24v charger with balancing

RuurdRuurd Registered Users Posts: 15 ✭✭
In this time of the year i desperate need a charger voor my 24v 180ah battery bank. what i got is a step down transformer. The spec's are:
pri. 230v ac 50hz.
sec. 2* 12v 24amp.
What i am planning to do, is connecting 2 fbr's to the 2 separate 12v outputs, and connect them in series to the battery bank. this basically gives me 2 12v chargers, one for itch battery. According to my calculation's, i need to drop the voltage from my generator a bit.

230/12=19.17. I need 14.4 volts dc so : 14.4+1.4 (diode drop) =15.5vdc.
15.5/1.4=11.07vac.
11.07*19.17=212vac pri.

Now is the question is : are my calculation's correct, and can the avr on the generator be adjusted for 212 v ?

Comments

  • RuurdRuurd Registered Users Posts: 15 ✭✭
    Some extra info, the generator is gx200 honda clone and gives 220vac 10amp 2200w continuous, i rebuild it for lpg, put a lpg carburator on it and a cill.head from a gx160, so i got a bit higer compression ratio. According some carttunning forums it wold give a compression rating of 10.5;1. for lpg this wold be very nice. 
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    Constant voltage charging is usually a bad idea.  So is high ripple.   I recommend that you buy a multi-stage charger.
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    Yes a new multi-stage charger would be nice, but i don't have the funds for that, so i am going this route. Constant voltage is the same what an car alternator dos, and that is working in millions of cars over the world. And i need a form of balancing for the battery bank. In my setup it dos that automatically.
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    edited December 7 #5
    ?
  • dennis461dennis461 Registered Users Posts: 85 ✭✭
    Automobile charging system is not a good comparison, IMHO.
    Also, what is this "... connecting 2 fbr's to the 2 separate 12v outputs, ..."
    fbr is a what?
    Camden County, NJ, USA
    19 SW285 panels
    SE5000 inverter
    grid tied
  • BB.BB. Super Moderators Posts: 26,872 admin
    An automotive alternator is a 3 phase device that runs at fairly high frequency (RPM)--When rectified, you have much less ripple voltage. And there is a regulator to control the charging current and keep the battery voltage at ~14.2 volts or so.

    With a single phase genset, you are running 60 or 50 Hz and your actual rectified voltage is the square root of 2 times the RMS (average) DC voltage. I.e., 14.4 volts * sqrt(2) = 20.36 volts peak. (note: if you are using  a 4 diode full wave bridge rectifier, you will have 2x diode drops).

    So, in order to have a high average charging current, you need a fairly high peak voltage from your transformer. And with a simple rectifier, you end up with high peak current (when the sine wave voltage is high) and no current flow when the sine wave is less than battery voltage. This is can cause your transformer to run hot, the rectifier needs good heat sinking, and you either need to monitor the battery bus voltage, or make some sort of regulator to prevent over charging of the batteries.

    https://en.wikipedia.org/wiki/Rectifier

    Obviously, this is done all the time with typical automotive and industrial battery chargers--But it does make it very difficult tor the genset with the "non-linear" current wave form. And if you are trying to both charge the battery bank quickly, but not over charge--With out some sort of active regulation, you can end up needing to baby sit the charger and turn it off when the battery is full.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    edited December 7 #8
    @ dennis461, with a fbr i mean a 4 diode full wave bridge rectifier. I think when i use 1 of them one for each 12v output i would get 2 separate dc output's, one per battery. So each battery draws the amps it need to get to 14,4 / 14,2 volts, and balance's the battery bank beter.

    @BB , I got a victron battery monitor witch has a programmable relais, so i can let the charging start/stop at every parameter i want.
    For the peak voltage i calculated 14.4 v +1.4v (2*diode drop) = 15.5v /1.4 (sqrt(2)) = 11.07 vac. Do i have that wrong ?
  • BB.BB. Super Moderators Posts: 26,872 admin
    Of course, the transformer+bridge rectifier have to have a voltage higher than the battery to get current flowing... So, I would suggest that the RMS AC transformer voltage should be higher than 11 VAC.

    Are you winding your own transformer(s) or just trying to find something off the self?

    Also, beware that if your battery voltage is very low (or dead, or you are charging with heavy DC loads), the transformer needs to be capable of current limiting without overheating. I had a store bought 1 amp trickle charger that I connected to my dead car battery and it overheated (popped the plastic cover) because of the high current into the dead/near dead battery (fortunately nothing else happened--The trickle charger continued to work with the case popped open like a clam shell)..

    I am a little bit confused about your application... Is your intent to charge a 24 volt battery bank with 2x 12 volt battery chargers?

    If this is your intent, you will need two transformers (or a "24 volt" transformer with a center tap) to get isolated or 2x 12 volt in series charge controllers.

