New battery wiring for 40" motor yacht. Your opinion?

[jms28]

Hi there,

We own a 1990 Cranchi Mediterranee 40 which is based in Greece and we're currently overhauling the old lady. Top priority has the power supply.

So far, the boat has 2 x 150 Ah batteries as both starter and consumer batteries. Clearly not ideal, as we had to painfully realize on many occasions; the most dramatic one of which was the engines not starting in the middle of the night in a lonely bay when the anchor came lose due to heavy winds...

I have to admit that I'm anything but an expert, but I've been reading through quite some stuff in the past weeks in order to start building my knowledge on marine electrics and considered various options for the best solution. The only thing that is for certain so far though, is that starter and consumer cycles have to finally be separated!

The boat has 2 x Volvo Penta TAMD61A engines and hence two alternators. My Greek electrician now came back with the following proposal for 1 starter and 2 consumer batteries:

What's you opinion on this? Pros, cons? What to consider? Any suggestions how to improve?

I have some thoughts on this as well, but will leave it at that for now in order to see what the experts say. The floor is open

Many thanks!

 

[jms28]

Hm really no one? :sleeping:

Some questions on top, which will hopefully also help to push this topic

1). With 2 engines I obviously have 2 alternators. Where should these go to? One to the starter battery, one to the house battery bank? Or both to starter? Or does it actually matter, since the circuit is combined by the ACR when charging anyway?
2). Similar to above: where should other charging sources go (battery and solar charger)?
3). Would it make sense to fit a B2B charger instead of the ACR? Similar function, but boosting the output, right?
5). Finally: Still need to check if the alternators are actually ok, but provided they are, would A2B charger(s) between the alternator(s) and the batteries make sense?

Hope this finally get's the ball rolling.

Many thanks in advance!

 

[BruceK]

My own system is significantly different in that one engine does the house bank and the other engine the starter bank. There is a relay shunt that can combine house and starter battery banks to turn the engines should the starter bank fail. The downside to this is if the alternator on any one engine should fail there is no fail over charge, it's happened.

I am not fully clued up on ACR's nor yours in particular, my experience is usually seeing them on single engines powering two banks. In those instances it charges the starter battery first and once that has reached a certain threshold starts on the house battery bank with the result of if you do many short hops your house batteries may never get an equal share. Is yours dual sensing? I believe that may overcome this (?) Another grey area for me is how will two alternators on the same circuit react? Do you get the benefit of both, will they both excite?

Sorry if this answers more my curiosity than yours, but if yours pans out I can see advantages to it over mine and may follow suite.

 

[prv]

The system in your original diagram is commonly used in sailing yachts with one engine, which is what I’m familiar with. The charge from the alternator comes back down the same cable as powered the starter, and is shared with the house battery via the relay. Additional charge sources are typically connected to the house battery. Some relays sense voltage from either side and will share solar or wind with the engine battery, others only go one way and the assumption is that the engine battery is pretty well charged from its last run (like your car) and doesn’t need solar assistance.

I have an alternator booster on my sailing boat (the type where you have to solder extra wires inside the alternator) and it does make a big difference to the charging achieved during a short run out of the harbour, but I don’t know if this is necessary for you motorised folks who run your engines longer. I also can’t comment on whether there’s a better way of arranging the starting and charging on a twin-engined boat.

Pete

 

[petem]

Hi there,

We own a 1990 Cranchi Mediterranee 40 which is based in Greece and we're currently overhauling the old lady. Top priority has the power supply.

So far, the boat has 2 x 150 Ah batteries as both starter and consumer batteries. Clearly not ideal, as we had to painfully realize on many occasions; the most dramatic one of which was the engines not starting in the middle of the night in a lonely bay when the anchor came lose due to heavy winds...

I have to admit that I'm anything but an expert, but I've been reading through quite some stuff in the past weeks in order to start building my knowledge on marine electrics and considered various options for the best solution. The only thing that is for certain so far though, is that starter and consumer cycles have to finally be separated!

The boat has 2 x Volvo Penta TAMD61A engines and hence two alternators. My Greek electrician now came back with the following proposal for 1 starter and 2 consumer batteries:

What's you opinion on this? Pros, cons? What to consider? Any suggestions how to improve?

I have some thoughts on this as well, but will leave it at that for now in order to see what the experts say. The floor is open

Many thanks!

If I read this correctly, the proposed solution has the fatal flaw that House can discharge both batteries. The Fairline solution (on my boat at least) is as follows:

1) Two 'house' batteries for house and Starboard engine starting. One battery dedicated to Port engine starting.
2) Alternators charge their respective Port and S/B batteries.
3) Battery charger for 'house' batteries only
4) Momentary crossover relay that allows each engine to be started from the other battery bank in case of accidental discharge

The above ensures that you always have a good battery for starting.

