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Old 10-18-2013, 10:07 AM   #1
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Mainship 34 Batttery System

I just purchased a 34 and am trying to understand the battery system. There is what I think a parallel switch between the two banks. In the on position, I would expect the voltage to be the same on both banks as measured on the DC panel meter, but there is a noticeable difference. This is confusing. Does anyone have thoughts on this?

Also, on my twin engine boat, only the stbd alternator appears to be used for charging. Is the the case?

Ron Ciamaga
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Old 10-18-2013, 12:17 PM   #2
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You must mean a newish Mainship 34... since the originals were single-screw only...

In many twin-screw applications, there's a (often momentary) parallel switch that temporarily connects both starting batteries (or banks).. which in turn improves available cranking amps to start an engine. If you're seeing voltage change it suggests a) this isn't a momentary parallel switch at a helm unless you can see the meter from the helm, and/or b) the voltage change you're seeing is actually an equalization, bringing one low battery (or bank) upwards, and the other downwards.

Latter is very speculative on my part. What kind of voltage differences are you seeing on each battery (or bank) with and without the switch?

-Chris
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Old 10-18-2013, 02:30 PM   #3
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I had a single engine 34T and can comment on its DC wiring, but I am a bit of a loss on the twin.

Does yours have separate starting batteries for port and starboard? Is the battery switch you reference a 1,2,both,off type or an off and on type?

David
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Old 10-18-2013, 04:24 PM   #4
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Chris and David

Each engine has an alternator. The Stbd engine alternator is connected to a battery isolator. The two diode outputs seem to be connected on the same terminal at a on/off (spst) battery switch which I think parallels the two batteries in the "on" positions. The fact that they are connected together is confusing as this negates the function of the isolator.

I am new to the boat but am a retired EE. I'll get it figured out eventually but was hoping someone out there could explain how the voltages read at both the engine meters and house meters could read a .5 to 1 volt difference between the two banks. again, they are tied together.

Ron
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Old 10-19-2013, 07:19 AM   #5
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I'll get it figured out eventually but was hoping someone out there could explain how the voltages read at both the engine meters and house meters could read a .5 to 1 volt difference between the two banks. again, they are tied together.

Ron

Hmmm... that's a lot of voltage difference!

Perhaps test at the batteries?

Is there a third battery (or bank) on the boat somewhere? Perhaps a house or genset battery, that is normally isolated but can be paralled to start an engine?

-Chris
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Old 10-23-2013, 06:39 AM   #6
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Here's what my crawling around the engine compartment has determined so far. The battery located on the port side is for powering the windlass. The aft stbd battery is the house bank and is connected through the "Port" battery switch. The forward stbd battery I believe is the engine start battery and is connected through the "Starboard" battery switch.

I'm still working on deciphering the charging system. So far I know that the stbd engine alternator and battery charger charge the port windlass battery. I haven't determined how the stbd batteries are charged nor how the port engine alternator is connected. I have to do more crawling around.

Sure wish there was a wiring diagram for the boat
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Old 10-24-2013, 04:25 PM   #7
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Sounds screwy

So one battery (forward, starboard) functions as the start battery for both engines?

In a Mainship, I'd have expected one separate battery for each engine... and each of those batteries would also run approximately half the house, and half the bridge (one for electrics -- lights and horn and such -- and one for electronics).

What battery starts the genset? (Could be paralleled off one of the engine batteries... to free up a battery to run the windlass.)

-Chris
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Old 10-24-2013, 05:14 PM   #8
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Well, if you are a retired EE, then you obviously have the knowledge to sort it out.

But in my experience tracing wires on a 34T is a difficult job, particularly the smaller gauge stuff. But the 2/0 stuff is fairly easy to follow.

Anyway, for what it is worth, this is how my 34T single was wired:

There were three battery banks: bow thruster, bank 1 and bank 2. I did not have a genset.

The output of the alternator was wired through an isolator. One output went to the bow thruster battery and the other went to the heavy starter lug. The heavy starter lug was wired to the common terminal of the 1,2,both switch. Each battery bank was wired to the 1 or 2 terminal respectively of that switch.

One of the banks supplied power directly to the panel inside the stair opening. This panel is meant to be powered all of the time: it runs bilge pumps, etc and that is why it wasn't wired through the switch which could be turned off which wouldn't be good for bilge pumps.

The common terminal of the 1,2,both switch supplied power to the starter and to all of the house loads (the ones served by the panel inside the cabin).

I set up bank 1 as the starting bank and used the factory supplied 4D for that. I set up bank 2 with 4 golf cart batteries wired in series/parallel. So at anchor I switched to bank 2 to power the house loads and to save the starting bank. I would switch back to 1 to start the engine and then to both to charge them both.

It worked reasonably well. I thought about installing a combiner which would have made the switching automatic, but laziness and a fair amount of rewiring required to make it right, got the better of me.

None of which is to say that your twin is wired the same way.

Good luck sorting it out.

David
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Old 10-29-2013, 05:19 PM   #9
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Thanks for the detailed reply. My twin has a separate battery switch for the the bow thruster/windlass and it's charged by the stbd engine and battery charger. The other two batteries (8D's) also have a separate switch for each. one of those is the house bank, the other is a starting battery. At he helm, you can parallel these two if necessary. I believe that the house bank is charged off the stbd engine and battery charger. On that alternator, there is an isolator, the other leg of which is feeding the previously mentioned thruster/windlass battery.

We have been on long delivery of the boat so further investigation will be when we get in next week.

Ron
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Old 10-29-2013, 06:01 PM   #10
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Originally Posted by rciamaga View Post
Thanks for the detailed reply. My twin has a separate battery switch for the the bow thruster/windlass and it's charged by the stbd engine and battery charger. The other two batteries (8D's) also have a separate switch for each. one of those is the house bank, the other is a starting battery. At he helm, you can parallel these two if necessary. I believe that the house bank is charged off the stbd engine and battery charger. On that alternator, there is an isolator, the other leg of which is feeding the previously mentioned thruster/windlass battery.

We have been on long delivery of the boat so further investigation will be when we get in next week.

Ron


If you have two 8Ds in separate banks... I'd still expect each to act as starting (one for each engine) AND house (approx. half your DC panel for each battery) AND your bridge electrics/electronics (one on one battery, one on the other).

Thoughts behind that:
- An 8D hanging around as only a starter battery wouldn't take much advantage of it's 8D-ness (so to speak).
- Since you can parallel both 8Ds from the helm, I'd expect each could start it's respective engine without paralleling under normal conditions.
- I'd expect Mainship wiring to be similar to Silverton's.
- Using one engine to charge the windlass/thruster battery sounds reasonable.
- I'd expect all three banks are also charged by the charger (or may be labeled converter) when on shore power.

If true, turning off one battery switch and seeing what doesn't work may help track it down. Something in the house doesn't work... and something on the bridge doesn't work... Flip the battery switches and see what doesn't work now... And so forth.

If not that... maybe a 1-2-both switch is in there? So you can hold one 8D in reserve?

It'll be interesting to learn your findings...

-Chris
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Old 10-30-2013, 05:21 AM   #11
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Hmmm... just thought of another possibility, maybe...

Does the boat have an inverter? I guess I could imagine an arrangement where one 8D powers DC house and bridge loads, and the other 8D powers select AC loads via an inverter...

Might depend on total potential size of your DC house/bridge load... but our older Mainship 34 ('87) used a single 8D for everything DC. At anchor we ran AC loads from the genset, but another 8D and an inverter could have worked for everything except aircon...

-Chris
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