    You cannot run 1x 12 volt transformer to two bridge rectifiers and charge two 12 volt batteries in series (24 volt battery bank). You need to isolate (float) the two battery chargers from each other (or make some version of 24 volt battery charger).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    Yes i intent to charge a 24 volt battery bank with 2x 12 volt battery chargers, i already have a transformer. the spec's are : 
    Pri. 230v
    Sec. 2*12v / 24a

    i can hook the Sec. for 24v / 24amp ore 12v / 48amp.

    The rectified voltage is to high for what i want, that's why i plan to drop the Pri. voltage a bit. This gets me to the avr of the generator. According my calculations i need Pri. voltage of 212vac. i now that i can adjust the voltage of the generator, and want to now how much.

    (i am not a native English speaker, but i am doing my best :smile:)
  • RuurdRuurd Registered Users Posts: 15 ✭✭
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    I just made a schematic for what i plan to do.
  • dennis461dennis461 Registered Users Posts: 85 ✭✭
    The schematic is worth a thousand words.  What you have drawn will work with limitations. 
    1. The transformer winding's MUST be isolated from each other as you've shown. Some double winding outputs are actually a 24V single winding with a center tap, only three wires.
    2. The ONLY common connection is the jumper between top battery (-) and bottom battery (+).
    3. Now the problem, peak voltage from Full wave Bridge will be 12*1.414 = 16.9 VDC, which means as batteries charge up needing only a trickle CURRENT, the voltage will climb from some lower value (transformer output sags when pumping out full current) to 16.9VDC and ruin the batteries on the first day of operaion.
    4. Add two voltage regulators to the Full wave bridge output, something like this https://www.ebay.com/i/332130294787?chn=ps, with a capacitor on the full wave bridge output.

    Camden County, NJ, USA
    19 SW285 panels
    SE5000 inverter
    grid tied
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    Oke, now we are getting some where :smiley: 
    The transformer winding's are be isolated from each other and for the problem of the peak voltage i was thinking of lowering the voltage from the generator a bit.
    The voltage regulators you suggest are very interesting and i wil look in to them.
    Only i think that when i can adjust the voltage from the generator a bit it , the resulting dc voltage should be relative stable.
    For a , lets say 0,5 v drop/rise on the dc side it would meen i have a voltage drop/rise on the genearator side of aprox 9,5 vac. I think that the generator avr wil keep that muts lower.
    But i also wil take a look at the voltage regulators.
    Thank's
  • BB.BB. Super Moderators Posts: 26,872 admin
    With gensets (AC), it is usually not very easy to hack a change to the regulated voltage with avr (the little I know).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    The gen-set i got now, is given to me because it was dead. After playing with it for 30 mins, i got it running again and found out that the avr was blow. i measured al the windings and it seems to be oke. i ordered a new avr for it and aspect it to get it deliverd ani time now.
    The new avr has a potmeter on it so i can adjust the output voltage from the generator. For now the question stil is how much i can change te voltage output.
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    This is the old blow avr, the little bleu potmeter is for voltage correction.
  • dennis461dennis461 Registered Users Posts: 85 ✭✭
    I'm starting to think you would be better off buying a 240VAC-24VDC 50 HZ battery maintainer.  Your transformer looks to be around 33 watts, pretty small. On e-bay for $13 US.
    Camden County, NJ, USA
    19 SW285 panels
    SE5000 inverter
    grid tied
  • RuurdRuurd Registered Users Posts: 15 ✭✭
    The transformer is 600va, i now this fur sure because the it came out of a old high amp 12volt battery charger. For now i am gonna build the charger/ balancer just like i drawn in the schematic. I have a lot of parts laying around in my shed, and why buy when i can build it ?
    In summer i got more than enough power from my solar set up, only in winter i got nothing.
    We have here already more than 3 weeks heavy overcast weather, and i need battery charging now. I DONT have the funds to buy a expensive battery charger, so i have to go this route. If i had the funds i would by this https://www.bluepowershop.nl/victron-multiplus-12-00-35-16.html. Also i would go back from 24 volt to 12v. i work in jacht building and 24v systems suck. The battery's always die prematurely vs 12v banks. The biggest killer is unbalance in the battery banks. I havent seen a good product to counter this, so i am gonna build my one.
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Very intersting charger module you linked to on ebay.  But it only talks voltage, and says nothing about how much charge current it can handle.  For battery charging, you want at least 10A, and to limit generator run time, 20A would be nice. 

    But there is a flaw.
    15V x 15A = 225w per transformer.   A transformer & rectifier type charger has a low power factor, so your 225w charger will end up consuming close to 350W from the Generator.  And then add the 2nd charger for the 2nd battery, need a generator good for 700W continuous.

    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

Sign In or Register to comment.