Battery dump and 12V charging on a 48V bank

I have a 48V bank of 8 6V deep cycle batteries running through a MagnaSine charger/converter running a whole house system and it all works great, Power source has been a Honda generator to date. I just installed a Turgo wheel generator on a creek and wish to connect this to my battery bank. Problem is the output is 12V from the hydro generator.
The MagnaSine pulls 3 times the amperage as the Hydro will put out. I have a slave 12V battery on the Hydro with a 1000W (2000W peak) inverter, and it won't drive the MagnaSine running a 12V to 120ACV.

OK, the question: Can I run the 12V (14.7VDC actual) output of the Hydro to the 2 center batteries in the bank? I would be connecting to battery 4 and 5 in the string (for 12V), and was thinking that since it's a long string it might dump to the others reasonably well ballance-wise because center batteries in a string always run lower, right? How far off am I in my thinking?

Also, just for the sake of TMI, the Hydro is capable of 60A peak running at 12V.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,609 admin
    Re: Battery dump and 12V charging on a 48V bank

    No, there is no good way of connecting a 12 volt charger or load in the middle of a 24 / 48 volt battery bank...

    You are charging 12 volt of battery in the middle of the string, but not any of the others. So, the string becomes unbalanced (some batteries are more charged than others). The undercharged ones will sulfate (if less than 75% state of charge for days or weeks at a time) and the full batteries will overcharge/excessive equalization which will boil off excessive water from the electrolyte and will cause excessive corrosion of the positive plate grid and early life failure.

    About the only way to get the power from the 12 volt hydro is to charge a 12 volt bank and use a 12-120vac-48v battery charger (or 12 to 48 volt charger).

    You might contact Midnite solar and find out if their new Classic Controller can interface your 12 volt hydro system to a 48 volt battery bank (controller is a few months from production release -- last I read).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery dump and 12V charging on a 48V bank

    never charge/discharge individual batteries in a larger string as it will throw it out of balance without a doubt.
  • whispererwhisperer Registered Users Posts: 5
    Re: Battery dump and 12V charging on a 48V bank

    OK, thanks guys for the quick replies. I guess that idea is out. Darn it, that seemed like the easy way.... ;)

    Has anybody built a diode bridge to address this type of issue? I would think that if running 4 parallel 12V to 4 bridged 6V batts (12V for each pair) this could be done? I haven't drawn it out, maybe you can't get there with a diode bridge?

    Obviously a 48V charger that was capable of 50-60 amps (running on 120VAC from the Hydro 12V inverter on the slave 12V battery) would do the trick. I'm just trying to find a way around the parasitic losses involved in doing it that way.
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: Battery dump and 12V charging on a 48V bank

    It's the oppsite of what I was trying to do, but one of the things I looked at was a 12v to 48v converter. It works in either direction. The trick is how much power you are trying to move from one side to the other. Take a look at these.

    http://www.solarconverters.com/eqlist.html
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • whispererwhisperer Registered Users Posts: 5
    Re: Battery dump and 12V charging on a 48V bank

    Thanks Brock. This unit seems to be a good match: http://www.solarconverters.com/equal2HP.htm

    I would be able to push 360W into my 48V bank running at (I'm assuming) 30A load (50%) from my Hydro.

    The house runs about 10KW a day useage so 8640WH per day would be getting me close.

    Also, there seems to be 2 ways to use this unit: one of which is a plain batt EQ, of which it says that you can pull power from any particular batt with no fear when using this unit. Can I assume that I could ADD power to a 12V segment with no mal-content to my batt string? That runs against the earlier advice, I'm assuming because this unit is connected and constantly EQing the batts?
  • BB.BB. Super Moderators, Administrators Posts: 32,609 admin
    Re: Battery dump and 12V charging on a 48V bank

    No, you cannot add/subtract energy from any single cell/battery in a string without compromising the health of the string... Could you put 4x 12 volt battery chargers on each of the 4 12 volt batteries in a 48 volt string... Probably yes... But it gets more complicated as you start cycling the bank and if the 4 chargers do not add equal amounts of power at the same time...

    I am not sure that the converter you are looking at is, by itself, ideal for the task.

    Your system becomes fairly complex---water turbine, controlling its speed, the 12 volt destination (typically a battery), controlling the 12v bank state of charge, the upconverter and controlling its power throughput so that it does not damage the 12 volt bank, or overcharge the 48 volt bank... (setting the 12 volt charge profile will just be duplicated on the 48 volt bank... Also, may eliminate the need for the 48v dump controller.

