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Lead Wing's BMW E30

Posted: Fri, 26 Aug 2016, 19:50
by leadwings

My EV has been going for 6 years now, so I thought I would post a list of the issues I have had. In general I have been very happy with the performance and reliability, and while there have been issues there have been less issues with it than our 2008 VW Passat!! (though admittedly the EV has done a lot less km in the 6 years we have had both). Considering this is a 30 year old car and a home conversion (ie to me a prototype level of development), having issues is to be expected.

While every home conversion is unique, I thought I would make the notes below in case any of them are of use to others – as other people’s posts on forums have been of great use to me.

Tail Shaft Vibrations
In my conversion we removed the gearbox and put the motor where the gearbox was, and as the BM is rear wheel drive the drive shaft connects straight onto the back of the electric motor. The E30’s had a funny rubber bush adaptor and 3 bolt flange on the drive shaft and back of the gear box. In hindsight we should have taken the spline mount from the back of the gearbox and used it to make up an adaptor to the back of the electric motor to help get proper alignment.    When we first got the car going there was a shake/shudder, particularly around 40 to 60 km/hr. It took a few visits to the mechanics before they got the alignment right – there is still a slight shudder at 50 km/hr.

Reversing Contactors Stuck
The car has a forward/reverse switch where the gear leaver was controlling the reversing contactors. However as it was originally wired, you could switch from forward to reverse while under power – arcing the contactors. While I was aware of this and avoided doing it, I suspect when the car was in the mechanics for the tail shaft work they may have switched it under power, and shortly afterwards when I was driving the car (at 8pm at night with my 8 month pregnant wife in the car) the contactors welded.

Luckily it was not too hard to bypass the reversing contactors, so it became a forwards only car and got us home. I pulled the contactors and replaced the welded contact faces (I happened to have a spare contactor) and the car was up and running again.

To avoid it happening again, the 12V power to the speed controller enable now goes through the other set of contacts in the forward/reverse switch, which is a 3 position double pole switch. So in the forward position the switch powers the forward contactor with one set of poles and the speed controller 12V enable with the other, middle position is “neutral” and disengages the forward/reverse contactor and the ESC, and the reverse position powers the reverse contactor and the speed controller 12V enable. So I you flick form forward the reverse the ESC momentarily loses its enable signal, so cuts the drive power so there should not be any power through the reversing contractors when they switch. This means it takes slightly (1 second) longer to switch from forward to reverse, but this in reality is not an issue.

One Battery Tends to go High on Charge
This was an odd one. One cell in particular tends to go high (ie over-voltage) on charge. Most of the time it is just is the first (well ahead of the others) to go into top balancing, but sometimes it actually trips the charge system out on high voltage (ie cell gets to greater than 4.2 V). Now I figure it must be a weaker cell than the others, but even on deep discharge long drives (100 km plus, 130+ A Hr discharge from a 160 A Hr cell) I am not getting low voltage warnings from that cell. Maybe it had higher hysteresis on charging than the others?

This has not been an issue since I have lowered the pack voltage (see next item).

Balancing Module Shunt Stuck and Other Fault
When I first set up my charging system, I set the set point for the charger voltage too high (3.65V per cell) which resulted in the balancing shunts in the monitoring units on each cell bypassing till charging was turned off. As this results in the shunt generating heat, a couple of them failed after about 6 months. I don’t consider this a criticism of the EV Power system, as they are not designed to be dissipating around 3W continuously for a period of time (ie hours on end).

When they failed, the shunt was passing continuously at around 0.5 A draining the batteries down over time. Luckily I caught this before the cells were completely dissipated (one cell was 2V when I found it) and so I changed the cell module and recharged the depleted cells, and the cells have been fine since. In now have my charging set at around 3.5V per cell. This results in the odd cell shunt coming on for top balancing, but then turning off once the pack is balanced.

I also had another cell monitor fail but not with the shunt open, but it did cut the “I’m happy” daisy chain to the BMS resulting in a warning buzzer going off. Unfortunately this was an intermittent fault, but eventually I found the erroneous unit and replaced it.

I now have a half dozen spare cell monitors in case others fail.

Parasitic Drain Losses
As I bus/ride my bike to work most days of the week, and when the kids were first born the wife used the other car (getting newborn twins into and out of a 2 door car is a pain!) the car was only getting used by me on weekends, and sometimes not for a few weeks. I was finding that there were parasitic losses from the 12V system when the car was sitting unused (I suspect in back feed to the 12V/144V converter??). I can’t remember the exact figure, but I remember working out it was about 20 A/Hr per week from the main pack – not huge, but a waste and a pain. And if left for a few weeks may flatten the main pack.

I thought about adding relays either side of the converter, but in the end under the bonnet next to the 12V battery I have a battery isolation switch on the lead to the 12V battery and the big red button on the main pack, and I just switch both off when I think the car won’t be used for a few days. One day I may try and find the losses and put something more elegant in place, but it does for now. This is also useful if I know the car will be sitting for a long period (eg going away for holidays) that the batteries are all isolated and won’t drain down while I’m gone.

