery pack (ebay) I can get up to 7 hours running out of it with my nav program running. Got mine on a deal via Vodafone and comes with it’s own built in sim card, so can access the internet when in range. Combined with a 30 watt solar panel, a small wind turbine and two 120 amp hour house batteries, this setup worked really well last summer sailing in the west of Scotland.

Can you give me brands?

[Solitude]

How far do you plan to cruise? Why not paper charts. You may be making your needs more complex than they need to be. What happens when you run out of power at the same moment you need to navigate. You need paper as a back up any way.

BTW I see your on a new boat. What happened to Ruffian?