Porsche 914 EV Conversion

OCTOBER 12, 2007

The major project of the day was finishing the rain gutter under the engine compartment lid. The original gutter was too deep and interfered with the rear battery box. As described in a previous post, I purchased a piece of ABS plastic from TAP plastics and bent the edges to make a rain catch. Here's the plastic that I bent a few weeks ago. ABS plastic has the nasty property of deteriorating quickly in sunlight, so I spray painted it with three coats of Krylon black satin paint to protect the pl

Engine 100

Engine Cheap Installation Store 100

Porsche 914 EV Conversion

OCTOBER 13, 2007

Since I'm stuck indoors today to recover from a sore throat, I put together the following schematic to drive the fuel gauge based on the pack voltage. (Click to enlarge the image) With the exception of the 4N25 opto-isolator, which I salvaged from a dead UPS, all parts are available at Radio Shack. I hope to implement this soon. Comments and feedback are welcome.

Fuel 100

Fuel Available Parts 100

Porsche 914 EV Conversion

OCTOBER 10, 2007

After receiving admonishment from two mechanics about driving around with a resonant frequency, I dropped the transmission out of the 914 and gave it to the experts at Rennsport Systems this morning for a precision overhaul. This is the fourth time dropping the motor/tranny, so I was able to do the whole process in less than an hour. Giving up the tranny was an ego battle for me because I had spent so much time rebuilding the transmission in the first place.

Porsche 100

Porsche Motor Motors Motoring 100

Porsche 914 EV Conversion

OCTOBER 8, 2007

I started commuting to work again today. I think the transmission is making slightly more noise than before but otherwise the car is fine. The RPMs are limited to 5300 RPM, so I won't have any resonant activity. I'm really happy that the tachometer is hooked up. It really helps me keep tabs on what happens to the motor/transmission at different speeds under different driving loads.

2000 100

2000 Water Parts Motor 100

Porsche 914 EV Conversion

OCTOBER 6, 2007

Well, the car is all back together again. I really can't say it's any better than before; however, I've learned a tremendous amount in the process. After balancing the flywheel twice, adding rubber grommets, replacing the transmission mounts and putting in a new pilot bearing in, I still can't get the vibrations to go away or diminish much. Given that the second transmission didn't vibrate much at all, even over 7000 RPM, I'm really suspecting the existing transmission has a bent shaft in it or

Connect 100

Connect Connected Light Fuel 100

Porsche 914 EV Conversion

OCTOBER 5, 2007

Last week Craig at Camp914 offered to lend me another transmission to see if I had vibrational issues. I drove out to Camp914 this morning. I wish to express much gratitude to Craig for letting me borrow this spare tranny. Since it's an older tail-shifter and many of the external pieces are missing, he even gave it to me. Here's my test setup again.

Kits 100

Kits Plug-in Plug Oil 100

Porsche 914 EV Conversion

OCTOBER 6, 2007

After receiving an updated.css file (ccShell config file) from Azure Dynamics for the DMOC445, I was able to access the EE1SpeedoDiv variable. After setting this to a non-zero value, I attached a scope to pin 25 of the main DMOC connector and (yay!) got a pulse train corresponding to the RPM of the motor. Here's the pulse train on the oscilloscope. It has a 50% duty cycle and swings the full 12V range.

Light 100

Light Kits Green Buy 100

Porsche 914 EV Conversion

OCTOBER 6, 2007

I purchased a new pilot bearing for the flywheel to see if replacing it would help with the rattles. Flywheel - it's what's for dinner! I've found during my transmission rebuild that heating up components in the oven (200 F) sometimes helps with removing the bearings, so I heated up the flywheel prior to replacing the pilot bearing. I also put the new pilot bearing in the freezer to make it smaller.

Installation 100

Installation Purchase 100

Porsche 914 EV Conversion

OCTOBER 1, 2007

After spending most of yesterday researching machine resonance, I chatted with one of the mechanical engineers at work today about the resonance problem. After drawing a picture of the motor/transmission assembly, it became rather obvious to both of us that we have the equivalent of a vibrating violin string. The motor/transmission is attached to the car somewhat rigidly at both ends.

IDEA 100

IDEA Motor Motors Motoring 100

Porsche 914 EV Conversion

SEPTEMBER 30, 2007

My friend Rick dropped by tonight to run the accelerator cable and monitor the RPM on the laptop while I put my hands on the motor/tranny to get a better feel for what's going on. We ran the motor with the transmission attached for weight without the clutch friction plate. I also put the transmission in first gear to guarantee that the input shaft was not turning and contributing to any vibration.

