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  1. #1

    Battery charging rate - charger vs Alternator

    Now that our boat is in the Chesapeake Bay and our use pattern is totally different than it was when we lived 5 minutes from the boat, we spend a lot more of our cruising time on the hook than we did when we lived in Long Island. A recent thread about Inverters and batt charging got me wondering...

    Anyone have a rough (or accurate) idea of the charging rate of a standard type batt charger vs the charging rate for the engine/alternator on the same batt bank?

    I'm specifically interested in the 32v banks and the original Lamarche Charger. I'm assuming that the charge rate of the main eng alternator is higher than the charger delivers but I don't know that for sure and don't have any manuals, etc here in Mexico.

    So what will charge the batts faster, the charger (genny providing a/c) or the main engine spinning the alternator. Further, as someone suggested, will the inverter (Outback) charge the batts faster than the LaMarche batt charger if the inverter is connected to do so (mine isn't)?

    I'm asking this because as the admiral and I were discussing our upcoming boat cruise, we recalled that the last time we were out on the hook, the batt bank supplying inverter power did not fully recover after a couple of days. It supplied the needed a/c power with no problem but after doing this for this period and running the genny for a couple hours a day to charge, the batt bank would not spin the engine for starting on the third day. The parallel start switch, of course, is there for that purpose and worked fine.

    So obviously the batts weren't being completely recharged and the genny needs to run more than we were running it per day OR a more "powerful" or efficient charger needs to be involved.

    For any of you using the 32v oem system for inverter power - how long do you have to run the genny per day to top off the batts charge-wise. I realize this is totally dependent on your inverter loads, your charger and your batt AH capacity but a rough idea would be helpful.

  2. Battery charging rate - charger vs Alternator

    Mike: Following is a copy of my December 2005 post: "DC SYSTEM DESIGN"
    Fast charging depends on (a) the regulator and (b) the relationship between the amp hour capacity of the bank being charged and the capacity (in amps) of the alternator or battery charger. Doesn't matter what the charging power source is. but the regulator control is critical.

    An alternator and a battery charger of the same capacity (amps) and using the same regulator will charge a bank at the same rate. A three stage smart regulator will control either so as to charge faster than an old (taper) regulator which gradually tapers off the charge.

    To get the fastest charge, use a big bank with AGM batteries and a big charger/alternator..with a three stage smart regulator....details follow below. Your original LaMarche charger is likely a ferroresonant taper type charger and will be generally SLOW in recharging. I replaced a 60 amp Sentry ferroresonant (old technology, likely similar to your LaMarche) with a "smart" 40 amp Statpower and the new smart charger was FASTER than the old!!!

    I have three 40 amp Statpower plus and 150 amp from an inverter/charger so I can charge 250 amps at 12 volts when my genny is running. (It's more than I need for six 220 amp hour 8D deep cycles because I don't let them deep discharge.) I can run for weeks and weeks at about 45 minutes daily gen run time, about one hour daily if I also run a freezer in addition to my fridge.

    All this discussion is accurate regardless of whether the bank is 12v, 24v, or 32 volt.

    DC SYSTEM DESIGN
    When your charging source ( amps) is properly matched to your battery bank capacity (amp hours), and your battery bank capacity to your daily load in amp hours, you can reduce genny run time to a minimum. This is VERY valuable for long term cruising away from shorepower because a balanced dc (battery) system reduces genny run time (and wear and tear), limits noise periods, and extends battery life. It pays for itself in marina fee savings.

    Design steps are NOT rocket science:
    (1) Determine your daily amp hour load, (say, 150 amp hours, is typical).
    (2) Pick batteries (amp hour capacity) of your choice at least three or four times the capacity of your daily load, or more, (This limits daily discharge cycle depth resulting in longer battery cycle life, permits more rapid charging, and daily charging reduces sulphation.) (4 x 150 is about 600 AH, about three 8D's. Four or five is even better.)
    (3) Size your charging source to about 25% of the battery amp hour capacity for wet cell, 40% for gel, 100% for AGM. (If well cell, you should charge at about 25% of 600 or 150 amps. AGM's will take close to 600 AH!)

    You should be able to recharge from, say 50% to 85% or so in a hour.

    Poof: you have a well balanced dc system! Of course you need the genny power to charge at this level, and perhaps power AC loads at the same time (such as a water heater and microwave) if so desired.
    One way to help this along: perhaps eliminate electric cooking (a heavy draw) and convert to propane. If you run your genny all day anyway, as for air conditioning, the above accomplishes little.
    Last edited by REBrueckner; 04-16-2008 at 11:35 AM.
    Rob Brueckner
    former 1972 48ft YF, 'Lazy Days'
    Boating isn't a matter of life and death: it's more important than that.

  3. #3

    Re: Battery charging rate - charger vs Alternator

    Your Alternator is proubably 60A
    your Lamarche is proubably 40A
    Your Outback is proubably 60A

    Your Alt will only out 60 if it's turning fast enough around 1600 RPM

    You would be wise to hook up the outback to charge it's a much more modern sophisticated charge source than the old Lamarche it can be programmed to work any way you want it to and is capable of equalizing.

