Boat rewire: Am I going to die

[mikedefieslife]

The electrical system on my boat is a mess. Overloaded bus bars, unfused positives, chaffed battery cables, missing grounds, uninsulated terminals in the bilge, cheap self combusting Chinese LED strips, to name just a few of the issues I've spotted.

I plan to address it this winter with a bit of a rewire, and would like something of a sense check on my diagram below. How badly am I going burn and die?

Just knocked up in Illustrator so not a really schematic, but should give an idea of what I'm proposing.



Appreciate any feedback on further simplifying it, or any additional safety features I've missed.

You'll notice that my boat does not have a grounding plate. I plan to use the engine block as a common ground. I should have drawn that a bit clearer, but that's what it is supposed to be.

[newhaul]

The main thing I see . Why isolate all three batteries combine them into a single 675 ah house bank and the isolated starting battery. Reasoning is first simpler wiring for supply power. 2) more ah available to run your house loads. 3) larger bank to absorb shock loading from inverter usages. ( 3000 watt inverter won't run for long on a mere 225ah) likely start draw will cause undervoltage trip )
4) actually will charge faster as a single bank ( sounds weird but will come up to 80% of 675 ah faster than if separated into 3 smaller banks with same charger. ) other than that seems reasonable to me.

[mikedefieslife]

They will always be run as single bank (should have added that in the notes). The switches are just so that I can easily isolate and remove a pair if needed. Other than an emergency, the banks would always be run as 675ah. I agree actually running separate smaller banks is old fashioned and a waste of resources.

I was debating whether or not to get rid of the starter battery altogether, but since I have two 80ah batteries lying around, I might as well keep one of them.

[senormechanico]

What Newhaul said about combining banks !

[newhaul]

Originally Posted by mikedefieslife

They will always be run as single bank (should have added that in the notes). The switches are just so that I can easily isolate and remove a pair if needed. Other than an emergency, the banks would always be run as 675ah. I agree actually running separate smaller banks is old fashioned and a waste of resources.

I was debating whether or not to get rid of the starter battery altogether, but since I have two 80ah batteries lying around, I might as well keep one of them.

definitely keep a separate starting battery.

[DeepFrz]

Yes, connect all three batteries together on the positive posts with a fuse right on the post and then one lead to the Pos. bus bar. Then you can fuse a lead/leads to your bilge pump/pumps so they can be on always.

[thomm225]

Originally Posted by DeepFrz

Yes, connect all three batteries together on the positive posts with a fuse right on the post and then one lead to the Pos. bus bar. Then you can fuse a lead/leads to your bilge pump/pumps so they can be on always.

I haven't updated the electrical system on my boat which is 43 years old, but I did fuse the batteries that I have in parallel which feed all my electronics and lights, etc (with quality fuses)

These were recommended by folks here and for once I didn't disagree. They are quality Blue Sea Terminal Blocks and Fuses that mount on your battery post.

https://www.bluesea.com/products/519...k_-_30_to_300A

[TreblePlink]

What is the rationale for not tying DC negative to the lead keel? If your mast takes a lightning hit, or even a nearby induced hit, a bunch of that energy will couple into all the wiring inside the mast.

Conventional wisdom is that during such an event all "grounds" remain at or near the same potential to minimize damage.

[mikedefieslife]

Originally Posted by TreblePlink

What is the rationale for not tying DC negative to the lead keel? If your mast takes a lightning hit, or even a nearby induced hit, a bunch of that energy will couple into all the wiring inside the mast.

Conventional wisdom is that during such an event all "grounds" remain at or near the same potential to minimize damage.

It's a catamaran. I don't have an lead. The engine is connected to a drive leg. The leg lifts, but is does always have some contact with the water. That's the only decent grounding I have.

[Cavalier]

I've just been over the same process myself. After I opened up the breaker panel and looked behind, then followed cable-runs and mapped-out the circuit, I couldn't sleep well.. so I tore the lot out and rebuilt - including the breaker panels.

On the breaker panels I installed ELCI/GCFIs in two groups for the AC-panels, relating to both shore-power inlets. I used "restricted off" breakers in a separate DC group for the 3 bilge pumps. See: https://www.bluesea.com/products/742...ingle_Pole_15A
I liked this, as I wanted to keep a very tidy circuit topology around the battery banks (and under the bunks), and I didn't like the idea that cherry-picked circuits would bypass the breaker-panel and run directly to the batteries. However, the only items that do run direct to the positive and negative "house" rails are the windlass and an electric winch (via individual fuses and a high current DC switch).

