Battery loads and charging questions-gctid358926

[Jeffw]

I know this has been discussed in many other threads, but I am trying to understand my situation. The boat is a 2000 2858 with 7.4 Mercruiser Bravo Three, Kohler 5.0 genset, with one battery selector to control one starting battery and 2 6v. Trojan T-105 house batteries. There is also a 2000 watt inverter/charger, and (I believe) the original equipment charger. I will post more details if necessary on those.

Battery 1 I assume is the starting battery, and I think it should be for starting the engine and the generator only. All other loads should be on Battery 2, the house T-105s. I believe the PO installed the inverter/charger to charge just the house batts from shore or genset, and the original charger to charge the start batt, and could do so using inverted power from the house batts if necessary. This sounds logical to me, but maybe not efficient.

What do you all think? And when underway, should MBSS be in 1, 2, or both? Any other comments welcome...

[2850Bounty]

jeffw wrote:
Battery 1 I assume is the starting battery, and I think it should be for starting the engine and the generator only. All other loads should be on Battery 2, the house T-105s. I believe the PO installed the inverter/charger to charge just the house batts from shore or genset, and the original charger to charge the start batt, and could do so using inverted power from the house batts if necessary. This sounds logical to me, but maybe not efficient.

What do you all think? And when underway, should MBSS be in 1, 2, or both? Any other comments welcome...

Using HLBB power to power an inverter that would in turn power a second battery charger for the #1 cranking bank, would be a rather inefficient use of the HLBB, IMO.

Although since the #1 bank is separate from the HLBB..... technically it could be done!

However, if the HLBB has enough capacity to power the #1 bank battery charger, you may as well switch over to #2 and fire your engine up.

This would avoid using the charger.

Occasionally firing up from a large enough HLBB won't kill it.

I crank my Stbd engine from my large HLBB exclusively.

When I think of something along the lines of this, I think of perpetual motion when Mickey Mouse was in the bath tub floating on a lake.

Water started spewing up through the bath tub drain and it looked like he'd be sinking shortly.

Mickey takes the shower pipe and sticks it into the spewing drain, and the shower head propels him forward. OK.... I'm old.... what of it?

Jeff, if the main battery switch is an MBSS... key word "selector" switch, then the "common" terminal, or "output" terminal of this switch will feed all O/B 12 vdc demands.

Exception to this would be a Xantrex (or similar) Charger/Inverter, and/or any direct battery connections (often a power trim pump, for example).

Whether on #1 or on #2, the boat's 12 volt system won't (or shouldn't) know the difference, other than.... (and a key point here) the selected Battery Bank's capacity.

The CCA capacity of your #1 Cranking Bank will be different from your #2 HLBB, which has a greater Amp Hour capacity.

Bottom line.... you could crank from your HLBB and you could power your TV or DVR from your SLBB.

But of course we don't do this.

Your O/B Chrg/Inverter should be Independent of the MBSS.

If Xantrex or similar..., it will charge the HLBB via the same power cables that supply the heavy 12 vdc for the inverter side.

If there is a second charge out put, it will use a small conductor and will be independent of the HLBB.

As for running re; 1/ALL/2... you'll get a mix of suggestions here.. no one better than the other.

My take is to NOT charge while combined.

I prefer that the alternator can sense the bank independently, assess the charge rate, and cut back when needed.

Although for short durations, it's not a deal breaker.

Long haul.... I always charge independently.

Or.... you can add an ACR or VSR and/or other means of battery management, and let it do this for you.

Those suggestions may or may not fit your needs.

In simplistic terms, I'd fire up on #1, warm engine while still on #1 and then make your choice.

In many cases, engine warm up is long enough to bring #1 back to a safe SOS.

Then switch to #2 while under way. This tops off the HLBB.

As mentioned, some are OK with running on ALL/BOTH for a while.... some even longer!

If you install the correct Blueseas ACR unit, it can be configured do this switching while cranking for you.

You won't even need to touch your MBSS.

Jim McNeely would be a good one to speak with about this.

.

[Guest]

Jeff is this boat new to you? A couple of comments, If your boat is wired as my 2855 Cierra Sunbridge was everything including the house is wired through a 50 map breaker on the back of the engine. If this is the case I would run the house bank around this and separate the engine from the house system. The second concern is the size of your house bank and the size of your inverter. I don't think that battery bank will run the 2000 watt inverter for very long.

[2850Bounty]

Scary wrote:
1... everything including the house is wired through a 50 map breaker on the back of the engine.

2... If this is the case I would run the house bank around this and separate the engine from the house system.

3.... The second concern is the size of your house bank and the size of your inverter. I don't think that battery bank will run the 2000 watt inverter for very long.

1... Yes, all but any add-ons that may have by-passed and/or no longer use the engine/hull harness for the power source.

I'd suggest leaving it that way.

In a pinch, the #1 Start Batt will power the helm and the house loads when switched to #1.

2... That is doable, but can become a bit complicated.

I'd think that an ACR or VSR will take care of any concerns Jeff has in this area.

However, ofter larger boats are set up as you say.

3... Agree if pulling the max load.

With a generator on board, he'll likely not be using inverter power for any heavy demands. But I hear what you're saying.

Re; #1, I actually like to see a small independantly powered breaker panel for Nav gear, etc.

One that would be separate from the OEM hull harness, but still uses the MBSS Common terminal.