Motor 100

Motor Motors Motoring Porsche 100

Porsche 914 EV Conversion

SEPTEMBER 30, 2007

At the suggestion of Paul J, I started doing research on vibration analysis today. There are several online tutorials regarding vibration analysis. I'm currently reading this one: [link] This paragraph taken from the "Natural Frequencies" section is somewhat noteworthy: 'The multitude of spring-mass-damper systems that make up a mechanical system are called "degrees of freedom", and the vibration energy put into a machine will distribute itself among the degrees of freedom in amounts depending o

Motor 100

Motor Motors Motoring Energy 100

Porsche 914 EV Conversion

SEPTEMBER 29, 2007

After successfully spinning the flywheel and pressure plate at 9000 RPM, I felt confident that things were looking good with the motor. I re-installed the clutch friction disk and bolted on the transmission. After spinning up the system, it started rattling and skittering across the floor around 5500 RPM. Geez. This is a royal pain. After pondering this a bit, I tried the following experiment: I unbolted the transmission, removed the friction disk inside the clutch that attaches to the transmiss

Motor 100

Motor Motors Motoring Installation 100

Porsche 914 EV Conversion

SEPTEMBER 28, 2007

Today had some ups and downs. I got the adapter hub from Electro Automotive back today. I installed it on the motor shaft and, to my delight, it had less than 1 mil of runout and wobble! That's how the hub is supposed to work. I put the flywheel and clutch back on and spun them up to 6000RPM without much vibration, so things are looking better. Before I mated the motor to the transmission, I wanted to try out the SPEEDO output on the DMOC445 that Beth at Azure Dynamics talked about in the previo

Motor 100

Motor Motors Motoring Installation 100

Porsche 914 EV Conversion

SEPTEMBER 21, 2007

I recently sent off an e-mail to Azure Dynamics, the maker of the DMOC445 AC motor controller in the 914 kit. I asked how I could tap into the motor encoder signals to create an RPM signal for the tachometer on the dashboard. It turns out that the DMOC controller already has a PWM (Pulse Width Modulated) output that can be used for this. There are also some LED signals that display system status without having to use the serial port.

Re-Charge 100

Re-Charge 2007 Kits Connect 100

Porsche 914 EV Conversion

SEPTEMBER 19, 2007

Rats. After putting the adapter hub from Electro Auto onto the motor shaft no less than twenty times, I'm pooped. I tried filing down several different faces of the hub to get the runout and wobble down and failed. It's going back to EA tomorrow morning for a new one. I'm thinking that attaching the flywheel shouldn't be this hard. The flywheel and clutch assembly has been balanced by two different shops and the second shop said the first shop did a fine job, so I'm pretty sure it's not the flyw

DC 100

DC Motor Motors Motoring 100

Porsche 914 EV Conversion

SEPTEMBER 17, 2007

I took the flywheel/clutch to Dan Halls Machine Shop this morning and just picked it up half an hour ago. Dan basically said that it was fine. He spun it as fast as the machine would go and it was only out of balance by 2 grams on the flywheel and 2 grams on the clutch pressure plate. Apparently this really isn't a lot for flywheels. The motor adapter hub from Electro Auto still has 4 mils (thousands of an inch) runout, so I'll try to attack that next.

Convert 100

Convert Auto Motor Motors 100

Porsche 914 EV Conversion

SEPTEMBER 15, 2007

Since I live in the Pacific Northwest, I get rather concerned that rain entering the engine compartment will cause problems with the electrical wiring. Many other 914 EV'ers have protected their wiring inside conduit boxes and other shields. I just following the ElectroAuto directions and bolted the relays and terminals blocks to the engine compartment wall with wires dangling from them.

Purchase 100

Purchase IDEA Engine Water 100

Porsche 914 EV Conversion

SEPTEMBER 15, 2007

Well, it's time to bite the bullet again and see what I can do about the car vibrations. My friend graciously helped me remove the motor/tranny from the car again this morning and assisted with crude vibration measurements. We removed the motor/transmission from the car and re-attached it to the AC controller wires while on the ground. After spinning up the assembly to approximately 5000 RPM, the whole assembly started vibrating across the floor like those toy footbal players on the vibrating ta

Motor 100

Motor Motors Motoring Porsche 100

Porsche 914 EV Conversion

SEPTEMBER 13, 2007

Since I don't work Fridays, this is the end of my second week commuting to work fifteen miles each way. Two things have definitely made the car more fun to drive. 1. The batteries are broken in so I have more current to work with and more importantly 2. I've learned some of the tricks to driving the car. The biggest trick involves starting from a dead stop.

