I'm following the constant current circuit in the datasheet but can't seem to get the current to stay constant for more than 5 seconds. I have a meter inline to monitor the current and it dips about 0.01A every 3-5sec. I have a heatsink on LM338 and resistor along with a fan. Temp on LM338 hovers around 30C and same for the resistor. I'm using a 0.24Ohm 100W resistor to try to get constant 5A out of it. Power supply is a Meanwell 25.8VDC 20A. Battery is 21.6V 4400mAh LiPo and has builtin cell balancer. I adjusted the PS voltage to ~27V to get 25.8V out of LM338.
Here's how I have it hooked up:
Power Supply V+ > LM338 VIN
LM338 VOUT > 0.24Ohm 100W Resistor > Positive terminal of the battery
LM338 ADJ > Positive terminal of the battery
Power Supply Ground > Negative terminal of the battery
The current should stay the same for at least 70% of the charge but it just keeps dropping as the voltage slightly increases. This results to the charging time being nearly 2 hours with the last hour or so doing pulling less than 0.30A when theoretically the charging cycle should be done in about an hour at the most. I tried stock power supply that came with the battery and the current stays at 3A for at least 40 minutes before dropping.
What am I doing wrong here? I got these LM338T's from Mouser so I doubt that they're fake. Am I going at this the wrong way and should use something other than LM338?
Any help is greatly appreciated.
Here's how I have it hooked up:
Power Supply V+ > LM338 VIN
LM338 VOUT > 0.24Ohm 100W Resistor > Positive terminal of the battery
LM338 ADJ > Positive terminal of the battery
Power Supply Ground > Negative terminal of the battery
The current should stay the same for at least 70% of the charge but it just keeps dropping as the voltage slightly increases. This results to the charging time being nearly 2 hours with the last hour or so doing pulling less than 0.30A when theoretically the charging cycle should be done in about an hour at the most. I tried stock power supply that came with the battery and the current stays at 3A for at least 40 minutes before dropping.
What am I doing wrong here? I got these LM338T's from Mouser so I doubt that they're fake. Am I going at this the wrong way and should use something other than LM338?
Any help is greatly appreciated.