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Old 13-05-2012, 02:56   #1
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Plotter restarts when bowthruster is used, supplementary battery ?

Plotter restart when bowthruster is used seems to be a common problem.

I had the idea , (BUT I D'ONT KNOW IF IT IS GOOD!),

to install quite near to my plotter a supplementary battery like this:



and to connect it in parallel mode with the plotter.
A little diode should avoid that the battery helps pushing the bothruster when I use it and should keep the plotter working for the 30 seconds or so I use the borthruster.

here you can see the technical data of that battery:
http://www.produktinfo.conrad.com/da..._12V_2_2AH.pdf

would a battery like this be good for my purpose?
what sort of diode do I need if this idea is ok?
something like 5 amps 100v ?
do I need one single diode to be installed on the +cable?
should I install this battery near the 470Amps trojan batterybank or near the plotter or doesnt this matter?
hope that some electricians will help me forward.....
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Old 13-05-2012, 03:46   #2
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

Some plotters particularly the Raymarine brand are sensitive to voltage drops.
The first thing to check is that all the connections to the plotter are good and the wire size is oversized. Are the batteries in resonable shape if this is a recent problem it is probably more a sign of the battery voltage dropping
If you can use a multimeter finding the voltage at the plotter verses at the battery is very helpful.
The supplementary battery may work. I have one mounted in my boat to emergancy power well above the waterline and it's easy to and cheap to set up, but you are better to get a AGM battery, if you have a flooded house bank, so the charging voltages are low. A diode won't work.

Often turning the brightness down on the plotter will fix the problem, if you can live with that.
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Old 13-05-2012, 04:04   #3
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

Our thrusters are on separate batteries isolated from the main banks, but all batteries charge simultaneously.
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Old 13-05-2012, 06:17   #4
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

You might try placing a large capacitor (like found in automotive stereo set-ups) in the supply to the plotter. The capacitor will even out the voltage decrease and keep the plotter from dropping off.

Your battery idea would work, but I think the capacitor would more likely to work over time.
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Old 13-05-2012, 06:20   #5
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

Something like this (maybe not so fancy).

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Old 13-05-2012, 07:56   #6
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

IMHO, any of the following can be your problem:
  • Your batteries are weak
  • there is no electrical separation between banks in the charging circuit
  • the wire size is insufficient to the thruster and/or plotter
  • there is a wiring error and the thruster is drawing from the wrong bank
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Old 13-05-2012, 08:08   #7
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

If it were mine, I'd put in a additional battery up forward just for the thruster and you can use it for the windlass as well. It takes a lot less wire. Most of which would be a charging circuit (#4 to #2 wire depending on the length) with a combiner up forward.
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Old 13-05-2012, 08:48   #8
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

If you have long power cables to the bow thruster and only use the thruster while the main engine is running you can hook up the thruster to the engine start battery. That works well and isolates everything on the house bank.

You can add a DC-to-DC converter and hang all your instruments (plotter, A/P, depth, speed, wind, etc) off the converter and protect their operation from all kinds of adverse conditions. That was my choice and it has worked great for six years.
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Old 13-05-2012, 08:59   #9
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

The KISS solution doen't need batteries, capacitors or diodes.

Make sure that your plotter Positive and Negative supply route does not share cable with the cables going to the thruster. If they share cable and connections on the way back to the battery the voltage drop caused by the thruster is picked up at the point where power branches off for your instruments.

In particular a separate supply directly from the battery just for instruments can cut noise in audio equipment and VHF radios.
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Old 13-05-2012, 09:30   #10
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

I agree with Andina. If though the BT is drawing down the same battery bank that your instruments use then a separate battery and a diode rated for the current that is drawn would work. A smallish battery isolator would work. The voltage drop across the isolator would not be enough of a drop for your instruments not to work.

If you have the option, BT's really need their own dedicated batteries located near the BT to keep them from causing problems with the rest of your electrical system.
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Old 13-05-2012, 10:10   #11
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

I used a small motorcycle battery for the digital on my Ham radio. Worked well to keep interference out.
BTW, why does one need a plotter to dock? :>)
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Old 13-05-2012, 17:00   #12
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Re: Plotter restarts when bowthruster is used, supplementary battery ?

Actually if you are using a support battery at the instrument panel you don't even need an isolator or diode to keep it charged. Figure out what the MAXIMUM average load is on the instrument battery and then use a charging line back to the main battery with the gauge and length calculated to have about a 1/2 volt drop.

This will act as a RC filter using the wire for the Resistance and the Battery for the Capacitor. The time constant will be plenty long enough to stop instrument drop out and noise and under most conditions the instrument battery will be fully charged since the voltage drop on the resistor approaches zero as the battery approaches the same voltage as the supply side with worst case 1/2 volt..
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