fechter wrote: ↑
May 11 2018 8:35am
Just for comparison, the 35s version of a chinese LTO BMS goes for US $142.60. The 20s version is $127.88. Together, you could do 55s.
This is about the cheapest one I could find that would possibly handle 55s worth of LTO cells.
Option 3... (or maybe about my 9th or 10th option... I've lost count.)
The problem with two separate BMSes, is that it's harder than it looks to balance between sub-packs. So I with my 3 x 12S, If two of the packs were at the balance voltage, the third one would find it almost impossible to balance and be brought up with the other two. I'm not sure if that's because of some odd change of resistance issue, which causes most of the current to go off to the shunt resistors, rather than the cells acting as resistors.
However, I have seen whole battery balancers. So I do wonder if I made it say, 56S, and got two 30S BMSes then (running as 28S), then tried to balance at a pack level as well as a cell level, whether this would make the above problem a bit easier.
I can't find one for high voltage packs at the moment, but they claimed that any time there was ever more than a 100mv difference between the batteries, it would shunt power from the higher to the lower, completely isolated, so the battery could even be in use while this occurred.
All that said, my favoured solution is currently the Supercapacitor balancers. I'd seen them in 6 strings before, and assumed they were like a 6S BMS, but seeing them in single capacitor formats, makes me think that they are effectively just a cheap but better version of what I am trying to do with the Zeners - a blind and dumb circuit to waste off energy as soon as the trigger voltage is hit.
eBike: Q100H on 16S with Phaserunner FOC Controller
eMotorscooter: Vectrix VX-1 on 36S
eCar: Mitsubishi Outlander PHEV... Waiting for warranty to expire
eHouse: Still on grid, but with LTO batteries and 3kw LF inverter...
After 5 builds, the best advice I can give, is start with high quality products. I prefer http://www.ebikes.ca