Plotters reboot when engine(s) are started

[DipperToo]

Hi,
I recently purchased a Nimbus 370 with twin Yanmar 230 engines.
I have just has 2 axiom plotters installed and both of them restart when either engine is started. Even with one engine running (can be either), starting the second also makes the plotters reboot.
The engines have their own twin 75AH battery bank with a quad 75AH house battery bank.
There is an old Xantrex battery monitor where the shunt has twin shunts to monitor the starter and house batteries, but I cannot see how that would affect things as the ground is common.
The previous owner had an older Raymarine hybrid plotter which apparently did the same thing.
It is almost like in a car when you start the engine the radio/media display goes blank but on a 2001 boat I cannot see there being anything particularly sophisticated.
Any ideas to track the reason?

 

[Sticky Fingers]

Sounds like the domestic batteries are connected to the engine start, do you have the devils’s connector? (1–2-both switch)

 

[DipperToo]

No. This is what is puzzling me. That was my first thought.
There are 3 separate isolators; 1 and 2 for the port and stbd engine and then a third for the house batteries. There is also an emergency jumper switch which is not active. Without each specific engine isolator turned on, that engine cannot be started.
Originally I thought maybe a spike from the alternator on startup, but the plotters reset as soon as the engine is turned over.
I was also wondering if a faulty split charge diode arrangement might be at fault, but on both engines?

 

[Sticky Fingers]

The jumper switch still smells like the more likely culprit, big current draw on starting causing voltage drop on the linked domestic side. Are you sure it’s not active, even if unintentionally?

 

[DipperToo]

99% sure. I will be back on the boat mid next week and will double check. The switches are all of the type which have a 'key" you insert and turn and there is no key in the jumper switch.

I agree that for such a current drain something quite significant needs to be involved.

That is why I wondered even if the battery switches to the engines are on if the split diodes might contribute somehow if they are faulty?

I will also check that the emergency switch directly couples the battery banks before the other isolators.

Thanks for the tips.

 

[Sticky Fingers]

I’m no expert. Hope you get it sorted !

 

[jfm]

Thr raymarine plotter might switch off if it sees a positive voltage on its negative connection. This condition could happen if the plotter’s negative is connected to a bus bar or something that is close to the starter motor negative but slightly remote from the battery negative. .
To test this theory you could take a temporary negative from plotter direct to the battery -ve terminal itself and see if problem goes away.

 

[kashurst]

You have a poor power connection to the plotters and, or weak batteries.
The battery voltage will drop whilst cranking the engine but it shouldn't be enough to restart the plotters.
Or the plotters wiring has been done poorly or is damaged/corroded.
The shunts you mention could be part of the problem. One side of each shunt should go directly to the battery negative, the other end is effectively the negative connection for everything else, except the starter motors.

Put a voltmeter directly onto the battery terminals and crank the engine, see what happens.

 

[jrudge]

I am with Kashurst

 

[DipperToo]

Thanks everyone.
The puzzling thing is why the house batteries seem to be dropping their voltage, but Kashurst has given some ideas.
I also found that before I replaced the halogen lights with LED that the lights dimmed when the water pump ran (and on shore power).
I will first check the wiring on the antique Xantrex shunts and I also noticed that the Xantrex whilst showing the correct voltages for each battery also flashed a red light when monitoring the engine batteries which were replaced just 2 years ago and have been hardly used.
If I cannot see anything overly obvious then it may be time to get a good engineer to have a look at things.
It might be prudent for me to check the batteries themselves as well.
I only recently changed to Hayling Island to moor my boat so need to find a good electronics guy.

 

[Refueler]

Just thinking ... you say you have a Split Charge Diode as well as the switches to control batterys.

I'm tending to that Split Diode may have developed a fault - possibly a short ... when you crank an engine - the starter battery volts drops as usual - the split charge diode if now faulty may actually allow the domestic side to connect and get that voltage back up - but is now dragged down as well ..

