Instruments turn off when starting engine having added extra battery,

[sailor211]

I had a dedicated engine start battery and two 60AH service batteries. Each battery has its own switch.

As two 60 AH batteries is too little I have added two 110V batteries making the house battery capacity 340 Ah.

Engine battery is separate with its own seitch, but all neutrals 0V are connected.

There is a VSR for charging and the service batteries are joined as one bank. The only change I believe that I have made, is that there are now extra batteries and the +ve is taken from one end of the bank and the -Ve as at the other end which I believe is correct, Where as previously it was +ve and -ve of the house batteries was connected to one battery and the second battery was connected +to + and -to - This I believe not to be best practice.

What is likely to cause the instruments (plotter) to restart on engine start?

Is it poor -Ve connection?
VSR?

I thought I had just increased the house battery capacity.

TIA

 

[salar]

I had the same problem, and it being a fishing boat I have lots of sensitive plotters and things. The reset is caused by a voltage drop, and the only way there coud be a voltage drop is if your starter battery is connected to your domestic circuit and pulling the voltage down while it cranks. They can share negative obviously but the positive circuit needs to be separate. You can switch the other batteries in to help with starting in an emergency but normally the starter and house circuits should be separate from one another. Have you tinkered with the VSR connections in any way, or is there any other connection that coud be causing a bridge between the circuits?

 

[srm]

I always keep my engine start battery separate from the domestic bank with no change over switch. After the engine starts the "intelligent" charger links the alternator to the two banks. This way there is no voltage drop on the domestic bank when starting the engine and no risk of accidentally discharging the start battery.

 

[Buck Turgidson]

try disconnecting the VSR and starting to see if you still get the voltage drop.

 

[ithet]

Do you have solar? This could be providing enough volts to engage the VSR prior to starting. I have this issue.

 

[davidmh]

Your plotter & insruments seem connected to the starting battery which will cause the drop out you describe. Check by isolating the engine battery and switching on the instrumenst . I would wire all the accesories etc on to the house battery.

 

[Refueler]

Yep ... sounds like you've wired your gear to starter battery instead of domestic bank.

OR

When starter battery voltage drops - the domestic is somehow being pulled in as well ... but that would mean some connection is in error.

 

[vas]

2X60Ah and 2X110Ah /= 340Ah (imho)
OK, obvs that's not the issue, as others said move accessories to house bank and clean check all connections specially black from battery to engine block.

 

[sailor211]

try disconnecting the VSR and starting to see if you still get the voltage drop.

This i will look at. I did not think i had changed anything but obviously have.

 

[sailor211]

Do you have solar? This could be providing enough volts to engage the VSR prior to starting. I have this issue.

I had not thought of this so will look at the VSR and solar connection.

 

[sailor211]

Yep ... sounds like you've wired your gear to starter battery instead of domestic bank.

OR

When starter battery voltage drops - the domestic is somehow being pulled in as well ... but that would mean some connection is in error.

I will look carefully, I think there is only two wires to the engine start battery, but the -ve are connected. Somewhere something is joining the two banks.
Thanks

 

[PaulRainbow]

I had not thought of this so will look at the VSR and solar connection.

This is most likely the cause, but should not really happen with an adequate starter battery, so check the engine battery is good.

If it is the VSR closing due to the solar, you can fit a normally closed relay to the VSR negative and connect the relay coil to the starter motor solenoid connection.

 

[Boater Sam]

A poor negative connection somewhere will cause the neg to rise when you are cranking, resulting in an effective voltage drop on the cabin batteries.

 

[PaulRainbow]

A poor negative connection somewhere will cause the neg to rise when you are cranking, resulting in an effective voltage drop on the cabin batteries.

Seriously ?

If you completely disconnected the negative cable from the engine battery it wouldn't affect the domestic systems, as there won't be a circuit.

 

[bedouin]

Does any of the wiring that connects the plotter -ve also carry the starting current?

There will be considerable voltage drop in the cables between the starter battery and the starter motor. If your plotter shares any part of that circuit then it will suffer a voltage drop. I have this set up and do sometimes get the GPS detecting significant voltage drop.

 

[PaulRainbow]

Does any of the wiring that connects the plotter -ve also carry the starting current?

There will be considerable voltage drop in the cables between the starter battery and the starter motor. If your plotter shares any part of that circuit then it will suffer a voltage drop. I have this set up and do sometimes get the GPS detecting significant voltage drop.

The -ve is common throughout, as it is on most boats, but that cannot cause a voltage drop if the engine battery and domestic batteries do not share +ve.

 

[bedouin]

The -ve is common throughout, as it is on most boats, but that cannot cause a voltage drop if the engine battery and domestic batteries do not share +ve.

I hesitate to contradict you given your expertise but it can - and does on my boat.

If the negative goes from the domestic negative, to the starter negative, to the starter motor, there will be a voltage drop between the starter battery and the starter motor. If the negative from the domestic battery flows along the same wires that carries the starting current then it will share (some of) that voltage drop. Note this is not about the dropping of supply voltage in the starter, but just the voltage drop in the starter cables.

Routing the domestic supply in such a way that it doesn't share any of the starting current will solve that. You could also reasonably say that this shows that the negative cable is not really up to the job!

 

[B27]

..

What is likely to cause the instruments (plotter) to restart on engine start?
...

TIA

The power supply section of the plotter being designed by an idiot who doesn't own a boat, allegedly.

 

[PaulRainbow]

I hesitate to contradict you given your expertise but it can - and does on my boat.

If the negative goes from the domestic negative, to the starter negative, to the starter motor, there will be a voltage drop between the starter battery and the starter motor. If the negative from the domestic battery flows along the same wires that carries the starting current then it will share (some of) that voltage drop. Note this is not about the dropping of supply voltage in the starter, but just the voltage drop in the starter cables.

Routing the domestic supply in such a way that it doesn't share any of the starting current will solve that. You could also reasonably say that this shows that the negative cable is not really up to the job!

To get a voltage drop in the domestic systems by starting the engine, you need a circuit between the two systems. You cannot pull the voltage of the domestic systems down by just having a connection between the negatives.

 

[doug748]

I had not thought of this so will look at the VSR and solar connection.

Yes, and Boater Sam's post 13 may well have a general bearing on matters.

I don't know the size of the engine or the electronics involved but I sometimes start my 20hp engine on the domestic ,100Ah, deep cycle battery and the Plotter, VHF, AIS and sounder all function without a flicker. So if the above + battery, connections wiring size all come up good, you should be ok?

.