Click for Ocean Alexander Click for Nordhavn Click for Northern Lights Click for Apolonnian Click for Westport

Best Way to Charge House Battery Bank

Discussion in 'Technical Discussion' started by DOCKMASTER, Nov 25, 2019.

You need to be registered and signed in to view this content.
  1. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    683
    Location:
    Ketchikan, Alaska
    I'm looking for input on how folks charge their house battery banks. I have P&S 24v banks for engine starting and some hi amp systems like BT and windlass. These are charged by 24v engine mounted alternators and a 24v charger fed by A/C from shore or gen.
    Then I have a 12v house bank for a bunch of other stuff (gen starting, lights, downriggers, heads, pot puller, heat circuit, etc). This is bank is 4x group 31 AGM batteries. Currently the only way the house bank is charged is from an A/C fed charger with power from a gen or shore. Whereas this works because I always have a gen running it gives me a single point of failure if the charger quits. I would really like to be able to charge this bank from an engine source while running but CAT does not offer a secondary alternator option. So the options I see are:
    1) Do my own custom on engine 12v alternator and drive off the crank
    2) Find a PTO alternator to drive off the live PTO on the ZF gear
    3) Use a 24v to 12v battery to battery charger and charge the 12v house bank from the 24v starting bank
    4) install a secondary, back-up A/C fed charger.

    Any other ideas? What are others doing for this? The gens have 12v alternators but Northern Lights says they are not recommended to charge a house bank like I have and are mainly just to charge a gen starting battery. Thanks in advance for any input.
  2. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    We have 32, 24 and 12V banks.
    I can type a book, later..

    Let me make sure I read correctly what you typed.
    Single 12V battery bank (4 x G31s).
    This single bank starts the gen-set and all the ships 12v options
    (reads like your gen-set is already charging this bank).

    Your looking for a permanent automatic charging method from your mains to charge the 12V bank after the gen-sets alternator and 120Vac mounted battery charger (?).

    DCv to DCv converter charger would be my first choice followed by a bolt-on alternator on one of the mains.
    I have both installed on our boat.
    Last edited: Nov 25, 2019
  3. Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    6,169
    Location:
    Miami, FL
    In my opinion this is a lousy set up... the generator battery should be used for the generator only. Some 24v boats uses the gen battery to run a couple of light 12 v loads, that’s fine. But the gen should be isolated so it can never be run down

    Using a main to charge a house bank is fine as a back up but typically boats spend a lot more time anchored than under way so nothing wrong with using the gen to run a charger to charge the house bank. It all depends on how you use the boat like time on the hook vs underway, how good is the ventilation (most modern boats need air con and run the genny most of the time). Usually if you loose the genny it s game over

    i d rather have a second charger in case the primary fail. Which has happened to me.
  4. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    683
    Location:
    Ketchikan, Alaska
    Yes, you are correct. Except the gen-set is not currently set to charge 12v house bank. I am looking for opinions or options on a secondary means to charge house bank. Could be from m/e's, a back-up charger fed from a/c, dc to dc off the 24v or? I was curious what others are doing.
  5. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,667
    Location:
    Fort Lauderdale
    Easy, they make Battery isolators that you can run one of the engine alternator leads to. It generally has a few 24 volt leads and 1 12 volt lead that you can use for your purpose.
  6. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    683
    Location:
    Ketchikan, Alaska

    If I want a dedicated battery for gen starting I would need to install another battery. Currently I have an emergency connect from a m/e starting battery so I can start a gen if 12v bank is dead.

    I always have a gen running for refrigeration, fish box ice, etc so that's not an issue. Just looking for back-up means to charge the house bank if charger dies.
  7. Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    6,169
    Location:
    Miami, FL
    You could split the bank and use one of the G31 for the Gen and the rest for house. House should be deep cycle anyway. The genset alternator will charge its battery

    if you run the gen all the time, you can just use the battery charger to charge the house bank. Modern chargers are pretty reliable. Personally I keep a spare on board but that s because we spend a lot of time on the hook in the Bahamas. If the Charger fails, charging from the mains isn’t going to help because we d have to run one main a few hours a day.

