[DRIVING] - Z3(00)

Tell us about the project you do with the open inverter
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bobby_come_lately
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Re: Z3(00)

Post by bobby_come_lately »

Ev8 wrote: Sat Sep 11, 2021 4:34 pm Nice work, I’ve just picked up an old myford lathe to help as I start working on the dc to ac swap for my RX8 I can sympathise with you lack of workspace I have a small corner in a friends garage I do electrical jobs for and an unpowered lock up garage that you can’t access with a car! But we do what we can with the space available right!
Totally. Love where I live but I just wish there was more space for projects!

Old Myford sounds really good. I'd like a proper one really but space determined what I could have, as much as budget.

I need to start letter dropping houses round here with garages again and see if anyone needs a bit of cash in return for letting it out.
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Re: Z3(00)

Post by bobby_come_lately »

PASS!

After a bit of a rollercoaster over the last two weeks, including another failure, the project has finally passed its MOT. Now the grin-wearing owner of a fully electric BMW Z3. Full story to come when I get a chance. Short version: brake flaring is a PITA, and always use PTFE on threaded hydraulic connectors.

Anyway, thanks everyone for the support and advice, hugely appreciated. Very happy man.
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Re: Z3(00)

Post by Ev8 »

Awesome well done
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Re: Z3(00)

Post by bobby_come_lately »

Ev8 wrote: Wed Sep 29, 2021 3:25 pmAwesome well done
Cheers!
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Re: Z3(00)

Post by bobby_come_lately »

Full, and very long update here. Forgive me, I normally repost everything to the forum but this one is just too much effort and it's late at night:

https://projects.tomcheesewright.com/20 ... ercoaster/
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Re: Z3(00)

Post by Jack Bauer »

Great work. Lots of lessons learned:)
I'm going to need a hacksaw
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Re: Z3(00)

Post by bobby_come_lately »

Cheers - and thanks for all your help. I've been asked to write a magazine piece about the project and will be giving you a suitable plug!
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Re: Z3(00)

Post by rstevens81 »

Damian screams no!!!! As his inbox fills with silly questions.
Rule 1 of EV Club is don't buy a rust bucket....
Which rule does everyone forget 🤪
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Re: Z3(00)

Post by bobby_come_lately »

Ha! I shall point them to buying things not asking dumb questions.
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Re: Z3(00)

Post by bobby_come_lately »

Through a weird series of connections, I got a phone call from a journalist on Thursday. She was looking for an EV owner to speak to about the fuel crisis. And...

https://www.manchestereveningnews.co.uk ... o-21728637
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Re: Z3(00)

Post by bobby_come_lately »

My first full week as the driver of a DIY EV was…eventful.

Let’s start with the bad. On Tuesday, I did what you might call an ‘accidental full range test’. As in, I ran out of juice on the way to collect my daughter from a class and had to dump the car and jump in a taxi to get her. Because I haven’t really worked out the range yet, and nor do I have a real gauge in the car for how much juice is left in the batteries, this was perhaps predictable. Hope is no substitute for electrons.

In order to recover the car I had to swap the modules for spares on the side of the road. This attracted a few comments and interesting conversations. Big thanks to my friends and neighbours Brook and later Owen (who has a very cool YouTube channel) for helping me to push the car to safety.

I was worried I hadn’t done the batteries much good, running them down to about 2.8V. But actually with some gentle charging on the bench, hooked up to a variable power supply and a bodged version of the battery management system, they came back up to voltage with very little persuasion.
20211020_071712.jpg
Turns out 2.8 is about the minimum specified for the pack so I hope there’s no lasting damage. Unfortunately, I killed yet another Teensy – the microcontroller running the BMS – in the process. These are parts that should not be consumables.

Gauges and charging
So, a ‘fuel’ gauge is something of a priority. This is a work in progress, using a CANbus-controlled variable resistor hooked up to the original sender lines (thank you Jamie). I could put this behind the dash but I’m trying to avoid taking that out for now.
20211020_071751.jpg
FuelCan by @Bigpie – CANbus controlled variable resistor
Also a priority is automating the charging process. For two reasons. First, I can’t really afford to spend hours sat outside in the car with my laptop while it charges. And second, I keep screwing up the charging sequence and blowing pre-charge resistors.

Typically I’m very careful the first time, and get the car mostly charged. Then I have to go in for some reason, so have to turn everything off, disconnect my laptop and take it inside. When I come back out, I do things in a slightly more distracted fashion. e.g. forgetting to stop SavvyCan from spamming out the messages that control the charger before I connect it up and turn the car on. As soon as the car gets to pre-charge, the charger kicks in and the pre-charge resistor is toast. Again, these are parts that should not be consumables.

