LiFePO4wered/USB

A complaint I sometimes heard about the LiFePO4wered/USB (the only complaint really) was that the battery didn't fit well in the battery holder. This was definitely justified: being a perfectionist myself, it was something that bothered me as well.

There's a solution now: all new units will be shipped with a new battery holder and cell that provide a much better fit:

The new cell is smaller (shorter) because it has a flat top instead of a button top. The old battery holder had a reverse polarity protection feature in the plastic, and although the new cells seem to work in it, the feature is really designed for a button top cell. So I decided it was safer to switch to the new battery holder I've been using for the #LiFePO4wered/Pi and also use it for the LiFePO4wered/USB now.

The only relevant difference (aside of a much better looking unit :)) is that the battery holder pins are shorter than they used to be. I already altered the product brief to allow for the variation in physical dimensions a while back.

Since I am using a contract manufacturer that's right here in town (Colorado Tech Shop), I asked them if I could come over to observe when my panels were assembled, and they graciously permitted me to do so. Below is a video compilation showing some of the assembly process:

Thanks for sharing some of your experience with me Luis! :)

I now have 300 LiFePO4wered/USB boards with the thermally improved layout that is needed to build the #LiFePO4wered/Pi. They are also available for your own projects on Tindie!

Because of my continuing development of the #LiFePO4wered/Pi, I have ordered new LiFePO4wered/USB panels with the new thermally improved layout. Read the details here!

Since not everyone is following both this and my #LiFePO4wered/Pi project, I'll add a log here to link to a cool new development for the LiFePO4wered/USB. To deal with heat dissipation issues limiting the charge current for the #LiFePO4wered/Pi, I made a thermally improved layout of the LiFePO4wered/USB board.

Check out the thermal images in this project log!

Jeff Crystal from Voltaic Systems was nice enough to send me a 3.5W and 6W solar panel to experiment with. Since these are bare panels, I was pretty sure that connecting them directly to the LiFePO4wered/USB charger was not going to work well. For one thing, the unloaded output voltage of the panels is 7V, and the MCP73123 enters overvoltage protection at 6.5V. So once charged, and not loading the panel, you could end up in a situation where the battery wouldn't be charged again because the panel's voltage was too high. It would be flaky at the least. So I decided to add a buck regulator to keep the voltage at 5V and below.

It still didn't work well. The system would end up in a hiccup mode. The charging chip would decide the voltage was high enough, turn on the charging current, which would make the voltage sag, and the chip would stop charging. Over and over.

The problem is that the LiFePO4wered/USB uses a fixed charging current, set with a resistor. So I decided to add a little transistor current source circuit connected to the PROG pin of the charging chip to see if I could make the charge current dependent on the input voltage, so the charger wouldn't instantly dunk the panel voltage when starting to charge. It seems to work great!

I will need to do some more testing with this, but it could make it possible to add a solar option to the LiFePO4wered/USB in the future.

LiFePO4wered/USB is in the @tindie #CyberMonday newsletter!

Only today, it's $2 off with code C73700C.

https://www.tindie.com/products/xorbit/lifepo4weredusb/

For anyone who is interested in buying the version with soldered tabbed LiFePO4 cell, it is now live on Tindie! :)

LiFePO4wered/USB with tabbed LiFePO4 cell

I got a battery spot welder, so now I can weld on my own tabs for a version without the battery holder! Lighter, more compact (reduced height), better looking. Coming soon to Tindie. :-)

LiFePO4wered/USB is now open source hardware! The Eagle design files were uploaded to Github, and I just added a link to the project. Enjoy, and don't forget to support my development by buying some on Tindie! :-)