Yikes. Ok, I’ll scrap that idea. I may end up using two voltage boosters and alternate in between the two as needed in lieu of a digital pot.
The project is for a motorized dome door opener for an observatory (a new, and rather large, refracting telescope at the South Florida Science Center). The entire observatory has been overhauled and it fell on me to upgrade the dome door from hand operated to motorized and remote controlled. The motorized and remote-controlled part of the project has been fully completed. But I still need to solve the battery charging part of it.
To fully understand the project you’ll need to read what I posted about it on reddit (it’s a quick read): https://www.reddit.com/r/arduino/comments/fadh6a/arduinoenabled_observatory_dome_door_opener/?utm_source=share&utm_medium=web2x
However, I still need to be able to charge the batteries without getting up on a ladder every time and hooking up the charger to the two terminals. As I’m sure you would know a dome in an observatory is usually rotating while tracking stars, which eliminates the option of having the motor controller for the dome door permanently plugged in to an AC outlet (hence the need for a battery-operated system). Also, since time and money are a constraint, a copper or metal track installed on the perimeter of the dome that provides the necessary power to the motor controller (through a sliding contact) would be unfeasible and probably unreliable.
Two options come to mind:
- A small solar panel outside of the dome that charges the 12V batteries, or
- A Qi charger inside of the dome. The transmitting coil is stationary and the receiving coil would spin with the dome. When the dome is not being used, it is returned to it’s home position (where the two coils are side by side) and the batteries are charged.
I opted for the second option. The Qi charger I purchased is giving me 12V. I needed the voltage booster to get it up to 14V to charge the batteries, but I also need to reduce it to around 13.8V or 13.5V to give it a floating charge once the batteries are fully charged (this is where I was looking at the digital pot option). However, I can simply use two voltage boosters and switch in between them with a relay shield once the battery has reached a certain voltage (I bought a high-precision voltage sensor to tell me when this should be done).
I would have saved myself the headache by buying a charger off the shelf. But the problem is those chargers are AC to DC, and the Qi chargers obviously only provide DC. So, in summary I’m trying to build a battery management system that runs solely on the DC provided by the Qi charger. I think I’m almost there but I’m open to any other ideas on how to do this.
If you or anyone has a better idea I’d appreciate your thoughts and inputs.