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Old 05-07-2013, 09:35   #1
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Can I safely/smartly combine these bat banks?

Our Hylas 54 is a passage making boat. The only way I could get my wife to sell the house and throw the lines was to buy a boat with modern conveniences. Hence we have a trash compactor, ice maker, dishwasher, etc. connected to the Prosine 2.0 inverter/charger. Point being that we use a lot of amps! All batteries discussed are brand new are 12volt Lifeline 8D AGM’s with 255amps each.

First things first, none of this discussion involves the 4D engine start battery. It is independent of the two “HOUSE” banks and the “BOW” bank (serves the windlass and bow thruster only). The 2 8D’s on the “BOW” bank are currently not accessible for “HOUSE” usage. They get charged as an independent bank from the Prosine charger (and maybe the engine too, never checked).

We live aboard now and will spend the next several years cruising; the BVI during this winter and the Med for several summers after. I’m thinking about bringing my “BOW” battery bank [510amps] to the rotary battery selector position #2 so that I have the option to combine it with my “HOUSE” bank [1020 amps: currently broken into 510 amps on #1 of the rotary dial and 510amps on #2 of the rotary dial that I leave in the “BOTH” position].

Yes, that means a total of 1530amps of house batteries. It just seems wasteful to have two huge 8D’s sitting there in the “BOW” bank being used so infrequently. That seems like over kill to me, especially when you consider that a) the engine is always running when both are in use and b) we typically run the engine for at least 30 minutes leaving or entering harbors.

I believe that Nigel Calder says that your batteries in a bank should be located near each other. Does this remain as important for giant 8D’s and adequately sized cabling? For small batteries it seems more critical.

Bank “Bow” located in the bow
Bank #1 is located in the aft cabin (45’ aft of the Bow batteries)
Bank #2 has one 8D midships and the other 8D 20’ aft near Bank #1 (violating Nigel but seems to have been no problem so far)

1) Should I combine banks #1 and #2 into just #1 on the rotary dial AND bring “BOW” bank onto #2 of the rotary dial?

2) Any harm in using the “BOTH” position so that I have access to all 1530amps at all times while sailing or moored even though the batteries will all be at different distances from the panel and source of charging? (except when I know I need to use the windlass or bow thruster I will isolate so that the ensuing voltage drop of those huge loads does not knock the Raymarine bits offline)

3) The bow thruster and windlass are direct wired to the “BOW” battery bank (with fuses) and will work on any setting of the rotary switch. Is there some sort of “Diode” (one-way current flow) type device that I could put in-line with the “BOW” bank so that even while in the “BOTH” position, the bow thruster can’t draw from the 4 8D’s on the “HOUSE” and knock the Raymarine devices offline? That would save me from every having to remember to move the selector switch off of “BOTH”.

Another big advantage of having the 1530 amp battery capacity would be that I could reduce my daily DOD (depth-of-discharge) before charging and therefor get more life cycles from the batteries.

Mark Powell
s/v TARA
Hylas 54
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Old 05-07-2013, 09:58   #2
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Re: Can I safely/smartly combine these bat banks?

Hi Mark,

Some random comments on a few of the issues.

Yes it's better to have battery banks close to each other but properly configured you will not kill all your batteries or create a black hole in the universe if they are not.

Without knowing the specifics of the equipment you're running and their respective power requirements the Prosine 2.0 sounds a little small for some of the loads.

If you connect the bow banks to the current house banks to power the Prosine you will need a huge size cable. If the Prosine is putting out anywhere close to 2 KW 125 V AC that equates to drawing over 150 amps from the battery. Would probably take 4/0 (that's 0000) size to do that safely.

Yes you can use a diode or some type of one-way to prevent the bow thruster from drawing from the house banks.
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Old 05-07-2013, 12:24   #3
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Re: Can I safely/smartly combine these bat banks?

I had the Hylas electrical expert in Ft Lauderdale wire both the trash compactor and the dishwasher to the Prosine inverter after we looked at their load requirements. They joined the ice maker and microwave that were already connected to the inverter. We make sure we are never running too many devices on the inverter at one.

I typically charge the batteries with the Prosine while on the generator. I like to charge faster. With a 1500amp bank I wonder if I could find a bigger charger/inverter?
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Old 05-07-2013, 12:59   #4
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Re: Can I safely/smartly combine these bat banks?

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Originally Posted by tulsag View Post
I had the Hylas electrical expert in Ft Lauderdale wire both the trash compactor and the dishwasher to the Prosine inverter after we looked at their load requirements. They joined the ice maker and microwave that were already connected to the inverter. We make sure we are never running too many devices on the inverter at one.

I typically charge the batteries with the Prosine while on the generator. I like to charge faster. With a 1500amp bank I wonder if I could find a bigger charger/inverter?
There are probably bigger chargers out there but of the common marine units I know about, all top out at 100-120 amps. Maybe dual chargers? I'm not sure about how two smart chargers will interact but I know Victron inverter/chargers are designed to parallel so it must work.
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Old 05-07-2013, 14:01   #5
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Re: Can I safely/smartly combine these bat banks?

From my viewpoint one should have everything connected in to one big bank with the ability to disconnect any one bad battery if needed. A big load will get most of its current from the nearest battery and the more distant batteries will supply a small amount of the total current draw at the time of usage. Latter the batteries will equalize. At no time will real large currents flow a long distance for a long time.
So smaller cables can be used with no danger. The fuses at the wiring connecting the batteries are to protect the wiring, not the load. The cables going from a battery to a large load must be big enough to carry that load but the cables connecting the BOW batteries to the rest of the batteries are not going to carry the whole load of any big user, like say, the bow thruster.
I don't have a separate "start" battery for instance.
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Old 05-07-2013, 15:16   #6
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Re: Can I safely/smartly combine these bat banks?

I totally agree with Cowboy.

Differences in wiring length are significant only while drawing 200 amps for the inverter to power some high current appliance. More current will come from the closer batterie(s) but so what. The closer batteries will discharge slightly quicker. But charging currents will be much smaller and become miniscule as the batteries get to full charge.

So, combine all three- house 1, 2 and bow with switches or wiring into one big bank and forget about it.

David
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Old 05-07-2013, 19:34   #7
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Re: Can I safely/smartly combine these bat banks?

I'm sure I understand why a load would pull more from a battery physically closer than one more distant. A load has no way of knowing how far away the battery would be. Wouldn't it matter more the voltage of the battery and the resistance in the wire connecting that battery to the load.

So compare a more distant battery that's fully charged and connected with a large, low resistance cable vs a partially charged battery with a small wire with higher resistance and maybe corroded connections. Which one will supply more current to a load?
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Old 06-07-2013, 09:29   #8
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Re: Can I safely/smartly combine these bat banks?

With the distance between them and the cost of cables large enough to share loads you cannot expect them to run loads equally. Since they can only reasonably support their "local" loads the connection between them will be a "charging" line, not a load line.

The length of the line and the lighter gauge will provide the isolation you wanted. During temporary low voltages of the bow batteries under load there will be some current flow from the house bank but the total amp-hours transferred will be negligible in view of the short duty cycle for bow thrusting.

During the day between charges, the house battery voltage will start to drop so some "charge sharing" current will flow from the bow batteries and support the house bank but it will be the house batteries that are supporting the load(s). With the long term duty cycle going in this direction the bow batteries can provide considerable amp-hours.
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