Another electrical question

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Sandy Stone

Sandy Stone

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Jun 2, 2007
404
Beneteau First 375 Slidell, LA
We are the proud new owners of a 1986 Beneteau First 375 with a Volvo auxiliary, a model 2003 I believe. The boat was rewired by the PO (or someone he hired, I'm sure) and it looks like a very clean installation. It is a classic Nigel Calder three battery switch setup: house battery disconnect, start battery disconnect, and emergency cross-connect. The alternator output is wired directly to the house battery positive, and through a battery combiner to the start battery positive. All very nice, until I accidentally discovered the other day that I could crank the engine over with all three battery switches in the off position(!).
Naturally I started looking around, and discovered that there is a cable, presumably installed by Volvo, connecting the alternator output post to the starter supply post. This means, in effect, that the starter is permanently wired directly from the house battery. Of course, I am very uncomfortable with this, since if there is a fault in the starter I would be unable to disconnect its supply current to avoid a fire.
The obvious solution is to remove the cable from the alternator to the starter, but I hate to mess around with the OEM setup without understanding why it was built that way in the first place. Does anybody know what purpose the offending cable might serve, and what the side effects would be if I removed it? TIA.
 
Scott T-Bird

Scott T-Bird

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Oct 26, 2008
6,432
Catalina 320 Barnegat, NJ
My alternator output is wired to the starter supply post. I think it may be common practice because it is simply a short convenient run which feeds alternator output to the batt via the starter cable. Of course, with the starter cable being run thru the switch, there wouldn't be an issue of power being permanently supplied. When I installed my combiner, I didn't run my alternator output directly to the battery ... yet. That is a small project that I need to get on ... When I do, I will disconnect the short jumper to the starter post.

In your case, the PO simply didn't eliminate the jumper from the alternator to the starter post. Now you have a direct power feed from batt to alternator to starter. I would just eliminate that jumper ... it's no longer needed or wanted.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
If wiring direct to the house bank and adding a combiner or Echo type charger, as has been done, then you want to remove that jumper between the alt and the starter.

This can be dangerous in that you are now trying to start the motor with the small alternator cable and the VERY SMALL jumper wire. Not good!

Who ever did the install and conversion to a combiner or Echo did not fully understand what they were doing and missed removing the alt to starter jumper..
 
Stu Jackson

Stu Jackson

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Feb 26, 2004
23,362
Catalina 34 224 Maple Bay, BC, Canada
Reply #11, here, describes the reasoning why that wire was there. I agree, remove it, once you assure yourself that the AO goes to the house bank (which you have) and that the starter is fed by a single wire from the battery bank output(s) to the starter. It looks like the PO missed the concept when he made the changes.

You have a very good system.

http://c34.org/bbs/index.php/topic,4949.0.html
 
RAD

RAD

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Jun 3, 2004
2,330
Catalina 30 Bay Shore, N.Y.
A little note: on my system after I turn the engine battery off I can still crank the engine cause the combiner was still engaged.....scratched my head in confusion over this
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,760
Canadian Sailcraft 36T Casco Bay, ME
RAD said:
A little note: on my system after I turn the engine battery off I can still crank the engine cause the combiner was still engaged.....scratched my head in confusion over this
Click to expand

Something is wired wrong. The combiner connected to the house bank should not pass current though a switch turned off.

Combined or not the switch should disconnect the starter from the start battery.
 
RAD

RAD

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Jun 3, 2004
2,330
Catalina 30 Bay Shore, N.Y.
Maine Sail said:
Something is wired wrong. The combiner connected to the house bank should not pass current though a switch turned off.

Combined or not the switch should disconnect the starter from the start battery.
Click to expand
Thats what I thought and now you got me thinking, I will say that when I've gone back later I cannot start the engine so current is finding its way around that switch and it has something to do with the combiner
 
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