Where to place a power meter in a solar battery charging circuit

Thread Starter


Joined Apr 26, 2016
I have a very basic question about solar charging. I'm constructing a low-power, 12V portable solar charging system with a 4.5Ah LiFePO4 battery. My controller has panel, battery and load terminals. Ideally, I would like to place an inline watt meter, like the Watt's Up or Powerwerx, between the controller and the battery, where it would monitor both charging and discharging. However, I don't believe this type of power meter can support current flowing in both directions (i.e., one way while charging, the other while discharging). So, I could monitor either panel power generation (because the controller protects against reverse current from battery to panel) or load power consumption (because my load won't ever be a current source). But I couldn't monitor battery power bi-directionally as I would like to. Do I understand this correctly?


Joined Mar 19, 2016
Generally speaking, you would want to measure the power that is coming in from the solar panel cause that is what can fluctuate. In case of discharging, you can always "predict" what will be the discharge rate since normally you draw power from a battery at a constant rate, the notable exceptions being variable loads like motors with speed governors, which I don't think you are driving, are you? Hence you normally wouldn't want a power meter at the output side unless there is a specific need to.

As for your question, I do not believe that you can monitor power bidirectionally with the watt meters you have mentioned.