One Starting Battery For Two Engines?

[Submarine Tom]

If you're trying to cut weight and save space don't do it by eliminating a starting battery, get rid of one of those engines.

If you're having such a hard time making up your mind remember: Keep it simple.

-Tom

[Frosty]

If your isolator fails (unrepairable black box)you have no charge at all to any batteries, your gen would need to run yet the gen alt is not included in the charging system.

If you must have only 1 battery then I would have critcal engine, (the first to start and last to stop) that charges the start battery. I would not use an isolator but connect the gen alt to the house and the battery charger to all 4.

You will still neeed a knife sw to pull in house batt for engine emergency start

Another point is that with 300Hp detriots you probably have 2x160A motorola alt just charging a batt start. With that power you could easily use an invertor while on the way ansd switch in house batts for charging.

[nnyerges]

Thank you FROSTY for your comments. You always put me to meditate on the design and give me good ideas.

The Isolator has 2 alternator inputs. It is likely that one of the diodes can be burned, but there is the other alternator sending charge to the STARTING and HOUSE battery. However, in 20 years, I had more chance that a tree trunk pup the hull and sink the ship that all diodes of the Isolator burns. In that case, I still have the GENSET battery to start the engines. By the way, why a knife switch? What’s wrong with the batteries interconnecting switches?

I case a dead/shorted STARTING battery or a stuck starter solenoid that drains the battery, I will add to the design, two separate STARTING battery switches (like A1 and A2), 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.

[nnyerges]

Originally Posted by Frosty

You will still need a knife sw to pull in house batt for engine emergency start

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)

[RayThackeray]

Originally Posted by nnyerges

It’s insane to start the engines directly from house battery, with all loads connected.

Er, I think it's a bit strong to use the word "insane". If that's true, then that would make the majority of boaters insane, including me - who has been connecting the house bank to start the engine frequently over the last decade or so and over 20,000 miles of cruising, with never a problem.

[gonzo]

Smaller boats with a single battery start the engine with the house battery

[nnyerges]

I can resume your comments with this conclutions:

1. The DD671N/310HP engines starter of aprox. 160Amp continus start and 1200Amp cranking current, can be started with the HOUSE battery, with all service loads connected (lights, electronics,etc)

2. If 1 its true, is no need of switch C, to start the engines from house battery.

That is insane for me. Even you car ignition switch disconnects all service load during starting. I do care for transient currents and posible starter faults in ignition from a big starter motor like that.

I accept the conclutions, if you temporary disconnet all electronics and critical loads and only left resistive/inductive loads like lights, pumps, etc. during starting

Maybe im wrong?

[gonzo]

It is not too much work to disconnect the loads for the few seconds it takes to start and engine.

[nnyerges]

Based on all observations, I will rethink the design, to create version 2.0. I have only two last questions:

1. In case of an emergency, if I need to start the engines with the GENSET battery, can I leave the GENSET ON or Should I turn it off?

2. The ISOLATOR of my drawing is a 2ALT IN and 3BATT OUT type. The outputs are connected in parallel with the INVERTER/CHARGER. That’s OK. The question is: Can I connect the third remaining ISOLATOR output in parallel with the GENSET alternator (genset battery positive bus) all the time? I think its the same case as connecting a parallel switch between to starter batteries (paralleling a starboard & port engines alternators), but with the advantage of having a diode through them

[Frosty]

Theres many ways you could do this and not one of them will be prefect. One good battery some where on board and a pair of jumper cables will get you home.

You could argue that the gen is the most important engine.

[nnyerges]

#1. There still no answer to question #1

#2. There is a forum topic, about direct paralleling two alternators (Can you parallel two alternators?). Maybe I suspect that it can be done, with care. If you connect two alternators in parallel, the two feedback loops will interfere with one another, unless you isolate the two alternator feedback loops by putting one additional rectifier diode per alternator downstream of the feedback loop. This extra diode drop will require that the regulated alternator output voltages be increased by the same amount.My question is quite different: One alternator is the result output of the isolator and the other is the alternator of the GENSET (Connecting the third free stud post of the isolator, to the positive bus of the GENSET)

Added:
Case1:
If my design where with the ideal of one starboard engine battery, one port stating engine battery and the house battery, it was a perfect match for using a dual VSR or ACR. My design is only with only one starting battery for both engines and one house battery, with two alternators charging the starting battery and the house battery. The third battery is only for the GENSET (depending of question #2). I want/need only 3 batteries, if I can use two independent batteries for each engine and the house battery and have the GENSET's starting from one of those batteries, I will be the happiest marine in the world and I’m sure I will use an ACR. I think the original post could take a 180 degree turn, analyzing how to connect the GENSET's to any of those three batteries.

Case2:
How about a battery for each engine (charged by the respective alternator) and use the house battery to start the genset. The house battery can be charged with two VSR and the two engines, or charged by the genset?

[nnyerges]

How about my new design, based on the three basic boat charging condition cases:

1. Cruising: I'll keep using my ISOLATOR (2INx3OUT) connected to the alternator of each engine. The outputs go to the starter battery, house battery and the third output, optionally the generator battery through a switch, to keep that battery charged, just in case that for some reason, do not count with both generators, which is quite unlikely, but can occur. Inverter / Charger OFF.

2. Anchored: Genset ON, as need it, charging his battery and connected to the house and starting battery using two ACR. Inverter/Charger OFF. Both ACR are going to be overridden by the engines starting ON switch, so both ACR's are disabled when engines are running (case 1), to prevent any issues of paralleling alternators.

3. ShortLine. Inverter/Charger ON for all batteries as need it.

NOTES:
1. Negative bus and other protections not show for simplicity
2. Optional two fuses or two ON/OFF switch or one OFF/1/2/1+2 selector switch, to avoir starter-solenoid shorts or failures
3. Optional In case of both gensets unavailable
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DIAGRAMS
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Original topic: Twin Engine + Genset + 3 Batteries Configuration
at http://www.boatinghowto.com/showthre...-Configuration

[nnyerges]

Happy New Year to all,

This is the definitive design for my 3 battery/2Engines/2Genset main DC switchboard. I start to connect the panel and planning to finish in the middle of February. Then I will upload some pictures of the installation. The following pictures are in los resolution, but I have uploaded a PDF hi resolution file for each of them, that you can see it in the following forum: http://www.boatinghowto.com/f28/twin....html#post1220. Also, you can see some pictures of the construction of the panel on that topic.

Circuit diagram:

Simple working diagram:

Board Layout: