Hello, First post here, but have visited many times in the past.
Working with MAX712/713 to charge 1 NiMH Panasonic HHR-75AAAB cell (750mAh). I am able to charge the battery with the base circuit provided, with some modification.
1. Manual for the charge controller indicates a minimum charge block output of 6V. Most phone chargers I have are rated at 5V, 9V and 12V DC. When the circuit is plugged into this charger, the output is just under 5V DC (cheapo DMM, not oscilloscope) and the circuit charges the battery.
How do I interpret this requirement correctly? Do i need a charge block that will only output above 6V?
The given conditions make it impossible to calculate R1. I have tried changing R1 resistance until i get at least 5mA at V+, but the resistance needs to be dropped to nearly a short circuit to get this result. I suspect things are functioning as intended and I need to bump up the input voltage. Currently, am charging with ~2.5mA to V+.
2. I am trying to achieve the 450mA of current to the battery (as per battery fast charge spec), and am able to achieve this with RSense=~0.7 Ohm. This is derived from manual formula. Concern is that resistor Q1 gets hot to the touch after several minutes of operating (~70-80C, temp does not run away), I have it at about 250mA charge now and the heat does not build in the transistor at all. The transistor is rated to 165C, but It doesn't mean that it should dissipate that power. Maybe this concern is a result of the power requirements.
Thanks in advance!
Phil.
Working with MAX712/713 to charge 1 NiMH Panasonic HHR-75AAAB cell (750mAh). I am able to charge the battery with the base circuit provided, with some modification.
1. Manual for the charge controller indicates a minimum charge block output of 6V. Most phone chargers I have are rated at 5V, 9V and 12V DC. When the circuit is plugged into this charger, the output is just under 5V DC (cheapo DMM, not oscilloscope) and the circuit charges the battery.
How do I interpret this requirement correctly? Do i need a charge block that will only output above 6V?
The given conditions make it impossible to calculate R1. I have tried changing R1 resistance until i get at least 5mA at V+, but the resistance needs to be dropped to nearly a short circuit to get this result. I suspect things are functioning as intended and I need to bump up the input voltage. Currently, am charging with ~2.5mA to V+.
2. I am trying to achieve the 450mA of current to the battery (as per battery fast charge spec), and am able to achieve this with RSense=~0.7 Ohm. This is derived from manual formula. Concern is that resistor Q1 gets hot to the touch after several minutes of operating (~70-80C, temp does not run away), I have it at about 250mA charge now and the heat does not build in the transistor at all. The transistor is rated to 165C, but It doesn't mean that it should dissipate that power. Maybe this concern is a result of the power requirements.
Thanks in advance!
Phil.