Automating charging
Automating charging isn’t quite as easy as it sounds. Right now my car has three modes:
  • Off
    On (pre-charge)
    Run
‘Run’ means that everything is on: dc-dc converter, cooling pumps, vacuum pump, power steering. But it is also the only mode in which the contactors are closed – i.e. the batteries are connected directly to the charger and inverter and not through the pre-charge system. For charging, I want the contactors closed but only the water cooling system enabled. And I want drive to be disabled.

Originally I did this with a switch and a button in the cabin.
  • The switch turns on the ‘on’ mode relay. This has the water cooling pumps and fans on it.
    The button tells the inverter to close the contactors, but it doesn’t turn on the ‘run’ relay. This locks out the direction switch, ensuring the car stays in neutral.
The problem with this right now is that the switch is also connected to the ‘charge mode enable’ line on the BMS. If this were working properly, it would start the BMS communicating with the charger to tell it to pull in current BEFORE the contactors are closed, blowing the pre-charge resistor (and possibly more). And, because the dc-dc converter enable line is connected to the ‘run’ relay, the 12V system wouldn’t charge while the high voltage system does. This could see the 12V battery go flat due to the drain of the cooling pump.

So, what’s the answer?

Three options.
  • I add an extra relay that is latched when the ‘charge’ button is pressed. I move the ‘charge mode enable’ line to this relay, and add a connection for the DC-DC converter enable line here. This will need a diode on it to stop current feeding back to the rest of the distribution from the ‘run’ relay. This is the simple option
    I finally get around to adding a proper VCU – vehicle control unit – an extra brain that does a lot of the smart stuff. Like turning things on and off at the right time.
    I add a sensor to detect when the charging plug is inserted (another Jamie innovation). This triggers the ‘on’ relay and the charge mode line to the BMS. The BMS code is tweaked to send a ‘run’ signal over CANbus to the inverter and ONLY starts sending out the commands to the charger once this is confirmed. I move control of the DC-DC converter over to the BMS as well, having it trigger a relay whenever the inverter is in run mode, ensuring the 12V battery remains charged.
3 is my preferred option right now. It avoids me redoing all the wiring on the project at this stage and keeps things very neat. To that end I have printed a case for @Bigpie's PP detector (snigger) and installed that under the front bumper next to the charging port (which I had forgotten also needs redesigning/mounting, and is broken anyway as I tripped over the open flap cover). I am building up a second BMS to modify and test code on and hoping to get that installed at some point in the next week, along with the additional wiring to the ‘run’ relay.

Right now, CANbus communication between the BMS and the inverter isn’t working and I don’t exactly know why, so that might be the stumbling block. Investigation needed.

Cooling & heating
The one fix I have made to the car is on cooling, albeit only a temporary measure. On my first days driving the car, the temperature sensor on my inverter was frequently hitting 100 degrees and the coolant temperature was settling out after a long journey (~5 miles is long at this stage) at about 70 degrees. My radiator is too small and there just wasn’t enough water in the system to give it a chance to chill.

At the same time, it is getting bloody cold and I needed some heating. So I figured why not plumb the cooling loop into the heater matrix and kill two birds with one hose?

It half worked. Cooling is sorted. The inverter rarely spikes over 70 now and the coolant settles down at more like 30 degrees, especially if you put the heater fan on low.

But because the cooling has been so effective, I don’t really get any heat into the cabin from the blowers. Ultimately, I need to pull the whole lot out, fit a bigger radiator, and a proper heater and pump to the heater matrix, as well as a header tank to fill it. I’m assembling parts for this but not there yet.

Speed and range
Let’s finish up the bad stuff before I get onto the good. Simply put, range is a fraction of what I was hoping for. And the performance is a bit pathetic.

At the moment, maximum range seems to be about 15 miles. I was expecting over 20 and hoping for more like 30-40. I’m not sure why it is so poor but it may be connected to the issues with performance.

The car still trips out if you try to increase the current to the motor beyond certain levels. When it works at these higher levels, performance is more respectable. But the frequency of the cutouts and their unpredictability makes it undriveable.

There are various things that could be causing this and I will try to address them. But I have come to the conclusion that fundamentally this motor is too small to deliver the sort of performance that I want. So I will definitely be upgrading that before too long. In fact, not sure if I have already mentioned it, but I already have the upgrade…

The good things
OK, that’s all the negatives out of the way. What about the good stuff?

The car drives brilliantly. Despite all the changes to the weight distribution, handling remains confidence-inspiring and I’m now quite happy chucking it around roundabouts. There are a few knocks and rattles to sort but otherwise, I’m very happy to just get in it and go (assuming it is charged).

