Hi,
After a several page search, I didn't see this brought up so I thought I would start a new topic. I am designing a circuit that is powered by a 12V lead acid battery with solar assist. A 2W panel is attached to basically trickle charge the battery during the hours of sunlight and use the battery at night or bad weather.
I have the EVM for this chip and I have made a couple of modifications to suit my needs. I decreased the maximum charge current to 200mA, increased the regulation voltage to 13.7V and tried to adjust MPPSET to 17.0V. I only have resistors to make 16.2V or use the default 17.8V but that hasn't been the issue yet.
I have an ammeter in series with the battery to monitor the current going in and out. When the solar cell is fully covered, the drain on the battery drops to about 40uA which is fine. If I partially uncover the cell enough to generate some voltage, but not enough to charge, the BQ24650 starts pulling current from the battery. It uses between 2 - 7mA which is no good. I need to sustain that off current. With the panel fully exposed in the sunlight, charging happens properly.
Previously, we have used an off the shelf controller and I built a FET circuit to completely disable it when solar voltage output was too low. This allowed me to achieve just a few microamps of drain, basically just pull resistors and FET drive. Now we are integrating a controller into our own design and things must change. This chip looks fantastic, but I really need it to shut off when charging isn't happening.
Can anyone recommend a solution? Worst case is that I put my custom FET circuit on this design to force the ~CE net low (copying the ~CE jumper on the EVM). My circuit always required us to adjust a pot in sunlight to set the active point for charging. I was hoping to use a smart chip that handled all this on its own.
Thanks so much!
Michael