Laptop discussion; Power use, type, etc....

[majdrew]

Hi everyone!

I'm considering buying a 23' sloop, which has only dc power..  no house batteries..

Can anyone tell me what electrical requirement I'd need to power a laptop pc on board?
Would a solar panel and wind generator and say, 2 batteries be enough?
I would be intending to spend extended periods offshore..

How does everyone else manage?

Warm regards,

Mark.

[CapnK]

Welcome aboard, Mark! :)

That's not an easy Q to answer - there are a lot of 'depends' involved. No, not adult diapers... ;)

Depends on the power draw of the laptop.
Depends on the output capacity of your solar panels...
...as well as the same for the wind generator.
Size of your house bank.
Intended use of the system - an hour a day, or all day?

There are some similar discussions around here. I think that your most efficient system would be one of the 12V computers, mini- or micro-ATX form factor. By having a system that runs natively on 12V, you aren't losing any of your generated power to a conversion process, like you would using and inverter to produce 120V or whatever for a laptop.

Also, as another possibility - seems like most laptops run on 18-20V, so you could install a 24V power system in your boat, and thus power a laptop with house current, and without having to use an inverter.

[Joe Pyrat]

I just encountered this issue and was surprised at how much power a laptop draws.  Not something that's an issue when you have an A/C source.

I have two laptops aboard, a high powered Sager system, and a moderately powerful Gateway.  My Xantrex Link 20 (battery monitor) reports a draw of around 9 to 12 amps depending on which computer I use (Sager draws more) and if the refrigerator kicks in.  I use the Sager for running my navigation software (XP) and the Gateway for email (Vista) via cellphone link and hauling around in the dinghy since it is a less expensive system and I do not lose the nav stuff if it goes in the drink.

Note, the Sager has to be operated using an inverter which contributes to its power draw, the Gateway has a separate power supply with a 12v connection. 

Due to the high power consumption (the frig only takes a bit less than 3, but of course it runs 24/7) I do my computing while running the engine to recharge the batteries.  Due to the nature of computing (time seemingly disappears) it makes the battery charging go much more rapidly. 

The Gateway will operate on battery for a fairly long period if you are not running the CD drive or accessing the hard drive frequently.  Storing files on a thumb drive seems to help with this.

I have an old Toshiba A45 (XP Home) which which will run quite a long time on its battery (although I have not tried the nav software on it) so my suggestion would be to find the lowest power system that will operate the software you want to run and go with it.  I haven't ever tired one of the 12v computers CapnK suggested, but that might be just the ticket.  I did build a a Micro-ATX system, but it was not a 12V system (120VAC) and by the time you added in the power for the monitor, and inverter, I decided to go with a laptop.

Like Cap said, there is really no easy answer, it will depend on what you want to do with the system, and how much you want to use it. 

You say you are looking at a 23ft sloop, usually boats of that LOA use an outboard for power, in which case your battery is your house battery.  If it has an inboard engine, and you are planning on more of an electrical load than just nav lights (and even then), I'd suggest you try an fit a house battery so you have some options if one battery dies.  Also WRT the outboard, if so equipped, take a look at one that offers battery charging so you can get the benfiit of both purpulsion and battery charging when you use it.

Ramble, ramble.   ;D  Oh well, that's my 2 cents worth, enjoy...

[AdriftAtSea]

Define extended periods offshore, and define what your typical use patterns for the laptop would be.   How much power is generated by a wind generator depends on how strong the wind is, and how much the solar panels contribute is pretty much determined by how sunny it is.  If you run into a overcast windless stretch of days, neither will contribute a whole lot to the battery bank.

Most of the time, solar panels and wind generators are installed to postpone having to run the engine to top the batteries off.  Unless you're going with the very new TPL-type batteries, you really should only discharge the batteries to the 50% charge level, and unless you have a lot of passive charging capability, you'll generally only be getting the batteries back to the 85-90% charge level. This means that your daily electrical budget should be:

( .35 * amp-hour capacity of battery bank / # of days without running engine or using shorepower) + average power generated passively

If you have a 500 amp-hour battery bank, two 130 Watt solar panels, and you wanted to go for five days between running the engine, your daily electrical budget would be:

(.35 * 500 amp-hours / 5 days) + (5 hours * 2 panels * 8 amps)/day = 35 amp-hours / day + 80 amp-hours / day = 115 amp-hours / day. 

An 85 Watt laptop uses about 7-8 amps / hour.  If you use it for navigation, and sail 10 hours a day, you're going to use 75 amp-hours alone on the laptop.  A small tiller-pilot can draw 5-7 amps per hour.  If you use it for self-steering on a longer passage, you might be using as much as 60 amp-hours per day.  Lights, refrigeration, radio, instruments and other electrical loads aren't accounted for. 

