Laptop/plotter current draw?

[bumblefish]

How much difference is their between the requirements of the dedicated chart plotter and the laptop running some plotting software?

<hr width=100% size=1>...If you can find the simple solution to a complex problem, you've got it wrong!.........

 

[Talbot]

lots. The average plotter current is measured in milliamps. The laptop requirement will depend upon type, but is at least 2-3 amps and sometimes a lot more. Furthermore the plotter is designed for work in a salty environment. The best place for them is so that you can view the screen from the helm.
Yes I know that you can get a waterproof screen and drive it from the laptop, but that is yet another draw on the current, and does not allow you to interface with the plotter from the helm position. The biggest drawback is the size of the screen although the new plotters with larger screens (see <A target="_blank" HREF=http://www.iboats.com/products/377/14782_navman_5500_and_5600_series_gps_chartplotters.html>here</A>) do make this easier, it doesnt compare with a 14" screen when doing the planning, so why not do the planning on the laptop, and then use the plotter for actual navigation - secondary benefit is that you have a back-up navigation system.

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[MainlySteam]

I think that you are a little out with your reference to drawing only "milliamps". Even the little Navman 5500 to which you point draws 500 of them with the backlight on. Any half decent plotter will draw an amp or two.

John

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[Robin]

I think too that some people only do relatively short trips, so the difference in consumption is less marked and fosters the idea that it is acceptable in all cases. However if you look at consumption in ampere hours over 24 hours then it really shows!



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[Talbot]

OK gov - fair cop, but 500 milliamps is still a lot better than a laptop (and it is still milliamps so I was not wrong! /forums/images/icons/smile.gif)

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[MainlySteam]

OK, will let you off this time. After all, I now realise that my freezer only draws milliamps too - about 45,000 of them /forums/images/icons/smile.gif

John

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[pandroid]

Its not true. I measured a couple of laptops from the boat supply, and the difference is whether they are charging. With the laptop fully charged an average laptop draws about 1.2 amps from the 12v supply. This can go up to about 3 when charging, but varies (it can be as low as 2.2)

By contrast, the Raymarine Radar/plotter draws up to about 3 amps, but is usually less (its practically a PC after all....)

Its a good idea to set the laptop to have a very short screen timeout (e.g. 3 minutes) as this is one of the heavier draws.

We've run both with no issues at all. After all a single Nav light draws 2 amps.

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[Robin]

To compare a combined plotter and radar with a straight plotter is not at all valid. That is one of several reasons why I would never have a combined unit, if I don't need the radar on then it doesn't need to be wasting power, even on 'standby'.

As I said, our Navman 5500i plotter AND dGPS combined draws 500mA, our 10" Raytheon plotter and dGPS combined draws 800mA, both can be reduced with the lighting off. Your figures for the laptop are considerably higher even taking your best case scenario. Also required in the laptop equation is the power loss in the inverter and the additional energy used when the hard disk is running, then there is the GPS to add to it - do that and THEN you have a valid comparison of average power consumptions.

The fact that a single nav light draws 2A is very relevant. Take that and multiply it by say 8hrs night use and the total used is 16Ah. Now add in all the other users like autopilot, fridge, Navtex, instruments, plotter/radar, GPS, VHF, cabin lights, CD/radio etc all multiplied by their consumption over 24hrs. Now compare this with 50% of your service battery capacity (the safe limit) and see how it looks!

I made a spreadsheet up to cover the loads on each of our two service banks and the various free inputs from wind and solar power, to see the effect of a 24hr trip under sail. It is very educational and believe me the odd bit here and there really adds up over 24hrs. Our gas alarm (just 300mA) adds to 8Ah per day....

These things matter not a lot if you only cruise between marinas and shorepower connections as a great many do, or if you motor or motorsail a lot as a great many do.

I have nothing against laptops, I have one sitting on my lap right now! It does get to ride on my boat too, but not as a plotter because I don't like the power consumption or the risk if I go below and drip salt water on it. Both my plotters by contrast are waterproof, the Navman (submersible to 1m for 30 mins) is in the cockpit.

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[MainlySteam]

I agree. We run a notebook for navigation and have never found the power consumption to be an issue, and that is probably the core of the argument. If one has the power capacity it is not a problem.

I have never monitored the current closely but suspect your figures are a little higher than we experience, and that is with using a charting program aimed at commercial vessels (so it maintains a log of everything, including every string that comes in on the NMEA bus from all the sensors and autopilot - so the hard drive is writing full time).

Some boats have problems due to power constraints even running their nav lights. That is not an argument to be used against nav lights. Similarly, because some cannot provide for the power needs of a notebook, that is no argument against computer based charting systems as some seem to think is appropriate to argue. In fact, some larger more competent dedicated plotters use more power than a notebook.

I do concede that I am slightly biased in that here we get all the NZ official charts (all NZ, plus a number of the Pacific Islands, plus international large scale for all of the Pacific and Tasman) virtually free (at cost of putting them on the CD plus distribution which is less than GBP20), which basically means buying a plotter not using the official charts is a waste of money and a plotter that does use them burns more power than a notebook and is megabucks more expensive.

John

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[alan]

I would suggest that the real issue is not power consumption (this can be remedied by extra batteries e.t.c.) of the P.C. but reliability. Most PCs (however there are some manufactured especially for the marine market) are not suitable for the marine environment in terms of effects of salt water and "vibration". I personally would not like to put my life in the hands of a hard disk/CD drive being thumped up and down in a force 7 !!!

As a follow on to this argument: has anyone tried holding all their software on a non-mechanical device (e.g. memory stick) and using the C-Map PC interface module for the charts (I think USB connected)??

Alan.
Nettuno, Italy.

<hr width=100% size=1>Alan Cloke