Hello,
In my project I need to charge 12V, 60Ah Lead Acid Battery, and I choose the BQ24450 to do the charge control.
The source will be 18V DC power, with a Imax=1.15A. That means Risns=250mv/1.15A=0.22Ohm.
Vth=10.33V Vth= Vref * (RA+RB+RC//RD) / (RB+RC//RD)
Vfloat=14.1V Vfloat= Vref * (RA+RB+RC) / RC
Vboost=14.4V Vboost= Vref * (RA+RB+RC//RD) / (RC//RD)
As it is obvious i decided to make the Charger with Pre-Charge at page 10 of the datasheet.
The value of the resistors are: Rc=47k; Rd=1.5M; Rb=18k; Ra=220k; Rt=510Ohm; Rp=15k
I choose the topology of External Quasi-Darlington, because the final objective is to have a 6.25A charger (Risns=0.04Ohm and Rp=2.7k).
The Led Status Driver was same use of other member os the forum, and i decide to use it (Car Battery Charger with BQ24459)
I mount the circuit, but i have a few problem, even without a battery on the connector the Vbat=18V, this is normal?
Then when I connect the battery, Vbat raise to 15V/16V, it seem that Vbat is still 18V with battery attach.
Can you help me to see where is my problem?
Thanks,
