24v alternator to charge (2) 12v 8D banks

[rwells36]

I've twin QSM-11 engines with a 24v alternator on each engine charging their respective pair of 24v cranking batteries (8D's) and an 8D set for 24v bow thrusters. My 12v system consists of (2) 8D house batteries and another pair of 12v (2) 8D's paired with a 2500 Watt Inverter. I have a 24v charger, 12v house battery charger, and a separate 12v inverter battery charger.

My objective is to use one of the 24v alternators to charge my pair of 8D 12v inverter batteries while under way. This presumably would supply energy to two (2) 7 amp appliances for refrigeration while making way (thus avoiding the need to operate my genset).

QUESTION:

Should I use a voltage step down (24v > 12v) on the existing 24v alternator?

Or

Should I use the existing 24v alternator as a spare and purchase a 12v alternator to charge the batteries?

Or

Should I use the existing 24v alternator as a spare and purchase a combination DC/AC alternator to bypass the inverter?

Or

Will a single 24v alternator be sufficient to charge (3) sets of 24v 8Ds?

Or

Something entirely different from all of the above.

[Teknishn]

24v alternator to charge 12v batteries? Umm, no....just no. Ever thought about using the 220vac to run your 110vac household lighting? What do you think would happen?

12v batteries need a 12v charging circuit. Using 24v to charge your batteries is asking for premature battery failure due to overvoltage and overcharging (which in worst case scenarios results in battery overheating and possibly a battery blowing up). Use your 12v house and inverter chargers. Even stepping down your voltage from 24 to 12 will not work effectively because of the alternator's internal regulator circuit is still thinking in 24v mode.

I have no experience with 8D batteries so what I have stated above is based on my experience with larger batteries (lead-acid, AGM's, and Gel's) with battery banks running in the 920-1200Ah range. Seen some nasty stuff happen over the years......

[rwells36]

After some digging I think my best option is what's called a Cruising Alternator. Q: if wired for 24v currently will I have to re-wire for 12v? Also, am curious about recommended AMPS for the alt.

[smac999]

First of all you need to combine the house and inverter banks. That's just silly to have 2 banks. Charge and discharge them. Together. They will be much happier and your system will be much simplier.

How is your 24v Alt currenty charging an engine battery and thruster battery? Acr? Diode block? Or are they just physically wired together? (In which case you don't have a thruster bank)

The best would be to add a 3rd alt to the system if possibly. A large ~125a+ external reg one. But this may be hard to mount to engine

If not pissible I would look into 24v to 12v Chargers and charge the house bank from one if the engine banks. (And hence its alternator). Get one that only engages when the 24v system is under charge. Otherwise it'll drain your engine bank.


Though if you don't run both engines together both of those become issues if you are only charging from one side. And you'd have to add the same system to both engines. Probably worth it anyways for the charger so you power from both alts

The fact that you don't currently charge your house bank while underway is crazy and a horrible design by the creator

[rwells36]

Smac999, the purpose for this post is to address the "crazy and horrible". The engine(s) configuration will not support 2 alternators. Separation of the house (12v) and inverter (110v) batteries isn't a bother or concern; I rather like it that way. My interest is only the communities best recommendation to design a 12v charging system using the engine(s).

[rwells36]

smac999, is this the sort of product you are thinking of?

http://www.promariner.com/en/05503

[Cadence]

I just wonder why so many people speak of stepping down DC voltages? JMHO, it would be better to buy a 12 generator and keep the removed one for backup on your other engine. A schematic of what you have would help. I suppose you could charge a pair of series 12V 8Ds at 24V and pick off 12 with blocking diodes which would be expensive for the amperage you would need.

[TeddyDiver]

Originally Posted by rwells36

Or

Something entirely different from all of the above.

Insane to have 4 separated battery banks IMHO. You didn't mention much about where the house and inverter bank are located but they should be as one if not others too if possible.
So put all your charging into one 24v house bank of four 8D's and 24v chargers to charge the starting and bow thruster batteries. Get DC/DC inverter to get 12v and 24v inverter charger for AC's from a single house bank..

BR Teddy

[soerencarlsen]

yes you can charge your 12v batteries, hopefully you have noted that your 24v comes from 2 12v batteries as I have never seen a 24v batteri.
you just run a jumper lead from one of you 12v starter batteries to whatever you need. some sort of diode should be fitted so the current only flows one way.

[rwells36]

Victron has a product

https://www.victronenergy.com/invert...argers/quattro

That according to their web site would serve the purposes of the need for a DC - DC Charger/Converter

[sainted]

You don't say what kind of boat you have or what your standard running configuration is, so I'm going to assume that yours is a power boat and that you run with both propulsion engines unless one of them fails. It seems to me that like most US power boats, yours was designed to run with the generator operating 24/7, so the presence of an inverter is bit puzzling.

If I were designing your system from scratch, I would specify a 24v inverter/charger with a 24v house bank. I'd make all the dc loads I could 24v, and those that I could not (electronics mostly), I'd supply with a 24/12 converter.

If you don't want to re architect your system, I'd recommend replacing the alternator on one engine with a 12v high output eternally regulated model. I would use a battery charge relay to allow the remaining 24v alt to charge the starting banks for both engines, and a charge relay to allow the 12v alt to charge both the house and inverter banks. You'd likewise have to segregate the battery chargers.

You'd still have redundancy courtesy of the gen set, so if either shine our alternator failed you could still operate.

[rwells36]

The boat is 55' Novatec CPMY with twin diesels.

[Mikado]

24V Alternator charges your 24V 8D battery bank. Also need a DC/DC converter to drop voltage to 12 V and then thru an ACR to charge the 12V starter bank.

To simplify, I would change the starter to 24 volts which would make your entire charging/starting system 24V and then for 12V run thru 24V-12V DC/DC converter to 12V buss bar and then everything 12V runs off of that.















dc

[smac999]

Originally Posted by soerencarlsen

yes you can charge your 12v batteries, hopefully you have noted that your 24v comes from 2 12v batteries as I have never seen a 24v batteri.
you just run a jumper lead from one of you 12v starter batteries to whatever you need. some sort of diode should be fitted so the current only flows one way.

definitely don't do this... it won't work and you'll mess up your engine batteries in the process.

also the diode is useless as you will still be draining the engine battery into the house battery while not running the engine with or without it.

you need something voltage based so it only charged the house bank while the engine bank is under a charging voltage.

[smac999]

Originally Posted by rwells36

smac999, is this the sort of product you are thinking of?

DMC 24V to 12V Batt to Batt | ProMariner

I have not used that product but that looks exactly what I was talking about. and better then the ones I've seen before.

that would be the easist solution. 3 wires to connect and you're charging the house battery from the engines. if you added an ACR between the house and inverter bank it would charge both. (better to just join them but...)

alternitily you could buy 2 of them so both engines would charge the 12v banks. and give you 80a to the house / inverter. I would still use the ACR. and wire one to each 12v bank. that ways the banks care share and either can get up to 80a

there are other solutions. but this one leaves all the existing stuff as is and just adds a new box and a few wires.

changing the whole house system and inverter to 24v would be the best solution but thats probably $10,000

changing one alt to 12v. and having one alt charge both 24v banks (well all 3, you still haven't said how the thruster bank gets changed from engine) with acr(s) and one alt charging 2 12v banks with an ACR is another solution. but more involved.

if you wanted 150a of engine charging this would be a good solution. since you only wanted a few amps the dc to dc charger would work fine.