Electrical Question

[popeye]

Why does my gps switch itself off when I start the engine?. Also the log trip sometimes resets to zero.
And the vhf goes from working channel to 16

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[MedMan]

I guess you have only one battery or, if you have two, the master switch is set to 'both'. Starting the engine draws a huge amount of current and briefly drops the voltage of even a new battery by a significant amount. All the devices you mention will be sensitive to such a drop and automatically turn off and/or reset.

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[muchy_]

It sounds like you are robbing the power from all your equipment to start the engine and so everything resets.
It maybe the way its wired that makes it do this or I suppose if your battery is weak then that could cause it too.

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[richardandtracy]

Check that the electrical installation's not a direct copy of a car installation. In recent years there's been an EC requirement to drop the volts to all non-starter motor equipment when the starter is used.

I had this bit of kit on my F reg 2CV. When I tried to cure a headlight high resistance I re-wired the car, omitting this resistor and relay. Lo & behold, the interior light stayed on when using the starter. The difference was enough to enable my passenger to keep reading a map, where before it would have been impossible. The added volt drop due to this thing could easily reset the equipment you've mentioned.

Another thought occurs too. Have you tried listening to Long Wave at the same time on a radio? If it disappears in static when the starter is used, you could be having massive electrical interference from the starter motor. This too could reset the GPS and VHF.

Regards

Richard.


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[andyball]

quite right....some marine set-ups are like this , with one terminal of the ign switch for loads that go off when the starter is used, + one for things to stay on regardless. Cd simply be that the items are connected to the one that switches off. However the log "sometimes" zeroing sounds more like the voltage drop mentioned earlier.

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[omega2]

fit a dedicated battery to your ancilliaries, or switch them off at engine start.

<hr width=100% size=1>J HAMER

 

[Dave_Knowles]

I had a similar problem with my autohelm. What often happens is we add more and more things and then get a voltage drop because the feed lead is too small.

In my case to get over this problem I ran a seperate wire directly from the battery via a fuse to the unit. It may be worth therefore taking a feed wire of reasonable size from the battery via a small fuse box to feed just the three items.

<hr width=100% size=1>Dave
Southampton - uk

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[stuartw]

The best, but the most expensive solution, is to fit a dedicated DC-DC converter, which will feed all your important nav equipment. The converter will accept anything from say 6 to 18 volts, and produce a regulated 12volts output, irrespective of the battery voltage - down to it's bottom limit that is.

The other huge advantage is that they are heavily filtered. Which means that all the electrical noise produced by motors etc, does not get to your equipment, so they get a very clean constant 12 or 24v.
They are not cheap, similar in price to small switchmode battery chargers around £100 ish


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[clio]

its the reason lots of older cars had a ballest resistor in the ignition circuit, so that you could still get a spark with the voltage drop due to the starter draw. its not out of the ordinary to get a 6 volt drop in a twelve volt system. most electronics will drop out under 9volts. the computers controlling modern cars have a voltage regulator built in, they operate on about 5 volts

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[Strathglass]

I have a seperate. Instruments and emergency battery. This is charged through a diode from the normal domestic battery. But domestic loads and engine starting cannot discharge it.

The battery is a 12 volt 7 Ah sealed lead acid battery which, because of it's light weight and small size is mounted above the chart table along with the instruments well clear of the bilges.

Although this battery was integrated into the electrics during the initial wiring of the craft it should not be impossible to retrospectively fit one.

The reason for fitting the extra battery was to give some battery power for instruments in the event of a knockdown but whether the instruments themselves would continue to work is another matter. It would certainly remove your problem of the electronics resetting themselves when starting the engine.

Iain


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[drawp]

Stuart. I think that this must be a pretty common problem. With my single battery installation, the log, GPS and autopilot all shut down when I crank the starter. Can be embarrassing if the autopilot is engaged at the time. All the wiring is of a heavy gauge so haven't been able to cure it that way. The DC-DC converter sounds like a good idea. Can you recommend a source for a reliable unit? Thanks.

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