    Brian

  4. #4

    Re: Battery charging rate - charger vs Alternator

    Good info Reb!

    Brian, since you mentioned it, I seem to recall that the LaMarche is 40AH. So I guess another project when I get to the boat (ONLY 5 MORE DAYS!) is to connect the Outback to enable it to charge.

    Am I correct in assuming - again, no instruction manual here - that the Outback could, if connected to both battery banks, completely replace the Lamarche as the boat's 32v battery charger?

  5. #5

    Re: Battery charging rate - charger vs Alternator

    Calder's book has a very detailed discussion on this and the worksheets to help with the figuring. It'll amplify REB's comments and provide explanations and options.
    Trav
    45C 447, Series I, '72
    Pensacola, Fl

  6. #6

    Re: Battery charging rate - charger vs Alternator

    You can download the manual from outback but I'm pretty sure the outback is not a multiple bank charger Which means that without some other device it can only regulate and charge one bank. There is equiptment available to make it work on 2 banks but most of that stuff is 12V only. An isolater would work but I don't like them at all because you will get a voltage drop thru it. One thought might be to use the isolater and adjust the charge rate on the outback up to compensate for the voltage drop but I'm not sure if that adjustment would be linear or constant through the voltage/ amperage range. When I hooked up mine I combined both banks to make one big bank I did this so I could use the outback to charge and have the largest possable battery capacity. So I combined start and house bank into one obviously this presents a problem if that bank was taken down to far as I would not be able to start an engine or generator. To fix that I built a seperate bank of golf cart batteries dedicated to the generators so now I can always get a gen started to get things charged if I run them down. Using the outback to charge greatly reduces the amount of water the batteries need and the frequency in whick they need it. The outback is a modern Bulk/Absorb/ float type charger much better than the old Iron Horse Lamarche.

    Brian
    Last edited by Brian Degulis; 04-16-2008 at 11:50 AM.

  7. #7

    Re: Battery charging rate - charger vs Alternator

    THanks - I found the manual on the Outback site...

    So, I guess what I would do would be to disconnect the charging capability of the Lamarche to the one batt bank and connect the outback charger to that one, leaving the Lamarche circuit to the other bank in place.

    OR - combine both banks and connect the Outback with the possibility (slim based on what I've experienced so far) of depleting both banks. Since I have a separate 12v system to start the NL genny, if both 32v banks were too depleted to start the mains, the genny/charger could still be started to charge them. Obviously not ideal in an emergency but workable I suppose.

  8. #8

    Re: Battery charging rate - charger vs Alternator

    Quote Originally Posted by MikeP View Post
    THanks - I found the manual on the Outback site...

    So, I guess what I would do would be to disconnect the charging capability of the Lamarche to the one batt bank and connect the outback charger to that one, leaving the Lamarche circuit to the other bank in place.

    OR - combine both banks and connect the Outback with the possibility (slim based on what I've experienced so far) of depleting both banks. Since I have a separate 12v system to start the NL genny, if both 32v banks were too depleted to start the mains, the genny/charger could still be started to charge them. Obviously not ideal in an emergency but workable I suppose
    Combining the banks works well for me it gives me more capacity when I'm inverting and even if you don't need the aditional capacity your better off keeping the % of discharge as small as you can. I didn't remove the Lamarche It's a back up and aditional charge capacity if I need it.

    Brian

  9. #9

    Re: Battery charging rate - charger vs Alternator

    Mike,
    If you want to get all of the functionality out of the Outback, you need the Mate control module. This will allow you to change the default settings for charge rates, etc. You might also want to send a PM to Jcrlaw on the forum. He installed another part for the Outback and I can't remember thier name for it. It also plugs in where the Mate does but it offers even more control of the charge and invert functions. He needed it to monitor total AH draw down as he didn't want to let his brand new Roll/Surrettes get too low before charging. The Outback will also start your genny when needed to charge the batts if you set it up that way (another module, I think).

    I had thought about using the charger off of the Outback for the house back while leaving my other charger on the start(sbd) bank, but since my Major Power charger is a newer smart charger, I have not done that (yet). The only reason I might consider it is to increase the charge rate to the house bank as you are thinking and to give some redundancy.
    Sky Cheney
    1985 53EDMY "Rebecca"
    ELYC on White Lake--Montague, MI

  10. #10

    Re: Battery charging rate - charger vs Alternator

    You definitely need to monitor the amp/hr drain by using an Emeter or Link 10 meter. You do not want to overdischarge those batts. You do not want to discharge them more than 50%. If you do you are killing that batt bank. An Emeter will allow you to monitor volts, amp/hr discharge and charge , amps being drawn/charged back into the batts real time and time to go (at that discharge rate ) . You can program all the parameters and also it keeps a history that can be useful. It also has a neat little graphical read-out that shows where you at a glance. Lead acid batts are not the best for inverter use as they cannot withstand the high charge currents that an AGM can and therefore take longer to charge back up .Personally I don't like the idea of using house /starting batts for an inverter. ................Pat

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