12 volt Wiring Connections

[Rebotco]

Can some of you sparky experts verify the wiring proposed below will work OK, without blowing me to kingdom come?

My engine bay (cruiser stern) is a rat's nest of wiring at the mo, and I would like to tidy it up.

Have I missed anything vital - or included anything dodgy?

All criticism received with thanks!

 

 

[Alan de Enfield]

Add :

 

Isolator switch between the solar panels and the MPPT

Fuse between batteries and MPPT (as close to the batteries as possible)

Fuse bilge pump

Isolator switch on starter battery ?

 

 

Battery Charger ?

Edited September 13, 2019 by Alan de Enfield

[WotEver]

Looks ok to me, except the split charge relay should ideally have a fuse in the engine battery feed. Does this drawing help?

2 minutes ago, Alan de Enfield said:

Fuse between batteries and MPPT (as close to the batteries as possible)

Fuse bilge pump

Good points. 

[Rebotco]

1 hour ago, Alan de Enfield said:

Add :

 

Isolator switch between the solar panels and the MPPT

Fuse between batteries and MPPT (as close to the batteries as possible)

Fuse bilge pump

Isolator switch on starter battery ?

 

 

Battery Charger ?

Yes, thanks.  I should have shown those fuses!

Is an isolator really necessary on the starter battery, which is only in use for a few seconds?

1 hour ago, WotEver said:

Looks ok to me, except the split charge relay should ideally have a fuse in the engine battery feed. Does this drawing help?

Good points. 

That is really useful.  Almost made to measure for my setup. Great, thanks.

[Alan de Enfield]

8 hours ago, Rebotco said:

Is an isolator really necessary on the starter battery, which is only in use for a few seconds?

It is convention to have one.

 

If you get a short it can be dumping 100's of amps.

 

Many years ago I had an 'engine fire' - long story short - the lifting eye from the top of the engine fell / broke / vibrated off and fell down onto the starter motor and getting jammed between the + terminal and the engine block. It melted everything before I could get to the battery terminals to disconnect it.

 

Safety devices are for the odd occasion when you need them.

 

Switching off the starter battery isolator mans you can safely work on the engine without risk of someone coming along and turning the key when you have your fingers  in a vulnerable position.

Edited September 14, 2019 by Alan de Enfield

[Tony Brooks]

So far the correct diagram has been shown it has not been explicitly stated that the OPs is wrong.

 

1. The alternator feed on a VSR system should run to a battery, not the VSR, the VSR just links batteries.

 

2. There should be isolators close to both batteries so the WHOLE system is isolated apart from a very few exceptions.. This is a BSS requirement.

 

Yes you do need to isolate the engine battery as well as the domestic.

 

3. If you want to fuse the domestic main supply, which is best practice, I would suggest the fuse shown and the idolater be swapped don the diagram but I would fit the domestic fuse as close to the isolator as possible. I would have two cables on the isolator's output stud. One feeding the fuse and domestics and the other from the alternator. This minimises connections on the charging circuit where voltdrop tends to be critical.

[WotEver]

17 minutes ago, Tony Brooks said:

I would have two cables on the isolator's output stud. One feeding the fuse and domestics and the other from the alternator.

Tony, you’ll note that on my diagram I avoided running the alternator via the isolator, opting to fuse it instead. It could possibly lead to an argument with a BSS examiner (although I doubt many of them would notice) but I hate the concept of the alternator running through an isolator due to the high currents flowing through the switch plus the possibility of disconnecting it when the batteries are demanding a high current. 

[Alan de Enfield]

11 minutes ago, WotEver said:

Tony, you’ll note that on my diagram I avoided running the alternator via the isolator, opting to fuse it instead. It could possibly lead to an argument with a BSS examiner (although I doubt many of them would notice) but I hate the concept of the alternator running through an isolator due to the high currents flowing through the switch plus the possibility of disconnecting it when the batteries are demanding a high current. 

Mine were wired up via the isolator but I have never bothered to correct it.

 

 

[Tony Brooks]

39 minutes ago, WotEver said:

Tony, you’ll note that on my diagram I avoided running the alternator via the isolator, opting to fuse it instead. It could possibly lead to an argument with a BSS examiner (although I doubt many of them would notice) but I hate the concept of the alternator running through an isolator due to the high currents flowing through the switch plus the possibility of disconnecting it when the batteries are demanding a high current. 

