Nevilleh's BMW

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Post by antiscab » Tue, 20 Apr 2010, 01:36

its possible i may have had a dud cell....

from my experience the charge rate doesn't really matter unit the cell is full.

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Post by Nevilleh » Sun, 25 Apr 2010, 15:08

The motor controller saga continues!

I re-fitted it to the car and found it a bit sad. The wheels turned, but only slowly and a quick check with the 'scope showed a duty cycle of only about 10% at full throttle. Obviously going into current limit and no amount of fiddling with the preset pots made any difference, so out it came again.

A fair bit of circuit tracking showed the IGBT drive pulse is fed to the current limit op-amp via a comparator, which is perfectly fine except that there was a resistor missing from the board! The pull-up for the open-collector output! This meant that there was no bias applied to the current sense diode, so it never conducts. Anyway, I fitted a 39K pull-up and it all started working - at least with my 150V bench supply and a 2 kw heater as a load. But the pots now adjust the threshold where the current limit kicks in, so I am hopeful.
This is the controller returned after the first one blew up and I guess it never had a resistor right from new. Really puzzling and I have written to LS to ask about it.

Interesting that the current sense is delayed by 10 uS from the drive pulse so you always get a 10uS min driver pulse no matter what.

Discovered a bit about the "on" resistance of IGBTs too. They look pretty linear once you get past the initial "knee" so that's why people use them as their own current sensor. Seems like quite a neat idea provided they are all matched fairly well.

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Post by weber » Sun, 25 Apr 2010, 16:17

Nevilleh wrote: A fair bit of circuit tracking showed the IGBT drive pulse is fed to the current limit op-amp via a comparator, which is perfectly fine except that there was a resistor missing from the board! The pull-up for the open-collector output!
That would be the pullup resistor I mentioned here. Image
viewtopic.php?p=24307&t=1446#p24307
Interesting that the current sense is delayed by 10 uS from the drive pulse so you always get a 10uS min driver pulse no matter what.
The delay is necessary to ensure that the device is fully on and the collector voltage is all the way down before checking for desaturation. Otherwise it would falsely trip.
Discovered a bit about the "on" resistance of IGBTs too. They look pretty linear once you get past the initial "knee" so that's why people use them as their own current sensor. Seems like quite a neat idea provided they are all matched fairly well.

It is fairly irrelevant whether it is linear, it only needs to have voltage being a monotonically increasing function of current.

Don't think of it as a current limit but rather as an instantaneous power limit for the turned-on switching device, whether it be MOSFET or IGBT.
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Post by Nevilleh » Sun, 25 Apr 2010, 16:55

Yes, that's the resistor all right. No current sense without it!

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Post by Nevilleh » Fri, 30 Apr 2010, 18:40

This LS controller is frustrating me a lot!
When I fitted a resistor as mentioned above, it all worked fine on the bench with a 35V power supply and a 2kw heater as a dummy load. But when I upped the supply to 150V I could only get about half power and the rate of response was much slower ie I could turn the throttle pot quite a bit before anything much happened. It seems that the spikes produced when switching at the higher voltage and current (a whole 5 amps!) cause the current limit to operate. Removing the resistor and hence current limiting makes it all work fine.

I am surmising that LS couldn't get it to work properly, so they just don't fit the resistor - but I find that hard to believe too. Anyway, I have written to them to ask about it and I await their reply, but for the moment I can't make it work properly. They don't have an email address, so I am trying snail mail.

edit:
I've set it up with a single IGBT driving a 12V quartz-halogen lamp and I can get enough spikes to cause the problem. So I hacked the circuit board and fitted a series 1K resistor and .001u capacitor to ground to act as a low pass filter and that fixed it quite nicely. At least for that configuration. Now to re-assemble the whole thing and test it on 150V again. Fingers crossed!
Last edited by Nevilleh on Fri, 30 Apr 2010, 09:31, edited 1 time in total.

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Post by Squiggles » Sat, 01 May 2010, 00:01

"Trouble is, there's no decent ground on the controller board, just a skinny track meandering all over the place."

Are you kidding?

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Post by Nevilleh » Sat, 01 May 2010, 01:41

No!

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Post by Squiggles » Sat, 01 May 2010, 01:43

Is it more than single sided?
Is it date stamped 1948?

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Post by Nevilleh » Sat, 01 May 2010, 01:50

Its double sided alright, but the design is really 1994. That's what they get for pinching the Curtis. But I am determined to make the bloody thing work! When I do, I will throw it away and replace it with a micro based board even if I have to design a whole new one. Wouldn't be hard to do it better.
Maybe, if it drives the car OK, I'll cut my losses, put it on eBay and use my Cougar one (that I haven't built yet) instead.

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Post by Squiggles » Sat, 01 May 2010, 02:20

When you start to design your PCB go four layer, use the internal layers for GND and VCC. There are benefits that make the small additional cost worth it.

