# VW Polo 86C (1991) AC conversion



## jhuebner (Apr 30, 2010)

*VW Polo 86C (1991) AC industrial conversion*

Now that I'm getting close to finishing the conversion that started out with a Renault R4, I shall start a build thread.

First, the specs:
- 152 LFP040AH in series for an idle voltage of ~500V
- 18.5kW Industrial ACIM (Lenze MFEMAXX132-22C1C)
- Homebrew AC controller (using 1200V, 400A IGBTs)
- Homebrew BMS
- Inverter Charging
- LiFePo4 System battery charged by an ebay AC/DC (no DC/DC converter)
- Audi vacuum pump (8E0927317) for braking with Audi pressure sensor (036906051G) and homebrew control electronics (some resistors, an NPN transistor and a relay)
- Heating element from a 230Vac heater with a custom solid state relay
- 800V, 16mm² "solar cable" for the DC connections
- 4x6mm² for the motor connection
- Lots of wood, aluminum and fibreglass

I have kept as many original components as possible. For example the original throttle had a pot already, so I could use that. I added another rear defroster switch for cruise control and a pot that controls max regen torque.
I use the existing temperature and fuel gauge as well as the warning lights. Reverse gear is selected with the transmission.

Drive video: http://youtu.be/70uQymh2TGQ

Nov 2014: The car was approved by TÜV Nord to be road worthy

Okt 2015: The car has now done 9000km with 120km commutes. Had a few issues with the charger and a screw from the transmission came loose. No other issues.


June 2017: replaced EMW charger with "software charger" i.e. using inverter and motor as a boost mode charger


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## cts_casemod (Aug 23, 2012)

Forgot to ask on the other topic, what voltage is your motor? 208V Delta?
I would add some temperature probe to those batteries. 
Being that they are all in series it might make driving in winter a bit tricky as the rear ones may be hotter and offer better soc that the front ones.
Regeneration below freezing is a big no as well.

Looking Nice, good work


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## jddcircuit (Mar 18, 2010)

That is a lot of cells.
Excellent job. Very inspiring.

Jeff


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> Forgot to ask on the other topic, what voltage is your motor? 208V Delta?
> I would add some temperature probe to those batteries.
> Being that they are all in series it might make driving in winter a bit tricky as the rear ones may be hotter and offer better soc that the front ones.
> Regeneration below freezing is a big no as well.
> ...


Yes 208V delta but its not connected in delta right now. So [email protected] nominal.
The BMS has a temperature probe. Not for each cell, just for ambient temperature. 
Regarding the freezing issue: in my other car I witnessed that the batteries become a bit "soft" as in high resistance when its freezing. So the sag or rise of voltage happens much faster than in warmer temps. Thus, the usual voltage monitoring should be sufficient for protection.
As you've driven along for a while the issue heals itself as heat is produced inside the cells.



jddcircuit said:


> That is a lot of cells.
> Excellent job. Very inspiring.
> 
> Jeff


Thanks


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> 208V delta *but its not connected in delta right now*. So [email protected] nominal.


What have you done to change that, rewind? Weakening the field above 90Hz or is it in star?
For most motors 208V refers to 60Hz (190 @ 50Hz), so 415V @ 120Hz for constant torque (double horsepower). 



jhuebner said:


> The BMS has a temperature probe. Not for each cell, just for ambient temperature [...]
> So the sag or rise of voltage happens much faster than in warmer temps. Thus, the usual voltage monitoring should be sufficient for protection.
> 
> As you've driven along for a while the issue heals itself as heat is produced inside the cells.


I was worried about regeneration. No charging should be done below 0C, so the voltage should be regulated to 3.3VPC by the controller when this is happens (Average cell voltage) so that:

a) There is not excessive regeneration (Forcing you to use the brakes)

b) Any excess will be consumed by the loads (DC-DC, Heater) but only a small amount will go into the batteries

c) Your controller will dump the excess into a resistive bank (useful in winter anyway)


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> What have you done to change that, rewind? Weakening the field above 90Hz or is it in star?
> For most motors 208V refers to 60Hz (190 @ 50Hz), so 415V @ 120Hz for constant torque (double horsepower).


Ok, thats a conincidence. It is connected in star.
Lenze has a special series of motors for inverter operation only. So all rated values are at 120 instead of 50 or 60 Hz.




cts_casemod said:


> I was worried about regeneration. No charging should be done below 0C, so the voltage should be regulated to 3.3VPC by the controller (Average cell voltage) so that:
> 
> a) There is not excess regeneration (Forcing you to use the brakes)
> 
> b) Any excess will be consumed by the loads (DC-DC, Heater) but only a small amount will go into the batteries


Frankly, turning off regen below some temp limit wouldn't be a big deal.
Speaking of charging, the batteries will have to bear with that. I will charge them at -10C. That may wear them out sooner, it doesn't instantly break them.

