I’ve thought about that. I agree that most of the battery charger ICs are designed to be part of a device like a tablet or laptop.
In the end, I may end up going with the flexible option.
Before I do that, I want to explore the more integrated parts to see if there is one I can make work.
I’ve already eliminated quite a few of the low part count ICs so because they don’t meet requirements.
Going the Arduino + power supply route puts the parts count up a lot and possibly the load on the Arduino. It means my code and external hardware is responsible for safety checks.
Some of the charger ICs have programmable temperature, voltage and time checks. They go into a fault mode if when any of the limits are exceeded.
Since I plan to have 4 independent chargers, part count is important.
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I’m impressed by just how few external parts the new charger ICs need.
This is an SLA charger I built in 2012. It charges a single 6V battery. Look at the parts count!!
OnSemi have a couple of parts that might have worked. They are in microscopic packages.
OnSemi also have a controler for next-generation power packs. Along with supporting the latest high speed charging protocols, the IC can communicate with the device it is charging.
It was interesting to look over but not useful for this project.
I’m sure we will see much smarter power packs in the near future.
I bought a Litokala 500 engineer from Alibaba for $14 shipped, taking one of them apart might be instructive. The insides of one of the USB doctor measurement devices might be useful too.
i ll check back in 3 months if the project is still going strong.
i will be off on Xmas season vacation until mid January, enjoying ski trip with family and friends.
I generally use Eagle early in the design process to get a rough schematic and block diagram. Eagle is a bit quirky but works better than any freeware I’ve tried. I also use LTSpice to simulate parts or all of a project. I don’t much care for the schematic capture in LTSpice. I often use Eagle to get my ideas down and then go on to simulations.
Cadsoft GMBH sold out to Autodesk last year. :cry: My Cadsoft EAGLE 7.4.0 doesn’t play nice with MacOS 10.12. :disappointed: I’ve installed Autodesk Eagle 8.4.3. I’ll need read up on what’s new and then merge my device library.
EAGLE 8.4 includes spice. I may stop using LTSpice and do capture and simulation in Eagle.
For those following along, here is the product page:
There are plenty of tutorials on YouTube and now support from Autodesk.
Are you making these to sell? Will you be sharing your Eagle files here? If you’re not doing this as a community shared project, then do whatever works best for you. If you ARE going to share the files, then it might be nice to keep in mind OSH Park pricing as well, which is $5 per square inch with free shipping for three copies on all 2-layer boards. A lot of members here use Eagle, and also OSH Park. With that fixed pricing, the smaller the design is, the better.
Mine arrived yesterday. They sanded most of the part numbers… I’m not going to post any images. There are a couple of videos on YouTube if you are curious.
It is about what you would expect. A micro controller for the display board and another one on the mother board. There are a few power transistors and chokes. The USB power out circuit is at the top by the jacks.
I made two design choices yesterday. Both are open for discussion. It is easy enough to undo this early in the design.
The LTC4015 can reduce charge current if Vin drops below a hardware set threshold. Typical use would be when Vin also powers a device. If the device starts drawing more power, the charger will throttle back. In this application, it would be used if we program a current that is too big for the power supply.
I decided not to implement under voltage current limiting. I will leave it up to the end user to source a suitable power supply. Leaving it out simplifies the board.
Cell count is set in hardware by three pins. The LTC4015 does not monitor individual cells and cannot balance a series string. I’m leaning towards hard wiring this to one cell only.
The other option would be to tie Cells 2 low with jumper selection on Cells 0 and 1. That would allow 1,2,3…6 all the way to 9 cells in series. 3 and 6 would be for 6 and 12V lead acid. If I do that, I’ll design for 15 or 20V Vin Max and 8A I charge max. The higher current would make this more useful for Pb batteries.