    If the 48v up converter is bi-directional--you may wish to place a properly rated Schottey blocking diode (and heat sink) in the 48 volt output of the converter to prevent the 12 volt battery from draining the 48v bank... Or place a couple switches in the 48v converter input/output leads so you can turn it off when the water turbine is shut down (such as for summer drought).



    I guess it is all doable-but it is getting a bit complex in figuring out how to take out an appropriate amount of power from the 12 volt bank and up convert it to the 48 volt bank...

    Basically, I would be looking a up converter that would monitor the 12v bank according to this rule:
    • 12v bank at 12.7 volts => 0% transfer to 48v bank
    • 12v bank at 13.2 volts => 50% transfer to 48v bank
    • 12v bank at 13.7 volts => 100% transfer to 48v bank
    Put a dump controller on the 12 volt bank:
    • Start dump at 13.8-14.2 volts
    • Stop dump at 13.8 volts
    Put a dump controller on the 48 volt bank
    • Start dump at 59 volts
    • Turn off dump at 58 volts
    • Turn off Water Turbine at 59 volts
    • Tun of Water Turbine at 51 volts
    Other charging sources to 48 volt bank:
    • Do not charge above 58 volts
    • If equalizing 48v bank, set dump controller to turn on at 62 volts
    The up converter, if it is an accurate 4x step up converter (accurate to a 1/10th of a volt or so)--then controlling the voltage level on the 12v bank should be good enough to keep the 48 volt bank accurately charged.

    Just a guess at what your system setup may look like--If I was trying to design such a system. What you are asking for is not straight forward if you cannot get a water turbine controller that can take care of the 12-48 volt matching for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • whispererwhisperer Registered Users Posts: 5
    Re: Battery dump and 12V charging on a 48V bank

    Wow, thanks BB. It's going to take a few minutes for my brain to let all that sink, but I'm with you.

    What the system looks like at the moment (and it functions excellent and is reliable but power source is a Honda generator):

    Power source - Honda 3KW generator with automatic start controlled from the inverter/charger.

    Inverter/charger - MagnaSine 3KW inverter side and 48VDC charger side.

    Storage - 8 6V deep cycle batteries in series for 48V.

    My short term goal here is to integrate this 12V hydro supply into the mix. There is no drought here that will affect the hydro output. Max output of the hydro generator is 60A at 15VDC measured. I don't want to run it that hard so I'm figuring 30A to be safe. That is still 450W and SHOULD run the house for the day no problem.

    Maybe one issue I likely didn't make clear (my fault) is that I want to keep the existing system intact and in place. If/when the bank drops charge then the generator will automatically start and all is well.
  • BB.BB. Super Moderators, Administrators Posts: 32,609 admin
    Re: Battery dump and 12V charging on a 48V bank

    I figured you wanted to keep the existing 48 volt bank... The rest of the stuff I suggested are add-on's to keep the various battery charge levels within safety margins...

    The Water Turbine (and wind too) need a constant load--so you need a dump controller to put some loads on the battery bank(s) to prevent them from overcharging.

    Solar PV arrays (and gensets) you can just turn them off and there is no damage--whereas if you turn off the load for a Wind/Water turbine, they typically over-speed and damage/destroy themselves.

    I would really suggest to call Midnite Solar and find out if their charge controller can do a boost on your 12 volt turbine--or possibly run it at 48-60 volts to charge your battery bank.

    Their Charge Controller is still in Beta so there is no released spec. sheet on it yet.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • whispererwhisperer Registered Users Posts: 5
    Re: Battery dump and 12V charging on a 48V bank

    Bill, thanks very much for the replies and info. I will call Midnite Solar and find out if their charge controller will do the trick for my application. I understand the dump controller concept and agree that this would be the normal way to handle this but with the particular hydro unit I have that won't be an issue. I will definately look at that if I up-size in the future. The Turgo wheel generator I am using won't overspeed by design.

    Thanks all for all the info and replies. I have read it all several times and am much more informed and enlightened as to what can and can't be done. Thank you and much appreciated! I'll be back when a permenant solution is running in the application.
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Battery dump and 12V charging on a 48V bank

    Whats the alternator on the hydro unit? I'm thinking it may be just a automotive alternator, and if you re-regulate it, you can get 48V . You may have to fiddle around with resistors/ballasts to come up with the right field current.
    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

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