Reworking DC system on 36, What's the purpose of Solenoid Panel

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Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby Mitchritt127 » Thu Apr 04, 2019 11:02 am

Hi everyone, new here and to Grand Banks, I just bought a 1979 36 and I had some questions about the DC system. The previous owner never had a true house bank he just used the 2 8D starters for house power and alternated using port and starboard just using the boat for quick afternoon trips.

I would like to move things around so that the port side battery (currently 8D) is the starting battery for both engines and the starbord side will be house. Now I'm no expert but I've worked out what I think will work in order to switch it around and maintain having one alternator from each engine charge their respective bank.

My plan is to move the starter motor lead from starbord battery to port, then move the leads from the starter switch, breaker, stop switch, ect over to the port side of the battery switch, this subsiquently gives the port battery full contol of starting both engines while leaving the alternators where they currently are.

My main question is what to do with the leads in the solenoid panel that seem to connect both battery banks in parellel upon starting and if that even is what they do??? My theory is disconnecting them will stop the batteries from connecting and essectialy isolate the banks.

I attached the DC schematic I got with the boat, which seems fairly accurate as all previous owners didn't upgrade or modify the battery system to my knowledge. Thanks for any help/input.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby wkearney99 » Wed Apr 24, 2019 8:45 am

In all the boats I've owned each one has, at one time or another, needed to parallel the battery banks to start an engine. Usually due to a drain on the bank, but sometimes from a battery that's inexplicably died. I'd never eliminate the paralleling option. I would probably not set it up to have both engine starting from the same bank. If anything I'd think some sort of A/B setup for the house bank would be a better solution. But boat DC systems (and their AC shore power charging) is one area where I defer to professionals.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby bill.read » Wed Apr 24, 2019 10:06 am

I concur with wkearney99 having experienced simultaneous 8D failures on both batteries, but with enough charge in combining to allow me to get to safe harbor. What benefit do you see in redesigning a system that is meant to provide a backup option? If you are concerned with battery discharge, install a simple battery monitor such as Blue Sea, Balmar or others.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby mdhervey58 » Wed Apr 24, 2019 4:53 pm

Yes, the solenoid panel parallels both batteries when either starter button is pressed and only while the button is pressed. I have a very similar setup on my 42 Europa and have thought about changing it to what you are talking about in order to rewire the banks to make one larger house bank and one smaller starting bank, providing more usable house capacity. However, I have talked myself out of it because I don’t want to give up the redundancy that the original wiring provides. After all, just about the most important thing on a boat is that the engine starts on demand. Now, to address my capacity fears, I am adding battery monitors to both banks instead so that I can manage that better.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby wkearney99 » Wed Apr 24, 2019 6:53 pm

Ah, so it parallels automatically every time? I've had other boats that specifically required pressing/holding a parallel button while starting.

I second the recommendation to have good battery monitoring. The WORST thing you can do to batteries is run them below 11volts (11.5?). The issue being draining them actually decreases the battery's ability to be recharged and limits the capacity. There are various products that'll shunt the supply if the voltage drops too low, to prevent battery damage (Blue Sea makes one, likely among others). Better to have house power disconnected rather than damaging the batteries and/or leaving you without power to start back up again.

I mentioned the AC charging as many of them now have integration with a smarter display, along with various battery management features. MasterVolt and Victron come to mind. I have Mastervolt inverter & charging gear and the EasyView 5 touchscreen is a handy way to monitor various battery/power states.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby Mitchritt127 » Thu Apr 25, 2019 8:54 am

The system as it stands is not wired as a backup option, it parellels the battery banks automatically upon pressing the starting switch and then again whent the oil presure switch is closed. This forces the two banks to be combined whenever running the engines. What I would like to do is eliminate this automatic parelleling and isolate both banks, while keeping the 1, 2, both battery switch the same so if needed I can parellel both banks manualy. I do plan on installing a battery monitor which will help keep track of my battery usage, life, etc.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby FrugalWife » Fri Apr 26, 2019 8:58 am

This is an interesting discussion. My boat, of course, also has the automatic paralleling of the battery banks ... me thinks all GB's have this feature. I actually like the starting & charging circuit designed this way as it does pretty much ensure enough starting juice every time and at the same time provides a re-charge to all batteries after starting. What the set-up does require is having a good habit to switch the batteries to "House" when at anchor or dock and are using onboard lights, etc. I consider myself a long time owner after 14 years and have found the set-up to be reliable and safe. IMHO only.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby mdhervey58 » Fri Apr 26, 2019 8:17 pm

Mitchritt127, respectfully,
that is not what the schematic says and not what happens in this case. The schematic is under normal operation with the engine running so that oil switch is closed with no oil pressure when starting. To assume otherwise,
the aux relay would not pick up the starter solenoid to start the engine. So, the batteries are only paralleled when the start switch's are pressed. Yours may be wired differently. My Grand Banks manual recommends against paralleling both alternators when the engines are running so I would imagine that they would not do that intentionally.
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Re: Reworking DC system on 36, What's the purpose of Solenoid Panel

Postby Mitchritt127 » Tue Apr 30, 2019 8:47 am

mdhervey58,
Ahh, that was my main question, thank you for shedding some light on it, to me it looked as though the relays were active when the oil switch is closed, but that switch opens when proper oil pressure is present, this makes more sence thank you.
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