[DRIVING] VX220 with Tesla SDU

[catphish]

Today I replaced the bad battery module. I think there was a little liquid damage to the BMS slave module that had caused some corrosion and shorted one of the cells causing it to partially discharge. The corrosion all cleaned up nicely but I decided to replace the module anyway. With that done and the charge port now installed, I took the car for a proper drive home! The main outstanding problem is the wheel alignment, which I will get professionally aligned tomorrow. Otherwise it's driving well, it's smooth and temperatures are steady.

During the test drive I investigated the hesitation at 55mph. This turned out to be an overcurrent derate, so I increased fweak from 220 to 250 and this solved it. Performance is now excellent at high speed, and very smooth at all speed/throttle values, but quite weak off the line. I will experiment with increasing boost and driving with different values of slipmax to see what feels good.

Once I'm happy with the drive, the last step will be creating some gauges, at least a way to show battery voltage to begin with.

In terms of range, my enthusiastic 18 mile drive resulted in a discharge from 3.77v to 3.58v. I guess this is around 25% SoC, which seems reasonable. I noticed while driving that my regen is much too weak. I was using the brake for almost all braking, and would have preferred not to. Hopefully by increasing regen I can improve the driving experience and improve efficiency.

[johu]

Superb and good to hear current limiting can prevent complete trip outs

[Peter]

Are you using brake plus pot2 setting or throttle back off regen ? I am using brake plus pot2 but have realised I must be wasting regen energy.
As regen in my case is relative to motor speed as I am slowing down I need to add more brake.
Increasing pot2 can adjust this but with higher motor rpm the regen can be quite aggressive. At one point (early days of testing) I set pot2 too high and touching brake to give brake signal I locked up the driven wheels and performed an emergency stop !! Glad I was wearing my seat belt

[catphish]

Are you using brake plus pot2 setting or throttle back off regen?

I'm using redundant throttle mode (pot and pot2 both come from my accelerator pedal). I'm currently using
brakeregen=0
offthrotregen=-20

So all my regen happens wen letting off the throttle, but this value of -20 doesn't seem to provide *any* noticeable regen while driving, so I'll definitely be experimenting with increasing it, as well as potentially adding some brakeregen for when I touch the brake.

What values have you settled on?

[catphish]

Spent a little time tuning today.

I've increased boost from 2200 to 2700, which provides a much more consistent response.
I've increased fweak to 250 which prevents current derating from occurring at 55 mph and keeps current below 500A all the way through.

I suspect I still need to tune my slip parameters though. I am having to set ampmin as high as 30, and my regen is barely noticeable at all, even at -30 or -40. Hopefully increasing fslipmin will improve this.

It would be useful to have a spot parameter with AC current so that I can try to achieve a consistent AC current throughout the rev range.

[johu]

You'd have il1rms. Just plot either one of them to check consistency accross rev range.

You deleted that other question, I would have asked: does potnom ever reach -30% ?

[catphish]

You'd have il1rms. Just plot either one of them to check consistency accross rev range.

You deleted that other question, I would have asked: does potnom ever reach -30% ?

Sorry, I decided that thread was perhaps a little premature and I should do some more of my own research and testing first.

potnom does go to -30 when throttle is released, and there is (accordng to the chart) some regen, but it's negligable. Here is a graph showing what happens. The red line is potnom and it's at -30 for most of the chart. fslipmin is 1.

I realised that in your SDU config, you have fslipmin=2 so I wonder my low fslipmin is the reason why my regen isn't effective, and why I need to set ampmin so high.

Thank you for your assistance.

I will look at using i1rms for comparing current across the rev range for now.

[catphish]

According to that chart, my 0-60 was 8.0 seconds. Certainly should be able to improve on that once I have these voltage and slip parameters set correctly and I'm a bit more confident in all the mechanical bits! Raising boost will have already helped I'm sure.

[catphish]

The next time I test I will add i1rms to the chart, and swap idc for the measurement from my ISA shunt. This should provide much more detailed data about what's happening. I'll also experiment with increasing fslipmin from 1 to 2. I have a *lot* of trials to do before I fully understand the optimal configuration!

[catphish]

I've started a separate thread here to discuss my inverter configuration / tuning process in more depth: https://openinverter.org/forum/viewtopic.php?p=43216

There's not too much more to do on the car itself now, the main remaining items are the inverter tuning, upgrading the driveshafts, and creating some kind of display / gauges for data like cell voltages.

