True power consumption of laptops vs chartplotters?

[Duffer]

The pros and cons of using electronic charts on a laptop as against a chartplotter have been raised many times and I don't want to go into them again here. However one of the main complaints against laptops is that they use a lot more power than a dedicated chartplotter, perhaps twice as much. When I mentioned this in a previous post, another forumite rubbished this and said they actually use half as much - less than 20 watts. So who is right?

Clearly if your laptop battery lasts 2-3 hours, you charge it on shorepower before you leave, go sailing for 2-3 hours, then recharge it on your return then you haven't drawn any current from your ship's battery whatsoever whereas a chartplotter would have done. However if you want to sail across the channel you will want either to plug it into an inverter (which will use some power converting 12v DC to mains AC and back to e.g. 19v DC) or to recharge it every 3 hours or so which may take half an hour but use more power. (There are very few 12v laptops out there - don't ask me why.)

Laptops vary from desktop replacements with power hungry processors to ultraportables with small screens and ultra low voltage chips costing over £1,000 so basically every model is different, so let's assume a current best buy for around £500 with a 15" widescreen, a Pentium mobile 1.7ghz processor, 40+gb hard drive, 512mb RAM, DVD RW and Windows XP. How much power would this laptop use on a 16 hour cross channel trip compared with e.g. a Raymarine C70 chartplotter which I understand uses 40 watts at full brightness (which it needs to be in order to be visible in daylight)?

Clearly both the laptop and the chartplotter can be turned off regularly or the brightness turned down to save power but for the sake of argument (and ease of use) let's assume both are left on for the duration.

If it is a myth that laptops use more power then I don't mind in the least being wrong as I carry both - but I think we all need to know the true power consumption of these items which we are increasingly fitting on our boats.

 

[AlistairC]

I've built a mini PC for my boat and for friends, and if you know what you are doing, you can keep the consumption low.

Mine draws about 20watts with the screen on and about 10w with it off.

 

[Twister_Ken]

I know it's breaching the terms of the question, but why would you leave a lappie on at full whack for a x-channel? After all, if I wanted to stare at a screen all day, I could stay at my desk and not bother going sailing.

Set it to sleep after a minute or two of non-use, and then just wake it up when you need it (in my experience, not very often). I know my lappie will last for days on one battery if it's sleeping and is rarely woken up (what I do when travelling and just want to pick up emails every few hours).

 

[AlistairC]

I think there are a few decent reasons such as:

AIS CPA calculations & Alarms- very handy
Driving the autopilot (although most just upload routes to the GPS)
instant plotting ability.


I guess the question is whether the original poster wanted to use the laptop instead of a dedicated plotter or just as a planning tool.

 

[dk]

Laptops vary in power consumption. my old one drew 7.8A using a small 60W inverter plugged into the cigar aux socket. My new one has a low power Intel M processor, which only draws 5.2A with the same set up. For some laptops you can get a DC/DC converter, which is more efficient than an inverter, but more susceptible to power fluctuations so be wary when buying a cheapo on the net. Either way i tend to charge it up when the engine is running and use the internal battery when it's not. This works fine for around 12 hours general use, providing you set the power save mode on the laptop to turn off both display and processor after 3 mins without use. Obviously if you leave the display on all the time, it will depend on your laptop's battery duration.

 

[AlistairC]

I'm thinking of starting to make boat PCs as a little sideline business, anyone think there would be interest in something for about £600 that draws 800ma? or 1.6A with screen on?
If not then I wont bother! /forums/images/graemlins/smile.gif

 

[Shuggy]

I think my power consumption figure got rubbished implicitly! I stand by it though - 5.7 amps even when fully charged, running through an inverter. Unless my NASA battery monitor is wrong...

I use it on battery when the engine is off (and let it go to sleep) but when it wakes up I need to start the chartplotter software up from scratch as it won't recognise the dongle when it's been asleep.

 

[Gin]

As an aside- when driving to Spain 4 years ago we took a Dell Inspiron loaded with Route 66 mapping software and this (and a Garmin 12) shared a simple curly cable plugged into the car cigarette lighter.

I wasn't aware until reading your post that this was unusual

 

[Nickel]

I think that sounds like an interesting idea.

