HV Motors and Big Boy Amps

General Technical Discussion & Projects
1

First I just want to say if I got any facts wrong please feel free to correct what I said.

So I’ve been meaning to start this for awhile now. With the new Stormcore 100D and Rion Tronic coming out a lot of people are moving to higher voltage. What we are missing is a motor that’s not a crazy low kv (90kv Maytech) but also supports the amperages we want.

So back story on why you might want to run higher voltage on your board.

Summary

The main thing (in my mind) is more speed without a decrease in torque. We all know upping your gearing so you can hit higher speeds makes your torque drop away. Higher voltage solves that by adding speed by putting more volts into the motor making it spin faster at the same gearing.

Another reason to go higher voltage is the torque. 16s 100amps per motor will be more torque then 12s 100 amps per motor. This is a big thing if you live in a hilly area or just love torque and take offs.

Finally, efficiency. The higher the voltage the more range you will get. A 13s4p battery will get more range then a 12s4p battery, if the same cells are used and you were to ride both batteries the exact same. For example (hypothetical so not true but gets the point across) A 13s battery at 60amps will feel the same torque (if geared for the same top speed) as a matching 12s battery with 70amps being used. This means the 13s uses less power to reach the same torque and top speeds as the 12s battery which leads to a better mpg aka wh/mi or wh/km.

Alright, on to the real point

So here’s the real point. We don’t have motors that can do these voltages. Alright yes we have motors built for cars like Nissan Leafs and Tesla’s, but those don’t fit our application.

Really speaking, we can’t get those motors we want without buying in a large quantity.

For example I was all set to do a KDE Motor Groupbuy (suppliers of Hoyt motors) for custom made 63100 25s 250a rated motors. These would’ve been the bees knees, but they cost $386 dollars per motor. Now you might be saying, “Hey that’s pricy but if it lives up to its expectations then why not?” Well I’ll tell you why.

KDE wants $2250 as payment for the custom motor design and tooling etc. This means that if we bought 20 motors (10 sets) it would cost $498.5 per motor excluding shipping. If we sold/bought 24 sets (48 motors) it would cost
~$438 per motor. In my head I knew that personally, I’d sell stuff and I’d buy 2-4 motors at that cost. But I knew that seriously speaking, we wouldn’t make up that other 44-46 motors.

The point of this thread was so that we could help each other and try to find or have made a motor that fits all our high voltage needs.

Special shoutout to @ahrav for proof reading this

10 Likes
2

From my basic understanding of motors and the ohm’s law: the simple answer would be to have a larger stator, right? Not just longer, but actually fatter. You’d need to have more windings using thicker gauge magnet wire. More windings and thicker armature wires equals more resistance which would reduce overheating in the motors when we do apply more voltage (AND I’m sure there’s more to that than just an increase in resistance).

4 Likes
3

We have. 80xx motors are rated 15S and higher.

Edit: for me interesting what you need to run higher voltages save. Wonder what LHB did different on the 80kV maytechs. My guess is just that the windings have bigger isolation that’s all it needs to get a higher volt rating.

5 Likes
4

I know folks have varied experience with this company but as @Andy87 mentioned there are some options. @DEEIF these claim to go to 18s

https://alienpowersystem.com/shop/brushless-motors/80mm/c80100-outrunner-brushless-motor-130kv-7000w/

4 Likes
5

Actually I saw these! I’ve been told they turn into heaters if ran at 18s though, another problem is their bearing, it’s only rated to 5k RPM or something along those lines.

4 Likes
6

Do you mean reduce resistance? I thought resistance in the conductor contributed to heat, so having less resistance would reduce heat

7 Likes
7

oh god, I don’t know anymore. I havent studied motor theory in years. Lemme know if I should delete that post lol

I always thought Heat produced = Voltage^2 / Resistance

so in our case, we’d be increasing voltages past the usual 12s so we’d need higher resistance to keep heat produced low. Now I just can’t seem to remember if it means to have larger thicker wire windings or an increase in number of turns of windings…

Lets call the local mad scientist who’s always on

@k00k

4 Likes
8

i believe higher voltage requires better insulation on the conductors

4 Likes
9

good to know IIRC @malJohann is running 18s on Sk3

both @ducktaperules and i asked damon about his testing of higher voltage with stormcore and motors, but unfortunately damon did not have data so we could better understand what actually happened, so we’ll take his word for it. last i looked in june damon’s testing of higher voltage was stalled due to financial constraints.

