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bwilson4web · 08-05-2012, 03:28 AM

You're going after a 12V replacement and I'm going after a 48V eBike replacement for a lead-acid battery. In my case, this is my first thoughts:

Risky areas to resolve:

series shunt regulator - I've specified a 3.6V Zener but there is also a 3.3V that might be a better part. Bench testing will help resolve it. Also, I need to SPICE the Zener and current limiting resistor with both parts. From DOAX's charts, it looks like the 3.3V might be a better part because the current limiting resistor gives a slight, over-voltage to achieve peak charge.
MOSFET + Schottky relay - I may have the wrong symbol for the MOSFET and it isn't clear if I'll need a reverse biased Schottky to pass regen current into the string. I've also shown a directly driven gate and this might be a case where reverse bias of the MOSFET puts the gate and attached microcontroller at risk. My fall-back is a relay but "UGH!"
30A vs 50A - the eBike has a 0.5 hp motor which should be ~15A sustained but I haven't measured the peak current draw.

I haven't seen a series, shunt regulator like this before but it is an obvious solution. Using ordinary Zeners means I need to model the thermal effects. In theory, as the part warms up, the Zener threshold voltage should go down which increases the draw from the peak cells towards a normalized voltage for all cells. In other words, helping to level-charge the peak cells. The key will be a collective heat-sink for the 15 Zeners.

I have not show thermistors for cell-strings. If I can have one for each of the LC6803s, it should be fairly straight forward. I did go with Linear instead of the TI part because I only need two instead of three chips and it has a 1/4W, built-in, per-cell, MOSFET. After all, what is 'time' to a computer and it may be this low, rate might be enough for cell balancing and not require the series shunt.

Bob Wilson

08-05-2012, 03:28 AM	#53 (permalink)
bwilson4web Engineering first Join Date: Mar 2009 Location: Huntsville, AL Posts: 843 17 i3-REx - '14 BMW i3-REx Last 3: 45.67 mpg (US) Blue Bob's - '19 Tesla Std Rng Plus Thanks: 94 Thanked 248 Times in 157 Posts	You're going after a 12V replacement and I'm going after a 48V eBike replacement for a lead-acid battery. In my case, this is my *first* thoughts: Risky areas to resolve: series shunt regulator - I've specified a 3.6V Zener but there is also a 3.3V that might be a better part. Bench testing will help resolve it. Also, I need to SPICE the Zener and current limiting resistor with both parts. From DOAX's charts, it looks like the 3.3V might be a better part because the current limiting resistor gives a slight, over-voltage to achieve peak charge. MOSFET + Schottky relay - I may have the wrong symbol for the MOSFET and it isn't clear if I'll need a reverse biased Schottky to pass regen current into the string. I've also shown a directly driven gate and this might be a case where reverse bias of the MOSFET puts the gate and attached microcontroller at risk. My fall-back is a relay but "UGH!" 30A vs 50A - the eBike has a 0.5 hp motor which should be ~15A sustained but I haven't measured the peak current draw. I haven't seen a series, shunt regulator like this before but it is an obvious solution. Using ordinary Zeners means I need to model the thermal effects. In theory, as the part warms up, the Zener threshold voltage should go down which increases the draw from the peak cells towards a normalized voltage for all cells. In other words, helping to level-charge the peak cells. The key will be a collective heat-sink for the 15 Zeners. I have not show thermistors for cell-strings. If I can have one for each of the LC6803s, it should be fairly straight forward. I did go with Linear instead of the TI part because I only need two instead of three chips and it has a 1/4W, built-in, per-cell, MOSFET. After all, what is 'time' to a computer and it may be this low, rate might be enough for cell balancing and not require the series shunt. Bob Wilson __________________ 2019 Tesla Model 3 Std. Range Plus - 215 mi EV 2017 BMW i3-REx - 106 mi EV, 88 mi mid-grade Retired engineer, Huntsville, AL Last edited by bwilson4web; 08-05-2012 at 03:40 AM..