Motor heat comes from the copper resistance, which is current ^2 * resistance. There’s a little bit of heat that comes from the mechanical friction of the bearings and stuff, and yeah that will go up with extra motor rpm, but that’s pretty negligible in comparison to the wire heating. Since the voltage is higher by 20 percent, for the same wattage on a 12s system the current is only 80 percent. So the heat is 0.8^2, or 64 percent the heat generated by the 10s setup.
You could totally reduce the number of cells in parallel, reduce total system weight, all without reducing battery range or max power. Let’s say you have a 10s6p system and reconfigure to 12s5p. Same 60 cells, same weight, same electrical wattage. You lose max battery current, but make up for it with mechanical gearing, so there’s no torque penalty. And because you’re drawing less current to make the same torque, you make less heat and can actually downgrade your motor to a smaller, lighter one without losing performance. You could drop from 6374 (with 80A max current) to 6354 (with 70A max current) and save 300 g/0.8 lb per motor, without any loss in performance! I think anyway, I’m ignoring motor wattage specs here because they confuse me. 1000W is VERY different at 3s than it is at 12s. I think the wattage specs are likely just kind of made up marketing numbers, even more so than the other technical specs. Itd be awesome if someone could clarify this though.
@Hummie, can you walk me through the no load thing? I don’t know how that works.
VESC can’t handle 12s? That’s a pity, hopefully the 6.0 starts getting accessible soon!
It’s not a bottle neck. Texas Instrument’s DRV830x chip is currently the only chip on the market to run with a max 60V. You have to go for a different design and topology using dedicated mosfet drivers and a 12V circuit to drive higher voltages and currents.
It is the part of the design constraining it to 60V. That’s literally what “bottleneck” means, because this thing replaces all that but only goes up to 60V
@Jmding… the KT constant is torque per amp… so the torque is directly proportional to the motor current, not the battery voltage. you cannot expect the same torque with 80% of the motor current by increasing the voltage from 10S to 12S.
for example 10S vs 12S, 60a motor current limit, 60a battery current limit, full throttle acceleration – during acceleration you get the same torque, same heat and same efficiency from both motors, but the 12S can spin faster.
12s fully charged is nearly 10v short of the drvs voltage limit. If the vesc cant handle 12s its not because of the drv. Ive been running 12s now for hundreds of miles, however i use active cooling with increased capacitance too.
This is 100% false. I’m not going to repeat this very many more times unless I start invoicing for my time. If you’re not an electrical engineer yet are speaking as-if this is fact, then maybe take a step back.
Firstly, when you are driving inductive loads (like motor windings) the voltages spike plus and minus when fed with square waves.
Secondly, most consumer goods are designed to operate at about 60% of their ratings. This means things keep working. When unexpected things happen, there is room. Things like automobiles and things where safety matter a lot more use bigger margins. So using that formula, it’s only good for 8S. So 10S is even pushing it. For something your life could depend on.
Feel free to push this 12S thing all you want but when you hurt yourself because you don’t listen, I won’t be there for you. When other people hurt themselves because of your bad advice, that’s between you and them.
Also, if you jumped off a bridge and lived, it means I can jump off a bridge and live too.
My first build was 12s with Car esc’s and I had a lot of problems with overheating motors and electronics.
When I switched to Vescs, I also switched to 10s and have not had any overheating problems since.
I did have a lot more power with 12s and the esc’s. So much that it was hard to control.
The Vesc/10s setup was much tamer.
Well I have to recant my statement because there is now documentation for a 100V DRV835X.
Now the bottleneck it the max voltage of a BLDC motor. It’s great, but Gate Drive is 1A and the buck regulator can only output 350mA because of the high voltage.
I have a couple of 12s builds on older vescs(Chaka and enrtion, way before focbox) and they are still alive(knock on wood). But I’m not an engineer or even close to that. Must have gotten lucky with my vescs if they weren’t rated for what I was running them for.
I care about people’s safety and if you were going around suggesting to folks they can safely jump off bridges, I’d do the same thing. It’s not “condescending”. It’s “being responsible and caring”.
@chuttney1 What about the LM5109 drivers? 100v max. It is not integrated like the DRV so you need 3 if my memory is correct. But it works, I do have 2x VESC built with this at home. It just didn’t receive love from the community.
I think it was stated that the DRV is being run in the VESC above “safe” limits above 40v no? But a lot of people are able to run 12-13s safely with the new ones. So why not.
Anybody here is able to run high voltage without safety. Then A lot of people are able to run 12s and recently 13s without reporting blown ESC during ride after many miles, which I deem safe to a certain extent.
