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  #11  
Old 07-27-2010
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Originally Posted by jarcher View Post
Thanks Mitiempo, I think that's what I meant to say. I go from the house battery neg terminal to the shunt, then from the shunt to the neg bus. Then I wire the neg bus to the engine block. Then I wire the neg terminal of the start battery to the bus.

The reason I am trying to figure out where the starter current flows is so I know which wires to size for the start current. It seems that with this arrangement no start current actually flows through the shunt. Why is it a 500A shunt then?
ALL wires should be sized to start your motor. What ever size your batt cables currently are is what the jumper should be. What if you need to start on the house bank? Many sailors do this anyway as regular practice and use the "start battery" as a reserve or back up only....
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  #12  
Old 07-27-2010
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Quote:
Originally Posted by mitiempo View Post
I would use a bus as it is neater. Only one lug on the block.
I suppose that is just a matter of preference. I'm only recommending two lugs on the block. Throwing an unnecessary bus into the mix for the sake of a neat installation counters with added circuit length, additional contact resistances, more points for corrossion and requiring inspection, additional complexity, components, cost, and the added posibility of ground loops or other grounding issues. I'd place two lugs on the block because you can (without disadvantage), it's simpler, and it's less expensive.
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Old 07-27-2010
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I suppose that is just a matter of preference. I'm only recommending two lugs on the block. Throwing an unnecessary bus into the mix for the sake of a neat installation counters with added circuit length, additional contact resistances, more points for corrossion and requiring inspection, additional complexity, components, cost, and the added posibility of ground loops or other grounding issues. I'd place two lugs on the block because you can (without disadvantage), it's simpler, and it's less expensive.

Less expensive? Have you price 2, 1 or 1/0 wire lately? Two unnecessary runs, one from each battery to the block, can get rather expensive considering the distance the wire needs to travel from batt compartment to engine on many boats. Just did one last week that required a 13 foot run of 2/0 cable.

Most DIY's are buying Ancor wire, and 1/0, a very common size, is $11.99 ft at West Marine. With a Blue Seas 2003 3/8 Powerpost you can buss both banks together and then run one wire to the block instead of two. This is a very common and widely accepted practice amongst marine electricians and is actually preferred to have one single ground point..

Let's say you have 8 feet of wire between the battery neg terminal and engine. One 8' 1/0 wire from WM would run you $95.92 without terminations. Add a second wire and your now at $191.84 without terminals. The power post is $10.99....
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Last edited by Maine Sail; 07-27-2010 at 12:26 PM.
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Old 07-27-2010
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I already have the negative bus installed and hooked up to the shunt anyhow. I just need to measure for and order cables to go from the neg of the start battery to the bus, and from the engine block to the bus. The existiong cable from the engine block to the start battery neg is too short by just a bit.

What would happen if I tie the negatives of the batteries together and leave the engine block directly on the starter battery neg post? I could still move the alternator line to the house battery. The downside I can see is that the charging from the alternator won't be monitored. Is there any other down side?
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Old 07-27-2010
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As long as the shunt is the first connection after the house battery negative everything in or out of that battery will be monitored, shore charger, alternator, and any other sources. The negatives ultimately all have to end at the block, ideally in one place.
Wiring house negative AFTER THE SHUNT to start negative and then to the block from the start battery negative works.
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Quote:
Originally Posted by mitiempo View Post
Wiring house negative AFTER THE SHUNT to start negative and then to the block from the start battery negative works.
Oh, cool! That would be easiest, since the cable from the block to the start battery neg is in place. I probably even have a cable on hand that will reach from the start neg to the bus. Thanks!

I'll still wire the echo charger negative after the shunt, move the alt wire to the house positive and then I'm done! Hm, I can probably even get this done before tonights race.

Thanks everyone, you were all a huge help!
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I can agree with that ... if that is the setup and the distance between batteries and engine block. I don't buy wiring from West Marine, I don't require 0/1 for starting circuit, and I don't have to run 8 feet. I made, at most, a 4 ft run w/ 4 gauge.

Certainly, if 8 ft is the run, 0/1 gauge is required, and a hefty bus bar is pre-existing that is the route to take. I didn't imagine his setup on what I thought I noticed was a 30ft boat would be very much different than mine ... short runs and minimal cabling requirements. But if you're talking Power Post instead of bus bar ... those surely are cheap. I thought we were talking bus bar, 4 gauge, and short runs.

I just prefer to consolidate grounds to the engine block best I can. With most noise originating from the engine and daisy chained grounding, I'm just worried about ground loops. I've done too many clever wiring runs in vehicles that I had to, in the end, really simplify to eliminate ground loops.

Then, sometimes ... just wire whatever way comes most readily and it'll work out the gate...

Best wishes.
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Old 07-29-2010
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Thanks again everyone. I wired this up today and it at least appears to be working. I won't know until the charger decided the house battery needs charging. then I'll see if the charging voltage makes it over to the starter battery.

But the green light on the echo charger is on solid, so I expect its fine.
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Old 07-29-2010
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I reviewed my setup after reading this thread and seem to be in general compliance except that I have my starter battery negative attached to the same end of the shunt as the engine ground. I know I could have extended it straight to the engine but it seemed to serve the same purpose in this configuration. Does anyone see a problem with this setup?
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That is fine, really the same as using a bus. As long as there is nothing connected to the battery side of the shunt except the battery itself.
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