VESC at high Voltage (and KV)

General topics and discussions about the VESC and its development.
akira9a
Posts: 15
Joined: 23 Mar 2016, 13:00
Location: Paris
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

VESC at high Voltage (and KV)

Postby akira9a » 23 Mar 2016, 13:05

Dear all,

What a great place to discuss this piece of hardware.
First things first, thank you Ben for sharing your knowledge with us.

I have in mind to use VESC and high voltage (10 or 12S) with motors that have quite large KV (240).
If you are in a similar situation (running VESC at 10 or 12S and KV >=200), could you share your setup specs and the eventual problems you had ?

I heard that 12S should stick below 200KV.
Now I am considering 10S with 240KV.
Would that be OK ?

Then there are Tacon 110 at 295KV. Are they usable with VESC ?
Shall I try to reconnect it in star instead of Delta to lower the KV ? Are there conserquences in doing so ?

Cheers,

jaroslavnovotny
Posts: 49
Joined: 16 Feb 2016, 13:10
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby jaroslavnovotny » 23 Mar 2016, 14:28

Hello Akira,

you should pick your motors based on rpm they are meant to run at and by their efficiency curve (which is a function of rpm):

Image

The same motor with different amount of copper turns on coil or different winding termination style (different kv) will be the exact same motor with exactly same efficiency, torque, etc. on different voltage (and thus different current also). For example 200kv motor on 24V @ 10A will have the same mechanical properties as the same type of motor with 100kv @ 48V @ 5A.

Now the VESC is not very good at handling voltage over 40V unless you exchange 50V capacitors for 100V ones or you wait for the 5.0 version. The current it is able to handle depends on cooling and is roughly limited to (imho) 100A.

I don't know where you got that there is some limitation of kv at 12S - kv and voltage itself does not tell anything about the stall current which is the real limitation. The kv limitation would be meaningful if someone tested exactly your motor (or very very similar) with VESC with different kv ratings.

So you are better with lower voltage higher current motors. You should also optimize this with your battery options for max. battery life.

akira9a
Posts: 15
Joined: 23 Mar 2016, 13:00
Location: Paris
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby akira9a » 23 Mar 2016, 15:06


jaroslavnovotny
Posts: 49
Joined: 16 Feb 2016, 13:10
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby jaroslavnovotny » 23 Mar 2016, 15:46

I see, the MOSFETS have also a switching frequency limitation in conjunction with current limitation. Makes sense and I forgot about it.

So 44.4V (12S) * 200kv = 8800 rpm. Considering a usual outrunner has 16 magnets the erpm = 8800 * 16 = 140800. So that should be the maximum. Most ESCs are limited to 100k erpm, which is maybe also to what the VESC is limited under a load.

If your motor has also 16 magnets that makes the limit at 10S equal 8800 / 36 = 244 kv.

akira9a
Posts: 15
Joined: 23 Mar 2016, 13:00
Location: Paris
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby akira9a » 23 Mar 2016, 15:57

That seems a very nice calculation indeed 8-)
It could give a good first order idea on the limits.
Thanks !

joe90
Posts: 49
Joined: 15 Dec 2015, 16:52
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby joe90 » 23 Mar 2016, 20:56

Turnigy SK3 motors have 14 magnets
1 electrical revolution need 2 magnets: one north one south pole.
Those are 7 pole pair so you need 7 electrical revolution for 1 mechanical revolution
In theory the VESC run 100 000 erpm
so you can go as high as 100 000 / 7 = 14 285 rpm

For 12S = 50V
so 14285rpm/50V = 285kv max

I would not use more than 250kv on 12S because most motors have tolerances and real kv can be higher.
Based on this 300kv on 10S is about the max you can use.

this is what I understand
Michel Cote
Twin v4.7 + SK3 6374 149KV
Bicycle
2500W peak/unit on 12S

akira9a
Posts: 15
Joined: 23 Mar 2016, 13:00
Location: Paris
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby akira9a » 24 Mar 2016, 08:46

The motors I intend to use as dual rear are 6354.
They have a larger number of poles (both sk3 and tacon 55mm have 9T).
That would limit it to 277KV in 10S.
With margin, I should stick to 250KV even in 10S.
This would rule out the tacon 110 in dual rear (since it is 295KV) except if I go for the delta to star mod.

For the tacon 160 (8T), your calculation would give a 312KV limit for 10S.
The tacon beeing 240KV, this is reasonable for a dual diagonal.

Thanks for you input !

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby rew » 27 Mar 2016, 09:56


jaroslavnovotny
Posts: 49
Joined: 16 Feb 2016, 13:10
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby jaroslavnovotny » 27 Mar 2016, 12:47


rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: VESC at high Voltage (and KV)

Postby rew » 27 Mar 2016, 13:24

You're right. All motors work that way. So my 50A max motor should be rated at "max 1.25V". That's going to allow about 250RPM! Great!

Peak power output is going to be about 1/2 of 1.25V * 50V. (32W)
Under those conditions it is hard to break that motor.

What I mean with "modern" is that people have realized that it is the current going through the motor that mostly determines power-loss in the motor, and that the powerloss in the motor is the determining factor for breaking the motor. So in my case, the manufacturer has said: You could use up to 42V on that motor, as long as you externally limit the current to below 50A.

So now I have a blue dotted line for my motor that goes from 1kA at 0 RPM down to 0A at 7140 RPM. (I have 170 RPM/V IIRC). But the manufacturer recommends staying below 50A for that motor. This reduces the torque for the graph until you hit 6783 RPM. The power-curve changes into a straight line from zero to the point on the parabola at 6783 RPM.

In reality that last part of the parabola is NOT real. It only occurs if you hard-limit the voltage to the 42V specified. That limit is there because mechanically the motor can only go so fast. So if you limit the current to 50A, and you are confident in the mechanics (maybe improve the bearings) you can go above that. Oh.... one more thing. If you go faster than specified, the losses in the iron core of the stator will increase. Possibly too high. When that happens efficiency will drop off and your motor will heat up. So be careful over-speeding your motor just because I said so.


[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Return to “General”

Who is online

Users browsing this forum: No registered users and 5 guests