Charging 24 Cell/675 Ah battery bank without using inverter/charger (external charger)

NetsuaNetsua Registered Users Posts: 2
I'm hoping to secure an external charger so that I can supplement the battery bank with an external generator when needed (a la generator support) while simultaneously using the inverter.  Running to 48V 4400 Magnum inverters in parallel.  I have identified the below for sale, but going beyond the manufacturers recommended use is beyond my technical understanding at the moment.  Is there any reason this would not work?

Would only be used for bulk charge.  Any long term charging/float absorb charging would happen with the primary inverter/charger.

Thank you  


  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Welcome to the forum Netsua,

    I did not find much on the model number for the charger shown...

    But here is a very good manual for a d ferro-resonant transformer type charger (similar in design to this one--Or at least close enough so you can figure out the basics?).

    Do you have 3 phase 208/240/480 VAC @ 60 Hz Wye or Delta utility power available?

    What AH rating is your battery bank? This guy seems like it would work for a ~1,350 AH nicely (10% rate of charge).

    Will you have some sort of automation to shut down the charger once the battery bank is out of float?

    What type of battery bank do you have? Flooded Cell Lead Acid, AGM, GEL, some other chemistry such as Lithium Ion?

    Do you have a manual/chart on how to wire the charger for different 3 phase voltages, and (it appears for Ferro-Resonate type) the tap settings increase/decrease charging voltage/current?

    Obviously, these types of units have been used for decades to charge forklift and other types of batteries very successfully. But getting into the details is critical here so you do not damage your very expensive battery bank.

    I guess you are in/around Kansas City Missouri? (not other voltages like 230 VAC @ 50 Hz, etc. for international usage). Ferro-Resonate transformers are usually very particular about line frequency.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Opps... I see that you have a 675 AH battery bank.

    135 Amps / 675 AH bank = 0.2 = 20% rate of charge

    That is a pretty hefty rate of of charge. I highly suggest that you have a battery temperature sensor to watch that the bank does not overheat during charging >~13% rate of charge. Lead Acid battery charging voltages drop as they get hot--So it is possible for a charger to dump more current/longer charging time as the battery gets hot and the charging voltage is reduced.

    Also, charging voltage in general is temperature sensitive... If the bank is in a ~75F room with good ventilation, then a "fixed" charging voltage is OK. If the bank is in a variable temperature area (very cold and/or very hot), then having accurate bank temperature allows the charge controller to adjust set-points as needed (not as important if you are doing float only--But how to know when you "exit float"--Use a precision voltage sensor to turn off bulk charger when voltage reaches 59.0 volts @ 75F?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NetsuaNetsua Registered Users Posts: 2
    I don't have 3 Phase Utility Power, only standard U.S. 240V Split Phase at 60hz.  I was hoping that "3 Phase" was more a reference to three phases of charging since the placard also indicates that 240V is an option and not just 208V.  But I could be entirely off base there.

    I also wondered about the rate of charge.  It does not appear to be adjustable with this unit.  I have a message into Trojan as my battery is Trojan T-105 Flooded Lead Acid.  

    As far as automation, the need that I have for generator assist is relatively infrequent, so I wouldn't mind a manual process here.

    I am near KC, was my poor attempt at masking the image that unsuccessful? :) 

  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    No--As an Admin here, I can see your IP address and take a "guess" at where the address comes from using an IP location website. For example, what it says "about you":

    Paste your address into the search box near the top of the page and it will "estimate" the IP location based on various databases (no "hard" information from your network provider, etc.). If you post with a cell phone, satellite, or a VPN, IP addresses usually do not provide accurate results.

    Knowing a poster's rough location helps a lot for us to move the conservation forward quickly (for solar, we need to know the location for Hours of Sun per day, nominal line voltage/frequency, any local code/electrical/supplier issues to answer most of the basic questions).

    True 3 Phase battery chargers are very common for larger outputs... One of the "neat things" about three phase power, it can output "constant current" DC output (vs a 120 Hz pulse train for a simple single phase transformer). And again for larger battery chargers (industrial, fork lift, etc.) they tend to be in facilities with 3 phase power (which can get very complicated very quickly). And larger facilities, major AC loads (larger motors, forklift chargers, etc.) are usually 3 phase.

    I don't know if this device could be converted to single phase (I have done worse)--But is not something I would attempt unless you have detailed schematics and understand Ferro-Resonate transformers (which I do not).

    15 amp GC charger:

    You might look around for a used Golf Cart battery charger... With all of the golf courses and carts out there--I would have to guess there should be some used chargers out there (I found one smaller one on my local Craig's List).

    Lots of 48 volt chargers on EBay in the 5-18 Amp range (similar pricing it seems).

    You can also look at "updating" your off grid AC inverters for inverter-chargers... Here is a 4kWatt inverter-charger with a 60 amp @ 48 volt charger capability (not cheap, our host--Many newer/high end AC inverters are now available with inverter-charger functions and some other neat stuff like networking, generator support, etc.). If you are familiar with Magnum, here is one of theirs:

    And, again, our host--Up to 20 Amp AC battery charger that is used for off grid/battery backup systems for $320 or so:

    And here is a place that lists a bunch of (not cheap) single phase fork lift battery chargers:

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    That battery charger is a 3 phase charger.   That's the only way to get the 7,000 watts to power it.

    "sometimes" you can run a single leg off 240VAC and get some reduced DC amps output , but  that can also be stressful on the rectifiers, and the electronics in the charger may inhibit operation with a missing phase or two.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

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