Taking care of it or not largely depends on the quantities we talk about.
If I can increase the cycle life from 8 to 10 years by implementing cold weather cases I'd consider it worthwhile. If I increase it from 19 to 20 years or 9.5 to 10 years I'd consider it a waste of time and convenience.


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> Ok, thats a conincidence. It is connected in star.
> Lenze has a special series of motors for inverter operation only. So all rated values are at 120 instead of 50 or 60 Hz.


Now I got it. But don't they work in constant horsepower above 50/60Hz? They might just be rated for operation up to 120Hz. Some even for 200. 

This might be useful:
http://forums.aeva.asn.au/forums/changing-an-induction-motor-voltage_topic1237.html



jhuebner said:


> Frankly, turning off regen below some temp limit wouldn't be a big deal.


You wont turn off, only reduce the theresold voltage. 
This way the motor will only brake enough to power your loads, BUT it will still do regeneration needed for traction control specially useful for a car without ABS on winter. You should also increase the delay time so that acceleration/deceleration are done a bit slower to avoid locked wheels

Ideally your controller should enable an external load when it reaches the theresold, so you still have regeneration, but you aren't killing the batteries with 2-3C Charge bursts



jhuebner said:


> Speaking of charging, the batteries will have to bear with that. I will charge them at -10C. That may wear them out sooner, it doesn't instantly break them.


You can charge them but at a very low C rate. Capacity is reduced by 50% (Check out the new leaf).



jhuebner said:


> Taking care of it or not largely depends on the quantities we talk about.
> If I can increase the cycle life from 8 to 10 years by implementing cold weather cases I'd consider it worthwhile. If I increase it from 19 to 20 years or 9.5 to 10 years I'd consider it a waste of time and convenience.


Its not always about how long they will last, sometimes its how much range you need. These cells usually fail with increased internal resistace, so altought the capacity may be similar they wont acept a fast charge or discharge so well. Bit like the old lead batteries.

Almost forgot, I tested a few LIFEPo4 and Li-Ions last year on cold weather. The Li-Ions, even at 0.2C had a permanent loss of capacity below 5C. The LiFEPO4 were a bit more forgiven but the capacity drifted and not equally between all the cells. Some most lost 5% or less, but one or two lost almost 20%


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> Now I got it. But don't they work in constant horsepower above 50/60Hz? They might just be rated for operation up to 120Hz. Some even for 200.


No no, this motor has never been designed to run off the wall. It can only be operated off an inverter. So everything thats usually rated at 50Hz is now rated at 120Hz. Judging by the weight (66kg), this motor would be rated 7.5kW at 50Hz. But at 120Hz its 18.5kW.




cts_casemod said:


> Almost forgot, I tested a few LIFEPo4 and Li-Ions last year on cold weather. The Li-Ions, even at 0.2C had a permanent loss of capacity below 5C. The LiFEPO4 were a bit more forgiven but the capacity drifted and not equally between all the cells. Some most lost 5% or less, but one or two lost almost 20%


Ok, that actually sucks. What exactly was your test?


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> No no, this motor has never been designed to run off the wall. It can only be operated off an inverter. So everything thats usually rated at 50Hz is now rated at 120Hz. Judging by the weight (66kg), this motor would be rated 7.5kW at 50Hz. But at 120Hz its 18.5kW.
> 
> Mine does 15KW at 100Hz / 380V with 55Kg, so it sounds about right what you are saying.
> 
> ...


A few discharge tests with the batteries frozen. 
Ive run some equipment with a data logger out in the street when everything was covered in snow and would fast charge them (2C) at those temperatures (-8, -10, -20 from the freezer).

Capacity was mainly constant, internal resistance increased (So less current could be pulled, limiting the C-Rate at high discharges).

The Li-Ion did perform in overall worse that LiFePo4.
I don't know how they will react with short peaks from regeneration or if they are at different temperatures. My batch was 12Cells.

One Thing: Its an old myth from lead that these batteries warm up when driving. 
The average current is only enough to warm up the middle cells during a drive IF they are inside a box. 

My 10Ah pack would get 10C above ambient, inside a box, in the boot with the DC-DC and the inverter heating the surrounding air. With brief 5-8C Discharges during aceleration. I imagine that yours, at 40Ah would get even less.

My Test pack would get 5C higher than ambient with a constant 2C discharge. (25 minutes)


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## jhuebner (Apr 30, 2010)

Quicks heads up.

I've put all the HV wires into orange tubes as thats a requirement for getting the car registered. Apart from that it looks cool and adds some protection of course. Will take some pictures sometime soon.
I installed the BMS on the front pack. I left the laptop with a small php script in the car and could watch the charging process in my warm appartment. What an improvement 
Unfortunatly I also found, that the IR communication almost breaks down as soon as the inverter is running. Didn't happen with the trunk pack so it must be caused by the proximity to the inverter. On the plus side, if the communication catches some values, they look plausible.

