We've got another thread similar to this one, and they both seem to be problems caused by a surge or lightning, rather than connector over-heating (i.e. cell drawing high current for a long time). related thread:
Got a few updates with @oakwater's iph board... it doesn't work (yet), but I got it to power up without making any more smoke! The relay coil won't operate the device and half of the contacts are toast (the rs485 "A" input is open while the "B" input is closed) so I pulled it to get a better...
www.troublefreepool.com
If anybody wants to try a repair... the input protection parts D3/D4 seem to be MCC SMAJ6.0CA devices ("tvs" diodes), the 485 chip is a ti SN65HVD485E, and the relay is an NA-5W-K (5v dpdt, but there are lots of substitutes). datasheets:
(mcc tvs)
https://www.farnell.com/datasheets/1684841.pdf
(485 chip)
https://www.ti.com/lit/ds/symlink/sn65hvd485e.pdf
(relay)
http://www.ic112.com/uploads/pdf/20171019/NA5W-K.pdf
I'm wondering if there'd been better protection on the 485 lines, then the parts listed above might not have died. Other folks have used 485 suppressors and I think one was from serialcomm... I don't know how well their units work, but they have gas discharge tubes as primary protection which is theoretically very good.
https://www.serialcomm.com/serial_r...85_surge_suppressor.product_general_info.aspx
These boards have good esd protection, but seem to have low protection from
large surge transients. I suspect D3/D4 (and the comm chips) are blowing up because when a large surge transient occurs, the tvs diodes (d3/d4) can shunt the voltage to ground, but there's nothing to limit or stop the current that's going to go through them... so they cook a little bit
This Analog Devices article has some good info (engi-nerdy but understandable) about electromagnetic events and how protection works:
Analog Devices, Inc., and Bourns, Inc., have partnered to extend their offering of system oriented solutions by co-developing the industry’s first EMC compliant RS-485 interface design tool that provides up to Level 4 protection levels for IEC 61000-4-2 ESD, IEC 61000-4-4 EFT, and IEC 61000-4-5...
www.analog.com