Battery Charging Voltage

[Timeless 2]

I have a question to ask the experienced on charging systems. I know that Lithium is the long term solution but that can wait for the winter. I have a twin engined cruiser on the Thames. There is 280ah bank for port engine and domestics with a 160ah for starboard engine only. They are connected with a VSR. The alternators on each engine are 60amp each. Went out for first time this year on Friday and domestic bank discharged very quickly. I know I need more capacity but last year I could keep fridges going and run television/ lights overnight and still have 50% battery in the morning and start both engines. When I have run low I run the generator and battery charger for an hour.
I monitored the voltage on each engine today individually. The starboard engine battery was 12.5 volts before start and operated at 14.1 with lights/ radio on. Went 14.7 with no load on. I thought this was ok.
Port engine was 13v before start. After start was 13.3v at tickover. Port side operates engine room fans. With these switched off and inverted off so no fridge load got 14.3 volts.
With both engines running 14 volts on monitor but with fans and inverter on showing a 5 amp discharge. I feel the alternator on port side is not coping with the load and the starboard does not seem to be raising the voltage under load like it managed when operating by itself. The battery’s are 5 years old and will have lost some capacity but before i replace I want to be satisfied that the alternators are working ok. Appreciate any suggestions,

 

[superheat6k]

That's a lot of battery capacity for quite small 60amp alternators. Any reasonable amount of discharge is going to take quite a while to get the energy back in. Have you got smart alternator controllers ? These will get more out from the alternators when running at slower revs.

 

[Boater Sam]

Running the generator for only an hour when the batteries are mostly discharged rather than charging them fully is a sure way to sulphate them. You likely have wrecked batteries.
60A alternator will be putting in less than half that after several minutes running, again leading to poor charging regime killing the batteries.

 

[Timeless 2]

It seems to me that the installation is original Fairline from 1998. The alternator sizes were taken from the TAMD 63 manual. I’m assuming they are original. There is no other Smart Control. There is only the excitation voltage on terminal 61a which originates through the VP control modules. I know it’s out of date and intend to upgrade over this winter. I estimate the consumption of the boat when running at 40 amps, that’s the fans and fridges. Overnight the monitor ranges from 8-18ah discharge. Engines started ok in the morning. The battery’s discharge was much faster this week than last year. Thank you for answers

 

[alahol2]

60A alternator will be putting in less than half that after several minutes running, again leading to poor charging regime killing the batteries.

That's not how it works, if the batteries are taking 30 amps from the 60 amp alternator they would also be taking 30 amps from a 200 amp alternator.

 

[PaulRainbow]

I have a question to ask the experienced on charging systems. I know that Lithium is the long term solution but that can wait for the winter. I have a twin engined cruiser on the Thames. There is 280ah bank for port engine and domestics with a 160ah for starboard engine only. They are connected with a VSR. The alternators on each engine are 60amp each. Went out for first time this year on Friday and domestic bank discharged very quickly. I know I need more capacity but last year I could keep fridges going and run television/ lights overnight and still have 50% battery in the morning and start both engines. When I have run low I run the generator and battery charger for an hour.
I monitored the voltage on each engine today individually. The starboard engine battery was 12.5 volts before start and operated at 14.1 with lights/ radio on. Went 14.7 with no load on. I thought this was ok.
Port engine was 13v before start. After start was 13.3v at tickover. Port side operates engine room fans. With these switched off and inverted off so no fridge load got 14.3 volts.
With both engines running 14 volts on monitor but with fans and inverter on showing a 5 amp discharge. I feel the alternator on port side is not coping with the load and the starboard does not seem to be raising the voltage under load like it managed when operating by itself. The battery’s are 5 years old and will have lost some capacity but before i replace I want to be satisfied that the alternators are working ok. Appreciate any suggestions,

If the Stb battery is is engine only, 12.5V before starting is lower than it should be.

Lower voltages with loads on is to be expected. If the port alternator is raising the terminal voltage to 14.3V it sounds OK.

I suspect the batteries need changing.

 

[PaulRainbow]

That's not how it works, if the batteries are taking 30 amps from the 60 amp alternator they would also be taking 30 amps from a 200 amp alternator.

Whilst this is correct, running the engines for an hour isn't going to fully charge the batteries.

 

[alahol2]

Whilst this is correct, running the engines for an hour isn't going to fully charge the batteries.

Agreed.
It bugs me that so many people think that big alternators mean fast charging.

 

[PaulRainbow]

Agreed.
It bugs me that so many people think that big alternators mean fast charging.

Me too, someone on the motorboat forum recently suggested fitting 2 x 250A alternators

 

[Chiara’s slave]

Me too, someone on the motorboat forum recently suggested fitting 2 x 250A alternators

Spending a fraction of that cash on a small/medium solar panel and controller is surely the way to go? Charge at a a few amps for ever, the batteries will surely be fully charged every time you go to the boat.

 

[PaulRainbow]

Spending a fraction of that cash on a small/medium solar panel and controller is surely the way to go? Charge at a a few amps for ever, the batteries will surely be fully charged every time you go to the boat.

Absolutely, i have several customers with modest sailing boats, 50/60W panels and mostly weekend sailing, they usually arrive to find fully charged batteries.

 

[Timeless 2]

Thanks for the advice received. I will be in touch later this year Paul so you can supply what I need to convert the house to lithium and have separate batteries for each engine. The shore power charger only charges the domestic bank so that might account for the Stb being low voltage. No problem starting engine. I think now that the batteries have deteriorated and that an upgrade to lithium is the way forward.

 

[Boater Sam]

That's not how it works, if the batteries are taking 30 amps from the 60 amp alternator they would also be taking 30 amps from a 200 amp alternator.

Hopefully, yes . But an hour on the gen is not going to charge the batteries no matter how large an alternator is charging, the simple fact is that it takes longer than that to fully charge a battery.
Keep part charging like that and the battery is toast.

 

[alahol2]

No quibble with you there.