Portland 100

Portland Plugin DC Gasoline-Electric 100

Porsche 914 EV Conversion

SEPTEMBER 11, 2007

I just got an e-mail back from Electro Automotive from CC-Power regarding the failed DC-DC converter. I prefer not to comment on it but simply wish to pass it on to others who might have wondered what the manufacturer said. Here goes: "The converters have been manufactured for over 20 years and we have 10,000+ units operating in South Africa at 120 volts, all using the same build, without any problems.

DC 100

DC South Africa Power Powered 100

Porsche 914 EV Conversion

SEPTEMBER 9, 2007

I just drove home from a meeting for half an hour with the headlights on. In the process of driving, the brake lights and turn-signals were also on. This is the first time I've arrived home with the DC-DC converter still working! Yay! I'm going to give it a week and see if anything else causes a failure. In the meantime, I'm going to report my findings to CCPower and Mike at ElectroAuto so perhaps they can modify the design.

DC 100

DC Convert Light Supplies 100

Porsche 914 EV Conversion

SEPTEMBER 8, 2007

After studying the oscilloscope waveforms, I believed that the current sense circuit was way too spikey. This is the "amp adjust" potentiometer output in the C400 schematic. I found that the inductive spikes were shutting off the DC-DC converter through the nShutdown pin on the SG3525A and causing craziness in the gate-drive pulse. Soooo, I picked a reasonable (.01uF) capacitor to filter out the current sense waveform and remove the inductive spikes.

DC 100

DC Light Convert Installation 100

Porsche 914 EV Conversion

SEPTEMBER 9, 2007

After talking with various people and realizing that the over-current circuitry was making the FET gate pulses way too large, I decided to hack the DC-DC converter circuit. Here's the new circuit (click to enlarge). I swapped out the IRFP350 FETs with IRFP460 FETs which have a higher voltage and current rating. To compensate for the larger gate capacitance and speed up the rise/fall time of the FET gates, I lowered the gate resistance from 27 ohms to 15 ohms.

DC 100

DC Cheap Convert Installation 100

Porsche 914 EV Conversion

SEPTEMBER 8, 2007

I spent most of Friday trying to figure out just what was blowing the DC-DC converter. Here's my full testbench setup. On the upper left, I have a 156V DC power supply. On the lower-left sits a 12V battery to act as an accessory battery. The 30Mhz $400 oscilloscope sits ready. The opened up DC-DC converter is front and center. I have the oscope covered with cardboard to shield out excess light so I can take pictures of waveforms.

DC 100

DC Volt Convert Supplies 100

Porsche 914 EV Conversion

SEPTEMBER 5, 2007

In my efforts to debug the failures of the DC-DC converter, I tried to capture a schematic of the board. I didn't have time to create a component for the SG3525A controller, but all the pin numbers are listed. I replaced the IRFP350 FETs with IRFP460 FETs which have a higher isolation voltage and larger drive current; however, they also have about twice the gate capacitance, which I didn't think of.

DC 100

DC IDEA Convert Parts 100

Porsche 914 EV Conversion

AUGUST 30, 2007

These last few days have packed with non-EV stuff, but I did take the DC-DC controller into the lab to see what was going on. First of all, there are no kick-back diodes on the inductors inside the converter. This kinda scares me since pulling on an inductor with a FET and then letting it go tends to create really high voltages (> 600V etc.). I hacked together a 160V DC power source by simply tapping off the bulk capacitor inside one of our power supplies.

DC 100

DC Convert Supplies Volt 100

Porsche 914 EV Conversion

AUGUST 26, 2007

I spent most of yesterday and a few hours today wiring up the PakTrakr system. It's a bit of a pain to disconnect the most negative lead before attaching the display, but that's minor nuisance. It seems to measure pack voltage well; however, the voltage measurement on each battery seems to be slightly inaccurate. The Zivan charger is balancing the batteries well and each of them is within an 8.48V-8.50V range (20mv difference is pretty good!).

DC 100

DC Convert Volt Plug-in 100

Porsche 914 EV Conversion

AUGUST 24, 2007

Just before noon, I drove with the ICE vehicle over to the 914, charged the accessory battery with jumper cables for about 20 minutes, then quickly drove the 914 back home to the garage for repairs. Since the stranded EV was only 2 1/2 miles away, I walked back to the ICE car and drove it home too. Since the DC-DC converter was blown and I didn't want to deal with it, I focussed on some other electrical problems I'd been having.

