Hacked Serial Cable Details and Bad Relay

A few people asked me about how I hacked together a serial port since AC kit people will need this in order to configure the controller correctly.


I basically took three 16 gauge wires (smaller would be fine) and soldered on crimp sockets at the end of each one. I also added heatshrink tubing so that adjacent signals wouldn't short out. The picture above shows the three wires plugged into the top three pins on the 8-pin connector on the controller. Yellow is Txd(controller to PC), blue is Rxd (PC to controller) and brown is ground.


Here's a view of the heat-shrunk ends with the sockets crimped and soldered on.


To connect to the PC, I got a female DB9 connector with solder cups. The solder cups were designed to handle 20 or 22 gauge wire, so I had to trim down the 16 gauge wire to fit into the cups. Txd to the PC goes on pin 2, Rxd goes on pin 3 and ground goes on pin 5. All connections were soldered to solder cups in the top row.

From there, I just used a long male-female 9-pin serial cable to connect to the male DB9 on the back of the PC. Again, if you use HyperTerm, the settings are 19200baud,N,8,1, no handshake.


Remember the flakey relay I found yesterday. Here it is, removed from the car. One set of contacts was highly resistive. I replaced this relay with the charger interlock relay from the front relay mounting board to get the car working. Afterwards, I pried off the clear plastic cover (off to the left in the picture) and used an extremely thin file to break through any corrosion on the bad contacts. The contacts on the common swing arm were actually slightly bent so only a tiny corner of the common contact touched the normally-open contact when the relay activated.

I'll keep this relay around as a spare since I replaced the front charger interlock relay with a normally-closed SPST relay from the auto parts store.

The car seems to start much more reliably now.

Next up: getting more performance and acceleration..... maybe.

Power calculations

After looking at the specs on the ElectroAuto website, I'm thinking that a maximum input power rating of 50000 watts is really too much. Here are the ElectroAuto specs:

AC24 Aircooled Motor

Length	Diameter	Weight	Controller	Efficiency
15.55"	9.45"	83.6 lbs.	DMOC445	83%

Specifications @ 156 V Input
	Ft.Lbs.	Amps	RPM	HP	KW
Peak/Maximum	54.57	280 rms	12,000	57.66 @ 4,500 rpm	43
Continuous	22.12	180 rms	12,000	18.77	14

55 Ft-Lbs peak is 75 Newton-meters. The controller is programmed for 100 Newton-Meters.
I'm guessing I should probably back off the peak wattage to 43,000 as listed in the chart unless I want to severely harm the life of the motor.

The original Porsche 914 2.0L engine had about 90 peak HP so this is definitely less. It looksl like I'll have to shift more often to balance the motor torque with my desired speed. The regenerative braking makes shifting really hard, so I'll probably have to utilize the regen-disable switch more often.

I also think I figured out what the high-pitched squeal/scraping noise was. The controller puts out a 10Khz PWM signal to modulate the three AC waveforms. I hear this squeal during acceleration and regeneration, but if I let the motor spin freely by putting the accelerator in the middle, there's no squealing. The squealing never changes frequency either. I didn't expect the motor to be that noisy... Live and learn.

The last big issue I probably have with the car is that the flywheel is probably out of balance. When the motor hits about 4500 rpm, the whole car starts vibrating rather nastily. This means I'll probably have to take the transmission off again and have the flywheel balanced, or re-turned by someone before general use. Urg.

I sure hope people don't have to put up with my mistakes on their own 914 AC conversions!

Good night.

Debugging, Debugging, Debugging...

Okay, things don't seem to be working too well. We have three issues:

1. The controller simply cuts out at high acceleration (bad)

2. Many times the controller doesn't even start up at all

3. There's very little power from the system, I can't go much above 30mph

After sending error logs to Azure Dynamics, they came back with the following:

"Vehicles with improper or substandard grounding and shielding sometimes exhibit nuisance errors flagged as EE3LastError = 16. Once every measure for improving the grounding and shielding has been taken, it is OK to disable this error if the problem persists. This can be achieved by setting EE2DisableChargedError = 1."

It's very true that I forgot to add the grounding strap to the DMOC controller that ElectroAuto provided. So I added the strap with anti-corrosion compound and made sure to scrape the metal clean on the bottom side of the bolt on the chassis to make a good contact.

Here's the grounding strap provided by ElectroAuto bolted in. Unfortunately, this didn't help much with the problem. I found that turning down IdsMax from 400 amps to 380 amps did help the problem. Also turning down the MaxAccelTorque from 100Nm to 85nM helped too.
Given that the car has not a lot of power to start with, I set the EE2DisableChargedError to 1 to get past the issue with all the original settings.


