Wiring Question

[Jonah]

(Solved: Scroll down for solution.)

Hi all,

The answer to this question is probably "go trace your wires, Jonah". But still, I thought I'd ask.

I recently returned from a four-week trip to find both starter batteries, and also my house battery, dead. Just before my trip, I discovered that my shore power cable had a grounding problem, so I picked up a new cable while on the trip. But that means that the batteries sat without a charge on them for almost a month. Who knows why they drained: maybe I left something on, or maybe it was the bilge pumps (I hear we got a lot of rain, but the bilge is pretty dry).

Anyway, absolutely nothing worked. Neither of the starter batteries was cable of trimming the outboards down, and my house battery couldn't even turn on the radio or GPS. The VHF did come on just a bit, but faded in and out.

But here's the thing: when I plugged in the new shore power cable, I had left both of the starter battery selector switches on "both". And when I flipped the switch for the battery charger, the stereo suddenly turned on. But the battery charger was put in new when I bought the boat, and the dealer told me they couldn't find the house battery, so they only wired the charger to the two starters. How, then, is the shore power (or battery charger) enabling the stereo to turn on?

I can only think of two possibilities: 1) the stereo is wired to the starter batteries (bad idea if I plan on anchoring with music for a while); or 2) the house battery is not wired to the charger, but is somehow wired to the starter batteries?

Thanks for any advice. I know little about electronics.

 

[everwhom]

Hmmm the "dealer couldn't find the house battery" thing caught my eye. Are you sure you have one?

My 330 has 4 batteries, but they are in 2 banks of 2 (so effectively just 2 big batteries). The "house" electronics share a battery bank with one of the motors (starboard as I recall) and the port motor has its own bank, shared only with the bow thruster.

I'm wondering if your boat is similarly wired?

You shouldn't normally put the battery switches on "both" -- that position should only be used if one of your batteries is dead and you need to start that motor. As I understand it, if I ran down my starboard battery from my house electronics, I would start by starboard motor by first starting my port motor (on it's own separate battery bank) and then switching my starboard switch to "both," starting the motor, and then immediately switching it back to "1" so it can charge up the starboard bank.

Hope that helps!

 

[Jonah]

Thanks everwhom,

Yes, I normally start my outboards on separate batteries (1 and 2), but had the switch on 'both' since I had hoped that the combination might have enough juice to start one or both of the outboards.

And yes, I later found the house battery, which was moved by the previous owner to under the aft cabin. He had an SB radio on board, and wanted to minimize the voltage drop with a shorter wire to the house battery.

 

[Jonah]

Hi all,

Just bumping this in case anyone is in the mood to explain how my charger (connected only to my starter batteries) can power my house-battery electronics, without it being the case that my house battery can drain my starter batteries (I hope!).

 

[Jonah]

Well, for anyone who's interested, here is the answer!

While tracing some wires for another project, I discovered a large breaker near the positive terminal of my house battery. It appeared to be tripped, and yet all of my electronics were working. I then remembered that the previous owner had moved the house battery to its current position (under the aft cabin) to minimize voltage drop to an SB radio that he had installed. Surely that was the reason for the large breaker ... but ... did he also re-wire house electronics to the new location of the house battery? From what I could tell, it didn't appear to be the case. So, I detached the positive lead, and sure enough, my DC panel still worked fine.

So there you have it: it turns out that I do not currently have a house battery. My helm and cabin electronics were apparently re-wired to my starboard starter battery when the previous owner moved the house battery to under the aft cabin. That would explain how my starter died while I was away, and it would also explain why plugging in my charger to shore-power would suddenly power my stereo, etc. But why wouldn't the previous owner have just installed a new battery under the aft cabin, and left the original where it was? Not sure about that.

Very glad to have learned this while at dock, and not while on an overnight trip, anchored in the middle of nowhere. Obviously, I plan on moving the house battery back to the battery platform in aft bilge, since that would be easier than re-wiring everything to its current location under the aft cabin. Unfortunately, the dealer installed my new charger in the place where the house battery previously sat. I have seen some images of batteries installed under the aft livewell, where the old 2-stroke oil tanks used to be. I do already have an access panel there, so might try that. If anyone has tips, let me know.

 

[SkunkBoat]

Can't really help you without knowing what you have so...

My tip would be-
draw out your battery circuit on paper as it is right now. Check it seven times to be absolutely sure you know exactly what it is doing, how it charges, what each switch and breaker does.
Look at your owners manual (download it from the gradywhite.com site) and see if your current setup matches the original. Note any changes.

Then decide what changes you might want to make.