One switch - house & engine?

[Lake-Effect]

Originally Posted by DefinitelyMe

I've never understood this approach [dedicated start battery] for a liveaboard cruising yacht. I understand that it's perhaps the most common setup and that people like it. Each to his own, but........ why? All that added complexity just to be ready for a 'what if' scenario that just isn't going to happen. If you live on your boat, any problem with the electrical system involving over-discharge of the battery bank (house battery bank if you have more than one) will surely be noticed long before you get to a point where they are dead? Surely?! Add to that the fact that very, very few cruising yachts rely on their engines exclusively for charging - so in the highly unlikely event that you are unable to start it due to low voltage you have an alternative charging source anyway - and the need for a separate, dedicated battery bank 'for redundancy' just vanishes. Doesn't it?

As an occasional electrical tech for boats (and an occasional cruiser and charterer), I've seen many instances where house banks get discharged or fail due to unknown loads, or solar charging could fail... if your bank consists of paralleled 12v batteries, one could fail and pull the others down... You could accidentally short the bank with a wrench and blow a 400 A fuse and not have a spare. (I've seen it happen; there weren't any fireworks, just a short snap and the fuse is gone). If you're in the middle of nowhere and any of these happen...?

Having a dedicated start battery means you still have a means of starting the engine, and a redundant 12v for emergency use (eg VHF, instrumentation).

Complexity? One starting or dual-use battery and one echo-charger, and a bit more wiring. That's all that's required.

[Stu Jackson]

These oft-repeated threads about battery switching usually have one thing in common: the OP rarely understands how switching in electrical systems works and how many OEM boats came from the factory, and many still do.


Here's how and why, as well as just about every switching method used that actually works:



OEM 1-2-B Switch Wiring History http://c34.org/bbs/index.php/topic,4....html#msg30101

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowner...d.php?t=137615

This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
http://forums.sailboatowners.com/ind.../#post-1332240


STANDARD DISCLAIMER: combining a good bank and a dead one is just plain dumb, as is the BS DCP switch for sailboats.


AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/in...teries.133773/


********************


These links come from:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

[DefinitelyMe]

Originally Posted by Lake-Effect

As an occasional electrical tech for boats (and an occasional cruiser and charterer), I've seen many instances where house banks get discharged or fail due to unknown loads, or solar charging could fail... if your bank consists of paralleled 12v batteries, one could fail and pull the others down... You could accidentally short the bank with a wrench and blow a 400 A fuse and not have a spare. (I've seen it happen; there weren't any fireworks, just a short snap and the fuse is gone). If you're in the middle of nowhere and any of these happen.?

But I think these are not liveaboard cruising yachts, are they? I feel most people notice dead cells, or shorts, or any other big problem really quickly. Within a few hours at the most, and remove the cause of the problem from the system long before it has a chance to completely drain the whole bank. What would I do if I blew a fuse in a remote area and didn't have a replacement? Well, I'd stick a wire in the fuse box until I could get one! It's hardly catastrophic. What would you do? Run your house loads from the starting bank? Run your engine for a few weeks until you made landfall?! Or just sit in the dark for weeks on end with no non-vital systems running for want of a fuse?! How does having a separate starting bank help you in this scenario?

[Lake-Effect]

Originally Posted by DefinitelyMe

But I think these are not liveaboard cruising yachts, are they? I feel most people notice dead cells, or shorts, or any other big problem really quickly. Within a few hours at the most, and remove the cause of the problem from the system long before it has a chance to completely drain the whole bank. What would I do if I blew a fuse in a remote area and didn't have a replacement? Well, I'd stick a wire in the fuse box until I could get one! It's hardly catastrophic. What would you do? Run your house loads from the starting bank? Run your engine for a few weeks until you made landfall?! Or just sit in the dark for weeks on end with no non-vital systems running for want of a fuse?! How does having a separate starting bank help you in this scenario?

I agree that experienced liveaboards know their boats better than most. But they're not all MacGuyver, nor do they always travel with their own fully stocked chandlery. What about fixing that bad cell right when you need the engine to get away from a lee shore? What size wire would you stick in to replace a fuse that will handle the starter, as a storm front opens up?

If you don't see the advantages of a dedicated starter battery... you don't have to have one, of course.