[MN Driver]

When you say regulated, are you talking about during charging with a BMS shunting. ..or do you mean while you are driving there is extra sag in these two cells and your BMS is reducing the throttle input? Also curious about your driving style in terms of C rates and typical depth of discharge?

I'm curious because based on my experience with lithium cobalt I've seen increased cell impedance(voltage sag/spike under load/charge), cells running hotter due to that same reason, and reduced capacity over both cycles and time. I've been trying to observe LiFePO4 for the same but it's a 'time will tell' situation and none of us has driven enough to ever wear out a pack on this forum that I know of outside of the one guy who murdered his pack with a very small capacity pack driving aggressively at high sustained driving C rates after very high acceleration C rated with a motorcycle using some of the earliest buys of 40Ah TS cells. That really wasn't an age/cycles thing though because the cells were very hot after a drive and his abuse caused a few to vent on separate occasions after overheating.

Be sure those cells that are regulating have terminal connections that still tight and clean as there have been a few others who have reported issues and backtracked once they found loose connection(s). Monitor the terminal connections after a longer/harder drive if they are warmer than the rest it could be the cells are a little weaker as internal cell temps will be best expressed through the terminals, or an imperfect connection.

Thanks for the update.

 

[bruceme]

When you say regulated, are you talking about during charging with a BMS shunting. ..or do you mean while you are driving there is extra sag in these two cells and your BMS is reducing the throttle input?

Charging, I took the head unit off my miniBMS as I blew several of them.

I'm curious because based on my experience with lithium cobalt I've seen increased cell impedance(voltage sag/spike under load/charge), cells running hotter due to that same reason, and reduced capacity over both cycles and time. I've been trying to observe LiFePO4 for the same but it's a 'time will tell' situation and none of us has driven enough to ever wear out a pack on this forum that I know of outside of the one guy who murdered his pack with a very small capacity pack driving aggressively at high sustained driving C rates after very high acceleration C rated with a motorcycle using some of the earliest buys of 40Ah TS cells. That really wasn't an age/cycles thing though because the cells were very hot after a drive and his abuse caused a few to vent on separate occasions after overheating.

Over my pay rate... What I know is that the batteries don't appear to be getting "old" yet, they are middle-aged I believe, but as you say, time will tell. On "C" rates, I do 200A absolute maximum, 150A for a hill (3min), at 55mph, I do 100A sustained; 45mph, 80A. etc.

Be sure those cells that are regulating have terminal connections that still tight and clean as there have been a few others who have reported issues and backtracked once they found loose connection(s). Monitor the terminal connections after a longer/harder drive if they are warmer than the rest it could be the cells are a little weaker as internal cell temps will be best expressed through the terminals, or an imperfect connection.

Thanks for the update.

Yup I check them regularly. They are tight and the whole pack is hot when I get home, but I'll see if those cells which regulate first are hotter. I don't believe all cells are equal and eventually one or two will betray the pack.