Brushless Motor Voltage
 

Hi,

I'm converting a nitro buggy to electric and trying to work out what electronics I want. I'm looking at Hobbywing (NOT HOBBYKING) because I run a Hobbywing ESC in my MT4 G3 and love it, anyway how do you find the limits of the motor? What is the max voltage? I.e can a 6000kv motor paired with a 150A ESC run a 6cell lipo (22.2v)? None of the spec sheets really outline this.

Any help will be greatly appreciated. Thankyou in advance.

what scale are you running in i would assume you are running 1/8 scale because you are talking about conversions. in theory it would work but 6000 kv on 6s is just a set up for failure. on a 6s setup buggy probably stay under 2650 unless you are going just for speed runs. around 2000 kv is better for general running

There really isn't a voltage limit on any electric motor. It's more of a how many total watts can it do before it fries kind of thing. The thing could run fine on 50 volts as long is it's never asked to pull more than a couple amps. Of course you could eventually get to the point that the rpms cause the rotor to explode too.

That being said, listen to the previous posters advice. That much motor with that much voltage is just asking for the smoke to escape. Not to mention drive-ability issues.

HOBBYKING is just a clone of hobby wing:D

Perhaps this chart from Tekin can be of some help, also assuming you are asking about 1/8 electric. My personal experience-opinion is even the low side of these recommendations are plenty for racing. An under powered 1/8 electric is nearly unheard of.


http://www.teamtekin.com/graphics/T8...2010_72DPI.jpg

Tekin T8 Voltage Recommendations Chart

Thanks guys very useful tips and information. The 6000kv on a 6cell lipo was just and example. Can someone explain how to work out how many watts a motor can handle and how to work out how many watts you're pulling. This motor here is the only one I've found with max voltage http://www.ebay.com.au/itm/HobbyWing...76d1029&_uhb=1
Does that mean all 6000kv motors have that voltage limit? I'm looking at a higher KV in a 1/8th so I can run a lighter battery that gives me the same RPM (EXAMPLE: A 2000KV motor at 22.2v will give me a RPM of 44400, A 4000KV motor at 11.1v will give the same RPM of 44400)

If I’m following correctly you are probably headed the wrong way for a lightweight setup. For a similar run time the lower volt higher kv setup won’t be lighter, as the cell capacity will need to be larger to provide the higher current needed to drive the higher kv motor and achieve similar power levels. It will likely be somewhat heavier even, as all else being equal it will be less efficient needing even more battery weight, and run hotter.

Better to go for a higher voltage low kv setup, within the limits of any possible racing class rules if you are headed that way.

As a rough example a 11.1V 5000mAh pack with the high kv motor could quite likely be replaced by a 22.2V 2500mAh pack with the low kv motor. Similar overall weight, with some advantage to the high voltage case even.

Are you planning on racing, general playing with lots of power, speed runs, etc? If racing do you know the rules if any at the tracks you plan on running at? That and any more details you care to share will help us provide better advice. Generally there isn't a way to calculate everything very well, due to lack of enough data on motors and such and too many possible variables in how the RC is used.

Hi,
First of the car at this stage is just going to be used for general bashing and running around. What you are saying about weight makes total sense, even though it will half my run time. What I'm having trouble with is finding out what motor needs what voltage, amperage ect. A 6S 2650mAh lipo weights 430grams, A 3S 5000mAh weights 412grams. What voltage to different KV's require, Can a 6000KV motor run on 2S 5000mAh weighing 276grams giving me a RPM of 50400 instead of a 3000KV motor running on 4S 5000mAh weighing 528grams giving me the same RPM of 50400?

Thanks for helping me understand this. Sorry for the noob like questions

And again, any of them can run on anything from 1s to 20s if you want to. The esc is the part that has voltage requirements, not the motor so much.

You're on the right track here. What you have to be aware of is that all motors have a certain max rating for wattage, amps etc. You need to know those things before setting it up.

Your example of 6000KV versus 3000KV and 2S versus 4S is correct in a vacuum. But there's also motor efficiencies to take into account. A lower KV higher voltage set up is always more efficient than a high KV low voltage. So the 3000KV on 4S will be noticeably faster with more torque than the 6000KV on 2S. The 6000KV will lose more energy through heat than the 3000KV setup.

Also the run time won't be half with the high voltage low kv example. Low kv motors use less amps, so the 22.2V 2500mAh lasts far longer than it first appears.

Power (Watts) = Volts x Amps

The low voltage high kv setup draws more amps to make the power, thus draining the larger capacity cells quicker. (All assuming correct setups including gearing of course)

One rule of thumb that is frequently mentioned, around 30,000 rpms seems to be the about the sweet spot (if not the maximum in my opinion) that works well for 1/8 electric buggies. 1400kv on 6S lipos, or 1900kv on 4S for ROAR rules seem to be the most popular. Much more tends to increase heat issues, reduces run time, generally any extra power is not very useable. Even a good 1700kv on 4S has an astonishing amount of power, the quickest one on track I have seen by far runs this setup.

Maybe a touch more if you want truly ridiculous power for fun, but again keeping temperatures in check might be a challenge and run time will be reduced.

This is only true for the ESC, due to the I2R losses. The motors will have similar efficiencies and temperatures if they are of similar construction and power output.

Very true, my point also runs with the assumption that a 3000KV motor that is designed to handle 4S USUALLY (not always) be of a different build than a 6000KV motor, which will (to most that I can think of) be a 540 can 2 pole motor.

Hi Guys,
Thank you for your responses. I have to be honest I am a bit lost and confused. If I am understand correctly, running a lower KV will be 1. More efficient due to amp draw of the motor draining the battery faster. 2. The high KV loses energy through heat, can someone please explain how energy is lost through heat? I have read through other sources that motors do have voltage limits, how true this is I’m not sure, the limits are 1800 -2100 6cell, 2200-2600 4cell, 2700-3800 3cell, 3900-9000 2cell? I want an extremely fast but light buggy!

I think I know why I'm getting confused. Motors have a max voltage according to the specs of some Hobbywing Motors, but other models with different KV do not list the max voltage nor do they list the max wattage!