It puts a massive smile on my face every time I get in it.

So, lots to do but still very happy with where I’m at. So happy, I have started project 2…
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Re: Z3(00)

Post by Ev8 »

Sound like exactly what happened to me, only I tried to limp home as it was only a couple of miles and some cells went under 2v under load, so I stopped and got a tow, cells quickly recovered with charging, time will tell if I’ve done lasting damage! Quickly learned that lithium ion batteries just fall right off a cliff!

I think base settings in the simpbms bmwphev firmware for battery lower battery voltage are super optimistic at 3v also a recommend trying to set a realistic usable capacity in the ah settings so your soc isn’t over optimistic, like the modules are 26ah but maybe set the software to 20ah I think I’ve got mine set at 50ah now with 3 paralleled packs and that seems to give a soc that runs out before I get to bum twitching cell voltages!
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Re: Z3(00)

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bobby_come_lately wrote: Wed Oct 20, 2021 7:05 am Automating charging

The problem with this right now is that the switch is also connected to the ‘charge mode enable’ line on the BMS. If this were working properly, it would start the BMS communicating with the charger to tell it to pull in current BEFORE the contactors are closed, blowing the pre-charge resistor (and possibly more). And, because the dc-dc converter enable line is connected to the ‘run’ relay, the 12V system wouldn’t charge while the high voltage system does. This could see the 12V battery go flat due to the drain of the cooling pump.

So, what’s the answer?
It seems like you have your charger hooked up AFTER main dc contactor? That is a mistake.
I have my chargers permanently connected to HV.
Also you need to setup precharge in such a way resistor comes on via some DC relay and it connects main contactor via that resistor.
If you have DCDC and Charger after DC contactor it will interfeere with precharge for sure.
OEMs fight that with series of DC relays and complex control, i just connect my charger forever :).

Also you need to have a signal for when charging is enabled. You dont want to do that manually. I use EVSE PP signal to trigger charge mode which also disables inverter.
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Re: Z3(00)

Post by Bigpie »

I have my DCDC/Charger connected directly to the HV bus in the inverter, I don't want the HV to the charger permanently live. I've just got code that will not send the charge control can messages until the inverter signals the contactors have closed. Same with DCDC enable.
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Re: Z3(00)

Post by bobby_come_lately »

The only way I would have charger permanently live is if it were physically co-located with batteries so that the input to the charger is effectively inside the battery box. I don't want permanently live cables if I can avoid it. I like the fact that HV is limited to the battery box as soon as 12v shuts off.

I already have pre-charge working fine. It's just a question of a secondary control of it for charging.
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Re: Z3(00)

Post by arber333 »

bobby_come_lately wrote: Wed Oct 20, 2021 7:05 am
The car still trips out if you try to increase the current to the motor beyond certain levels. When it works at these higher levels, performance is more respectable. But the frequency of the cutouts and their unpredictability makes it undriveable.

There are various things that could be causing this and I will try to address them. But I have come to the conclusion that fundamentally this motor is too small to deliver the sort of performance that I want. So I will definitely be upgrading that before too long. In fact, not sure if I have already mentioned it, but I already have the upgrade…
I have seen similar with old LiFe batteries. At the time for power demand system requires voltage x amps from poor cells. When at certain level cells cannot provide more amps voltage across them plummets. To keep the power inverter tries to compensate and demands more amps... spiral down to OC limit. I would suggest you can: add more cells or replace battery.
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Re: Z3(00)

Post by arber333 »

Bigpie wrote: Wed Oct 20, 2021 9:30 am I have my DCDC/Charger connected directly to the HV bus in the inverter, I don't want the HV to the charger permanently live. I've just got code that will not send the charge control can messages until the inverter signals the contactors have closed. Same with DCDC enable.
Then i would suggest you connect your charger independently from the DC switch via another DC relay that is turned on only for charger. It could be triggered only by connecting EVSE cable into your car.
If you happened to burn precharge resistor twice, i would suggest to eliminate risk not just to mitigate symptoms by dodgy software loop. Again i am ME and i like mechanical solutions over electrical/softwer :).

EDIT: if i understood now for charging you power your precharge relay and then close DCswitch to provide HV to charger&DCDC&Inverter. But your inverter is still live during charging! You could use really large resistor and preset delay, but you run into a risk you will not reached precharge voltage and would just be better not to use the resistor at all.
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Re: Z3(00)

Post by Bigpie »

For my setup (different to bobby_come_lately's) I have a VCU that will only enable the DC DC when in 'Drive' or 'Charge' modes, my Prius inverter board controls the contactors.