Okay, next up is the problem with things just not starting at all. I logged more variables and saw that the ISR2CarDirection status register was zero when the car failed to start and 1 when the car worked. This pointed to the "Forward" signal on pin 29 of the DMOC controller not getting properly grounded.

I double checked the connections on the neutral-start relay in the engine compartment and everything looked fine. I even looked at the contacts to make sure they were in the right place. It turns out when I wiggled the wires on pins 6 and 9 ("ground" and "forward"), the CarDirection bit randomly toggled between zero and one.

To debug further, I took two other wires with crimps and measured the resistance between the two contacts on the relay. The resistance was often infinite or around 5-10 ohms. This really caught me off guard since I put a lot of faith in relays, especially Potter and Brumsfeld's. I'm probably going to take the relay out tomorrow and see if I can open it up to see if something is damaged. I would have suspected my own wiring, but not the relay... (sigh).

I have to show off the car tomorrow to a bunch of friends and I can tap the neutral start relay now to get things running.


That leaves the problem of not having a lot of power. I could get up to about 30mph on residential streets in 2nd gear, but not much past that. I'm guessing I'll have to shift up and take the torque hit.

The power thing was really confusing to me because the current measurements as listed in the controller ccShell diagnostic tool said 400 amps. I wasn't seeing a huge voltage drop, so I didn't believe the controller, at least from a DC-current point of view. Sooooooo, I ran out to my favorite overpriced EV hardware store: WestMarine. They had a 150 amp shunt-based ammeter there for $90 (ouch).


This is the 150 amp ammeter shunt. It's in the place of the most-positive battery terminal in the fuel compartment. The shunt is remarkably small compared to the pictures I've seen of the ElectroAuto shunt. Also, placing it in the fuel compartment makes it much closer to the dashboard, so there will be less signal loss over the shorter wires to the dash.


Here's the ammeter dial itself (the camera flash whites out the background). It seemed to work quite well. At full acceleration, it pegs at 80 amps almost all the time. This is a lot less than the 400 that the ccShell window states. I suspect that the 400 amps is some internal calculated number of instantaneous current going through the stator instead of an actually measured value.

After messing around with several parameters, the only ones that affected the current draw were the EE?MinPowerAccel, EE?NormPowerAccel and EE?MaxPowerAccel. Since I haven't hooked up the dashboard switches and dials, the controller was operating in maximum power mode, so tweaking EE?MaxPowerAccel would limit the current to 40amps or raise it up to 95. I took a chance and bumped up the MaxPower from 31000 to 50000. I'll have to double check the power spec of the AC24 motor before using this too much.

Okay, enough for today. The kit requires the 12V accessory battery to run the exhaust fans while the car charges overnight, so I altered the circuit to use an external 12V laptop supply instead so I wouldn't drain the accessory battery.


Here's my temporary charging setup. The Zivan charger is in low-current mode (12 amps) and I have the 12V laptop supply also plugged in to run the exhaust fans.

Tomorrow: taking a break
Wednesday: dissecting the neutral-start relay and figure out why it doesn't work.
(I can replace it with the front charger interlock relay in the short term...)

Hoods Installed

Well, we're getting closer. My friend Rick and his friend Amy came over today to help install the front and rear lids. I was rather relieved when both lids closed without any interference. I installed the engine compartment cover this morning and realized that the rain gutter would have to be completely removed to not interfere with the rear battery box. With the rain gutter gone, perhaps it wasn't such a good idea to keep the two drain funnels and tubes in place...




I did a few more laps around the block this morning and played around with the parameters in the AC controller via the serial port. When I have the serial port plugged in, the controller fires up and things seem to work. If I power down and remove the serial port, nothing comes on. I'm trying to debug this further. Hopefully Azure Dynamics can get back to me by Monday to see if I've adjusted anything wrong.

I find that if I back off the maximum torque (EE?MaxAccelTorque), I can get get the car running without stalling, but I give up some power. I can also limit the stalls if I back off on the IsMax parameter from 400 amps to 380 amps. For some reason I find it very difficult to imagine that I'm pulling 400 amps from the batteries. The voltage doesn't seem to dip that low and I don't get much acceleration. I would think the car would have more pep pulling 400 amps.

With the serial port yanked, I had to push the car back into the garage for more analysis. This is all part of the learning process and I look forward to learning more...

