I used the TPS55340 in a 14 pin HTSSOP package with 0.65mm lead spacing on my BMS PCB. This thing has a thermal solder pad on the underside so is not easy to hand solder.
My solution was to purchase a cheap hot air re-work station off ebay. This works like a dream. You even see the little jiggle that occurs when components self-align as they go through the re-flow oven. Brilliant.
The 2mm JST PH series connectors are cheap (at least from China) they also have a 2A current rating.
You can also buy really cheap ready made 4 pin cables in bundles of 20 or 50 for a few pounds - which saves a heck of a lot of soldering/crimping!
I suppose on future boards, I can add on holes for mounting both spacings and the end user can pick the best for their needs.
If you haven’t noticed, I focus on cost quite a lot !
Do you have a link to this?
I’m with you there, i guess it’s just because all the stuff i work with is 2.54mm pitch so have lots of those lying around already. I priced the parts up for aliexpress vs farnell and it was a good £10 cheaper for everything but i’ve gotten 300 of each resistor/capacitor rather than 20 from farnell.
I brought a resistor sample book for $15 - it has about 30 resistors of every size and value - about 3000 resistors in total!
These are good quality connectors for the 2 pin input power connector…
This is the model but I forget which seller I used.
The price is crazy cheap but the hot air and the soldering iron both work very well.
I recommend you practice on some scrap before trying for real. The common mistakes are too much air and/or too much heat.
Too much air and the components become airborne. When you find the optimum settings start about 150mm from the target and move in slowly. This allows the PCB to get up to temperature without roasting the components.
Flux is very important. I use a no-clean low viscosity product from CPC.
Brian
Hi Brian, Looks a good iron, does the soldering iron come with just the one tip? I’m wondering if the hako tips work with it.
Col
There is a spare heating element but I think only one tip. (Must have a tidy up in the workshop)
Got chance to spend some more time on this tonight, so the web interface now has:
That looks really good Stuart!
I have some questions:
Hi @BrianD
I’m also pushing the voltage and temperature values over WIFI to emonCMS which can then be used to provide other graphs etc.
Going to have a go at writing the cell balancing code tonight!
Thanks @Stuart.
OK, I also have 4mV resolution (10 bit ADC on the Mega 328).
I also used an oversampling technique but the repeatability was not good. I consistently measured deviation of 10 to 20 mV.
After posting a request on the arduino forum I received some excellent advice from Tony Wilk who wrote a short exponential filter for me. This improved things significantly.
Here is a link if you are interested: Arduino nano A2D - Programming Questions - Arduino Forum
Thanks for that I’ll take a look at the code. I also get some bounce in the readings, however it won’t really affect anything, you are never going to get 100% accurate balancing with the type of circuit I’m looking at - and most cell manufacturers specify 0.1V maximum out-of-balance so not a problem really.
Agreed, in your case with only one cell it’s less of a problem. With eight series connected cells I have a cumulative error which can add or subtract the error of each cell.
The only published data I have seen regarding constant current cut off voltage is 4.2V +/- 50 mV
Have soldered one up, just missing the leds. Need to get some more ceramic resistors, just placed it there for the pic. Soldier paste isn’t here yet so did it by hand just to get going.
Wow, great to see another one in the wild!!
Let me know if you have some missing parts and I’ll post you some!
I’ve built another 4 modules today, took about 2 hours all manually soldered using paste and a hot frying pan!!
2 of the 4 didn’t work, so I unsoldered the CPUs (destroyed them in the process) only to find a wire in my Arduino programmer had broke off 
so the boards were fine.
Reminder to myself to check the obvious things first
Bummer on the cpu’s, hard to desolder in one piece though. Do you have any images of your soldered boards? I’ve only gotten one done as i was waiting for the solder paste to arrive rather than do any more by hand with the soldering iron and not having much luck so far. I’m wondering if i’ve read the circuit diagram correctly for the placement of the component orientation.
It does thanks, is the REG710NA-3.3 pin one nearest the R11 text?