I also made a decision on the DC/DC issue. There are devices available for 500V+ for around 300€ (http://www.feas.de/netzteil-snt9412-p-588.html). But since I'm a cheapshit I will use my ebay AC/DC converter (14V, 20A) to charge the 12V battery while the main pack is charged. Should I run into trouble I can always upgrade to something better. Don't comment on that, I'll try it anyway 

Apart from that I tackled the legal issues. Or at least tried to. Here is the best case: http://zeropolomobil.blogspot.de/
He ended up at an inspector that spent 3h looking at the car, trying it out etc. and in the end approved. No EMC/EMI certificate was needed so the whole procedure cost him 300€.

My own research was frustrating as hell. "Experts" told me about "be prepared to spend 10000€ on expert opinions", "the laws have changed significantly 2 years ago" bla bla. I don't know why they do it, maybe they have orders to keep DIY off the road.

Anyway, the zeropolo story gave me hope again that its not so difficult after all.


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> Quicks heads up.
> 
> I've put all the HV wires into orange tubes as thats a requirement for getting the car registered. Apart from that it looks cool and adds some protection of course. Will take some pictures sometime soon.
> I installed the BMS on the front pack. I left the laptop with a small php script in the car and could watch the charging process in my warm appartment. What an improvement
> ...


Good to know you are up and going again,
Thought you were all set some time ago? Where did you get the orange tube?

I had the same issues. Everything worked nicely on bench, put the motor on the car and the encoder signal gets erratic values. This happens because the extra torque/magnetization under heavy load makes the wires act as antennas and its a real pain in the ass. To solve I designed a circuit with a few transistors to make the signals low impedance (Using current mode) and the host converts this back into a high impedance voltage source (1's and zeros).

The DC-DC you can use a center tapped pack with 2 HP server power supplies. They have a current share pin, so you don't run the risk of unbalancing the pack. They can work in current mode if the impedance is high enough (lead accessory battery) and two are good for 100Amps. 20Amps will get you nowhere when you decide to turn the fan to defrost the windows, headlights, wipers, rear defroster... I have 50Amps and on cold rainy days I run 80% load with all the crap on and a charged battery.

Get used to that with DIY... is always a battle. I think some people are just jealous, then is my friend said that a friend told him story 

Keep up the good work


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> Good to know you are up and going again,
> Thought you were all set some time ago? Where did you get the orange tube?
> 
> I had the same issues. Everything worked nicely on bench, put the motor on the car and the encoder signal gets erratic values. This happens because the extra torque/magnetization under heavy load makes the wires act as antennas and its a real pain in the ass. To solve I designed a circuit with a few transistors to make the signals low impedance (Using current mode) and the host converts this back into a high impedance voltage source (1's and zeros).
> ...


I got the orange tube from ebay. A week later I found it in the local hardware store, too.
About DC/DC like said: I'll try if the battery alone supplies all the loads for a typical drive. I will switch the lead battery for 4 LFP40AHA that are left over. 40Ah = 40A for one hour  The most I've seen were 30A (Radio, wipers, lights, rear defroster). If it doesn't work I'll get an actual DC/DC converter built for the job.

Ok, apart from that here is my idea of the heater and my idea of a solid state relay:










What you see is an isolated DC/DC converter, an 800V npn-transistor and a hair dryer core. The transistors base is switched by the thermal contact inside. If it switches off, the transistor switches off and the led switches on. I've only tried this with some 140V, will get it in the car later.

Besides that I've installed a plug in the fuel filler region as well as an RCD and an interlock switch behind the rear panels. Car plugged in -> inverter won't start. Inverter running and car is plugged in -> inverter is shut down.

Now it started snowing and I'm done for today.


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## jhuebner (Apr 30, 2010)

Ok, I have done a few things in the last couple of months and meanwhile the car has done 1500km with no real (see below) problems.

I have installed the heater core from a cheap heating ventilator in the spot where the original water heater resided:









It is switched by a 1200V IGBT that is operated using an isolated DC/DC converter.

More things are:
1. Installed the EMW charger. Its set to charge at a humble 4A - at 500V though
2. Installed a fuse box. 6A for the heater (it draws about 4.5A), 6A for the charger, 4x25A in parallel for the drive system.
3. Hooked up the temperature gauge. It only ranges from 60-120°C where the motor can operate up to 170°C. Oh well... At 125°C an LED starts flashing (original logic from the VW gauge system)
4. Broke the fuel gauge when testing it...
5. Equipped the inverter with the latest revision hardware.

