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Old 30-04-2006, 15:03   #1
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Seeking Advice on Common Configurations

How little I know about these mid-size boats...

I have another little pesky issue. I have 2 battery switches in my engine room. (The big, round Perko switches)

One is for the starter battery. The other is for the house bank. The starte battery switch has and on and an off position. The house bank has 1, 2, both, or off.

When using my house batteries with the starter switch in the off position, I tend to lose the charge in my starter battery in what seems like the same amount that my house batteries are being used.

In what seems odd to me, the starter battery shares a common negative battery cable that runs through the house bank and acts as the "ground" for all batteries.

All this leads to a condition of not enough juice getting to my starter when (and ONLY when) my house batteries are low.

Is it common to have the starter battery grounded through all of the house bank?


Could this be causing my starter battery drain, or at least be eating up the starter battery's juice since the entire house bank's negative terminals are part of the starter battery's circuit with the starter?

Anyone had any similar problems?
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Old 30-04-2006, 16:55   #2
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isolating starter battery

Having a common negative is normal and will not drain your starter battery.
Your starter battery should be off so it is disconnected from the house circuits once you are under sail. The easiest way to check the switch functions for isolating the starter battery is to disconnect the positive wires from your house batteries so that the only battery left connected is the starter battery and then determine the switch positions that result in no power to the house.
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Old 30-04-2006, 17:36   #3
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My first guess, and it is a guess, is that your alternater charge wire (Single wire alternater?) is routed through the main battery switch, to charge the house bank, and also wired to the starter to charge the starting batteries. This will keep the starting batteries in the circuit all the time.
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Old 30-04-2006, 17:41   #4
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Yes, the common ground should include all of your battery banks. It sounds as though you have a situation somewhere where your starting battery + lead is connected to some other load, rather than just your starting system. You should be able to have both switches "ON" without any cross connect of your batteries. When your start switch is in the "Both" position of course, your batteries should be connected in parallel.

Edit: just saw Kai Nui's post, and wonder if you have diode isolators. One of the diodes may be shorted.

Phil
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Old 30-04-2006, 17:58   #5
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SImple test. Remove the hotlead from the house bank to the Perko switch, and see if the interior lights work when you turn the Perko switch on.
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Old 30-04-2006, 19:37   #6
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you gotta love simple tests Sometimes we get so involved with the trees and the forest ... Nice to have a great group of people who aren't predisposed to help us see the simple answer!
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Old 01-05-2006, 03:54   #7
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Thanks, guys. Kai Nui... great idea! I'll try that and post a follow up.
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Old 01-05-2006, 13:49   #8
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Not jumping in to be a know it all here, but just to take a different angle of the common earth. The reason is, that all earths need to be tied back to your main Boat earth at a common point. This is usually on the engine block somewhere and often close to the starter, as this is a high current demand device. So ensure you have good solid cable, good solid connections, all going from the battery negs, to one point on th engine block. If you don't, you end up with stray currents running around the boat and it can cause all sorts of issues, including Anodes depleating quickly.
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Old 01-05-2006, 22:36   #9
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Alan is spot on - I've worked in electronics (not marine) for 20 years. The single biggest problem is ALWAYS the ground. The hardest to find are the ground "loops". These happen when you are using different grounds within a common system. It creates potential (voltage) in places it should not be - this cause erratic and intermittant behavior with wierd symptoms. There is also the problem of inadaquate ground - this could be a poor connection, or perhaps too small a wire to ground. This typically causes a degraded performance and eventual failure.
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Old 01-05-2006, 22:44   #10
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I would discount the ground in this case for two reasons. One, it is simply a matter of the starting bank discharging, and Sean has not described any flickering, or other signs of a degraded ground. The other, is the Starting bank is not discharging at a different rate than the house bank. A short or intermittent connection caused by a bad ground would manifest itself either by a rapid discharge, or a failure to charge the starting bank.
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Old 01-05-2006, 23:07   #11
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Yes you are exactly right Kai. I was not suggesting any such issue being caused by the ground. I was just explaining why the ground was tied and single point fixed. Sorry folks, I should have not confused the issue.

Hey sean, so what happend with the test???
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Old 01-05-2006, 23:11   #12
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A little confusion keeps us on our toes
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Old 02-05-2006, 06:48   #13
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Speaking of ground... When gounding to the engine bloack... is it necessary to remove the paint to have a metal to metal contact? is the suface under the bolt head /washer adaquate?
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Old 02-05-2006, 08:32   #14
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Yes - to achieve an adequate ground, you must clean the block to a bare metal surface, under the entire contact area.
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Old 02-05-2006, 10:40   #15
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