Measuring the current directly is infeasible, due to the very large current range as well as the short duration of the high current pulses. A simple solution however is to measure the current through a RC filter circuit as shown in figure 1.
|Figure 1. Measurement setup.|
There are a couple of things to consider though when doing this.
- The time constant of the RC filter needs to be much longer than the measurement period of the multimeter used
- Electrolytic capacitors initially exhibit large non-constant leakage currents
- Resistive voltage drop
The leakage current of electrolytic capacitors may require a long time to stabilize. After 24 hours of operation my bank of 15000 uF still had 500 nA of leakage, but decreased to around 40 nA after 48 hours. Constant leakage currents due to the measurement setup are simply subtracted from the measured average current.
I've never had a problem with any significant voltage drops with this setup. However, the voltage drops can be made smaller by increasing the capacitance. Notice that the average voltage seen by the load is still dependent on the average current and the resistance.