20Kw motor and 300A ESC (ultralight aircraft propulsion system)

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nicobie   1.21 GW

1.21 GW
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Joined: Aug 07 2008 1:48pm
Location: Central Coast CA, USA

Re: 20Kw motor and 300A ESC (ultralight aircraft propulsion system)

Post by nicobie » Aug 11 2022 8:09am

Impressive :warn:

Glad to see you've done your homework. Mad skills.

👍👍
Ask for it by name.

my eTownie build thread: http://endless-sphere.com/forums/viewto ... =6&t=23701
Magazine article https://www.electricbike.com/nicks-etownie/

Mihai_F   10 W

10 W
Posts: 98
Joined: Oct 11 2021 1:14pm

Re: 20Kw motor and 300A ESC (ultralight aircraft propulsion system)

Post by Mihai_F » Sep 01 2022 1:41pm

I'm back with some updates, here is a continuation form the magnet coverage topic. viewtopic.php?f=30&t=117251

So, basically i added two 5x5x20mm N45 magnets end to end to form a 40mm long magnet that i inserted between the existing magnets, i positioned them so that the 40 rotor poles still go N-S-N-S-N-S with equal spacing.
After the magnet insertion i still had left 0.35mm between poles, i placed them to touch the big magnet all on the same direction.
This little spacing (0.35) was almost enough space to fill them with some lead foil in order to balance the rotor, but i was still 3 grams out.
The final result after this modification was very good, the before mod Kv was 36 (3300rpm no load at 91V) and after the mod is 34Kv (3070rpm no load at 91V), but now comes the good part, before the mod i had a 1000RPM drop from no load to full load (porp), now i have only 700RPM drop from no load to full load (porp), witch means it gained some torque as the Kv went down.
And the best part is that it runs supper smooth, no more jerkiness, no more wrong and weird hall signals, and the radio interference has dropped a bit and now the squeltch can clear it, mainly because it runs smooth and draws current more smother, all that jerkiness creater spikes of current and EMI.
The motor max temperature at 16kw went down by a few ~4 degC.
The weight pelanlity is only 300 grams added, but is way outweighed by the benefits.
I simulated at the ground a 30 minute flight, 40 sec 16Kw, 2 minutes 10Kw, 6 min 8Kw, and 21 min at 6 to 8 Kw.
All went well, except one thing, during this simulation i monitored the system parameters all looked ok, but at the end of the test in last 2 minutes i noticed an faster than normal decrease in motor RPM (throttle lever not moved), so i started to look for the cause, and i noticed that one of the batt cells (no.15) has dropped to 1,3V all other cells ware at 3,4V to 3,45V , i cut the power immediately, battey temp was only 40 degC, ambient was 25degC. A after the motor was stopped i left the system powered for about 5 minutes to monitor the battery, and cell no.15 went from 1,3V to 2,7V in about 3 minutes then stabilized there. So i said this is not good, why would that happen cell no.15 (and no.16) is only 2 years old (2 years ago i mod the pack from 20s to 22s) and all other 20 cessl are 7 years old, it makes no sense, then upon pack disassembly and investigation i noticed that cell no.15 witch is made from 12 cells (5000mAh) in parallel, had one tab of one cell unsoldered from the rest 11. Now one cell off out of 12 meas 55Ah (11p) instead of 60Ah (12p), but that 5Ah difference it might not be enough to cause what happened, or maybe being 5Ah short it got discharged faster than the other cells, but then the rest ware at 3,4v, a bit far from being discharged compleatly. I checked all other cells and all are fine and soldered well. So i have to charge cell no.15 back slowly and discharge it separately to check for current and capacity, but this is no good i broke the li-po rules, and i did not have the worning set if one of the cells goes below 3V, bummer.

So here are a few photos from motor mod, here is also my rotor puller.
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