[catphish]

After a few more test drives, I've identified the last of the unwanted noises, An improperly tightened bolt was allowing the SDU to move slightly in its mount. Re-torqued all the motor mount bolts to be safe, and now the car is nice and quiet (apart from the vacuum pump!).

The conservative tuning I have on there at the moment, which pushes 400A RMS through each motor phase consistently across the RPM range is really pleasant to drive. It's not winning any drag races, but very comfortable for normal driving.

I've given the car a long overdue clean, and just enjoying it for a while before I get stuck into the gauges.

Unfortunately my cells are currently way out of balance (3.71 vs 3.87) as a consequence of replacing one of the modules, so that's going to be balancing for quite a while, will probably take at last a couple of weeks for the BMS to sort out with its tiny bleed resistors.

[catphish]

I made some videos to show the finished car!



I've also informed the DVLA of the conversion, fingers crossed I get the documentation updated without any issues.

[Ev8]

Great job nice to have another ev conversion on the road in the uk, your video now really makes me want to up my battery voltage for a bit more performance

[Bigpie]

I've also informed the DVLA of the conversion, fingers crossed I get the documentation updated without any issues.

Prepare a nice spot on your most convenient wall to begin banging your head on.

[catphish]

I've also informed the DVLA of the conversion, fingers crossed I get the documentation updated without any issues.

Prepare a nice spot on your most convenient wall to begin banging your head on.

Yeah I'm already wondering if I'd have been better just not informing them at all, but it feels like the right thing to do and I don't want it hanging over me, nor do I want to risk running into more stringent regulation in the future. Hopefully I've provided them with enough information that I won't have to go through the hassle of an inspection, but time will tell.

[EV_Builder]

I've also informed the DVLA of the conversion, fingers crossed I get the documentation updated without any issues.

Prepare a nice spot on your most convenient wall to begin banging your head on.

oh dear! And that while UK had a much beloved SVA and IVA procedure in comparison with other countries...

[catphish]

After driving the car for a while and worrying about every little rattle (the worst of which turned out to be my keys that fell out of my pocket onto the aluminium floor), I've now started work on gauges. For now I have decided not to touch the stock gauges, and instead just add a small (2 inch) OLED display elsewhere on the dash. For now this will display battery voltage information and temperatures. I can also add more visual bars, which I will probably use for (approximate) state of charge.

[EV_Builder]

Nice!

[Alibro]

Yeah I'm already wondering if I'd have been better just not informing them at all, but it feels like the right thing to do and I don't want it hanging over me, nor do I want to risk running into more stringent regulation in the future. Hopefully I've provided them with enough information that I won't have to go through the hassle of an inspection, but time will tell.

Brilliant build mate, well done getting it on the road so quickly.
Pity it wasn't a couple of months older and it would have been zero rated for tax.

[SuperV8]

Good work,
I followed a VX220 the other day to work - looked spectacular; and tiny! - with all these modern bloated cars around you forget what car dimensions used to be!

[catphish]

The display is now finished and installed. With that done, and the SDU tuning complete, I think I can declare the car complete

[Boxster EV]

Just watched your videos. The car looks and sounds great.

Given it’s age, I think you’ll be fine with the DVLA.

[janosch]

Hi man, great project, I watched your videos a few weeks ago.

How do you feed data into the OLED display? Do you have another MCU and send it data via CAN or do you display data on it via I2C? Or something else?

I am having trouble with EMF and my I2C display dropping out when depressing the throttle and inverter working hard. Now investigating what the best course of action is, shortening the cables helped a lot, but didn't fully eliminate the problem - and I don't want my display in the engine bay

Currently waiting for a pair of PCA9615 that Johannes suggested, but wondering what your setup is.

[catphish]

How do you feed data into the OLED display? Do you have another MCU and send it data via CAN or do you display data on it via I2C? Or something else?

I am using this display: https://www.diymore.cc/collections/led- ... lue-yellow
And this board: https://docs.longan-labs.cc/1030018/

I was able to sandwich them together very neatly to create a fully integrated programmable CAN display. RP2040 source code here: https://github.com/catphish/vx220-oled/ ... /display.c

[janosch]

Nice sandwich! Source code and everything, great, I will dive right in!