Common Ground

echandler1971

Intro

With my 360 FV on land with both TAs and engines pulled, I felt it was time to clean up the wiring the previous owner left me with. It was a rats nest. 
One particular pain point was the seasonal installing and removing the 5 batteries she has. I'll only refer to the 4 batteries that matter going forward (5th is just for bow thruster). 
I'm streamlining to a common ground bus and for house and a common house positive bus so the multitude of random crap seemingly-stuck haphazardly on the house batteries can be once and for all attached somewhere permanent so I don't have to make sure I have 6 wires on this positive and 11 on this negative, etc, but would like to make the common ground bus be used by everything. The goal is to get me as close to 2 connections per battery as humanly possible while removing redundancies and confusion under the engines.

Question Setup

There are a multitude of seemingly redundant grounds tied mostly to the starboard (closest to batteries and battery switch) engine. Essentially, all 4 batteries' negatives as well as the house panel terminate on the starboard engine. Then there are seemingly multiple grounds from the sbd to port engine. Port engine has the Kohler ground daisy chaining through it. So, Port engine has a ground path through the starboard. Combined house current (2 AGM batteries in parallel) has a ground path through starboard engine as well.


Questions
1. Using the 600A common ground bus I've installed, can I safely ground the 5 batteries to this and then run 2 separate #1 grounds from the bus to the 2 engines, and I guess continue daisy-chaining the Kohler from the port engine? This would essentially be the same star format (loop free), but greatly-diminish the ground connections to the engines that seem to be quite a few.

2. These being Volvo Penta 5.7 GI-E, is there only 1 ground connection point, or are there multiple? I'm seeing 2 groups of ground wires laying on the floor, zip-tied together but in separate bundles. I thought there was just a single ground.

3. (harder existential question) My battery charger, in order to charge 2 house parallel batteries, has 2 sets of leads - one pair for each battery. Is there any difference between connecting them to the battery terminals themselves or slapping them on top of the wires coming from each battery, but at the busses? The issue here is that they are all the same electrically, but just can't wrap my mind around it. See the picture attached below of what I'm talking about.

Thanks

LaRea

Is it a single charger output charging the house, with two wires from that one output?  Or is it two charger outputs that each have their own wire?  

Great idea to simplify the battery connections!  I did that too.  Here's what I did on the 370.  I didn't run starter grounds through a bus bar -- just connected them to the stbd engine.  But I did reroute them through wiring trays to get them off the floor.  



On the negative bus, the worst case would be if you somehow are cranking both starter motors at the same time.  You'd be pushing an awful lot of current through that bus bar!

Conventional wisdom says that with a battery bank, connect ground to the first battery and load to the last battery.  That guidance makes sense when the bank has 5 or 10 batteries.  I doubt it matters with only two batteries. 

LaRea

I think the only reason I ran the house ground to the port engine was to use existing cables and connection points (without doubling up any of the cable connections).   

echandler1971

echandler1971

This is essentially the ground diagram I'm aiming for

echandler1971

LaRea said:

Is it a single charger output charging the house, with two wires from that one output?  Or is it two charger outputs that each have their own wire?  

Great idea to simplify the battery connections!  I did that too.  Here's what I did on the 370.  I didn't run starter grounds through a bus bar -- just connected them to the stbd engine.  But I did reroute them through wiring trays to get them off the floor.  



On the negative bus, the worst case would be if you somehow are cranking both starter motors at the same time.  You'd be pushing an awful lot of current through that bus bar!

Conventional wisdom says that with a battery bank, connect ground to the first battery and load to the last battery.  That guidance makes sense when the bank has 5 or 10 batteries.  I doubt it matters with only two batteries. 

So, in general, we are talking 3 connections to each engine, plus some minor stuff (TA, Trim pump, Neutrasalt)?  The only other question is can the house ground bus connect to the starboard, or is there an electrical/logical reason behind going over to the port side?

Thanks

echandler1971

LaRea said:

Is it a single charger output charging the house, with two wires from that one output?  Or is it two charger outputs that each have their own wire?  

Great idea to simplify the battery connections!  I did that too.  Here's what I did on the 370.  I didn't run starter grounds through a bus bar -- just connected them to the stbd engine.  But I did reroute them through wiring trays to get them off the floor.  



On the negative bus, the worst case would be if you somehow are cranking both starter motors at the same time.  You'd be pushing an awful lot of current through that bus bar!

Conventional wisdom says that with a battery bank, connect ground to the first battery and load to the last battery.  That guidance makes sense when the bank has 5 or 10 batteries.  I doubt it matters with only two batteries. 

I missed the first part of your question about charger outputs. This is a ProMariner ProTournament 360 Elite Series 36 Amp Quad Bank and the setup I'm using for a pair of paralleled batteries is a +- pair to each battery on outputs 1 and 2. I'm guessing it's best to keep them right on the terminals rather than going to the busses, since the path won't be clear from there. Also, I've figured out a better way by just attaching them to the back end of the bolts on the battery cable compression lugs so they are essentially part of a single connection.  All this because when the engines are in, it's tight quarters dealing with crap back in that corner. The fewer connections and tracking down random other misc cables that need to go onto each battery terminal, the better. That's why the goal is one connection per terminal, save for the paralleled ones that will have 2 each on one battery.

echandler1971

LaRea said:

I think the only reason I ran the house ground to the port engine was to use existing cables and connection points (without doubling up any of the cable connections).   

Ok, so what I'm going to do, which seems like it will be fine, is I'm replacing all my cables with tinned 2/0 marine cables (old ones were nasty) as diagramed, except that the port battery will connect direct to the port engine, everything else being the same.

echandler1971

New grounds are in and read - all 2/0 tinned. Engines and TAs go in Tuesday, May 28th.

TonyG13

Having never taken an engine or outdrive out myself, is it normal for the thru-bolt holes to be that close to the edge of the opening? Just doesn't seem right.

YYZRC

The Merc setup was similar - since the load is on the inner transom plate I don't think it matters.

echandler1971

This transom is solid fiberglass and is rock solid. The bolt loads are not lateral, as both sides of the TA have a ton of friction to stop lateral movement. This time, they are adding 5200 to the external seals to all but guarantee leak free use for many years to come. 

LaRea

Agree - that bolt placement is typical and the bolts won't see much side loading.