 

[tome]

Be careful that you're not comparing apples with oranges! I think you'll find it difficult to make meaningful comparisons

The main power draw, whether laptop or dedicated plotter, is the backlighting and this is related to the screen area. The brightest display I've seen by far is the Raymarine E series - this is genuinely sunlight viewable whereas there isn't a laptop to compare. Reducing the backlighting (eg at night or overcast) makes a big difference to the power budget. The E80 is an 8 inch 640x480 screen whereas the E120 is 12.1 inch 800x600

To kick off, I've measured the current draw of the E80 and E120 as follows (note that all measurements were at exactly 12.0 Volts for the sake of comparison):

E80 Full backlighting 1.8 Amps = 21.6 Watts
E80 Half backlighting 0.8 Amps = 9.6 Watts

E120 Full backlighting 2.7 Amps = 32.4 Watts
E120 Half backlighting 0.9 Amps = 10.8 Watts

 

[BlueSkyNick]

The E series has a chuffing great heat sink on the back, IIRC, but it doesn't seem to need it at the currents you have measured. /forums/images/graemlins/confused.gif

The C series has a plain plastic case, and the only difference I know is the networking capability or lack of it, depending on the version.

 

[npf1]

I've been a rugged tablet PC with a sunlight readable 10" screen with a pentium M processor for about 18 months and have noticed the following:

- the nav software loses contact with it's dongle if I hibernate more than once. (software dongle rather than a hardware one, would be a big plus).

- if I have the screen brightness up, the power drain is around 5A. Turning it down brings this to just of 3 A

- turning the screen off when not using it reduces the power drain just below 2A

- blue screen of death appears about once a day and despite trying to resolve the issue I've still not been successful. Hence, whenever in a difficult nav situation I plot on paper too.

- I like the idea of a dedicated plotter but the PC is far more versatile plus the nav software can do more than a plotter (but I've yet to use many of the features in anger!)

Nigel

 

[BlueSkyNick]

Interesting about the BSODs - I had no problems on one old DELL laptop with a serial interface. Then obtained a replacement with only a USB port, bought a convertor, and get too many BSODs for comfort using the 4800bps NMEA connection. Change to new connection from AIS engine (38400), stable as could be.

Now using Maptech's new CNP, instead of Offshore navigator.

Next step is to change serial interface currently assigned to printer port, ie LPT, to a COM port, and put NMEA stuff in through there.

 

[pvb]

It gets quite warm...

My C120 gets quite warm at the back after a while.

 

[Guest]

My experience in using both ...... Yes the PC does use more power ... and I think 20W is a bit on the loow estimate - but the writers reasoning was correct - that many read the power beick label and quote the 70W etc. on there. That is when it's charging battery as well..... which takes a large percentage of that wattage.

You also mention 12v ..... most notebook PC's will run direct of 12v without need for inverter / dc-dc brick. Plug in 12V .... you will have warning lights from not charging etc. .... some PC's will not fire up on 12V - so you disconnect battery and let 12V go for PC only. Note that mainboards are a lot less voltage than 12V ..... so a notebook steps down voltage to the board anyway ....

I get approx. 4 days use out of my Acer which is a combination of 12v + own battery ..... that is with caddy HDD, and passthru NMEA.

I have a chart plotter that requires a 3A fuse .... which indicates a reasonable wattage running ...

 

[porth]

Bloody hell guys, the more I read this thread, the more I love my paper charts...
But it sounds as if everybody else loves spending their time calculating Amps and playing with magic boxes. I must be weird. (In which case my wife is right as usual!)
Gerran

 

[AlistairC]

I dont know about anyone else, but I have a magic box to calculate the amps for me! /forums/images/graemlins/smile.gif

 

[tome]

[ QUOTE ]
I've been a rugged tablet PC with a sunlight readable 10" screen with a pentium M processor for about 18 months

[/ QUOTE ]

Not taking the p*ss, but what ruggedised laptop do you reckon has a genuine sunlight readable screen? Surely not a Toughbook?

 

[tome]

Nothing wrong with paper charts, though this doesn't necessarily mean you're not weird!

 

[Oldhand]

Daylight channel crossing of about 12 hours with built in mini PC running MaxSea continuously, battery consumption with all instrumnents on, a bit of autopilot and fridge run for half an hour, around 80Ah. Same trip with a 20W consumption Raymarine plotter running continuously and no PC use, battery consumption around 45 Ah. PC draws 3A with 15" LCD monitor asleep and 5.2A with monitor in use. Plotter normally used with back-light at 90% full brightness, which should be around 1.6A.

Advantage of running MaxSea continuously, it supplies a full log of all NMEA parameters at whatever interval one sets. This can be interesting for analysing what was good about the voyage and what went wrong, if it did!