There are two more things to do before attempting another visit to the TÜV people:
1. Get the fuel gauge to display something meaningful
2. Indicate that the car is ready to go. I want to add an LED to a reserved spot in the original VW gauge

Problems that occured in the 1500km test run:
1. On one occasion the inverter shut down while driving for no apparent reason. I.e. one of the shutdown signal fired for no reason. The inverter could be restarted by giving it the "start" signal. Never happened again. But I have a hunch it might happen again...
2. After driving pretty much full throttle for 15km the inverter shut down because the motor apparently overheated. Back then I was driving the motor with more slip than necessary so I hope this is not going to happen again.


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## jhuebner (Apr 30, 2010)

I fixed the fuel gauge and installed a "ready to drive" LED. It is in the blind spot that is only used by Diesel cars for the pre-glow (or whatever) light. The ECE-100 requires such a light because there is no engine hum to tell you the car is ready to go. I might find its fairly annoying at night and place another resistor on it. It is hooked up to the DC switch signal:










FB means "*f*ahr*b*ereit" - drive ready.












Here is the final layout of the engine compartment. All battery monitoring modules are installed and are working nicely. The auxillary battery is amde up of 4 40AH LiFePos and are still being charged by the AC/DC converter while the regular pack is charged. In summer its full after 30 minutes or so.

The fuse box contains 4x25A fuses in parallel for the inverter, 6A for the charger and 6A for the heater.










Orange tubing underneath the car.


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## jhuebner (Apr 30, 2010)

Last week I installed a current sensor board and a beagle bone acting as central unit to my homebrew BMS.

The current sensor board also contains a relay and a PWM output. I use the latter to drive the fuel gauge, The relay turns off the charger when done.

Today was rather frustrating. I installed new software on the voltage sensing board (26 of them). As a side effect some boards lost their calibration data and I needed to unmount and recalibrate them.

Then I figured that the boards restarted every now and then sometimes loosing their address and/or calibration data. I ended up ripping them all out as to finish software flashing on my desk.

That is work waiting for me that week.

I then decided to read a book on an almost fatal mountaineering tour to convince myself that there's worse than spending 3 days bent over a battery pack


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> Last week I installed a current sensor board and a beagle bone acting as central unit to my homebrew BMS.
> 
> The current sensor board also contains a relay and a PWM output. I use the latter to drive the fuel gauge, The relay turns off the charger when done.


Just a warning: newer gauges wont accept a PWM signal for the fuel gauge. They have their internal "pulse check" logic and go into a fault mode if the signals don't match.

A digital POT is what I am using on mine. Damm technology


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> Just a warning: newer gauges wont accept a PWM signal for the fuel gauge. They have their internal "pulse check" logic and go into a fault mode if the signals don't match.
> 
> A digital POT is what I am using on mine. Damm technology


That is stupid indeed. So the digital potentiometer, is that an IC? What do the gauges expect? Current? Voltage?


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## cts_casemod (Aug 23, 2012)

The cluster sends a 5V pulse and measures the voltage drop to GND across a resistive element (the fuel sender). The higher the voltage the lower the fuel level. Anything out of a certain range and the needle goes to zero

If the voltage is different from zero between pulses it goes into fault.


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> The cluster sends a 5V pulse and measures the voltage drop to GND across a resistive element (the fuel sender). The higher the voltage the lower the fuel level. Anything out of a certain range and the needle goes to zero


Thats horrible 

I hooked up the BMS central computer yesterday to be booted by the DC switch signal. Must have made a mistake and blew the transistor. That means: open up the controller and swap the transistor. That in turn means: remove the front battery pack because it sits on top of the controller.

Anyway, I'm glad I had to. When I opened up the controller it was soaking wet inside. That explains why the bus voltage measurement was sometimes off. Actually I'm surprised the controller still worked as it did. 

But worse to come: The screws of 2 phase cables had almost fallen out of the IGBT modules. Only 3 more turns and they were out. I'm totally puzzled by the fact that the car still drove normally.

I will clean everything up today, renew the sealing and give the screws more torque.


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## jhuebner (Apr 30, 2010)

Finally! I passed the EMC Test!










We tested as defined in the ECE R-10. One run from the left side, one from the front while the motor idled at 6000rpm, one idle run with the car turned off.

The poor car had to sit a the rev limiter for almost 2h. The motor heated up to 120°C.

The EMC expert of the company I work for did all the tests. That is really really nice of him. But he seemed very excited about the project and glad to help. He'll still get the mandatory case of beer.

The diagrams a a bit hard to read. Basically you do the runs and then compare them to the idle run. All frequencies where the idle run surpasses the limit are masked out.

All remaining frequencies that surpass the limits are scheduled for another run at different antenna heights. Sometimes the peak is gone because it was caused by a bypassing airplane or other artifacts like that.

So, by these standards the limits were never surpassed.

Here are some things that I did towards EMC compliance:
- Use shielded AC cables
- Use snubbers and good film caps on the DC bus
- Put a 1nF cap from DC- to GND and DC+ to GND
- Put a ferrite around the DC cables

All DC cables that run through or underneath the car are UNSHIELDED  I'm glad to still pass the test.