144V/12V Converter Stopped Working
I originally had a Mean Well 144V/12V Converter. This unit had a lot of openings for ventilation, and I suspect was not designed for the environment found under the bonnet of a car which is exposed to spray/mist/dust etc. So it is not surprising it stopped working.

I have a cheap 12 volt gauge that plugs into the car cigarette lighter to see what the 12 V system is at, and noticed the voltage was getting low compared to the usual 13.6 V. Quick diagnostics showed the problem was with the converter, and that it was beyond my ability to fix it! So I charged the 12 V battery conventionally, drove up to EV Works and bought a new 144V/12V Converter (which is supposed to be IP 65) and all has been good since.

Throttle Pot Broke
My original conversion had a 0 – 5K ohm type throttle pot. One day when I was driving along the field suddenly collapsed and the car stopped going. Being a Windows user I took the basic trouble shooting method – turned everything off and on again. All came up ok, but as soon as I applied throttle it would cut out again. Got a mate to tow me home, and plugged in the Zilla to the laptop. There was a loss of throttle signal logged error code. Using Zillaview I could see that as soon as the throttle got to 20% position it would lose throttle position signal. Diagnostics quickly showed the throttle pot in the throttle assembly was going open circuit as it swept. Google showed this was a common problem with the resistive type throttle pots.

Rather than replace it with the same type, I got a HEPA (ie hall effect) type and a hall effect to resistive type converter from ZEVA. No problems since.

Cooling Circuit Issues
I have mimic units on the dash that have red LEDs and buzzers for the error signals from the Zilla speed controller and the BMS. After around 5 years of use I noticed that sometimes under hard acceleration (a common state for the car) a warning would blip briefly then go away. Over a few months the warning would come on earlier and more often.

I plugged the laptop into the Zilla and checked the error codes – none made sense to the problem I was having, eg “main contactor stuck open” – pulled the contactor and all was fine. “low 12V” – battery was fine, that was probably from not switching the 12V battery on. Problem was intermittent and not stopping the car from being driven, so we continued to use it and ponder the problem. The kids had fun counting how often the car would beep on each trip.

When riding my bike home one day I was thinking this was like a problem I used to have in my old 1964 EH Holden cooling system. So I plugged the laptop into the Zilla, pulled up Zillaview and went for a drive. Zillaview is great because it shows all sorts of interesting stuff, including Zilla temp. Sure enough as I drove the temp went up, and a soon as it hit 55 C the warning beeped.   I kept driving hard, temperature went up and beeping became more frequent. Stopped driving and let it cool and the beeping stopped, started driving and as soon as it hit 55 C it started again.

In my EV conversion I have a cooling water circuit that goes from a 3L metal tank through a pump to the Zilla speed controller cooling plate, then through the old dash heater and back to the tank. I ran it through the dash for 2 reasons – one it is my “demist” heat (ie takes heat from the motor/drive system just like when it was petrol to demist the windscreen – well that’s the theory anyway and was sufficient to me not to have to put in another heater Image ) and the second is the dash heater would help dissipate some of the heat generated in the Zilla cooling water circuit. If the Zilla is say 95% efficient (should be better than that), at a roughly say constant 10 kW that equates to 500W of heat – not a lot, but not insignificant either if it is not removed.

Anyway I pulled the cooling water circuit apart and sure enough the ports on the tank were blocked up with red gunk – ie 30 years of old gunk from the dash heater from when the cooling water came from the cast iron block. Flushed it all out, re-filled the cooling system and went for a hard drive with Zillaview on – no problem, temperature sits nicely around 30 – 40 C.

Anyway it winds up while the Zilla beeps an error on high temperature, it does not log an error – so when I was plugging the laptop in and checking the error codes it was not showing up.

Throttle cable broke
This one unfortunately happened to my wife – I got a call saying the car has stopped. Being a hands on chick, she even diagnosed the problem – the throttle cable had broken (luckily quite close to home).   So I went an met her and gave her the keys to the other car so she was on her way. Sure enough, the 30 year old throttle cable had broken where it is clamped on to the throttle pot using my home made clamp from a bicycle brake assembly. I had actually noticed it fraying a few months before but forgot to do anything about it.

Anyway to get it home I tied a boot lace onto the throttle pot, passed it round the windscreen and tied a loop in the end for my finger and drive it home (only about 500 m luckily). Then ordered a new cable from ebay, filed the clamp to remove any sharp edges and was back on the road in 2 weeks.

Hope these are of help to someone.

[ Edited Coulomb: Repaired bad Unicode chars in preparation for conversion to phpBB ]

Lead Wing's BMW E30

Posted: Fri, 26 Aug 2016, 19:52
by leadwings
Having real trouble uploading photos today!