Adding to that, as somebody who’s spent a large proportion of their professional life doing industrial controls and automation, this is a primary consideration of any control scheme, you must design it - as far as possible - to “Fail Safe”, meaning that the unpowered state is that which is safe, or if you can’t be certain of that, the least likely to have dangerous consequences.
This is why motor starters always drop out when the mains fails and don’t restart automatically, but emergency lights are normally held “off” by a mains-powered relay (or equivalent) and the light comes on when the mains fails.
How to deal with the problem that when there is a load, the single battery undervoltage control relay disconnects the output. Because the load disappears, the voltage rises again, and the relay acts again. As a result, the relay is always in oscillation state
stuart
Found a software limitation “Pack over voltage (mV)” 65500. I have 20 cells 18650 = 84000 mV
When you enter a larger value, it writes what has been saved, when the page is refreshed, it writes other different numbers.
Many also talked about the problem of turning the relay on and off at the voltage limit values. In many systems, this is solved by two values. The first value is disable, the second is enable. Thus, by spreading these values among ourselves, we get rid of the problem of relay bounce.
Did you ever solve your issue with the CRC errors?
Similar setup to you, works fine when running on mains USB PSU, but get a few CRC errors when running on a stepdown converter connected to the batteries. Tried multiple converters and still same results.
As others have pointed out it could be your batteries, but yes, the rules need to have a recover value to prevent the oscillation. I made a version that had that with the rules, then rewrote that to be less generic. I don’t have rules, so much as I have max/min and recover settings for cells and the pack and temperature. Then you designate your relays to be either load or charge, and the logic of the code does the rest. You can also set the relays to respond to state of charge, but that’s only possible if you are monitoring current, which I am doing.
Just a note to say thanks mainly to Stuart and also others on here for all the work that has been put in over the last few years. I’m glad I hung in there as the v3 BMS nearly drove me nuts when it just wouldn’t communicate. V4 is so much better and improving all the time with the updates.
I started my battery storage project almost exactly 2 years ago when I collected my first cells from the local tip and started processing them. I now have just over 10kWh of storage in a 14s100p configuration though I’m only cycling about 40% of the capacity to prolong the life of the cells (all 1600mAh+ and 80%+ of original capacity still).
In the last 24hrs I’ve only imported about 0.25kWh hrs from the grid, roll on next summer!
My project is still a work in progress as I’ve not got current control of the Flatpack power supply implemented yet. This is also only a temporary location.
Hang in there everyone still working on their own build it is well worth it in the end.