Absolutely and I agree with you but as I read it the BSS does not list the alternator feed as one of the circuits that is allowed to bypass the isolator so its best to sick with the BSS requirements however illogical. If the OP is happy to argue the point with the BSS examiner it needed then good as far as I am concerned but wire it in a way that allows a swift change of terminal to satisfy a BSS examiner.

 

[Rebotco]

7 hours ago, Tony Brooks said:

So far the correct diagram has been shown it has not been explicitly stated that the OPs is wrong.

 

1. The alternator feed on a VSR system should run to a battery, not the VSR, the VSR just links batteries.

 

2. There should be isolators close to both batteries so the WHOLE system is isolated apart from a very few exceptions.. This is a BSS requirement.

 

Yes you do need to isolate the engine battery as well as the domestic.

 

3. If you want to fuse the domestic main supply, which is best practice, I would suggest the fuse shown and the idolater be swapped don the diagram but I would fit the domestic fuse as close to the isolator as possible. I would have two cables on the isolator's output stud. One feeding the fuse and domestics and the other from the alternator. This minimises connections on the charging circuit where voltdrop tends to be critical.

Thanks for that advice.  The point about the alternator feed is especially appreciated.

Can you enlighten me about a query on the negatives routes.  They seem to indicate that the starter motor and alternator bodies can be used as the negative connection, rather than dedicated cable to the batteries.  Would this mean the whole engine body would need linking to the battery negative, and would that be a good or a bad thing?  Sorry to be dumb, but I need to understand this!

[WotEver]

1 hour ago, Rebotco said:

Would this mean the whole engine body would need linking to the battery negative, and would that be a good or a bad thing? 

Yes, there should be a big fat neg cable coming from the engine or starter motor to the negative of the engine battery. That’s the only cable that should come from the starter battery negative other than the link to the domestics negative (which is often made at the negative bonding point on the hull). 

 

If you follow the existing negative connections from the engine battery, where do they go?

[Tony Brooks]

51 minutes ago, Rebotco said:

Thanks for that advice.  The point about the alternator feed is especially appreciated.

Can you enlighten me about a query on the negatives routes.  They seem to indicate that the starter motor and alternator bodies can be used as the negative connection, rather than dedicated cable to the batteries.  Would this mean the whole engine body would need linking to the battery negative, and would that be a good or a bad thing?  Sorry to be dumb, but I need to understand this!

 

Because of the potential for electrical corrosion metals boast should only have ONE negative connection to the hull. This is fine in theory but is usually a little more difficult in practice but more on that later.

 

This means that you should not wire your boat as earth return like a car where the steel body/hull acts as the negative conductor. The negative for every piece of electrical equipment should, in theory, be connected back to the relevant battery negative by a cable.

 

Unfortunately most  so called marine engines are nothing of the sort as they are based on vehicle or industrial engines so typically the starter, glow plugs (if fitted), warning lamps and instruments and often the alternator are in fact earth return units - even if they have a negative cable on them. Usually if they do the connection is nothing more than a stud on the metal case. This means the you MUST provide a negative path from the engine block back to the start battery negative terminal.

 

If you left it at that then the engine side of things would be fine but if a short to the  hull occurred on the domestic system there would be no return path from the hull back to the domestic battery negative so there would be no current flow and the fuse/circuit breaker would not blow/trip. To guard against that we need to connect the domestic battery negative to the hull also. Usually we simply join the domestic battery negative to the engine battery negative using battery sized cable and let the engine's battery negative connection to the engine do the job.

 

That is all fine and good but engines are often rubber mounted and the prop shaft runs in grease so there might be no connection between the hull and engine. IF a major fault occurred with no hull negative connection the electricity might us e a/the control cable(s) as the negative path and they can and do burn out so to guard against this we normally fit another heavy (battery cable sized) connection between the engine block and the hull. Usually the engine bed on a steel narrowboat. This can give two negative connections to the hull but as long as they are heavy duty cable and close to each other that will be the best we can do.

 

So the answer to your question is that you can make the engine battery negative connection to any metal part of the engine and if the starter has a suitable stud by all means use that but you can just as well use a starter mounting bolt of a flywheel housing bolt  for example. But make absolutely sure that fixing also has a bond to the hull.

 

 

[Rebotco]

Aha - the light is dawning!

So the problem is boats using unmodified car parts (Starter motor and alternator), leading to the need for bonding the negatives to hull and engine.

Ok I'll make the recommended modifications, and see how that looks.

Thanks for really good advice, which I'm beginning to understand!