I want to make a Li-Po battery charger using the Fez Domino (or Panda) to charge an on-board battery. The theory is pretty well known…
My question is if I’m looking for trouble here. What are the things I should watch out for (other than the danger of an exploding battery).
To make it even more interesting, I’d like to charge a 8.4V battery from the Usb port. This means I have to make a boost converter as well. It seems doable with the PWM and A/D ports - but I don’t know if the sampling rate is quick enough for this kind of thing.
Anybody else tried this before in managed code?
Before you ask why I’m not using an off the shelf chip, two reasons:
- I looked at BQ24115 - and got samples. It is ridiculous to try and work with on a DIY PCB.
- The Panda has all the peripherals and theoretically I have the programming skill so why not?
Rudie
With millions of handheld devices on the market, this is a very common need and expect many companies to offer chips to do just that, take USB and charge battery.
If you charge a two cell pack then you will need to also balance the two cells, ie, measure both cell voltages and keep them the same. This is to prevent one cell from charging faster than the other.
Yes, the off-the-shelf chips can be a pain. But I would say that that is the safest. The one I use only needs a current set resistor, everything else is taken care of. It is small and a pain to work with though. See MAX8601 for instance. Most of the connections are feedback. It is linear and for one cell though.
You don’t have to look at a boost converter too, you can change that buck converter in the document to a boost converter, then you still have more or less the same number of components.
You will probably have to amplify the current feed back.
Do not expect to do much else on the panda while doing this.