This would cause plotters to play games !!

 

[PaulRainbow]

You have a poor power connection to the plotters and, or weak batteries.
The battery voltage will drop whilst cranking the engine but it shouldn't be enough to restart the plotters.

Domestic battery voltage should not drop enough to reset the plotters when the engine is started, they are on different batteries.

Or the plotters wiring has been done poorly or is damaged/corroded.
The shunts you mention could be part of the problem. One side of each shunt should go directly to the battery negative, the other end is effectively the negative connection for everything else, except the starter motors.

The engines should also be connected to the load side of the shunt, or the monitors won't see the alternator charge.

Put a voltmeter directly onto the battery terminals and crank the engine, see what happens.

Good call.

Sounds like there are some issues on the negative side of things.

Would also be worth ensuring that the plotters do not work with the engine batteries on and the domestics off, in case they are wired wrong (as you suggested).

 

[DipperToo]

Would also be worth ensuring that the plotters do not work with the engine batteries on and the domestics off, in case they are wired wrong (as you suggested).

Thanks Paul for the additional info.
The plotter power comes from the fuse/switch panel which serves all the other domestic DC and istruments so I think the problem is more likely to be upstream.
I think it would be prudent at this stage to get an electrician to look at the engine/charging/Main Busbar wiring due to the high currents involved, but I will try to meter things to see what the donestic battery voltage does when starting the engines. I will probably have to use the lighter socket (powered from the same dc panel) at the helm to do this if I am on my own.
I will investigate further to try and isolate potential problam areas.
It takes time to simply find out on a 'new to me boat' where everything is located!
Many thanks for the asistance.

 

[Momac]

I disagree that its a battery issue. Voltage drop on engine start is the problem.
I have the same issue . MFD is positive wired to the main breaker switch dedicated to navigation instruments.
My starboard engine starts from the domestic bank and the same bank supplies power to the MFD.
I avoid the unwanted reboot by switching the MFD on only after the engine is started .
A diode arrangement to connect both the port and starboard battery positives to the mfds should in theory solve it. But to be honest I don't find this a big issue.

 

[PCUK]

So if you flatten the domestic battery the engine wont start?

 

[DipperToo]

I disagree that its a battery issue. Voltage drop on engine start is the problem.
I have the same issue . MFD is positive wired to the main breaker switch dedicated to navigation instruments.
My starboard engine starts from the domestic bank and the same bank supplies power to the MFD.
I avoid the unwanted reboot by switching the MFD on only after the engine is started .
A diode arrangement to connect both the port and starboard battery positives to the mfds should in theory solve it. But to be honest I don't find this a big issue.

Yes, Voltage drop on starting is the issue.
I tried having both engines running, then in turn stopped one and then restarted it (plotter reboots) and then I stopped the other engine and restarted it (plotter reboots again). Even if the starboard engine was for some reason on the domestic bank, then the fact that the plotters rebooted when starting the port engine whilst the starboard one was running suggests something else?
From the initial investigation, the two dedicated engine batteries (75AH each) go to 2 isolators. The first isolator does the port engine and thrusters/windlass while the second isolator does the starboard engine. All other DC services come from the house batteries (4x75AH) through its own isolator.
I think as has been suggested by others that I should be looking at grounding, the Xantrex shunts or even the split charge diodes (original from 2001).
My first job will be to see what the domestic voltage does on starting either engine. I can then work backwards from that going to try and ascertain what is causing such a drop. Even if the domestic batteries were approaching the need for replacement, while on shore power I fail to see how that might be part of the equation?
I do have a battery tester which I might test the batteries with to make sure that they are all OK.
Yes, one can live with it, but it would be nice to sort out!

 

[Momac]

So if you flatten the domestic battery the engine wont start?

Yes. But if this occurs there is a link switch . Start the port engine, press the link switch and then start the starboard engine. In practice it's rarely required.