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Post by Nevilleh » Sat, 01 May 2010, 13:15

Yes, good thinking, thanks for the suggestion.

I'm waiting for a reasonably priced ac controller!

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Post by HeadsUp » Sun, 02 May 2010, 04:03



given the choice of a 15 year old design in the Azure dynamics DMOC 445 for $ 5500 or a leading edge Tritium 200 kw controller for $ 6600 i dont think there is any argument

azure can kick itself in the bum and run all the way back to canada

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Post by Nevilleh » Sun, 02 May 2010, 13:07

Indeed. The choice is limited - and expensive.

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Post by Nevilleh » Tue, 13 Jul 2010, 20:01

My, how time does go by! Since my last post, I managed to get the LS controller working OK, but it still gets hot - too hot to touch even with the fans running, so I built an OpenRevolt one and that will be going into the car shortly. Unfortunately, I have been away for the past 6 weeks or so which means not a lot has happened, but now I'm back and raring to go.
Hope to fit the new controller this week and then do some tests - seems the thing to do is make a video, so I'll have a go at that too.
Pleased to see Weber & Coulomb making progress.

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Post by Nevilleh » Fri, 20 Aug 2010, 18:48

The Cougar controller is now installed and operating. The car has been driven on the road with it - done 38 kms - and it performs quite well.(although still not legal)
I had the two ADC motors wired in parallel which was OK for the LS controller as it could dump more than 1000A into them, but this one can only make 500A with the result being rather poor acceleration off the line. Apparently one can alter the controller parameters to change things like acceleration and so on and I did try changing the ramp rate from 6 to 12 but didn't see any real difference. Now I have re-wired the motors in series and the acceleration is quite reasonable with 0 - 60 taking about 6 seconds, but the top speed has dropped with the thing getting to 80 kph quite nicely but then dropping off quite a bit and just able to make 100 kph. (I didn't try for more as I was in a 60 zone!) I think another contactor or two and a series-to-parallel switch if I need that sort of speed will be the go.
Interesting to note that it draws about 60A at 60 kph and with a battery voltage of 143 that means the input power is only 8.6 kW. This is quite a bit less than what the parallel connection with the LS controller was. Since my battery holds about 20 units of electricity, that equates to about 2 1/2 hours of driving at 60 kph or a range of 150 kms!!
That current figure came from RTD Explorer and its not actually recommended trying to read the notebook screen with one eye and driving with the other.
All in all, I am pretty pleased with the performance so far and expect to achieve better results when I get a chance to fiddle with the controller parameters a bit.
Still haven't gotten around to making a video! And I haven't finished the BMS which really must now take priority.

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Post by EV2Go » Fri, 20 Aug 2010, 19:23

Congrats Neville on becoming mobile once again Image any chance of some updated photos?

Did I see a picture somewhere that you are using an Acewell electronic speedo? if so keen to hear your thoughts.
Last edited by EV2Go on Fri, 20 Aug 2010, 09:31, edited 1 time in total.

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Post by Nevilleh » Sat, 21 Aug 2010, 13:22

Yes, its time I did some new photos and I really want to try and make a video when I can figure out how to mount the camera. I must say its all a lot of fun! I stopped at a petrol station (used to be called "service station", but that's long gone) to pump up the tyres and when I left I nearly ran over a bloke who just walked straight in front of me from one of the pumps. Makes you aware of how quiet these things are.

No, I haven't used the Acewell speedo as the original BMW speedo works OK, being driven electronically from a sensor in the diff, but the odometer doesn't work for some strange reason. I only know how far I've traveled because it is a route I follow almost daily in a car with a working odometer!

I've studied the wiring diagrams but can't find any reference to it. It must be something to do with all the wires I have cut relating to the engine control unit, but its certainly not obvious so I suppose I will have to pull the speedo apart to see what makes it tick. If anyone knows anything about this, I'd be grateful for some advice.

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Post by Zapper » Tue, 31 Aug 2010, 05:22

Hi Neville,
I am keen on doing a 318 also.
Why did you choose 2 x L91 motors?
Would a single say Warp 9 have done (& fitted?)OK?
Have you found it OK with no g'box? (is the diff ratio OK?)
Is the acceleration OK at the hi & lo ends?
What revs are you doing at say 100k?
Your feeds are great - keep it up!
Regards
Zapper

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Post by Nevilleh » Tue, 31 Aug 2010, 13:39

I wanted a fairly light car with rear wheel drive that didn't cost too much and the BMW 318 (E30 model) fitted that pretty well. Light - obviously! Original weight about 1070 kg and finished up about 1150 kg - I need to check this yet on a weighbridge, that's theoretical.