Reference

Screen Shot 2020-09-15 at 8.48.35 PM
Screen Shot 2020-09-15 at 8.48.35 PM1542×434 82.2 KB

Screen Shot 2020-09-15 at 8.48.59 PM
Screen Shot 2020-09-15 at 8.48.59 PM1558×650 97.8 KB

Screen Shot 2020-09-15 at 8.49.15 PM
Screen Shot 2020-09-15 at 8.49.15 PM1584×1210 163 KB

3 Likes
10

As another data point I’m quite happy with my HV setup at the moment.

I’m running 18s on maytech 6396 140kv ( from lacroix). Usual crusing is at 60A per motor but when I want more power I regularly take it up to 100A per motor.

100A per motor at 18s is a fair amount of power. At 140kv on 5:1 it Pulls like a freight train.

7 Likes
11

If that works for you, why LHB does fry the 6374 and 8085 motors and escs after just some minutes?
Sometimes I don’t get what they are doing different over there.

3 Likes
12

Low HV motors suck. They have high resistance and overheat easily.
The way forward is high kV motors combined with big reduction ratio transmission.
IMO there is no purpose in HV so long as battery currents are manageable and for our application they are.
Moe has it right in that regard.

8 Likes
13

massive?

19 Likes
14

Not sure but i have wondered this myself. The only reasons i can think is that he got unlucky with motors that had bad construction, that he tried motors with a silly KV or that he some how fucked it.

Agreed. Before my 6396 140kV I was running 6880 190kv and I think I liked that setup more. HV and High KV sounds crazy but it seems to work quite well. I didn’t get any extra torque over the same settup at 12s and i capped the top speed to be similar so that i didn’t stress the bearings. But it seemed to be running much cooler than on 12s and my wh/mile was good. Also it didn’t start to slow down as i got towards the end of the battery.

Now ive switched to 140kV there is plenty more torque but even if im not using it i seem to have a constant battle with the heat.

9 Likes
15

This right here. Perm magnet motors like to spin fast. If you want to spin them slow, you’re going to end up with something much larger to distribute that extra resistance (heat).

6 Likes
16

This is probably also due to eddy current losses.
The RPMs a motor turns at a certain speed are dependent on the gearing ratio.
A low kV motor means that it will heat up more at high RPM due to core losses compared to a higher kV motor due to the higher electrical resistance.

6 Likes
17

Also just wanted to clarify a few things from your intro. for these examples i will use a 12s and 18s setup (mostly because it makes the maths easy).

Just to be clear only switching to HV will not get you more torque. Any motor will produce a set torque for a given number of amps. Whilst at low speed motor power is constrained by motor amps. If your sitting on the motor amp limit then the motor is not seeing the full voltage of the pack, torque produced by either setup would be the same.

HOWEVER the HV system has 50% higher motor RPM at full duty cycle. This means that you are able to increase the gear ratio, reducing the top speed and increasing torque. For example if you have 12s board with 4:1 you could switch to 18s and go 6:1 with the same top speed but 50% more torque.

HV alone does not increase torque. Shorter gearing increases torque and HV allows shorter gearing.

This is not really true.

Yes but 13s4p has 52 cells, 12s4p has 48 cells. more cells is more wh which means more range, this has nothing to do with the voltage.

For a more fair example lets take a 12s6p pack and a 18s4p pack. Both packs have 72 cells and both contain the same number of wh. For the most part you can expect similar range from both packs.

Whilst running at a higher voltage is theoretically more efficient with regards to heat losses, in reality you will find that these efficiency gains are negligible in comparison to other system losses like mechanical friction seen in your drives and tyres.

Again lets use 12s/18s example as it makes the maths easy here.

“A 18s setup at 40A motor current and 6:1 will feel the same torque as a 12s setup at 60A motor current and 4:1. Both setups have the same top speed.”

This is correct.

Not realy. The thing your forgetting here is that motor amps is not the same as battery amps.

lets say your at 3.7v per cell on your 12s and your at a speed that gives you 30% duty cycle. Your motor is seeing 3.7V x 12 x 30% = 13.32V so when accelerating with 60A your using ~800W.

now your also at 3.7v per cell but on your 18s settup. Due to the changed gearing your at the same speed which still gives you 30% duty cycle. Your motor is seeing 3.7V x 18 x 30% = 19.98V but for the same acceleration your only using 40A. this means your still using ~800W.

This shows the 12s and 18s settup both use the same power when producing the same torque.

16 Likes
18

Thanks for clarifying, that actually makes a lot of sense.

5 Likes
19

That’s just power. The question is which voltage and which amps lol.

1) Power = Volts x Amps
Volts = Rohms x Amps - > 2) Amps = Volts / Rohms

put 2) into 1) and
Power = Volts x Volts / Rohms
Power = Volts^2 / Rohms

5 Likes
20

OHHH. Thanks man :sweat_smile:

5 Likes