    curious to know what builder used 12V for house and 24V for mains... and setup a 12V house shared with generator. Lousy set up.
  8. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    Your gen-set starts from the bank but does not charge it?
    How is that possible?
  9. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    We also carry a spare 40A, portable, 12V charger. And a nice extension cord.
    Tenders and boats tied along side have been known to need a jump or quick charge.
  10. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    Stepped in what?
  11. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    I prefer a dedicated battery for each prime user - engines and generator.
  12. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    683
    Location:
    Ketchikan, Alaska
    The current arrangement is not original. Although a 12v and 24v bank is original the boat came from factory with only one generator. I don't know if there was a dedicated battery for it or not. Capt Ralph brings up a good point about a portable charger/jump start. I carry one of these already just in case I have an issue with the battery on the dinghy. Perhaps this is enough in case of an issue with the mounted charger. I'll give this some consideration. Thanks everyone for the input.
  13. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    I like this idea. Plus an ACR between the gen-set battery and the 12v house bank.
    This is also on our boat.

    Book typing is getting closer.
  14. ranger42c

    ranger42c Senior member

    Joined:
    Aug 20, 2013
    Messages:
    541
    Location:
    Chesapeake Bay, USA
    I think there might be some step-down (or voltage converter) ACRs or B2B chargers that could maybe take 24V voltage from your engine batteries to feed your 12V house bank while underway.

    -Chris
  15. Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    6,169
    Location:
    Miami, FL
    My boat used to be 32v (engines and house) with the genset 12v

    when i repowered, I wanted everything 24v but for some reasons Cummins charged another $1000+ per engine for 24v. So I went with 12v for the mains and converter the house to 24v (all new wiring thruout, new panels etc)

    i installed two Pro Mariner chargers, 12 and 24v

    The 24v house bank is only charged by the battery charger for now which is fine since we only use the boat for short trips. When we start using the boat to go to the Bahamas I will add a 24 alternator to one of the engines.

    I like redundancy and having a separate bank for each main, gen, house and eventually inverter is the way to go.
  16. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,667
    Location:
    Fort Lauderdale
    Princess uses a battery to battery converter (or isolator) to go from the charger's 24 volt output to all of the battery banks, it has 1 post that is stepped down to 12v and the others are all 24 v. They use the same brand of isolator for the engine alternator also. It's blue and I'll try to find a picture of it to find out the brand, but don't know it offhand, but don't have access to any newer Princesses currently. They have 2- 24 volt leads to charge 24 volt batteries, and 1 12 volt lead. I believe Mastervolt sells them and they have a diode or something to knock the voltage down for a 12 Volt bank.
    Last edited: Nov 26, 2019
  17. Pascal

    Pascal Senior Member

    Joined:
    Feb 29, 2008
    Messages:
    6,169
    Location:
    Miami, FL
    And when that fails? All your banks are compromised.

    About 10 years ago I woke up one morning on charter to a dead boat (Johnson 70) while on shore power The 24v Charger (Dolphin brand) had failed and somehow not only the house bank was drained but neither the mains or the generators would stay running. They would crank, fire up but shut down has soon as key or start switch was released. I was able to get things going by running one of the generators for 15’ while holding the run switch.
    Lesson learned, I want had much redundancy as possible when it comes to battery banks.
  18. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,667
    Location:
    Fort Lauderdale
    It would give the OP redundancy by allowing an engine alternator to charge his 12 volt bank. He already has a 120 or 240 volt charger, dedicated to charging the 12 volt bank but needs a generator running in order to charge the house bank.
  19. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    Before we get carried aweigh in using wrong terms; lets review what these devices are, that have been mentioned above.

    A battery isolator or diode pack is an electrical device that divides direct current (DC) into multiple branches and only allows current in one direction in each branch. https://en.wikipedia.org/wiki/Battery_isolator

    An ACR or Automatic Charge Relay parallels (combines) batteries during charging, and isolates them when charging has stopped and after battery voltage has fallen. An ACR is intended to keep a load from discharging both of the batteries. https://www.bluesea.com/support/articles/Charging_and_Charge_Management/1366/Automatic_Charging_Relay_[ACR]_Explained

    A DC to DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) to very high (high-voltage power transmission). https://en.wikipedia.org/wiki/DC-to-DC_converter
  20. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,439
    Location:
    Satsuma, FL
    To ad even more complication, I remember a dual voltage alternator on an old Roamer. 12V alternator for the house and bottom batteries with a 24v trickle charge for the mains top starting batteries.
    Without the benefit of a current controller (DC to DC converter), this would be the only dual voltage alternator I know of.