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Old 11-11-2011, 14:57   #1
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One Starting Battery For Two Engines ?

Hello all,

I am remodeling the entire electrical system of my boat and need advice to make my decision with respect to use two or one battery for starting the two Ditroit Diesel 310HP engines. I know that the most common is to use one battery for each engine and currently have two starting batteries (see DC-GENERAL-ORIGINAL.JPG)

Becouse space and weight problems, I need to remove one battery.

Obviously I can take out the HOUSE battery. Neither the GENSET battery, as it has its own alternator/battery charger and cannot be connected to the isolator. So I can only remove one of the engines starting battery (see DC-GENERAL-NEW.JPG)

The idea is to place the current HOUSE 1500AH 8D battery, to start both engines, eliminating the 1200AH. Place a new 8D DEEP CYCLE battery for the HOUSE. Switches A and B are used to draw a emergency parallel between any of the 3 batteries (including the GENSET battery). Switch C is for shutting the service when should start with the house battery. The two engine alternators are responsible for charging the starter and service battery through the isolator. Likewise, the AC / DC CHARGER is responsible for maintaining the 3 batteries charge, when the engines are stopped and AC is present.

I hear suggestions, criticisms and above all, I need the pros and cons that can give me, since if cannot remove the battery, I will have to do a big complicate job of remodeling the hull.

Thanks in advance,
Nicolas
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Old 11-11-2011, 19:00   #2
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I have 1 8D dedicated start battery that starts both Hinos . I also have 1 8D deepcycle for house loads. SB alternator charges the start battery & port charges the house. There is also a combiner switch to tie them together, the system works very well with no problems so far. Good Luck
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Old 11-11-2011, 20:02   #3
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Re: One Starting Battery For Two Engines?

Thanks Rivers. First Pro
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Old 11-11-2011, 20:51   #4
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Re: One Starting Battery For Two Engines?

The idea of having two separate engine starting batteries is strictly safety. There are plenty of batteries that will start multiple engines all by themselves.

- - But - what happens when one engine will not start due to either; a dead/shorted battery; or a stuck starter solenoid that drains the battery/starts a fire/blows the main battery protection fuse? You do not have another battery to start the other engine to get the boat moving.

- - So having "another" battery available for starting is, IMHO, a major safety item. Now that alternate battery could be a house bank battery or a dedicated genset battery (providing it is big enough). That is shown in your "new" diagram.

- - But (again those "buts"), your battery switch labeled "A" really needs to be two separate battery switches, one for each engine. If a fault disables one engine starting system as mention above, you do not want the other engine starting system to be disabled.

- - So I would suggest two separate battery switches, one for each engine with a connection between position "1" of both switches so the single battery can start either engine. But with a fault, either switch could be positioned to "2" to access the house battery or the genset battery.

- - And make sure there is no way any of the battery can be directly connected to another battery. You would not want a shorted engine battery sucking dry your house or genset battery.
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Old 12-11-2011, 07:29   #5
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Re: One Starting Battery For Two Engines?

ORIGINAL POST ERRATA: I mistake by placing on lead acid batteries AH, where "A" should say for cranking current of 1500A or 1200A. The 255AH Deep Cycle data its ok.

Quote:
Originally Posted by osirissail
I would suggest two separate battery switches, one for each engine
Thank you. You are right, I miss that. I will add another switch


Quote:
Originally Posted by osirissail
..make sure there is no way any of the battery can be directly connected to another battery
The configuration allows two batteries can be placed in parallel in case of emergency, setting the switches in position 1+2. Should not normally be parallel. I guess it's that you meant.


When necessary to use the service battery to start the engines, I put the switch C, ostensibly to prevent any reverse current to the equipment of the ship. Is it necessary? I already have a master ship service breaker, do i have to turn it off when starting engines from house battery?

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Old 12-11-2011, 09:40   #6
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Re: One Starting Battery For Two Engines?

Five concerns:

1. It's not great for the normally full start battery to have it at charging voltages whenever you are charging the house.

2. Most isolators have voltage drops that can lead to less than great charging.

3. You have a lot of cables. A lot of cost and/or voltage drop

4. You have a lot of switches to remember to set correctly

5. You don't show fuses (although that might just be for the diagram simplicity). There is a lot of amperage in this system. I fuse the battery cable and alternator cables close to the battery.

I use one battery to start two engines charged by the port engine.
The starboard engine charges the house. Charger is connected only to the house side.

There's a charging relay/switch between the house and start battery bus. Normally this is locked out because both battery banks are fine. But I can also use it as a parallel switch in unusual situations (say running on one engine, or if I have badly depleted the house bank and want to charge faster).

I connect the genset starter and the genset alternator to the starting battery side. This does a fine job of charging the start battery when running the genset without connecting the start bank to the main battery charger.

This is the charging relay I use. The remote switch allows me to control it from the helm while keeping battery cable length at a minimum.

ML-Series Automatic Charging Relays (Magnetic Latch) - PN - Blue Sea Systems

Carl
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Old 12-11-2011, 10:08   #7
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Re: One Starting Battery For Two Engines?