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## jhuebner (Apr 30, 2010)

So today I went to the TÜV to get the car approved.

The engineer was overall satisfied with the design. Now I have to fix a few minor things like protecting the AC input cable from tire splash, use self locking nuts for the motor mount etc.

After that the car is finally officially road-worthy 

I followed the guideline of "MB FZMO 764".


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## tylerwatts (Feb 9, 2012)

Congratulations


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## jhuebner (Apr 30, 2010)

Thank you


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## jhuebner (Apr 30, 2010)

So, today was the second and last visit to the TÜV. It took only 1/2 hour to establish that everything they found last time is now fixed. Now I have an official certificate that makes the car road legal 

I'd consider this TÜV station a recommendation for everyone who wants his conversion inspected:
Dipl.-Ing. Ulrich Siebold, TÜV Nord
Rudolf-Diesel-Str. 5, Göttingen

I'd consider this project 100% finished.

I never really calculated the cost and I think I never will. Inside the car is 
a 6000€ battery pack
a 1000€ AC motor
a 1000€ charger
a 500€ inverter (because the expensive parts were free)
a 300€ BMS 
about 1000€ of cables, wood, alloy, switch gear and other little things.
So lets make it a 10000€ conversion.

I invested about 5000€ in equipment, rent, prototypes etc.

The original top speed was 142 km/h, the new top speed is 120 km/h. Thats due to the motor hitting its maximum power at only 2800rpm. I took it on the Autobahn on my way home and hit 130 km/h (80 mph) in 4th gear. But it felt like being ready for take off, definitly not a high speed car.

I'm a bit sorry to have ruined the lightness. The original weight was 765kg, now it's 1045kg. Not sure what happened here. The batteries are 230kg but in turn the fuel tank is gone. Maybe cars a weighed with an empty fuel tank?

The energy consumption is around 200Wh/km in the hilly Kassel terrain.


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## Boxster-warp (Jun 22, 2014)

Hello
Congratulations 
I am boxster-warp from Germany too.
I come from the near off the "Pott"

I make a dc conversion and Hope my tüv say "its all ok"

Greetings Boxster-warp


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## jhuebner (Apr 30, 2010)

Thanks 

It depends largely on who inspects your car. Make sure to get the VdTÜV 764. It has all the requirements.

Before attempting to visit them I made a table with the number of the requirement and how I (think I) fulfilled it. I also sent them datasheets of motor, charger and batteries.

The engineer who checked my car was very pedantic on the high voltage cable protection. I couldn't quite relate to that. Basically I used the original clips of the fuel pipe for the DC cables. The DC cables are inside an orange plastic tube. The tube is interrupted for about 1cm where the clips are. So now he wanted me to cover the clips as well. Seriously, there was an unprotected fuel pipe in there before! If that gets damaged the effects are by far worse than a scratched high voltage cable. Anyway, I covered the clips and everything was ok.

Let me know if you need any more help.


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## jhuebner (Apr 30, 2010)

Here is the "emergency map" I made because it is also a requirement:


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## Boxster-warp (Jun 22, 2014)

Hello
Thank you for help when i needed.

The German tüv is already pedantic :-(
I think a ac conversion is easyer then a dc conversion.

I want a porsche boxster with warp 11 and netgain classic controller.

Its what Great That you a homebuild ac controller with tüv Proof have.
Greetings Ralf


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## jhuebner (Apr 30, 2010)

On thursday I handed the car over to a friend for some more testing. Immediately two things went wrong (that worked fine for over a year):

1. The precharge relay died
The small relays don't seem to be up to the job.

2. On his 10km trip the aux (12V) battery went dead. So the inverter was unpowered and the car stopped.

This might cast a shadow on my DC/DC converter-less design as some have predicted.

We charged the battery back up (Cells were sitting at 1.5V) and will swap the precharge relay next week.


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## jhuebner (Apr 30, 2010)

1/2 years into the experiment.

As some know I have been to Australia for the last 6 months. During that time I handed over the car to a friend for some test driving.

First thing he did was deplete the battery pack. My fault really because there isn't much to stop you from doing that.

Then the car stopped in heavy rain because the encoder is too exposed.

Next a piece of metal came loose in the charger and connected the IGBT output to the case. That caused the IGBT to short out. And that was it, pack depleted, charger dead. I have no idea how that piece of metal could go where I found it.

It was easy to get the car alive again. Fix the charger, replace the fuse, replace two dead cells and charge up.

I also discovered 2 problems with the cell boards:









Resistor R18 (4.7R) which is supposed to limit the effects of over voltage together with TVS D1 has gone bad on a couple of boards. Also the infrared diode LED1 likes to detach from the PCB. I'll replace it with a SMT version if I ever do a next revision.

Conclusion: small issues stopped the show.


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## jhuebner (Apr 30, 2010)

Added a self-retracting cable reel. So now I no longer need an addional cord for charging 










It's mounted underneeth the car.


