One Starting Battery For Two Engines?

[nnyerges]

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 1500A (cranking current) 8D battery, to start both engines, eliminating the 1200A. 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

EDIT: I mistake by Placing on lead acid batteries AH, WHERE A Should say for cranking current of 1500A or 1200A. 255AH Deep Cycle dates its ok

 

[BartW]

Hi tHere welcome to the forum,

In my boat i have one battery bank (24v) for starting 2 main engines, and another 24v bank for domestic and a small third battery Bank (12v) for the generators and 12v systems

One engine/alternator does charging of the starter batt bank
The second engine/alternator does charging of the domestic batt bank
The generators do the charging of the 12v batt. bank

Then i have 2x24v and 1x12v chargers from the 230v shore or generator supply, one for each batt bank.

I have 2 backup switches, one is to parallel the 2 x 24v banks
And the other to parallel the 12v batt with the center 12v from the engine starting banc

Alle very easy and straight forward.
I don't know if this is a normal setup in a modern boat, mine is 20yo

 

[halcyon]

I have 2 backup switches, one is to parallel the 2 x 24v banks
And the other to parallel the 12v batt with the center 12v from the engine starting banc

Alle very easy and straight forward.
I don't know if this is a normal setup in a modern boat, mine is 20yo

Around 20 years Prod builder adopted 1 bank engine start, and 1 bank services and engine start, just about the worst set-up possible.

Use either

port and starboard engine batteries and service bank,

or engine start bank and a services bank,

each allow engine start and clean service power supply.

If VSR is fitted, it allows the alternator charging the engine bank, to also help charge the service bank, act as remote emergency link start, and provide auto back-up if an alternator fails.

Brian

 

[Divemaster1]

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

.............EDIT: I mistake by Placing on lead acid batteries AH, WHERE A Should say for cranking current of 1500A or 1200A. 255AH Deep Cycle dates its ok

Sorry, don't really understand your problem ..... you have two 6/71's... or even 8V/71 NA's .... that is at least 3 Tonne of engienes ... coupled with the fact that they are about 2/3 bigger than the equivialent four stroke... and you want to save 50 - 75 Kg or a cubic foot of space???

Irrespective ... these engines need a lot of power to start .... I reduced my 24V system on my 6/71's down from 225 AH to 190 AH ... something I have regretted.... during the winter time I have to augment the power in the starting batteries with the domestic ones to get the RPM up for a clean, rapid start..... anything else would just plaily drain the battery turning them over with no joy... I cannot advise on how to set up your battery system..... but I can give you one advise .... "Don't under estimate the power requirements of a two-stroke Detroit at startup!!"... if they are 8V's .... then their requirement is even bigger...

 

[ccscott49]

My system, two battery banks, 1 x engine start bank, 220ah 24v, (for two ford six cylinder diesels) 1 x domestic bank, 440ah 24v, two engine alternators 55a each, port charges engine bank, stb, domestic bank, through smart regulator. 1 x genny start, 110ah 12v, charged by mains battery charger, 2 x mains 75a 24v battery chargers, plus a cross over solenoid to allow domestics to augment engine start. I have also installed a 1,2, both, off switch in the genny circuit ("both" disabled on the switch) with cables to one of the engine start batteries, (12v) for dire emergency genny start.
This works well for me, I know some folk say a battery for each engine, but I've never had any trouble with the system fitted and it all works well, well it has for 16 years in my ownership.
So I would say as long as the one battery for the engine start is of a generous size, then it should be OK.

 

[PCUK]

Waste of batteries having one for each engine. They are the least used on board so one for all the engines is absolutely fine and sensible. Just include a paralleling switch between the engine battery and domestics for emergency starting purposes and remember to leave it switched off at all other times.

 

[nnyerges]

Sorry, don't really understand your problem ..... you have two 6/71's... or even 8V/71 NA's ....

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.

By the way, a question remains: I place the switch C, ostensibly to prevent any reverse current to the equipment of the ship, in the 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?

 

[pappaecho]

First question for me is what is the spec for the house battery. Normally a house battery should be of the slowish discharge type often sold as a Leisure battery, which can take reasonable deep discharge,
The starter battery should provide high amps for a short period of time for starting, so using a single Leisure type may cause srating problems in winter at low temperaturem specially on the second engine.

Uf you are revamping the whole system, I would stick with two starter batteries, and move the house battery . House demand tends to be a lighter load over a longer period of time. If you buy 100 amps meter tails cable which is double insulated, you can move the house battery at little cost

 

[BartW]

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.

By the way, a question remains: I place the switch C, ostensibly to prevent any reverse current to the equipment of the ship, in the 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?

after looking again at your drawing, I don't see a problem with your 3 battery setup, actually it is almost the same config as I have, (I don't have the isolator)
Your question about switch C, I would put that switch, just as an extra tool, in case of a problem, to be able to isolate that battery bank,

when I got ownership of my boat, I didn't realise that the link switch between engine and service battery bank was on.
this caused me a problem when I drained all battery's, at night while on anker, (luckly I could still start the generator)
but further then that, having all battery's linked together during at least one season, didn't cause a problem.