Volt 100

Volt DC Light Electric 100

Porsche 914 EV Conversion

AUGUST 24, 2007

I cringe at the thought of having to send anything back to Electro Automotive for replacement or repair, so I took a chance and dissected the DC-DC converter to see if I could fix it. The company that makes the DC-DC converter is CC-Power in the UK, so I don't think sending it back to them would be timely either. Here's the DC-DC converter taken out of its black aluminum case.

DC 100

DC Convert Volt IDEA 100

Porsche 914 EV Conversion

AUGUST 25, 2007

I just got off the phone with Mike at Electro Automotive. We chatted about the blown CCPower DC-DC converter and the engine vibrations. Since I fixed the DC-DC converter, we agreed that I would try to find out which conditions would cause it to blow again, if it does. It seems that Mike is more of a mechanical person than an electronics person. He graciously faxed me a circuit to generate a tach pulse from an ADC8" or 9" motor, but he didn't really understand the circuit.

Golf Cart 100

Golf Cart Kits DC Personal 100

Porsche 914 EV Conversion

AUGUST 23, 2007

While cruising over to my girlfriend's house this evening, the whole system just shut down on the road. That was a rather scary experience. The hazard signals started flickering and nothing would turn on. After pulling over and checking the voltage on everything, the pack was nicely up at 150V but the accessory battery was down to 10.5 volts. With the key on, the DC-DC converter light was on; however, when I checked the DC-DC fuse, it was blown.

Battery 100

Battery Batteries DC Volt 100

Porsche 914 EV Conversion

AUGUST 24, 2007

Before the accessory battery discharge yesterday, I wrote down a list of things to keep in the EV in case there was a breakdown out on the road. I came up with the following items. Any comments for additions or modifications would be welcome. Emergency Equipment cable cutters small fire extinguisher (for electrical fires) Repair Tools Haynes manual for electrical diagrams digital multimeter wire crimper and extra pink,blue,yellow quick-connect crimps two battery wrenches wrapped in electrical ta

DC 100

DC Kits Convert Connect 100

Porsche 914 EV Conversion

AUGUST 24, 2007

Well, I ran out to Radio Shack this morning and got some more 5 amp fuses for the DC/DC converter. After plugging a fast-blow fuse in, powering up the car blows the fuse. I tried a slow-blow fuse and that went too. I then disconnected the 12V battery to see if that was causing a problem and it still blew a fuse. What's sort of interesting is that these glass fuses didn't just melt and break, they really vaporized and completely coated the inside of the fuse glass with metal bits.

DC 100

DC Convert Volt Plug-in 100

Porsche 914 EV Conversion

AUGUST 23, 2007

Despite the issues with the car, I've decided to start commuting 15 miles each way to work to see how the car does. By not revving the motor above 5000RPM, I can minimize the vibration problem. The batteries are starting to break in. I'm getting slightly more power on the freeway now and starting from a dead stop is acceptable. I've taken the 914 up to 70mph.

Batteries 100

Batteries Battery Installation Power 100

Porsche 914 EV Conversion

AUGUST 17, 2007

In my frustration to take care of the vibrating of the motor/tranny, I unbolted the motor from the front engine mount and raised it up with a jack. The clearance above the motor is tight so you can't raise it too much. After revving up the motor, it still resonates at 5000 RPM which leads me to believe that there's an issue with the motor to transmission coupling.

Motor 100

Motor Motors Motoring Engine 100

Porsche 914 EV Conversion

AUGUST 17, 2007

Going to NEDRA at Portland International Raceway was my first major excursion in the 914 since both the flywheel was balanced and the clutch was properly adjusted. The car handled very well and cruised on the freeway without much problem. I did get up to 65 but kept my speed mostly at 50 to not pull too much current while breaking in the batteries. Here's the wait in line for the ticket office at Portland International Raceway.

Portland 100

Portland Maintenance Honda Waste 100

Porsche 914 EV Conversion

AUGUST 17, 2007

This has been one heck of a week. I took the flywheel into an automotive machine shop to balance along with the attached clutch assembly. In the meantime, I tried to figure out if the real problem was the motor to flywheel adapter from Electro Automotive. I borrowed a precision dial gauge from a coworker and measured the wobble on the motor adapter.

Motor 100

Motor Motors Motoring Neighborhood 100