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## Tomdb (Jan 28, 2013)

nice idea just like a vacuum cleaner.

When designing a small urban car (max 45km/h) at my previous job we also implemented a self retracing reel. However the plugs were swapped at the factory for us, however this meant making the car idioot proof so you cant drive off with the charger connected or cable rolled out. 

However on a DIY car this wont be such an issue since the driver wont be an "complete" idiot.


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## jhuebner (Apr 30, 2010)

German TÜV let me get away with a logic that prevents you from driving off while the charger is powered. So at least you can't rip anything off the wall.

With just the cable rolled out you can take off with a tail 

And btw I am a complete idiot  With my former car I did take off with the cable plugged in. Fortunately it came out without doing any damage. Reason was that I was using an outside outlet at my former company and they had me turn it off from inside the building whenever I left. So there you have it: charger not powered but cable still plugged in...


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## jhuebner (Apr 30, 2010)

Repost:


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## Moltenmetal (Mar 20, 2014)

I put the interlock to prevent driving away while charging in place right from the get-go. I had a block heater in my gen 2 Prius in an effort to improve winter fuel economy, and drove away with that plugged in way too many times!


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## jhuebner (Apr 30, 2010)

Did a fun trip yesterday, 130km from Kassel to Bielefeld.

The car would have probably made in on one charge but I wanted some juice left. Therefor we towed it for about 10km behind my other Diesel car. That charged the pack at [email protected]=20kW  On that short trip we topped up 20%. The motor got very hot though as the cooling airstream was blocked by the car in front.

But cool experience, can't tow a petrol car and have put petrol back into the tank 

Downside: shortly before we got to the destination I had very hard regen and then over current trip. Turned out the optical encoder was touching the encoder wheel and failed to deliver a proper signal. Moved the encoder wheel a bit and all was good. Might have been due to the excessive motor heating.


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## jhuebner (Apr 30, 2010)

This weekend I made the trip from Oerlinghausen to Kassel and back. That is 114km one way.

I arrived with 30% SoC where 100% is 35Ah. That makes it 25Ah per 114km. While driving the battery on average sits at about 480V making 25Ah 25x480=12kWh. So 10.5kWh / 100 km. 

Off the wall I'd multiply it with the charging voltage of 515V for 11.3kWh / 100km. Must say I'm pleased with that, its less than VW specify for their e-Up (11.7 kWh / 100km)


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## Tomdb (Jan 28, 2013)

any idea of the average speed?


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## jhuebner (Apr 30, 2010)

Took me roughly 2 hours, so 60 km/h


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## cts_casemod (Aug 23, 2012)

Good idea with the retractable ones. Always a pain to unwrap the cable 
I just sent you a PM, somewhat it seems the forum doesn’t notify anymore!


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## jhuebner (Apr 30, 2010)

First official winter season has started. The heater works but it's not particularly powerful. Below 0°C you do want to wear a jacket while driving. It draws [email protected] so 2kW


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## EVElvis (Jun 20, 2009)

Hi Johannes

Thats good to know. 

Confirms my car will need a little more heating. Main challenge is to keep glass all clear?

lined my car with Superquilt insulation which should help keep some heat in.

How many km have you done so far with your DIY inverter ?

cheers


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## Karter2 (Nov 17, 2011)

> ..The heater works but it's not particularly powerful. Below 0°C you do want to wear a jacket while driving. It draws [email protected] so 2kW


 ..interesting ?
..i would have expected a 2kW heater to cook you in a small car !


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## jhuebner (Apr 30, 2010)

Karter2 said:


> ..interesting ?
> ..i would have expected a 2kW heater to cook you in a small car !


No, prrobably because the car is not insulated at all. When you turn it off it immediately cools down.



EVElvis said:


> How many km have you done so far with your DIY inverter ?


10000km or about 6000 miles


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## jhuebner (Apr 30, 2010)

Here is some cold weather experience.

It's currently down to -10°C and snowing. On Tuesday I did a 50km trip. The battery temperature was around -5°C. The voltage sag was terrible, down to 2.4V on full load. But I kept going and the batteries started to heat up. The sag went up to 2.8V and had arrived at around 3.0V when I arrived. The BMS showed an average +5°C pretty equally over the packs (back and front).

The 2kW heater was running most of the time. It kept the windscreen from frosting but it wasn't exactly cosy inside the the car.

Next, snow driving: drifting is awesome fun in an EV  I did find a weird bug though: when I slam on the brakes so the wheels (not the car) come to a full stop and then I step on the accelerator again, the controller does a strong regen braking and eventually the over current limit trips.

If I let the car come to a full stop and then take off again, all is good.


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## cts_casemod (Aug 23, 2012)

Tell me about cell sag lol! I have a full 80V sag at -5C if I push 2.5C on my battery. Last year I added a current limiter to the DC-DC converter, otherwise the caps keep blowing the fuse.

