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  What battery switch wiring would cause these symptoms?

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Author Topic:   What battery switch wiring would cause these symptoms?
Frank O posted 03-17-2007 06:49 PM ET (US)   Profile for Frank O   Send Email to Frank O  
While conducting various maintenance tasks today on my 1995 Outrage 21, I used a digital voltmeter to check the voltages across each of the boat's two batteries. (They're both marine deep cycle batteries, but not AGM. Also, it had been two weeks since the batteries were last charged during use of the boat; although I have a solar panel, it had been disconnected for several weeks.)

With the Perko four-position battery switch set to off, battery #1 showed 12.23 volts, and battery #2 showed 2.53 volts. I believe that battery #2 is the one that powers the bilge pump when the battery switch is set to off.

I then tried setting the battery switch so that I could briefly power up the GPS unit. I was surprised to find that the GPS (as well as all other instruments and lights) did not show it was receiving power if the switch was set to either the #1 or #2 battery. The instruments only showed they were powered when the battery switch was set to "all."

The marine shop that did the annual maintenance on my boat a couple of months ago put two new batteries, so it's plausible to me that they could have changed a cable around by mistake. But I'm scratching my head over what wiring would cause the above symptoms. If both the positive and negative leads from the batteries were connected and disconnected by the battery switch, I can imagine a scenario where you would need to have the switch set to "all" to complete an electrical path if the leads were swapped. But don't boats with two batteries usually have a common ground? Thanks for any thoughts on this.

jimh posted 03-17-2007 11:02 PM ET (US)     Profile for jimh  Send Email to jimh     
Battery #2 is dead. The electronics are wired to it directly. They only got power when you had Battery #1 in parallel.
Frank O posted 03-17-2007 11:14 PM ET (US)     Profile for Frank O  Send Email to Frank O     
Thanks, that makes sense. I assumed that the electronics and the engine were wired together, and the battery switch was toggling these between the two batteries, but evidently that's not the case.

jimh posted 03-18-2007 10:36 AM ET (US)     Profile for jimh  Send Email to jimh     
Here is my simple rule for diagnosing problems in a battery-operated electrical device:

In any electrical system which is operated from battery power, the first component to check when there is an electrical problem in the system is the battery.

Frank O posted 03-18-2007 08:59 PM ET (US)     Profile for Frank O  Send Email to Frank O     
Sounds like a good rule. In this case it was obvious from the get-go that battery #2 was dead, but what was news to me was how the batteries, switch and electronics were wired. But your explanation made perfect sense.

swist posted 03-19-2007 07:10 AM ET (US)     Profile for swist  Send Email to swist     
As a general comment, wiring electronics or most anything else directly to a battery defeats the purpose of having a battery switch in the first place. The notable exception is bilge pumps, which need to run regardless of switch setting.

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