My BMS sends out the can messages to control the charger, when in charge mode. Charge mode can only be entered if the contactors are closed.

Bobby_come_lately's current charging setup is rather more manual
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Re: Z3(00)

Post by bobby_come_lately »

Finally got around to editing some bits together.

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Re: Z3(00)

Post by Boxster EV »

Worth just fitting a HV PTC heater in the old heater box? Instant heat and a clean solution.
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Re: Z3(00)

Post by arber333 »

Boxster EV wrote: Fri Oct 29, 2021 6:41 pm Worth just fitting a HV PTC heater in the old heater box? Instant heat and a clean solution.
I thought of that one as well, but i dont like the smell of old socks :). Dust that settles on the core during summer makes a repulsive stink in winter...
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Re: Z3(00)

Post by bobby_come_lately »

arber333 wrote: Fri Oct 29, 2021 8:35 pm I thought of that one as well, but i dont like the smell of old socks :). Dust that settles on the core during summer makes a repulsive stink in winter...
Interesting. Didn't know that.

Long run, I may go down that route. The cleanness (and weight loss) of it appeals to me. But for now plumbing into the core is so easy - will be even easier once I've rearranged the engine bay for the new motor.
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Re: Z3(00)

Post by Boxster EV »

arber333 wrote: Fri Oct 29, 2021 8:35 pm
Boxster EV wrote: Fri Oct 29, 2021 6:41 pm Worth just fitting a HV PTC heater in the old heater box? Instant heat and a clean solution.
I thought of that one as well, but i dont like the smell of old socks :). Dust that settles on the core during summer makes a repulsive stink in winter...
Ha - not experienced that. I’ve either got a bad sense of smell or a better pollen filter. 😂
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Re: Z3(00)

Post by UStas »

bobby_come_lately wrote: Sat Sep 11, 2021 1:33 pm
Moar POWAH!
In the meantime I’ve been working on some other upgrades, starting with the inverter.

To date I have only been using half of its outputs – so called ‘MG 2’. But my control board supports me driving MG1 as well and bridging the outputs. This requires some simple soldering of jumpers on the control board (done) and then bridging the phase outputs on the inverter itself (half done).
20210910_150848.jpg
I’m using short lengths of 20mm2 wire for this, and fabricating copper connectors on each end. This is a bit of a pain of a job, but I’m getting there. Five connectors down and one to go. And some tidying. I want to clean up all the connectors and maybe add some more insulation, assuming it will fit inside the case.

Hi!
Did you fix the problem with inverter shuts-off due throttle kick-down?
You see effect after MG2+MG1 power gate paralleling?
Wich maximum current do you have?

Why you don`t paralleling MG1 busbars with MG2? Here is only 20mm2 per phase - it`s not enough
for 400+Amps phase current
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Re: Z3(00)

Post by bobby_come_lately »

UStas wrote: Wed Nov 10, 2021 11:40 am
bobby_come_lately wrote: Sat Sep 11, 2021 1:33 pm
Moar POWAH!
In the meantime I’ve been working on some other upgrades, starting with the inverter.

To date I have only been using half of its outputs – so called ‘MG 2’. But my control board supports me driving MG1 as well and bridging the outputs. This requires some simple soldering of jumpers on the control board (done) and then bridging the phase outputs on the inverter itself (half done).
20210910_150848.jpg
I’m using short lengths of 20mm2 wire for this, and fabricating copper connectors on each end. This is a bit of a pain of a job, but I’m getting there. Five connectors down and one to go. And some tidying. I want to clean up all the connectors and maybe add some more insulation, assuming it will fit inside the case.

Hi!
Did you fix the problem with inverter shuts-off due throttle kick-down?
You see effect after MG2+MG1 power gate paralleling?
Wich maximum current do you have?

Why you don`t paralleling MG1 busbars with MG2? Here is only 20mm2 per phase - it`s not enough
for 400+Amps phase current
So, to take those in order:
- Did you fix the problem with inverter shuts-off due throttle kick-down?
Not yet. Working on it. May still be temperature related. Experiments ongoing and a new video to follow in a week or so.

- You see effect after MG2+MG1 power gate paralleling?
Hard to say at the moment. I think the motor is the limiting factor not the inverter.

- Which maximum current do you have?
We recorded over 500A on Jamie's beetle last week with the same setup

- Why you don`t paralleling MG1 busbars with MG2? Here is only 20mm2 per phase - it`s not enough for 400+Amps phase current
Not sure I understand. That's what I and others have done without issue. The dimensions aren't much different to the busbars themselves. And you're not seeing huge current on those connections.
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