Replace battery and alternator on D2 55F

[Krumelur]

I want to order a new starter battery and alternator for my D2 55F and am looking for suggestions.
Currently, a 120A (?) alternator is installed but i have this gut feeling that it is due for replacement. I heard there is an affordable Mitsubishi model available as a drop in replacement?

The starter battery is currently 100Ah Fiamm L5 870A.
I think this is overkill and I consider a lower capacity version. Thoughts?

The aux batteries are 2x 100Ah LiFePo4 and charged by currently one Victron DC DC 30A charger but I will add a second one, giving me 60A of charging current.

Maybe you guys have suggestions. Thanks.

[symphony2]

You really don't need a 120A alternator, although the standard one is 115A. However you are limiting its output to 30A (or maybe 60A) to charge your lithium. Equally not sure why you need 60A for that size bank unless you are relying totally on the engine for charging. If you are running your windlass and (if you have one) bow thruster off the engine battery then sensible to have a decent capacity. Bavaria fitted 95Ah Exide AGMs as used in stop start diesel Jaguars and Land Rovers. I had those in my 33 and they were excellent so have fitted them to my current boat. They have a potentially longer life than your current type and probably similar price. The only reason for going smaller capacity is size, but the really small ones like Red Flash and Odyssey are more than double the price of conventional start batteries, but probably not double the life.

Hope this helps

[tiger79]

It takes so little power to start an engine that starter battery capacity is almost irrelevant.  What matters is the available cranking current, and you should look to maximise this.

It sounds as if you're limiting your current draw from the alternator to 60A.  There's still an argument for fitting a 115/120A alternator, as the rated output is only achieved at higher revs and won't be available at cruising revs.  So look at alternator output curves and try to find one which has a good output at lower revs.  I found that Prestolite/Leece-Neville alternators are particularly good in this regard.

[Krumelur]

I have solar on board, too. Still, running the fridge, Starlink, all the electronics, etc and having folks charge their devices easily draws 25A. It just adds up.

After a day of sailing and a night at anchor I need to recharge quickly while under engine. And then, 30A is just too little.

Good point about the windlass!

[SYJetzt]

  There's still an argument for fitting a 115/120A alternator, as the rated output is only achieved at higher revs and won't be available at cruising revs.  So look at alternator output curves and try to find one which has a good output at lower revs.  I found that Prestolite/Leece-Neville alternators are particularly good in this regard.

No need for an expensive alternator, the original VP/Mitsubishi 115A will work fine also under reduced revvs with 60A. I'm running my 115A Alternator with a 70Amp B2B charger in my lithium bank with no issues. Don't source a original alternator, every replacement from the aftermarket will work fine.

[Krumelur]

I had the part number of the Mitsubishi one figured out way back and I think it was under €200. Does that sound right?

[symphony2]

I have solar on board, too. Still, running the fridge, Starlink, all the electronics, etc and having folks charge their devices easily draws 25A. It just adds up.

After a day of sailing and a night at anchor I need to recharge quickly while under engine. And then, 30A is just too little.

Good point about the windlass!

Do you have a battery monitor to check your actual consumption rather than just guessing? If you are indeed drawing that sort of load you first need a bigger battery bank then a 60A B2B. But first get a real handle on your actual daily deficit (consumption minus typical solar generation).

[Krumelur]

Yes, I monitor the batteries and I can clearly see demand.
A bigger battery bank is always better, agreed. But when the bigger bank is empty it will take even longer to recharge using 30 A only.

[symphony2]

The charger should be matched to the capacity of the bank and your level of consumption. If you are using that amount you need a larger buffer capacity and bigger charger.

[SYJetzt]

I found this source for the aftermarket alternator for 199€, but be shure to get the right pulley dimension.
https://kohl24.de/de/lichtmaschinen/lichtmaschine-volvo-penta-a3tr0091-3587216-usw-14-
I would suggest to change the alternator , and keep the old one as spare.
Adding another B2B Charger will solve your problem...