code to change the motor amp limit

General topics and discussions about the VESC and its development.
Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: code to change the motor amp limit

Postby Hummie » 08 May 2017, 19:03

Since the duty cycle parallels speed and I would've only been able to hit 200 motor amps at startup but I'm sure I've pulled full throttle maybe at 2mph and that would still equate to higher than 160 motor amps and there was no problem.
If the shunt resistance is the issue putting one on that would allow the 200 motor amps, or maybe higher, seems an easy way to have more power.


But the answer that it would need a bigger load to hit the 200 motor amps...the motor amps produced at full throttle seem very reliably predictable based on motor amps x (duty/100) = battery amps. Load doesn't seem a factor other than to reduce the speed and therefore duty cycle and only the duty cycle seems to effect. But I'll log today and see what I get and post it up.

hexakopter
Posts: 86
Joined: 24 Dec 2015, 15:24
Location: Germany

Re: code to change the motor amp limit

Postby hexakopter » 10 May 2017, 18:26

Hummie wrote: But I'll log today and see what I get and post it up.

How long are your days Hummie? :lol:
Would be cool if you would share your collected data with us.

Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: code to change the motor amp limit

Postby Hummie » 11 May 2017, 18:02

Yuk yuk. What more you want. This is the most my thing has been able o record so far for some reason. Some of us don't even have a computer anymore. I was using a flip phone for the last year as well. We all aren't so techy
Attachments
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hexakopter
Posts: 86
Joined: 24 Dec 2015, 15:24
Location: Germany

Re: code to change the motor amp limit

Postby hexakopter » 11 May 2017, 20:00

I don't get what you try to tell me with your words (maybe because I am not a native english speaker), but the graph tells me that you didn't came close to your 200A you are speaking all over the place. Not even close to the max measurable 160A. So you are telling everyone in the electric-skateboard forum and also here that 200A motor current are the "Holy Grail" of acceleration without motor cogging and then you don't even use 40A in your build? :oops: What a shame.
Maybe you should try hall sensors or magnet encoders for your builds when you want cogging free acceleration from standstill and not use max settings you don't even come close to and tell others they should do the same.
I think I am out of this discussion, now where you have your proof of the "great 200A". :)

Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: code to change the motor amp limit

Postby Hummie » 11 May 2017, 20:07

As I said i don't ride 200 anymore as I'm on two motors and also tame it down to 160 as people said it was too dangerous, but this pic was at maybe 60 motor amps and I forget now. To me 200 motor amps was the best performance I've ever had as you say. I'm looking for the best performance as I imagine a lot of other people are too. We don't all want to have to add sensors or other parts. I'm telling u I can start cogging-free from standstill with 200 motor and other settings I've had, 60/60 or 70/70 didnt have nearly the same low end torque or smoothness and that's with two motors! To me it's worth finding out the details on.
It's as if you have nothing better to than stalk me and look for some snooty thing to say. Go ride your board maybe. You won't find any proof from me as I say I'm just lookin for answers. If u have all the answers don't waste ur time reading my questions as they wont help you
Last edited by Hummie on 11 May 2017, 20:10, edited 1 time in total.

hexakopter
Posts: 86
Joined: 24 Dec 2015, 15:24
Location: Germany

Re: code to change the motor amp limit

Postby hexakopter » 11 May 2017, 20:10

That happens when you try to help. :cry: Thats to much for me. Bye.
Last edited by hexakopter on 11 May 2017, 21:22, edited 1 time in total.

Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: code to change the motor amp limit

Postby Hummie » 11 May 2017, 20:12

Bye bye and hope I didn't ruin your day with my question

benjamin
Site Admin
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Re: code to change the motor amp limit

Postby benjamin » 11 May 2017, 20:22

There is no way you can ride with 200 amps current limit. Just think about it:

The VESC controls the current by measuring the motor current, compare it to the desired current and adjusting the voltage based on the difference. Suppose you request 170 A... The control loop will increase and increase the voltage and never see more than 160 A until it hits the short circuit current or something breaks. How fast is the current controller? Well, fast enough to reach the maximum modulated voltage in 1/100 of a second, meaning in an instant.

So, in an event like this, will something fail, or will the highest possible current that the battery can generate be applied? Lets find out by calculating the short circuit current at standstill (assuming your motor has 80 mOhm as seems to be the case from the other thread): 40 / 0.08 = 500 A! What do you think happens when applying 500 A? You probably guessed it: the magic smoke will leave the VESC. So there is no way you could have been above the 160A while riding, and setting the current limit higher than that makes no sense whatsoever.

Regarding running the motors at 200A in general, there is one thing you can try to simulate how long they will last: Take two motors, use two wires of each one to connect them in series and connect them in series directly to your battery. This way they will experience a bit over 200A each. Count how many seconds it takes until they catch fire.

Hummie
Posts: 109
Joined: 10 May 2016, 04:05

Re: code to change the motor amp limit

Postby Hummie » 11 May 2017, 20:48

Hey I have no rebuttal with science. I don't know what current actually occurred and I'll get back to 160 motor and at least look at that, the one one thing I know for sure, which in a way is everything, it rode great. The amp limits are two things it seems, both the true limit and also the speed at which the amps rise. Maybe I didn't hit 200 but it sure was awesomely smooth getting there. That's all I'm saying. It's a unique situation though with one high kv hub motor so...
But I'm done with saying the same thing over and over and so are u. It's all been said and while it was interesting and I'm still interested in how it works and what's possible it's too many teeth pulled and I'll wait for someone else to ask the question again or more experiences from others. I can ramble on but it's not to prove a point but just tell what was the best vesc experience for me

But damn it that begs another question as u mention Burning up the motor w 200 motor amps. As I understood it, and I've been told is not the case, while 200 motor amps could occur at, hypothetically, let's say 3% duty, it's pwm and not a continuous 200 but for fractions of a second and would never get over the true battery amp limit at let's say theoretically let's say that amps. Why would 200 amps on for let's say 5% of the time, have anywhere near the heat of 200 at full time. It wouldn't be 5% the heat but still it doesn't make sense that motor amps determine the heat and not battery amps

devin
Posts: 253
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: code to change the motor amp limit

Postby devin » 11 May 2017, 21:13

@hummie

apparently in the 48/200/200 test @ 35V Assumed Pack V with Sag, 0.0415ohm VESC detected winding (0.0830ohm lead-to-lead)..

I believe this is what happened (someone please correct me if I am wrong-- trying to understand myself!):

you could not have reached 200 motor amps because of the coded 120 motor amp override in the VESC software version you used.

This placed a limit to motor amps of 120.

also, we assumed your lead to lead winding resistance was 0.0415ohm based on VESC detection to calculate the settings, but lead-to-lead was really 0.0830ohm, because VESC calculates lead to virtual ground point for resistance.

Since the effective motor amp limit was 120A max

At 0 rpm, full throttle, 120A motor limit equates to:

120a motor amps x 120a motor amps x 0.0830ohm lead to lead = 1195.2W = 34.14a battery amps x 35v pack v with sag = 120a motor amps x 9.96v effective pwm volts

In simple terms I believe your "effective battery limit" when accelerating full throttle from very close to 0rpm was 34.14 battery amps.

So, I would expect to see 34.14 battery amps, 120 motor amps, 28.45% PWM Duty Cycle and 1195.2W Electrical displayed close to the beginning of a vesc log of when testing full throttle acceleration as close as physically possible to standstill. (In the 48/200/200 batt / motor /absolute test @ 35V assumed pack v with sag @ 0.0830ohm winding lead to lead)

If someone thinks this is not right, please tell me where my equation is wrong?

I am here to learn!


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