RWD because all the FWD cars have the gearbox integral with the diff and I really didn't want to keep the gearbox, on the grounds of both efficiency and convenience for driving. Plus I thought RWD would preserve better weight distribution and I think that is true as the two motors and frame of about 85 kg replace the engine, gearbox and radiator of 210 kg plus I have about 130 kg of batteries with boxes in the front and another 85 kg of battery stuff in the boot.

You can pick up a reasonable one of these for a few thousand dollars and they still look quite good in spite of their age. At least I think they do!

I originally thought to use a single big motor, but when I took the engine and gearbox out, I found the 9" motor wouldn't fit in the transmission tunnel. After a bit of investigation, I decided two Advanced L91s would deliver more power and torque and one would fit down where the gearbox was, while I could mount the other in front of it and still not take up all of the engine bay, leaving room for batteries and stuff. And that's what I did.

I originally wanted a Zilla controller, but they weren't making them when I wanted one, so I bought the LogiSystems thing, being the only other one I could find at the time that would do 1000A - which I wanted for the torque. Big mistake! The LS thing was a total piece of junk and if you read back you will see how much time and money I wasted on it. I built an OpenRevolt/Cougar one instead and that is now driving the car. I have the LS one going again and it works OK now that I have modified it, but it still suffers from a very jerky start, so I'm not using it. One of these days I will adapt a Cougar board to drive it and so get a 1000A controller again, but meantime I have made the Cougar do the job.

It is limited to 500A and I found that with my motors in parallel I didn't get enough torque to produce reasonable acceleration, so I have now wired them in series and it accelerates quite well up to about 80 kph then quite slowly past that ie you keep your foot down for ages and it slowly creeps past 90! I'm thinking of adding another contactor and switching from series to parallel at high speed. Oh no, a gearbox!

I'm still fiddling with the Cougar parameters to find the best settings and I'll do some real performance measurements eventually, but at the moment I'm quite happy with it driving in the 50 and 70 zones that abound here. It certainly doesn't hold up the traffic!

I note that the acceleration with the LS controller and the motors in parallel was better than I am getting now and it got to 120 kph OK, so eventually that's what I hope to see when I get the controller uprated to that level again.

If I was doing if all again, I'd really hang out for a Zilla and save a lot of heartache.

The diff is 4.1 to 1 and a lower ratio would be better too.
I don't have the tacho connected up yet, but you can calculate the motor rpm from the 195/65/14 tyre size and that diff ratio ie 3570 rpm.

One reason I haven't done any proper measurements yet is that it is still not certified to drive legally and I have a couple of little jobs to do to get that done. Things like finishing the 12V battery charger, getting the heater/demister going, new windscreen as this one has a big crack, signs saying "Electric" to stick on the front and rear (where do you get these from?) and it needs new tyres! Also, the speedo works but the odometer doesn't, which I find quite amazing. Anyone got any ideas about this? And my BMS is still not finished, but I have the circuit boards for this arriving today, so not too far away.

I hope all these meandering thoughts are helpful.
Last edited by Nevilleh on Tue, 31 Aug 2010, 03:45, edited 1 time in total.

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Post by leighf » Tue, 31 Aug 2010, 19:52

Hi Neville
I had an E30 323 and they are notorious for failing odometers (mine did as well). Apparently the plastic gears get brittle and crack. The BMW forums have info on this.

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Post by coulomb » Wed, 01 Sep 2010, 03:11

Nevilleh wrote: ... signs saying "Electric" to stick on the front and rear (where do you get these from?)

There is a discussion on this important topic in Barnard's Toyota MR2 - now Mr240.

Do you have a SuperCheap Auto chain in NZ? Or equivalent? Individual letters sounds like a reasonable way to go, or the Electric emblems from Cloud Electric (US$5.95 + postage; not sure where the $76 came from).

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Post by evric » Wed, 01 Sep 2010, 03:52

I think the postage on these was the killer. I'd like some too...
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Post by Johny » Wed, 01 Sep 2010, 15:58

The curly script doesn't suit mine so I was going to use these italic letters.
http://www.stickyletters.com.au/style_ital.html
or for straight ones these.
http://www.autoemblems.com.au/index.php ... 083442ebc3
I also found curved letters but they are in the USA.
http://chromeemblems.com/ind-letters-numbers.aspx

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Post by woody » Wed, 01 Sep 2010, 17:10

For older cars like ours, what about cutting the "ev" from Chevrolet / Chevelle badge?LikeImage TheseImage
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Post by Nevilleh » Fri, 03 Sep 2010, 15:58

leighf wrote: Hi Neville
I had an E30 323 and they are notorious for failing odometers (mine did as well). Apparently the plastic gears get brittle and crack. The BMW forums have info on this.


Thanks for that, I'll have a look. Haven't taken the speedo out of the car yet, too many other things to do!
And thanks to the others for ideas about "Electric". Super Cheap Auto do exist here - I never knew they sold sticky letters though.

Last edited by Nevilleh on Fri, 03 Sep 2010, 06:01, edited 1 time in total.

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