 

[prv]

If I read this correctly, the proposed solution has the fatal flaw that House can discharge both batteries.

Only if you connect the middle of the three isolators, which you normally wouldn’t.

Pete

 

[petem]

Only if you connect the middle of the three isolators, which you normally wouldn’t.

Pete

Doh, sorry hadn't realised they were isoloators! In any case, my point still partly stands, they need to be momentary crossovers, not something that can be left permanently on by accident or to get more power for the house systems. And therefore, it makes sense for the house battery bank to be larger than the other bank.

I'd also want to see how the alternators and charger(s) are wired to the batteries.

 

[prv]

it makes sense for the house battery bank to be larger than the other bank.

Certainly true - my main bank is 420Ahr, whereas my (single) engine start is a diddy 28Ahr

(High cranking-current AGM, though, and it only has a to turn over a 30hp engine in my sailyboat.)

I'd also want to see how the alternators and charger(s) are wired to the batteries.

I assume the alternator of each engine is wired to the starter motor via the factory standard engine loom. When the engine's running, it flows back the opposite way to how the starter motor was powered.

Pete

 

[jms28]

Hi all,

Thanks for all the helpful input so far!

I am not fully clued up on ACR's nor yours in particular, my experience is usually seeing them on single engines powering two banks. In those instances it charges the starter battery first and once that has reached a certain threshold starts on the house battery bank with the result of if you do many short hops your house batteries may never get an equal share. Is yours dual sensing? I believe that may overcome this (?)

On the Blue Sea website (see here and here) it says the following:

"ACRs or Automatic Charging Relays are automatic switches that close when the voltage on one of the batteries rises to a
level (normally 13.2V to 13.7V) indicating the battery is connected to a charge source and is partially or fully charged. The
switch then closes and shares the charging current with the other battery until the voltage drops to some lower level
(normally 12.4 to 13.1 depending on model) and the switch opens. This prevents discharging both batteries when there is
not enough current to charge both batteries.

(...)

An ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR′s contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries.

(...)

A dual-sensing ACR will sense an active charge source on one or both batteries and not solely on a designated battery. The ACR will operate if the measured voltage on either of the terminals is of a level to initiate a connection or disconnection."


Guess that answers some questions. But I potentially share your concern about the short hops, which is why I am torn between using an ACR or a B2B charger which, from what I understood, will start charging the house bank immediately while always prioritising the starter battery. In the manual of the B2B charger, it says that it "essentially tricks the alternator into working at the maximum rating of the charger. This system is designed to use only the surplus power. It ensures at all times, that the power required to run the primary system of the vehicle or boat is not compromised. This surplus power is converted into a higher voltage and is used to charge a secondary battery bank using a digitally controlled programmable 4 step charging curve. This unit is also totally isolated, thus, the starter battery cannot discharge through this system, even in the event of the unit failing."

The charge from the alternator comes back down the same cable as powered the starter, and is shared with the house battery via the relay. Additional charge sources are typically connected to the house battery. Some relays sense voltage from either side and will share solar or wind with the engine battery, others only go one way and the assumption is that the engine battery is pretty well charged from its last run (like your car) and doesn’t need solar assistance.

Ok, I didn't know that (boat is in Greece and I'm in the UK, so can't check on things quickly). I guess that also answers the question where the alternators will be connected then: as the intend is to make the starter battery a pure stater battery for both engines and the house bank to supply all consuming electronics on board only, the natural consequence is that both alternators will, by definition, go to the one starter battery, right?

Another grey area for me is how will two alternators on the same circuit react? Do you get the benefit of both, will they both excite?

Hm is that potentially problematic? Will certainly raise that with my electrician...

With regards to other charging sources, it says on the Blue Sea website that "there is an issue with multi-stage chargers which cut back to a lower charging voltage for “float“. If the charger is
supplying one lightly loaded battery directly and supplying a second battery through an ACR, and the second battery is the one that gets loaded, the system may not respond. The voltage of the first battery can be too low to trigger the ACR during the float stage while the loaded battery is being discharged. Because the ACR does not close, the multi-stage charger cannot see that the second battery needs charging current. This is usually resolved by connecting the multi-stage charger to the battery that has a load connected instead of connecting to the unloaded bank. Many multi-stage chargers also come with multiple outputs and the second output can be helpful in this situation and avoid loss of charge during the float stage."

I take from that that I will get an AC charger with two outputs and connect one to the starter battery, one to the house bank. Solar to house bank only I guess.

Sorry for all the questions here, but really need some clarity here as time is running and I want to give my electrician in Greece the go-ahead ASAP.

Many thanks!