FLIR E series 12V Charger

[KenGaler]

Hi all,

I need a way to charge my E4+ while in the field and NOT using that way-to-fragile micro USB connector.  So, I decided to design and make my own charger and offer it as open source.  Attached is the initial schematic.  The plan is that this PCB will be mounted in a small 3D printed enclosure that fits on the end of the (removed from camera) cell. 

Bullet points:
- Powered by 7.5 to 20VDC
- Charges at 2A
- LEDs indicates GRN when charging, RED if there is a fault such as a bad cell or over temp
- When charging is complete, it's current draw from the source drops to typically 85uA

Once the PCB is designed I'll release the native files.  If there is enough interest I may offer the PCB stuffed with the SMT parts.

Feel free to comment or ridicule.    :-)

BTW:  Selecting a part in the pdf displays the part data and the links to the datasheet and supplier will open in your browser.

Regards,
Ken

[Bill W]

I'd have something else for D2, small shottky say as the datasheet says rate over 100mA.
Is the NTC in the FLIR battery what is expected by the IC ?

Why two inductors, just for layout ?  I'd take a look at Wurth.
Could put a divider onto SHDN in case the input goes low, if that is likely.


Bill
www.fire-tics.co.uk

[KenGaler]

The 4148 should be ok, it's rated at 200mA.  I originally had the same diode as D4 in there but changed it to make it smaller.

Yeah, the two inductors look weird, I want to keep all the parts (except J1) under the height of the battery connector of about 1.8mm.  I had to use two to make them small enough. 

Ken
 

[KenGaler]

I attached a preliminary placement 3D pdf and updated schematic.  I don't know of any pdf viewers that will work with 3D other than Adobe, unfortunately.   

Some mods, I changed D2 to a schottky as Bill suggested.  I was able to find one in a smaller package although after the placement it really doesn't look like I need to be that small. 

Added a minimal EMI filter just because I'd feel guilty if I didn't.  It's not a commercial product and I'm not designing to a spec but it would be better if it didn't radiate too much.

Added a heat sink that will be taped to the bottom of the PCB.  I was going to slide this assembly into the plastic enclosure but now I'll have to think of something else.

OH, yes, the thermistor on the FLIR cell does look like a 10K B=3380 NTC that the LT part is assuming. 

Regards,
Ken

[KenGaler]

This is how the board will mate with the FLIR cell assembly.

[KenGaler]

OK, so I built up the prototype and tested.  My initial tests were charging at only 950mA.  As it turns out R1 & R2 are a little more fragile than most resistors and one of them opened.  After replacing both I was able to get nearly 2A.  I removed C5 so that the charge terminates a C/10 (~200mA).  With it installed, the charge continues with a small current until the timeout at around 3 hours.

There's not a huge interest in this but it works for me and now I can charge in the car and without worrying about breaking the USB connector.

The source and output files are too big to attach here so if anybody wants them send me a message and I'll be happy to send them.

Regards,
Ken