 

[ccscott49]

after looking again at your drawing, I don't see a problem with your 3 battery setup, actually it is almost the same config as I have, (I don't have the isolator)
Your question about switch C, I would put that switch, just as an extra tool, in case of a problem, to be able to isolate that battery bank,

when I got ownership of my boat, I didn't realise that the link switch between engine and service battery bank was on.
this caused me a problem when I drained all battery's, at night while on anker, (luckly I could still start the generator)
but further then that, having all battery's linked together during at least one season, didn't cause a problem.

Rather than have manual switches for paralelling, I have a solenoid, with button in Wheelhouse, to connect them all. So no danger of it being left on.

 

[nnyerges]

Your question about switch C, I would put that switch, just as an extra tool, in case of a problem, to be able to isolate that battery bank,

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)

 

[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

 

[ccscott49]

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)

In my case, unfortunately, my genset is 12v and egine start/domestics 24v, so no way I can use genny battery.

 

[halcyon]

B]2.[/B] The ISOLATOR of my drawing is a 2ALT IN and 3BATT OUT type. [/I]

Why so complicated ?


Connect port alternator to start battery, starboard alternator to service battery, throw away splitter, it only gives another point to fail in the charging system, and generates heats, thus power lose.

Fit a VSR between port and starboard batteries,
this will allow remote emergency start from service battery,
allow the port alternator to help charge the service bank,
if port alternator fails, the starboard one will charge the engine start battery.

Brian

 

[BartW]

In my case, unfortunately, my genset is 12v and egine start/domestics 24v, so no way I can use genny battery.

the same for me

Why so complicated ?

Connect port alternator to start battery, starboard alternator to service battery, throw away splitter, it only gives another point to fail in the charging system, and generates heats, thus power lose.

Fit a VSR between port and starboard batteries,
this will allow remote emergency start from service battery,
allow the port alternator to help charge the service bank,
if port alternator fails, the starboard one will charge the engine start battery.

Brian

+1

 

[ccscott49]

Why so complicated ?


Connect port alternator to start battery, starboard alternator to service battery, throw away splitter, it only gives another point to fail in the charging system, and generates heats, thus power lose.

Fit a VSR between port and starboard batteries,
this will allow remote emergency start from service battery,
allow the port alternator to help charge the service bank,
if port alternator fails, the starboard one will charge the engine start battery.

Brian

I do like the idea of the port alternator helping the stb, to charge the domestics, how do I wire this VSR thingy?

 

[davidej]

Why so complicated ?


Fit a VSR between port and starboard batteries,
this will allow remote emergency start from service battery,



Brian

Forgive me for sticking my oar in here, but this seems to suggest that the starting current would, in an emergency, flow thru the VSR. I thought that they were only designed to carry a charging current (say up to 60-80 amps) not a starting current of several hundred amps.

I have a separate heavy duty cable for emergency cross-start with its own heavy duty switch as well as a VSR to take care of charging.

But then I am only a raggie and perhaps I shouldn't post on a mobo thread.

 

[nnyerges]

..suggest that the starting current would, in an emergency, flow thru the VSR. I thought that they were only designed to carry a charging current (say up to 60-80 amps) not a starting current of several hundred amps.../ /....I have a separate heavy duty cable for emergency cross-start with its own heavy duty switch as well as a VSR to take care of charging.

I think "halcyon" idea of the VSR (Voltage Sensitive Relay) or ACR (Automatic Charging Relays), its OK only for charging or to start a small starter motor.

Now, going back to the two questions:

#1. There still no answer to question #1

#2. You have mention a "emergency cross-start cable" for starting, but well as a VCR?. It that means that you can connect starboard alternator in parallel to the port alternator to charge without a isolator, vsr o acr and also to start a big engine?

There is forum topic, about direct paralleling two alternators (http://www.boatdesign.net/forums/electrical-systems/can-you-parallel-two-alternators-26203.html). 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. But my question is quite different: One alternator is the result output of the isolator and the other is the alternator of the GENSET.

 

[Divemaster1]

........
#1. There still no answer to question #1

Back to basics ... below is an extract from DD 6/71 Service manual .... which you should consult before making any desicion on starting betteries.... and as you can see, there is a difference in recommendations pending on Operating environment and 12 or 24V systems...

 

[davidej]

#2. You have mention a "emergency cross-start cable" for starting, but well as a VCR?. It that means that you can connect starboard alternator in parallel to the port alternator to charge without a isolator, vsr o acr and also to start a big engine?

Sorry but I am not being much help.

I have a yacht with one motor but two batteries - a house (or services) and a dedicated motor start - not all that different to what you are being recommended

The VCR takes care of charging both from one alternator but (IMHO) will not help you start from the house battery if the engine battery is dead. You need a separate circuit for that with suitable cable to take the load