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Old 19-07-2019, 04:25   #1
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Wiring shunt

Hi fellows,

I ask you to check the basic wiring diagram. If you find any errors please let me know. I am not so strong with electricity.

I already have the components

Nasa BM-1 compact battery mon
2 house batteries
1 starting battery
2 solar panels 2*40W in series
Victron MPPT 75 / 15

The system is up and working except the battery monitor. Please check if the shunt is placed correctly on the diagram. My goal is to measure in and outgoing current of house batteries only.
Thanks!
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Old 19-07-2019, 04:59   #2
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Re: Wiring shunt

The shunt will do what you asked.
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Old 19-07-2019, 05:03   #3
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Wiring shunt

Itís perfect.

The drawing style also reminds me of a comic strip artist!! (Meant as a compliment)
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Old 19-07-2019, 05:08   #4
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Re: Wiring shunt

I think the shunt position is correct for what you're asking, but I've not yet installed a battery monitor myself, so I will defer to those who have.


Of greater concern to me - shouldn't the alternator and starter be connected directly to the start battery? There's no real reason to have the starter positive on a switch, or to have any significant length of wire in its path , and I would expect the alternator to feed the start battery first, then the VSR also charges the house when the engine is running. Also, if your House B switch is opened, or the house fuse pops, when the engine is running, your alternator would be disconnected from any battery, which could blow it, or damage any house electronics that see unregulated alternator voltage.
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Old 19-07-2019, 05:44   #5
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Re: Wiring shunt

This guys does a great series of videos on basic boat electrical systems. Some time on his YouTube channel and looking at the resources on his website would be helpful.

https://www.pysystems.ca/resources/diagrams/

Lake-Effect is correct in saying you NEVER want your alternator to not see a load. It will immediately damage the alternator if it is excited and producing output.

IMO you would wire the alternator directly to the start battery (no switch). Paralleling this connection to you VSR then out to your house bank. Your shunt is in the right place on the negative side of the bank with nothing bypassing it.

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Old 19-07-2019, 05:45   #6
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Re: Wiring shunt

Quote:
Originally Posted by Lake-Effect View Post
I think the shunt position is correct for what you're asking, but I've not yet installed a battery monitor myself, so I will defer to those who have.


Of greater concern to me - shouldn't the alternator and starter be connected directly to the start battery? There's no real reason to have the starter positive on a switch, or to have any significant length of wire in its path , and I would expect the alternator to feed the start battery first, then the VSR also charges the house when the engine is running. Also, if your House B switch is opened, or the house fuse pops, when the engine is running, your alternator would be disconnected from any battery, which could blow it, or damage any house electronics that see unregulated alternator voltage.
hmm... it was also my understanding for a long time that the alternator should charge the start battery first. I used to have it this way when I had 2 similar batteries - one for house and one for starting. After purchasing 2 bigger batteries for house and one smaller for starting I rearranged it. So that all charging (alternator, solar, shore) charge directly the house bank and through VSR the start battery. Mostly because of that article https://marinehowto.com/automatic-charging-relays/

I suppose voltage from alternator is pretty much regulated, so I wouldn't worry about house electronics. But I see it may be a concern when the fuse pops and there will be no load on alternator...
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Old 19-07-2019, 05:52   #7
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Wiring shunt

On this side of the pond, the alternator goes directly to the house bank. The starter bank needs very little charging, and that minimal current is easily handled by the vsr.

I would however, now that itís mentioned, move the alternator output to the other side of the house switch.

You will most likely need to service something on the house panel with the switch off far more often than you would with the alternator. Our boat is wired with a positive buss, the batteries are fused, then the alternator is fused to that buss. The alternator fuse is sized to protect the wires, the alternator will never be able to generate enough current to burn the fuse.

Weíve even fused our starter. Itís a 1200 watt motor, so even on an extremely cold start with low batteries it canít pull enough current for a long enough duration to pop the fuse thatís protecting the wire!
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Old 19-07-2019, 06:08   #8
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Re: Wiring shunt

Quote:
Originally Posted by Sailmonkey View Post
On this side of the pond, the alternator goes directly to the house bank. The starter bank needs very little charging, and that minimal current is easily handled by the vsr.

I would however, now that itís mentioned, move the alternator output to the other side of the house switch.

You will most likely need to service something on the house panel with the switch off far more often than you would with the alternator. Our boat is wired with a positive buss, the batteries are fused, then the alternator is fused to that buss. The alternator fuse is sized to protect the wires, the alternator will never be able to generate enough current to burn the fuse.

Weíve even fused our starter. Itís a 1200 watt motor, so even on an extremely cold start with low batteries it canít pull enough current for a long enough duration to pop the fuse thatís protecting the wire!
This is easy to do and I see the point. It is always worth asking because sometimes you do not see the obvious yourself... Thanks!
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Old 19-07-2019, 06:14   #9
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Re: Wiring shunt

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Originally Posted by mait View Post
hmm... it was also my understanding for a long time that the alternator should charge the start battery first. I used to have it this way when I had 2 similar batteries - one for house and one for starting. After purchasing 2 bigger batteries for house and one smaller for starting I rearranged it. So that all charging (alternator, solar, shore) charge directly the house bank and through VSR the start battery. Mostly because of that article https://marinehowto.com/automatic-charging-relays/

I suppose voltage from alternator is pretty much regulated, so I wouldn't worry about house electronics. But I see it may be a concern when the fuse pops and there will be no load on alternator...
That article makes sense. Having the alternator feed the house batteries directly minimises the charging current through the VSR in most situations. The main argument for connecting the alternator to the start battery is, in the uncommon case of a failed VSR, the start battery still gets charged by the engine so that you always have juice to start.

Still, the alternator should connect directly to the battery (whichever bank you choose). Most alternators need the battery as part of the regulation. You could give the alternator its own fuse, so that the house fuse blowing wouldn't affect it. And I don't think you need a switch on the starter positive; the engine key provides an interlock.
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Old 19-07-2019, 06:21   #10
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Re: Wiring shunt

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Originally Posted by Lake-Effect View Post
. And I don't think you need a switch on the starter positive; the engine key provides an interlock.


However if there is a problem in the system the starter key isn going to help you remove the power from the starter motor or the panel. The switch is mandatory IMHO for energy isolation.
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Old 19-07-2019, 06:35   #11
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Re: Wiring shunt

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Originally Posted by Sailmonkey View Post
However if there is a problem in the system the starter key isn going to help you remove the power from the starter motor or the panel. The switch is mandatory IMHO for energy isolation.

About the only situation I think a switch on the starter could be useful is if the starter solenoid fails and locks on. To work on the starter normally, I'd just be removing the positive lead from the starter battery first.


But the switch certainly doesn't hurt, if it's already there.
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Old 19-07-2019, 10:00   #12
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Re: Wiring shunt

Isolation switches for emergencies and safety while working on circuits should go on each battery bank.
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Old 19-07-2019, 19:59   #13
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Re: Wiring shunt

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Originally Posted by Lake-Effect View Post
And I don't think you need a switch on the starter positive; the engine key provides an interlock.

ABYC not only requires it. but it must be somewhere you can access from outside the engine room. so you can kill power without going into the engine room. I have seen a boat fire where the starter solinoid stuck on and kept cranking the motor with the key off. no battery swtich to stop it. starter wire finally melted and broke and it stopped cranking...

stuck windlass solidnoids and bow thruster solinoids are another thing that can happen.
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Old 19-07-2019, 20:03   #14
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Re: Wiring shunt

Quote:
Originally Posted by Lake-Effect View Post
About the only situation I think a switch on the starter could be useful is if the starter solenoid fails and locks on. To work on the starter normally, I'd just be removing the positive lead from the starter battery first.


But the switch certainly doesn't hurt, if it's already there.
if you have an ACR between your house and start bank, and it is engauged (pluged into shore power) and you remove the pos wire from the start battery. the engine is still live via the acr from house battery. the ACR's are not smart enough to shut off when this happens.

this is also why ACR's must be connected between switch and battery and not after switch.
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Old 20-07-2019, 09:19   #15
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Re: Wiring shunt

To me the opposite.

A true master bank switch isolates the battery from **everything** that carries any significant current. Switching off should be the equivalent of disconnecting the wiring from the battery posts.

Including essential safety-related gear, anything with a parasitic draw.
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