Also at -5C, the 5KW heater is fully on unless the fan is at speed 1 or 2. The car is warm and cozy tough. Lets see if it gets any colder here.

I fault my inverter if the speed suddenly drops to zero (or a large swing anyway). Technically the regen should brake the car with the motor online. If the user requests excessive mechanical braking and the wheels block or decelerate faster than the motor speed loop the inverter costs the motor.

This also avoids the wheels loosing traction due to excessive Regen braking (although that can be avoided with a slower speed loop)

I guess you could add a similar mod to your firmware


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## bigmotherwhale (Apr 15, 2011)

sounds like you need a heat pump, get an old air conditioning system and use it in reverse, 
COP of around 3 or 4 so you would be using 500w for 2kw of heat. 
if you use a car air con system they have a neat electric clutch that you could connect to the brake switch for further gains, i've been trying to get someone to do this but so far no one seems particularly interested.


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## cts_casemod (Aug 23, 2012)

bigmotherwhale said:


> sounds like you need a heat pump, get an old air conditioning system and use it in reverse,
> COP of around 3 or 4 so you would be using 500w for 2kw of heat.
> if you use a car air con system they have a neat electric clutch that you could connect to the brake switch for further gains, i've been trying to get someone to do this but so far no one seems particularly interested.



I tried it, it doesn't work. Even as low as 5C the evaporator turns into a solid block of ICE. It's fine above 10C with defrost cycles.

It could be debated that in cold climates where the relative humidity is low and the ice is not a problem this could work, but at such temperatures the COP would be close to unity as there wasnt much available heat to pump .

The bit of the clutch and the brake system... You know that the refrigerant needs to reach a certain pressure to produce work right? This takes a couple of seconds. On a case where the vehicle has regenerative braking there is not really a gain. Better power the A/C from the main pack.


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## bigmotherwhale (Apr 15, 2011)

Yes you are right about the clutch system, it wouldn't work very well now ive thought about it, pelters work do instantly but have terrible efficiency but still better than a resistor. 

there is still plenty of heat to pump at 5c

if the temperature is lower than -26 (for r134a) then switch to a lower boiling point substance, like propane it has a boiling point of -42 

as for the icing problem, you have the wrong type of evaporator, you need a flat plate in this application not a heat exchanger type, the plate will have to be quite big. you can find flat plate types in the back of some fridges and they are very lightweight. 

it makes no difference that the ice will build up other than you will be lugging round a big block eventually and you will have to defrost it. Ice without air pockets isn't a very good insulator.

BTW when you compress air, the tank gets very hot, if you could take away that heat to a cabin heater, you would have an open type heat pump that theoretically works down the boiling point of air. turn off the cabin heater and then run the compressor in reverse now where is the energy coming from to drive the compressor? its coming from the surroundings  good thing about this is that its self defrosting. very efficient indeed. 

im sure it can be made to work in some way, burning energy in resistors cant be the way to go. 
all the best.


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## cts_casemod (Aug 23, 2012)

bigmotherwhale said:


> Yes you are right about the clutch system, it wouldn't work very well now ive thought about it, pelters work do instantly but have terrible efficiency but still better than a resistor.
> 
> there is still plenty of heat to pump at 5c
> 
> ...


COP will go down with temperature regardless of the evaporator type and for practical reasons one wants to use what is already on the vehicle to avoid carrying any additional dead mass.

Have a look at the heater I use on my EV, that should convince you not to reinvent the wheel


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## bigmotherwhale (Apr 15, 2011)

whether its worth the weight is questionable, but i don't think changing style of heat exchanger is going to add any additional weight, and there are obvious advantages to a system like this if you can get it to work.

If the wheel you invent is twice as efficient as it was before i see no reason why you shouldn't do it, if you are inclined, if your happy then fair enough. 

I will certainly have play with something like this if i can, im going to use peltiers as i already have aload from my overclocking days. But i would like to get hold of scroll compressor or two, I love the idea of being able to double your money so to speak.


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## Moltenmetal (Mar 20, 2014)

The only way a heat pump system is going to be worthwhile is if you can use it in reverse for AC in summer, which you can- then it would rock. Otherwise, resistive heating is a small range hit in return for a much simpler, cheaper and more robust system. Of course your battery heating is going to remain resistive regardless.

COP in winter for an air-source heatpump is going to be pretty poor below about -5 C, but it'll still be greater than unity. But by the time you're down to a COP less than 2, your cabin heater will be undersized again and you'll need a resistive heater as backup.


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## bigmotherwhale (Apr 15, 2011)

If you are working against a gradient efficiency will of course suffer. 
How much will of course depend on the medium used.

there are other ways of increasing the efficiency such as extracting heat directly from the motor, power electronics, and also the gearbox to a certain extent.
if you can cool these down the efficiency of them will increase as well as removing the parasitic load from resistive heating. 

