Jack.Straw
Member
Hello. I am wanting to build a battery charger for a project i'm working on. First, the details:
Charger IC: MAX712 Data Sheet
Battery Pack: 6 AA Rayovac Hybrid NiMH 1.2v, 2100mAh
Power Supply: **broken link removed** - 19vDC 3.42A
Intended Charge Rate: 1C using voltage slope detection
There are a number of calculations on the MAX712 datasheet that i'm not 100% sure about. Can anyone confirm these values for me?
**broken link removed**
R1:
R1=(minimum wall-cube voltage - 5v) / 5mA
Is 19v my "minimum" wall-cube voltage since it's a regulated power supply? Assuming the answer is yes: (19v - 5v)/5mA = 2.8k ohm resistor?
Rsense (current sensing resistor):
Ifast=(capacity of battery in mAh)/(charge time in hours)
Ifast=2100mAh/1 hour = 2100
Rsense=.25v/Ifast
Rsense= .25v/2100 = .000119 = .119 ohm resistor?
PNP (Q1)
PDpnp = (maximum wall-cube voltage under load - minimum battery voltage) x (charge current in amps)
The 2N6109 on the datasheet shows a max of 40, but i'm worried about heat. Will a normal TO-220 heatsink like the one below be enough??
**broken link removed**
PGM Settings:
PGM0/PGM1 - Open/Open (6 Cells)
PGM2/PGM3 - Ref/Ref (90 min timeout w/ voltage slope enabled)
Other values (defaults):
Vlimit = Ref
TLO = Batt-
C1 = 1uF
C2 = 0.01uF
C3 = 10uF
R2 = 150 ohm
R3 = 68k ohm
R4 = 22k ohm
D1 = 1N4001
Thank you for any advice you can offer!
-Scott
Charger IC: MAX712 Data Sheet
Battery Pack: 6 AA Rayovac Hybrid NiMH 1.2v, 2100mAh
Power Supply: **broken link removed** - 19vDC 3.42A
Intended Charge Rate: 1C using voltage slope detection
There are a number of calculations on the MAX712 datasheet that i'm not 100% sure about. Can anyone confirm these values for me?
**broken link removed**
R1:
R1=(minimum wall-cube voltage - 5v) / 5mA
Is 19v my "minimum" wall-cube voltage since it's a regulated power supply? Assuming the answer is yes: (19v - 5v)/5mA = 2.8k ohm resistor?
Rsense (current sensing resistor):
Ifast=(capacity of battery in mAh)/(charge time in hours)
Ifast=2100mAh/1 hour = 2100
Rsense=.25v/Ifast
Rsense= .25v/2100 = .000119 = .119 ohm resistor?
PNP (Q1)
PDpnp = (maximum wall-cube voltage under load - minimum battery voltage) x (charge current in amps)
The 2N6109 on the datasheet shows a max of 40, but i'm worried about heat. Will a normal TO-220 heatsink like the one below be enough??
**broken link removed**
PGM Settings:
PGM0/PGM1 - Open/Open (6 Cells)
PGM2/PGM3 - Ref/Ref (90 min timeout w/ voltage slope enabled)
Other values (defaults):
Vlimit = Ref
TLO = Batt-
C1 = 1uF
C2 = 0.01uF
C3 = 10uF
R2 = 150 ohm
R3 = 68k ohm
R4 = 22k ohm
D1 = 1N4001
Thank you for any advice you can offer!
-Scott