Pictures from Randy

One of my fellow 914 AC kit EV'ers is Randy Pollock. He's been extremely helpful in my understanding of how this kit works. About three weeks ago, he sent me a few pictures on his own 914 AC EV project that uses the Electro Automotive kit. Here are his pictures and text (verbatim) from his e-mail: (Thanks Randy!)
---------------------------------------------------------------------------------
Hi all,

Attached are some pictures from my rear trunk now that I have the
Avcon receptacle wired to the Manzanita Micro charger. The junction
box next to the receptacle has two green idicator lights. If only
one is light, then 110V is present - 220V lights both. I have both
the Avcon charging station with will put out 220V and an extra cable
that I've added a 110V plug to the other end. So far I've only
tested the 110V cable and it starts up the charger as expected.


There is also a close up of the cooling fan I added. The small
component to the [left] (not completely wired yet) is a 105F on/90 F
off thermostat switch. When the trunk starts getting hot from either
the charger or the AC motor controller, the fan will kick on. It is
a very powerful side exhaust fan that should be able to turn the air
in the rear trunk over ever 30 seconds. It kicked up some dust under
the car when I tried it out. Note that the thermostat is mounted on
nylon screws so that it is sensing the air temperature, not the sheet
metal temperature.



The last picture shows the four 2" holes I cut behind my PORSCHE
reflector on the back of the car. You can't see anything from
outside, but since the reflector stands almost 1/2" off the sheet
metal, you can get reasonable air flow.


I do need to cut the mouse hole for the Avcon cable. It will be cut
out of the trunk lid. I have a spoiler that provides enough material
to make it work.

Just thought you would like to see.

- Randy

Closing the Boxes and Fixing the Suspension

I took a few minutes (just a few) to go out with friends to celebrate.


Here's my girlfriend Krista enjoying a very brief ride to the bottom of the driveway. The front tires still bottom out when I turn the wheels too hard, so I'm holding off major test drives.


Here are my friends (Krista, Ruth and Rick) just before we went walking to get some gelato on this fine day.


Okay, back to work after a good night's sleep. My first concern was the front of the car bottoming out. Fortunately one of the steps in the manual is to adjust the front torsion bars.
The Haynes manual covers this reasonably well.

The center of the torsion bars were supposed to be about 8.5 inches off the ground. Initially they were 5. No wonder I'm having issues.

Turning the torsion adjustment bolt was far too difficult with all the weight on the tires, so I jacked up each side of the front of the car and tightened both bolts until the center of the torsion bar was about 8 inches above the ground (after letting the front end back down).


Here's a closeup of the torsion adjustment nut. Its the nut on the very bottom that turns the vertical bolt that you can see the threads on. This picture was taken tooking toward the front of the car from just behind the front-right tire.


Next step was to finish the battery box covers. Here are the covers and hold-down bars in place for the front two battery boxes. For the rear bar on the front battery box (under the charger tray), the holes for the bolts line up exactly with the vertical walls of the cups on the bottom side of the cover (at least for the bar I was given). I had to re-drill these holes about an inch further out to the side to not interfere with the internal hold-down ups.

The hold-down cups on the bottom of the middle battery box interfered with the tabs on the speed-caps for the batteries. I took my cable cutters to one of the two tabs on each speed cap to fix this issue.


For the rear box, the lid was too big to fit between the passenger wall and the rear luggage wall, so I had to use vise grips to bend the rear luggage wall back about 1/8" so the lid would drop in.
I also had to knock off one of the hold-down cups on the bottom side of the lid because it interfered with the fusible link that I modified to fit around the speed-caps. With the other hold-down cups in place and the copper bars holding the batteries together, I didn't feel that this would be a huge safety issue.

The black wire going up over the roof of the car is the serial cable going to my laptop in the passenger seat.

After a few more test drives around the block, I've noticed that the controller tends to cut out suddenly under a heavy torque load. I can get the controller to die just by putting the car in reverse and flooring the pedal to leave the garage, so I don't think this is a reasonable limit. I'll be researching all the parameters again to see if there are some "unreasonable" limits I can increase without harming the system.

Next Up: Putting all the lids back on!

First Driving Test!

Well, I carefully fixed the black grounding wire to the motor encoders and the system seems to work fine now. I got the AC motor to rev up quite quickly in neutral. Both forward and reverse movements are fairly smooth.

For yucks, I drove the car around the block. It has very slow acceleration, probably due to all the battery weight. I drove it in second gear. Third gear seems to not want to go in, at least while the car is stopped. The regen braking seems to work fine. The front end is rather heavy with batteries and the tires scrape something in the wheel wells when I back out of the driveway down the small cement slope on the curb.

There is much to do, but I at least know it runs and that I'm probably not going to race it at Nedra...

Off to celebrate with a brownie and a very much needed nap. Yay!