Advantages of 10s?

Jmding · August 23, 2018, 6:17am

10s builds seem really popular, but it seems like 12s has a lot of benefits. The extra voltage means you can gear down 1.2x more, so for the same torque you only need about 80 percent the current, which means your motors are only subjected to roughly 64 percent the heat. That should pay off huge in long term durability, not to mention the instant 20 percent bonus in torque. Is it the erpm limit on the VESC that keeps us from going 12s? The more expensive BMS?

Adam0311 · August 23, 2018, 6:26am

true and many builders swear by 12s. Personally I’ve mostly used 10s because you still have a ton of torque and power using 15/36 gearing on 80-90mm wheels and it’s cheaper, lighter, requires less space. Also, unless you’re really heavy Or ride really long hills, the heat isn’t much of an issue with 10s and proper gearing.

Hummie · August 23, 2018, 6:40am

theres no less heat in the motors running 12s instead of 10s. less current taken from the battery for the overall same wattage yes but “motor amps” will be different than the amperage that comes from the battery. on your vesc you can set both motor and battery amps. if anything it would probably be slightly less efficient running 12s as youre riding further from the no-load speed which is most efficient.

youre less likely to blow up your vesc running lower voltage.

chuttney1 · August 23, 2018, 7:13am

I don’t think you mean lighter if you use 50 to 60 cells for a 10S5P or 10S6P versus 12S2P or 10S3P.

b264 · August 23, 2018, 7:14am

The components in the VESC are not designed to be run at 12S

Adam0311 · August 23, 2018, 2:19pm

I do mean lighter. The question is 12s vs 10s. the OP wasn’t suggesting using smaller P groups for the 12s.

AlanZhou · August 23, 2018, 2:34pm

Also 10S is way more than enough torque for most people unless your 250 Pounds and try to climb 30 Grade hills

Jmding · August 23, 2018, 3:19pm

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!

Hummie · August 23, 2018, 6:22pm

Jmding:

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.and there’s also the iron losses too which are solely rpm dependent. with the little motors we have much more so copper losses and ideally, if we were more interested in efficiency, we’d use bigger motors, to have thicker wire in there, and fatter wire with less resistance, or the other option would be to spin it faster, less torque and more speed, and thats when you will hit upon the iron losses increasing, hysteresis and eddy currents 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.strong text your copper losses formula is good but remember the current going to the motor is not the same as that is coming from the battery and its effectively transformed especially at the lower speeds/duty cycle. you will need the same current in the motor to get the same torque results regardless of the battery voltage. no free lunch with high voltage…or you could get an esc that could take a 300v battery and theoretically have a cool motor but not possible. the esc makes an “effective voltage” using pwm, flickering the on and off, and that is the voltage the motor sees. that’s what drives the current

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.yea specs are empty air and would depend on the motors ambient temp and what the magnet’s currie (demag) temp would be and what is considered an acceptable max temp

@Hummie, can you walk me through the no load thing? I don’t know how that works. no load speed is just the speed that the motor will spin with no load on it and based on its voltage and kv at full throttle. if you look up the grin motor simulator you can do a comparison of a 12s or 10s system with all other variables equal and the 10s will be a hair more efficient. the system is more efficient when running at it’s highest speed, or closest to its no-load speed running a super high voltage has the same effect as having a motor with a super high kv and its more inefficient. yes the wire resistance is less with higher kv but it needs more amps to get the same torque. it all balances out really and you CAN get about the same losses going maybe 2s and 1000kv or 20s and 100kv. its close but with the 2s system it will have to be capable of doing a huge amount of amps for the same performance, if even possible, and that esc is rare, or huge, or non-exisitent

VESC can’t handle 12s? That’s a pity, hopefully the 6.0 starts getting accessible soon!i run 12s all the time …but sometimes break

the grin simulator is a great tool that shows the whole system efficiency and demonstrates every situation possible

b264 · August 23, 2018, 6:45pm

VESC6 still uses the DRV chip, which is the bottleneck, and you really shouldn’t drive it with more than 10S

chuttney1 · August 23, 2018, 9:27pm

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.

b264 · August 23, 2018, 9:47pm

Which means it’s the bottleneck

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

professor_shartsis · August 23, 2018, 9:57pm

@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.

danielz · August 23, 2018, 9:57pm

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.

b264 · August 23, 2018, 10:01pm

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.

Namasaki · August 23, 2018, 10:16pm

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.

chuttney1 · August 23, 2018, 10:25pm

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.

DilatedPupils · August 23, 2018, 10:32pm

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.

danielz · August 23, 2018, 10:44pm

Its not false. and stop being so condescending.

b264 · August 23, 2018, 10:45pm

This statement is 100% false. The DRV83xx chip is the limiting factor in the design.