Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

It's the 30th!!! And you are in the future aren't you since you are in New Zealand? What happened Duncan?!?!

[duncan]

Hi Paul
Just got back in
We did the event on Sunday and drove home today
I will have to look and see if Jane managed to take any usable pictures

Anyway the controller was great
But I have made a mistake!
I went down to 130v (40S) - BIG MISTAKE!
On the track it will only reach 100kph (59mph)
So I stonked out of the corners and then my tiger turned into a ***** cat and I poodled down the straights

Great fun but not fast

I did the sprints around the track and used up my charge so I missed the first drag races
When I turned up for the second series they put me next to a Ferrari! - lovely big red one
I complained but they laughed

This was the first time I had been on a proper side by side drag strip
The lights turned and I got away in front of it!
About 100 yards down the track it flew past me
But I was in front for the first bit!
He did a 14 seconds and 110mph
I did 18 seconds and 59mph - I think I had already stopped accelerating when he went past

When I came back for another go they put me next to the Tesla - Dam that thing was fast I just followed him all the way

Great fun - now I need to get my voltage back up,
What is the limit with the new controller?

[duncan]

Sit site is funny - it has asterisked out a ***** cat
I will just have to say like a tabby cat

[Astro]

Originally Posted by duncan

...
This was the first time I had been on a proper side by side drag strip
The lights turned and I got away in front of it!
About 100 yards down the track it flew past me
But I was in front for the first bit!
He did a 14 seconds and 110mph
I did 18 seconds and 59mph - I think I had already stopped accelerating when he went past

Wow! An 18 second time with a top speed of 59mph. There is certainly nothing wrong with your acceleration. Can't wait to hear how you go once you get the voltage up on your pack.

So will you swap your pack set up to two strings of 80 cells (260v)? Or are you thinking of adding extra cells?

Raising the voltage will reduce losses as well. (cable power losses not necessarily race losses)
From what i have absorbed from this forum it is just the supporting equipments voltage ratings that cause people to go for lower voltages. Chargers, DC-to-DC converters, motors, controllers etc are all more expensive the higher you go with your pack voltage.
But for the vehicles performance and efficiency the higher the voltage the better.

[MPaulHolmes]

Man that was a hilarious story Duncan! It sounds like a lot of fun!! You should be able to do 350v-400v or so and a peak current of maybe 1200-1400amp. The igbts and ring cap are good to about 600v, but you don't want to go too close to that. Increasing voltage affects the pi loop. So we would have to maybe adjust a couple settings.

[Astro]

Originally Posted by duncan

...
When I came back for another go they put me next to the Tesla - Dam that thing was fast I just followed him all the way...

Did you notice what the Tesla's time and finish speed were?

[mrbigh]

Originally Posted by Astro

Did you notice what the Tesla's time and finish speed were?

Short and Fast !!!

[duncan]

The Tesla did 12.8 sec and 107 mph

[duncan]

Hi Paul

I’m trying to understand what is going on

On the ¼ mile I could look at my instruments
After a brief surge of acceleration I was pulling a continuous 200 amps (battery)
That is about right for a constant speed of 59mph (not very aerodynamic)

I had the pedal down still
My “theory” is that the controller was at max – 100%
But there was so much Back EMF that there was not enough voltage left over to drive more current through the motor
I had about (don’t remember the actual reading) 120v
So I think BEMF = 100v
Assuming that the motor was “saturated” and BEMF was proportional to current and speed that gives me a point on the line
3500rpm – 200Amps = 100v
Making up a quick spreadsheet I come up with

1000 amps to about 700rpm - 19Kph
800 amps to about 900rpm - 25Kph
600 amps to about 1100rpm - 30Kph
500 amps to about 1500rpm - 40Kph
400 amps to about 1900rpm - 50Kph
200 amps to about 3500rpm - 95Kph

And that is about how it felt - really fast off the line - then disappointing
So is that "reasonable" - or what am I missing

Specifically – am I correct about the controller?
Is that a reasonable amount of BEMF?

From that my 11 inch Hitachi motor is producing about three times as much BEMF at a given rpm/amps as the tables for a Warp9
I expected more – but not that much more

[MPaulHolmes]

Ya, all the controller can do is ramp up to 100% duty, at which point it's basically a dead short from the batteries through the motor. I remember you saying that at one point the battery amps were over 800 while testing it out? How fast was the motor turning when that happened? I don't know that much about motor back emf, but I'll post your question to the EVTech list and see what they have to say.