I do think a system like this is worthwhile, it is just complicated and may take a lot more effort to get working. 

My plan is to extract waste heat from the cooling loop of my car, but first i have to build one.


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## jhuebner (Apr 30, 2010)

I had some problems with the encoder that suddenly spawned. I took the whole front apart and rerouted the encoder cable to interfere less with the power cables. I also connected the shielding to the inverter chassis instead of the GND Pin 1 for a more direct connection.

Maybe most importantly I changed the low pass filter. R3 and R4 are now 500R and C1 remains at 22nF. That results in a rising edge cut off frequency of 7.3kHz and a falling edge cut off frequency of 14.5kHz. 

Before it was 5.4KHz and 60kHz. So vastly asymmetric with the spikes that the 60kHz lets through and the slowness of the 5.4kHz cut off.

I have changed the BOM accordingly.

Driving is now back to normal.


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## jhuebner (Apr 30, 2010)

Finally added a kwh counter to the BMS. Made it start at 0 after the last recharge.

I did about 20km city driving in 2nd gear. That took 3.45kWh out of the battery but also put 0.66kWh back in. Thats a regen rate of 20%. Must say I didn't expect that much.

Economy works out to (3.45-0.66)kWh/20km=140Wh/km


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## cts_casemod (Aug 23, 2012)

jhuebner said:


> Finally added a kwh counter to the BMS. Made it start at 0 after the last recharge.
> 
> I did about 20km city driving in 2nd gear. That took 3.45kWh out of the battery but also put 0.66kWh back in. Thats a regen rate of 20%. Must say I didn't expect that much.
> 
> Economy works out to (3.45-0.66)kWh/20km=140Wh/km


How are you getting your Wh Figures? Volts * Amps?


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## jhuebner (Apr 30, 2010)

cts_casemod said:


> How are you getting your Wh Figures? Volts * Amps?


Yes. I know it's cheating a bit, because you have voltage sag when pulling current and voltage rise when putting it back. But in summer thats only +/-3% on light loads, i.e. the battery sags to 490V and rises to 515V.

Just did a test drive on the Autobahn with the batteries nicely charged. Reached 150km/h  But the drive shafts seem to have quite some run out and the car vibrates pretty bad 

I also found out that I can shift gears when turning down regen all the way to 0. The motor then slowly looses speed and the next higher gear slides in smoothly. Same for shifting down, only you need to blip the throttle. But it takes a second or two until speeds match.

I tried this quite a while back by simply turning the ignition off and it didn't work at all. Maybe I can get some 0-100 figures now


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## jhuebner (Apr 30, 2010)

Winter driving update: planned a 90km trip with a lot of Autobahn. The summer range is 120km. It's below 0 currently. So I added 10 extra cells (+7%) rigged up on the rear seat and drove the car with full power for a while. Then charged it all the way up just so it finished at the start of the trip. Battery temperature had risen to about 16°C.

We got to the destination with 30% charge left.

On the way back there was no opportunity to heat the batteries by driving. Just relied on some heat being generated while charging.

Now the SoC tumbled faster and I got back with just 12% charge left.

The charge voltage measurement died back at the destination. That results in the charger taking ~10 minutes to ramp up to the full charge current. Maybe it happened because of the 35V extra?
Anyway it's a good motivation to throw out the EMW charger and replace it with "software" charging by the inverter.


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## EVElvis (Jun 20, 2009)

Good stuff, how is the heating in the car? Can you heat the car when it is on charge? 
Always thought that a good selling point for EVs in winter use would be the car can preheat with no need to scrape ice from the glass, often twice a day when it is frosty like today is in the UK. No need to start the ICE engine to let it warm up and leave it alone like many people do round where i live. Apparently many cars get stolen being left to warm up this way.
cheers


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## jhuebner (Apr 30, 2010)

Yeah I can preheat with the charger plugged in. The 2kW heating is struggling to keep the car warm below -5°C or so. Probably because it keeps sucking in cold air.

Defrosting works great though, just leave the blower on for 5 minutes and the wind shield is defrosted.

Today I didn't use the heater, I think we wouldn't have made it. We were in the car wearing gloves, caps and wool socks


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## jhuebner (Apr 30, 2010)

For a year now I am using inverter charging. I can set it to 3kW on one phase without fuse tripping. So thats an approximate power factor of 0.85.


The sheer mass and size of heat sink and motor allows me to charge at 3kW without using any fan at all. Still the 8kHz wine of the inverter is loud enough but not relying on active cooling eliminates another failure mode.



Car has now done about 20.000km


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## Boxster-warp (Jun 22, 2014)

Hello
Fine good work.
I think i Must Visit you and Look the nice Polo.
Greetings Boxster-Warp


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## jhuebner (Apr 30, 2010)

Thanks 
Sure, I live near Kassel


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