CarlF on your point #5 "I fuse the battery cable and alternator cables close to the battery."
Is this what you meant?
If so how are you protecting the alternator cable this way?

To OP nnyerges,
Just out of curiosity. On a boat that sports two 310hp Diesels how have you run out of room to need to eliminate one starting battery? I know space is a premium on any sized boat but this one has me stumped. What's so important that it takes up the space of a dedicated start battery which I'm sure the boat was designed for in the first place?
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Old 12-11-2011, 10:19   #8
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Re: One Starting Battery For Two Engines?

What is now the second start battery could be used as an additional house battery.
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Old 12-11-2011, 10:32   #9
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Re: One Starting Battery For Two Engines?

I ran a single cranking battery (Gropup 30 no less) for both mains and a genny for YEARS with zero problems. The House Bank was two seperate banks of golf car batteries. The Genny had no alternator. The mains could be used to charge any battery via a switch. The Genny charged all 3 banks via an inverter/charger. I could switch any bank to any starter as required.
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Old 12-11-2011, 12:42   #10
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Re: One Starting Battery For Two Engines?

Thank you all for your response. For simplicity, the diagrams doesnít show negative cables and fuses and other secondary connections.

CarlF, Iím a little confuse
Quote:
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I use one battery to start two engines charged by the port engineÖ then you say: I connect the genset starter and the genset alternator to the starting battery side. This does a fine job of charging the start batteryÖ
Is your genset starting battery the same as the engine start battery?.

I particularly prefer keep using the 2Alt/3Batt isolator, since it guarantees that if one alternator runs out, the other will keep charging. I never have problems with voltage drop whit that old diode isolator. Now I get I new schottky diode isolator, so the voltage drop difference would be much better. Also, my inverter/charger is an old style transformer/diodes 4 channels charger and have being working for more than 20 years, charging all 4 batteries at the same time, connected all the time, without any issue. Electronic charging relay/switch are great, but if want to keep the isolator and the charger, I think it doesnít match with my system.

The boat hull was designed for a space of 3x8D batteries (one for each engine and the house). The original genset (without alternator) was started with one of the engines batteries. At that time, the regulations were less strict. The boxes for the batteries were simple fiberglass boxes without lids and almost the same size of the batteries. When change the old genset, for two Onan (with alternator itself), the fourth 4D battery was added, without box. I decide to buy new boxes for the batteries and are significantly larger, so 4 batteries do not fit, even placing 3x4D batteries. That's basically the reason to return to a set of 3 batteries.
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Old 13-11-2011, 08:51   #11
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Re: One Starting Battery For Two Engines ?

A question remains: I place the switch C, ostensibly to prevent any reverse current to the equipment of the ship, in tha case i need to start the engines with the service battery. Is "C" necessary? I already have a master ship service breaker, do i have to turn it off when starting engines from house battery?
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Old 13-11-2011, 21:47   #12
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Re: One Starting Battery For Two Engines ?

I would use the 4D, to start all three engines. By reconnecting the generator starter cable to pin C of switch A. Then just interchange the four D with the first 8D. If switch C. is the same as the other two switches I would allow it to separate the two house batteries. This would give you the most possible variations depending on what might go wrong. One other possible change would be to add a three battery isolator to your generator alternator. Just my thoughts, Mike.
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Old 14-11-2011, 08:44   #13
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Re: One Starting Battery For Two Engines ?

Quote:
Originally Posted by Florida Mike View Post
I would use the 4D, to start all three engines. By reconnecting the generator starter cable to pin C of switch A. Then just interchange the four D with the first 8D. If switch C. is the same as the other two switches I would allow it to separate the two house batteries. This would give you the most possible variations depending on what might go wrong. One other possible change would be to add a three battery isolator to your generator alternator. Just my thoughts, Mike.
I think you are talking about the old diagram, since you are talking about a four D battery. The isolator is a 2ALT/IN-3BATT/out type.
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Old 14-11-2011, 17:55   #14
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Re: One Starting Battery For Two Engines ?

In an emergency start, I prefer to start the engines with the GENSET and not the house battery. Suppose that you are navigating with all your equipments ON, and for any reason your engines stop and your engine battery is death. You can't just set switch A from 1 to 2 and then set B to 1 (or your knife switch on).

It’s insane to start the engines directly from house battery, with all loads connected. It is preferable to stop the GENSET (if ON) and switch B to 2 to start the engines from the GENSET battery.
Using the house battery will be the last thing to do in a emergency at sea, because you don’t want to have issues with your ship equipments, you must have to turn off house load before. By the other hand, there is no problem to use the house battery anchored or at safe shore.

I was thinking in another option in the design: Having two engines starting batteries, the House battery only to service (just emergency switching) and start the GENSETS from one of the engines or house batteries. But how insulate the two gensets alternators? (GENSETS: Onan 9KVA 9MDKAL3367295)
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Old 14-11-2011, 18:06   #15
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Re: One Starting Battery For Two Engines ?

How about instead of one 8D for starting you go with 2 group 30's. One on each engine with a cross over switch so you could swap them or combine if needed.
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