A 500 amp-hour battery bank is a pretty sizable bank, and probably weighs in the neighborhood of 300 lbs. or so.  You'd need to have a sizable solar panel array with an MPPT charge controller to really take advantage of it. 

Finding space on a 23' boat for a 130 watt panel, which is about 2' x 5' is going to be a neat trick.  Finding space for a wind gen might be easier.  Finding space for the batteries would be a neat trick too.

Hi everyone!

I'm considering buying a 23' sloop, which has only dc power..  no house batteries..

Can anyone tell me what electrical requirement I'd need to power a laptop pc on board?
Would a solar panel and wind generator and say, 2 batteries be enough?
I would be intending to spend extended periods offshore..

How does everyone else manage?

Warm regards,

Mark.

[hearsejr]

 well you could save a few amps here and there by replacing the old light bulbs with new L.E.D. bulbs the use less power...just a thought.

I got a 1000w ...(1350w peak)..gen. for $160 (new),  just for those bad days , and I'll be adding a set of 80-100 watt solar panels and maybe a wind generator, but not sure yet. I'll also be converting the light bulbs to L.E.D. type bulbs to help save power.

[Captain Smollett]

An 85 Watt laptop uses about 7-8 amps / hour.  If you use it for navigation, and sail 10 hours a day, you're going to use 75 amp-hours alone on the laptop.

Does a laptop used for navigation on an ocean passage really have to be on 24 hours per day?  Do folks that use chartplotters or laptops with nav software keep 'em going all the time?

Personally, there is no way I'd budget 75 amp-hours per day to run a nav instrument.  A sextant uses no juice at all, and getting a fix from a GPS once or twice a day would use a negligible amount.

  A small tiller-pilot can draw 5-7 amps per hour.  If you use it for self-steering on a longer passage, you might be using as much as 60 amp-hours per day.

Score points for a wind vane or sheet to tiller steering on this one.

Drop those two power hogs alone, and you cut the budget by 135 amp-hours (using Dan's numbers)...PER DAY...that have to be generated somehow.

Think KISS, Mark. Simplify your electrical budget and you simplify a TON of other areas of the boat - less charging, less fuel if you 'top off' with the engine, less wear-n-tear on the engine if using it only for charging (which is really hard on engines), fewer batteries, less stuff that can break.  And, you earn a simpler, 'cleaner' lifestyle that is a benefit difficult to quantify.

It is possible to design an electric-less cruising boat.  The Pardey's used to do it, though I think they've made some concessions in recent years.  I think one should start here, pretend you have ZERO electrical capacity, then plan a reasonable charging system.  Set a budget you can meet (at the 50% discharge level) and add conveniences only that fit within that budget.  In my opinion, starting with all the conveniences and building a system to power them will yield huge headaches in the long run.

[CharlieJ]

Totally agree.

We carry at present a single Grp 27 battery. We have a second waiting for me to install. We have a 32 watt solar panel. I can't visualize finding space aboard the whole boat for a 130 watt panel, much less TWO of them- we'd have to carpet the boat.

On the boat I lived aboard, we had a wind generator- mounted way up atop the mizzen mast. On Tehani it would be a problem mounting a wind generator and getting it both high enough to be safe  and well enough braced to stay put.

We use a handheld GPS that runs 24 hours on a pair of AA cells. We plug it into the ships power, but the draw is extremely low.

We carry a laptop which we power from an inverter. But we only use it for short periods as a planning tool, or when we are anchored somewhere where we can access wifi. We also use a tiller pilot ( the reason for the second battery) but I'm working on a vane and we carry S.T.T gear aboard always.

Our 32 watt panel has provided the juice we needed for month( or longer)  cruises  with zero problems. We don't have AC power connections aboard- should we NEED AC power we have an extension cord.

The simpler your boat is, the easier it is to feed the power requirements

[s/v Faith]

I split the posts about Joe's "old Monitor in the boat barn" off here.

With regard to a wind vane, I considered this, but it's bulk and my intended use decided me on an electric autopilot that interfaces with my instrumentation.  Coastal cruising and island hopping in the Caribbean are mostly short sails with ample opportunities for recharging the batteries. 

However if you absolutely have to have a wind vane, I've got an old Monitor in the boat barn.   ;D

[Joe Pyrat]

Vinegarj, got this from Sailnet this morning and thought of you.   ;D

XANTREX XPOWER POWERPACK SOLAR 400


http://shop.sailnet.com/product_info.php/products_id/43619?campaignid=06072008s10

[vinegarj]

for now i'm going with a 40 watt panel and controller that i switch between batteries.  until i add some power hungry devices to the boat, this is providing plenty of juice from two nicely charged batteries.
as to a more energy efficient computer...does anyone have an opinion about the fijitsu tablet computers?  it looks like you can get a used one with a pentium III level processor for less than a couple of hundred bucks.