Plotters reboot when engine(s) are started

bedouin said:
There was a long thread on this issue a few weeks ago. You should look and see if any of the negative supply to the plotter is shared with the negative supply to the starter motor. (i.e. if power from the domestic to the plotter shares any wire with the power from the engine battery to the starter. If so you should run a separate negative for the domestics.
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Thanks. I usually search for previous threads but seem to have missed that one. Was it on this forum?
 
bedouin said:
You should look and see if any of the negative supply to the plotter is shared with the negative supply to the starter motor. (i.e. if power from the domestic to the plotter shares any wire with the power from the engine battery to the starter. If so you should run a separate negative for the domestics.
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Very interesting. I am wondering now if when the previous owner installed a dual shunt and reorganised the negative cables that this has caused the issue. I will try and trace the negatives from the dual shunt to see if indeed there is a 'sharing' anywhere. I suspect that the grounds are together at the downstream side of the shunt.
On my last boat I installed a Victron shunt (single) and the start battery negative was separated from the domestics and taken directly to the engines and not to the downstream side of the shunt. As all the Victron does is to monitor the start battery voltage whereas it looks at current etc for the domestics I cannot see this as causing any interference as the negatives will all connect together at the engine block anyway. This might solve the issue (hopefully)
 
DipperToo said:
Very interesting. I am wondering now if when the previous owner installed a dual shunt and reorganised the negative cables that this has caused the issue. I will try and trace the negatives from the dual shunt to see if indeed there is a 'sharing' anywhere. I suspect that the grounds are together at the downstream side of the shunt.
On my last boat I installed a Victron shunt (single) and the start battery negative was separated from the domestics and taken directly to the engines and not to the downstream side of the shunt. As all the Victron does is to monitor the start battery voltage whereas it looks at current etc for the domestics I cannot see this as causing any interference as the negatives will all connect together at the engine block anyway. This might solve the issue (hopefully)
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If you wire like this the battery monitor will not see any alternator charging.

Rather than doing this, run the negative for the plotters directly to the domestic battery negative post. This will, of course, mean that the plotter will not be seen by the monitor, but the plotter uses little current, whereas the alternator charging would be a significant omission.
 
PaulRainbow said:
If you wire like this the battery monitor will not see any alternator charging.
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All the negatives were bonded together at a common point on the engine but I took the domestic negative feed from tbe downstream side of the shunt, not the engine
I always saw the alternator charge current on the monitor and never had issues with fevices resetting.
 
DipperToo said:
All the negatives were bonded together at a common point on the engine but I took the domestic negative feed from tbe downstream side of the shunt, not the engine
I always saw the alternator charge current on the monitor and never had issues with fevices resetting.
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I don't see how you can see alternator charging if the engine/alternator bypasses the shunt.
 
PaulRainbow said:
I don't see how you can see alternator charging if the engine/alternator bypasses the shunt.
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Sorry not to explain more clearly.
The domestic battery negative will always feed via a shunt - nothing else connected to the battery negative directly. What has, I believe happened, is that the start battery negative connects directly to the downstream side of the domestic shunt and has a long run from there to the engines. All I did on my last boat was to make sure that the negatives were connected together closer to the engine, but I still took the domestic feed from the downstream side of the domestic shunt.
Charging was shown correctly and I had no spurious resets when starting.
I am hoping that by adopting a similar change to my new boat that it will solve the issues.
It does seem from other comments that it is quite likely the engine start negative causing the issues.
 
I found the previous thread from March which I have read.
Before going amy further, I will get an exact schematic of what exactly is connected and to include VSR/Diodes etc.
That will provide a baseline.
From the other thread ir seems, as also suggested here, that vsrs or split charge diodes could be faulty.

I will report back on the findings.

Thanks to all for the very useful ideas to follow up on.
 
Update. ...
Ww found ar the common point on the engine that there has been arcing on the negative connectors. This had the effect of reducing the actual voltage at the plotter to 10.5v. After cleaning and reconnecting the negatives we now only see a drop in voltage of about 1.2 and no reboots when the engines are started. This drop was explained as not uncommon in a 23 year old boat with long cable runs. If it starts dropping again then we will probably run new positive and negative cables to the main distribution board and busbars.
Many thanks to all for the suggestions
 
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