DIY Sensored BLDC ESC - Assembly Thread

[S.B.D]

Last night was a smokeless night. After fixing the controller we went on to use a current limited power supply and later on a fused 48V pack.
After an initial power up with the power supply - limited to 30V we came back to the dreadful 48 pack. This time a 5A fuse was added

Everything worked properly this time using the same type of components that failed last time. This strengthens my theory that the short circuit I found from Vbatt+ to a high side FET gate lead to the 4th of July effect.
One change I make was to increase all gate series resistors from 10 Ohm to 100 Ohm in order to decrease dI/dT stress on the FETs.

Here are some scope PICs I took:

Low side FET turn on time:

Low Side Gate turn-on time.jpg (198.33 KiB) Viewed 422 times

High side FET gate (Ground referenced)

High Side Gate GND reference.jpg (200.22 KiB) Viewed 422 times

Phase Voltage (Ground referenced)

Phase referenced to GND.jpg (199.32 KiB) Viewed 422 times

Also some Vids of the setup in work:
http://www.youtube.com/watch?v=yNC_Ar12cfw

http://www.youtube.com/watch?v=cNmBVIWDO1Q


A Lot of work ahead...

S.B.D

[S.B.D]

Hi,
Last night we connected the ESC to my friend's home built 6S LiPo Scooter. This scooter uses an RC outrunner Brushless motor fitted with external halls.
The controller worked great! The throttle endpoint adjustment via the USB interface was very simple.
First we programmed the current limit to 10A and started riding. ESC only slightly warm.
Next we stepped up the current limit to 30A. This heated up the ESC to very hot temperatures....need to implement the temperature measurement with the on board NTC thermistor....

It was very nice to finish a day without any damage.

Next up:
--Lower the gate series resistors from 100 Ohm to about 10 Ohm - would like to get your comments on this issue.
--Move the ESC from the scooter to test on a bike.
--Order a stick of IRFB3077.

S.B.D

[texaspyro]

need to implement the temperature measurement with the on board NTC thermistor....

I'm not too fond of thermistors as temperature sensors... non-linearities, and all that. And to drive/sense them properly takes circuitry. For most stuff, I like the LM34 style sensors. (note: in the TO92 package, the main source of heat input to the die is via the leads. I leave them long and pot them onto the surface to be measured with thermal epoxy. But then, I'm a temperature snob. I've built temp sensors with micro-degree resolution and milli-degree accuracy.

[S.B.D]

Hi Tex,

Thanks for the note.
I have experience with temperature measurements with various kind of probes (ntc, pt100, thermocouple 2,3,4 wire) and aware of the problems with NTCs.
I plan to port the code I used for a different project to read the same NTC. It uses a look up table every 5 degrees (copied from the datasheet) and than linear approximation between two points.
Even without calibration I don't see a problem to reach +/- 2 deg accuracy , much more than I need.

Milli degree...never done that... maximum accuracy I dealt with was about 0.2 Deg.

S.B.D

[S.B.D]

Yesterday we assembled the ESC on an e-bike with a rear hub motor.
The change to 5 Ohm gate resistors dropped the ESC temperature and even @ 40A it became only slightly warm.

We did find a few bugs:
- When the bike was moved in reverse the ESC acted as a brake. This is because of the current commutation state machine that leaves one bottom MOSFET "ON" according to the halls state.
Turning off all the bottom MOSFETs at minimum throttle should solve this.
- Starting the ride on a sharp incline cogged the motor. Need to figure out if this is due to an MCU reset, noise on hall signals.... Your comments on this will help a lot.
- Top speed seemed to be lower than that of an off the shelf 30A ESC, this needs to be verified empirically.

Things to do:
- Move to even lower gate resistance. Is 1.5 Ohm a good choice?
- Add a lead/lag phase compensation loop.
- Shorten hall & phase wires. Currently they are about 60cm !
- Move to IFRB3077 MOSFETs - ordered.
- Keep having smokeless fun..

S.B.D