Ok, my work asked me to design a charger for a sensor that is driven by a stepper motor. I accepted...but I think I'm a little over my head now.
I rectified the output of the stepper and fed it to a LM317. My goal was to maintain 5v and supply about 120 mA of current to charge a battery. The battery supplies a sensor that pulls about 50mA, which is why my current target was so small. I have several physical constraints limiting the speed that I can spin the stepper as well.
Before I had the battery selected, and the regulator in place, I ran some tests by putting resistors across the voltage to act as a load. I found that at 50 Ohms, I had about 6-7V and 150mA. Here are the issues:
Issues:
*I didn't account for drop out voltage. I am on the low end (mid 4's now) for voltage now that I have the LM317 added. Is there anything that can be done to minimize the drop out voltage?
*When the battery was selected, and finally attached it to the circuit, the voltage made large swings (-1V) which causes problems with the USB charger. Once the Voltage is out of range, the charger turns off. The only two things I can think of are: 1. Some sort of feedback issue due to the wrong capacitor ( I only had a 1000Uf sitting around) on the LM317. 2. The charger is drawing too much current, and without the available charge, the voltage is dropping. If it is number 2, how can I limit the battery so that it only tries to draw around 100mA? I need the battery to only draw what the 50 Ohm resistor was doing
I rectified the output of the stepper and fed it to a LM317. My goal was to maintain 5v and supply about 120 mA of current to charge a battery. The battery supplies a sensor that pulls about 50mA, which is why my current target was so small. I have several physical constraints limiting the speed that I can spin the stepper as well.
Before I had the battery selected, and the regulator in place, I ran some tests by putting resistors across the voltage to act as a load. I found that at 50 Ohms, I had about 6-7V and 150mA. Here are the issues:
Issues:
*I didn't account for drop out voltage. I am on the low end (mid 4's now) for voltage now that I have the LM317 added. Is there anything that can be done to minimize the drop out voltage?
*When the battery was selected, and finally attached it to the circuit, the voltage made large swings (-1V) which causes problems with the USB charger. Once the Voltage is out of range, the charger turns off. The only two things I can think of are: 1. Some sort of feedback issue due to the wrong capacitor ( I only had a 1000Uf sitting around) on the LM317. 2. The charger is drawing too much current, and without the available charge, the voltage is dropping. If it is number 2, how can I limit the battery so that it only tries to draw around 100mA? I need the battery to only draw what the 50 Ohm resistor was doing