Best and fastest lifepo4 charger

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nschizzano
nschizzano Registered Users, Users Awaiting Email Confirmation Posts: 24 ✭✭
in General Solar Power Topics #1
Regarding a charger from the gasoline generator. What is the best and fastest charger for this 200AH 12V battery? 100a will work?

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Here are the charging parameters ⚡️ 

Charging Limit Voltage: 14.6V
Over Voltage Disconnect Voltage: 15V
Over Voltage Reconnect Voltage: 14.2V
Equalizer Charging Voltage: 14V
Float Charging Voltage: 13.8V
Boost Charging Voltage: 14.4V
Boost Reconnect Charging Voltage: 13.2V
Low Voltage Disconnect Voltage: 10.8V
Low Voltage Reconnect Voltage: 12.4V
Under Voltage Warning Voltage: 11.6V
Under Voltage Warning Reconnect Vltg:12V
Discharge Limit Voltage: 10.4V
Over Discharge Disconnect Voltage: 10.4V
Over Discharge Reconnect Voltage: 11.6V
Over Discharge Relay Time: 0.8s
Equalize Durration: 120MINS 
Boost Durration: 120MIM

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
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    It seems that your 200 AH battery will take 100 Amps for 120 minutes (2 hours)...

    To figure out what size Genset... In general, I would suggest that you load your Genset to 50% (for fuel efficiency) to 80% (to avoid overheating Genset) of rated capacity--For typical AC generators... If you have an inverter-generator (the Honda, Yamaha, etc.) then you can get down towards 25% loading and still be relatively fuel efficient.

    So, for a 100 Amp @ 14.4 volt battery charger, assuming 85% "efficiency" (could be 90-95%, or could be worse--Need specifications for charger)--The math would look like this:
    • 100 Amps * 14.4 VDC = 1,440 Watt output
    • 1,440 Watt output / 0.85 generic "efficiency" = 1,694 Watts (or VA--Another discussion)
    • 1,694 Watts/VA / 0.50 minimum suggested Genset loading =3,338 Watt/VA maximum fuel efficient Genset rating
    • 1,694 Watts/VA / 0.80 max suggested Genset loading = 2,118 Watt/VA minimum longer life Genset rating
    • 1,694 Watts/VA / 0.80 NEC derating for continuous current branch circuit (keep wires/plugs cool) = 2,118 Watts/VA rated branch circuit W/VA
    • 2,118 Watts/VA / 117 VAC =  18 Amps ~ 20 Amp minimum suggested breaker/branch circuit wiring
    Note that Battery Chargers can wildly vary in their AC to DC "efficiency"... You have transformer types (typical/older DC battery chargers) that can be less than 85% efficient. And there is the "VA" (volts*amps) rating--Or power factor which can get down into the 0.65 or 0.60 "efficiency" (power factor is when the AC voltage/current is drawn in less than "perfect 1.0 sinewave" and draws more "current" that is needed for Watts)... As an example:
    • 1,440 Watts / 0.60 PF/Efficiency power supply / 2,400 VA (many gensets max VA = Max Watts)
    • 2,400 VA / 117 VAC = 20.5 Amp RMS draw
    • 20.5 Amp RMS draw / 0.80 continous current NEC derating = 24.5 Amp RMS rated branch circuit = 25-30 Amp rated branch circuit...
    Most home loads will load a genset to 50% or less of rated power for average loads... A refrigerator may draw 120 Watts running, and 600 Watts starting (a few seconds)... And "frost free" fridges may have a 500-600 CalRod heating element for defrosting...

    When charging a large battery battery bank, the discharge battery can hold charging current for 2 hours (100 AH rated in your case) or longer (5 hours for a 20% rated charging current from near dead)... So that can push the wiring/plug temperatures quite high... And for NEC (north American codes), continuous current draws are derated by 80% (or 1/0.8 = 1.25x larger branch circuit) for longer branch circuit life.

    Gensets will, mostly, consume fuel based on Watts & Watt*Hours used), but the wiring/alternator should be rated on VA (they higher current for "poor power factor" loads causes wiring in alternator to run "hotter"). The rough conversion between Watts and VA:

    VA * Power Factor = Watts
    Watts / PF = VA

    Power factor typically runs from 0.50 to 1.00 for "typical home" AC loads... A filament lamp = 1.00 PF. The old CFL lights, many ran at 0.50 PF (very poor). A typical AC induction motor can be 0.65 PF.

    The PF for a battery charger can vary between 0.6 and 0.8 and I would start with 0.85 for an "unknown" type PS. It just depends on the charger's design. Newer "electronic" based chargers tend be be more efficient (upwards of 95% efficient)... Older designs can be much less...

    For more (and very interesting) information on AC generators--This is a very nice link:

    http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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