The PO has 8 6V batteries wired in series and parallel to give 12V and 800Ah. However, the batteries were old and sometimes didn't have enough power left over to start the engine adequately without producing significant drops in system voltage during cranking. I'd have to sit there on calm days waiting for the solar to put enough power back into the bank to start the engine. Clearly, the PO had possibly taken the bank way below 50%s.o.c. (let alone 80%) on many occasions, and the bank was 7 years old.

With a new bank, not being abused as much, the problem shouldn't occur. However, the thought of a family member leaving a high-drain device on over-night (or whatever other reason) got me thinking about having a separate battery for the starter.

I reconfigured so that I had 6 6V batteries, 12V 610Ah, for the house bank, and a separate starter battery.

I isolated the starter and house as per ABYC with a "0 1 2 both" switch, but also linked the positive-bus-bars of house and starter with a BlueSea ACR. The negative lead from the ACR (to the neg bus) goes through a switch so I can disable the ACR if I wish.

The good thing is that now the starter automatically gets topped-up whenever the house has a charge source, such as solar or shore-power, and the house bank automatically gets charge when from the alternator via the starter bank. However, whenever the charging source is removed (and the voltage falls back towards rest voltage) the ACR disconnects the link between the two banks.

I know the concept of a starter battery flies in the face of Nigel Calder's recommendation, but his argument is based upon a "most optimum economic" approach. The idea being that a very large house-bank would work between than a separate starter and house bank, as a larger overall Ah capacity would mean that you eat into your SOC less each day, so your battery bank cycles less and lasts longer as a result. However, this gives you absolutely no backup incase something happens to your house bank (however unlikely). Anyway, starter batteries are cheap, so if you're having to replace single battery every few years, it's relatively cheap insurance IMHO.

[TreblePlink]

Originally Posted by mikedefieslife

It's a catamaran. I don't have an lead. The engine is connected to a drive leg. The leg lifts, but is does always have some contact with the water. That's the only decent grounding I have.

Good reason.

I wonder what the best lightning protection scheme is for a cat? Gotta provide a good current path from mast to water - otherwise it will find a path through equipment and prop shaft? Maybe there is a submerged metal plate somewhere?

[billknny]

A couple of things...

An engine in general makes a poor negative bus bar and a poorer yet lightening ground, and those two systems should NOT be the same anyway. You can not count on an engine actually being grounded to the water, if that is what you are hoping for. And if you DO send a lightening strike through the engine and transmission, count on all the bearings and gears to be welded together.

I don't see enough charging capability to justify the size battery bank you have. Is there something missing other than a 50A alternator and a 20 A solar system?

[newhaul]

Originally Posted by billknny

I don't see enough charging capability to justify the size battery bank you have. Is there something missing other than a 50A alternator and a 20 A solar system?

and you base this opinion on what? Perhaps the op is a marina hopper with no more that 3 or so days off shorepower.

[mikedefieslife]

Other than winter now, I'm only ever in a marina for fuel or water.

The boat came with 675ah battery bank, which has served me well anchoring this summer. I've only owned the boat since May.

The 400w of solar produce between 80-100a a day in summer which seems adequate, but I would like to add more and get better efficiencies using separate MTTP controllers rather than the single PWM, but that is for another day. I agree it would be nice to have charging sources over 10% of battery capacity, that being said my draw is minimal. The largest is a freezer at about 3 amps when the compressor is running.

I'm in the Med, so unfortunately I spend 80% of my travelling time motoring.

At the moment most items are run back to the batteries for grounding. The boat is 40 years old, like most catamarans doesn't have lightening protection.

[TreblePlink]

Originally Posted by billknny

...
An engine in general makes a poor negative bus bar and a poorer yet lightening ground, and those two systems should NOT be the same anyway.

Perhaps not. But why?

Conventional wisdom is that all "grounds" tie together at the lowest impedance point (to ground or water) so that during a lightning event all remain close to the same potential. This concept is well accepted.

The idea that you can isolate DC wiring and equipment from strike energy is wishful thinking if you have radio or light cables up the mast. Or anything tied to steel stays.

Why is a boat an exception to the single-point-ground method?