Saturday, July 13, 2013

More fuses?

Yes, there are more fuses. There is the stock fuse box which controls all the normal car electrical components.

The Porsche (1976) uses a bullet type of fuse, where the filament is external to the ceramic component. I've never seen these before, but a couple were broken, so we starting switching a few, and then the signals worked (WOOHOO!!). Unfortunately, now the headlights didn't work. Luckily, it was because we pulled the fuse for the headlights to swap with the signals, and a quick swap back confirmed it was because of the swap.

The original fuse holders are tarnished, as are the fuses themselves. We've ordered the replacement fuses and are going to change out all of them, since they look original to the car and some of them have questionable status when they are put in. We are also planning on replacing/revamping the fuse box itself, as the contacts are worn and tarnished, and that is hurting the performance.

Thursday, July 11, 2013

Well, we've cleaned up the Porsche a bit.

Erick and I have run through the battery management system (Valence) and we aren't having any luck. For some reason, it is speaking (electronically, CAM) to us and our computers (we've used 3 so far) haven't been able to translate the chatter into anything intelligible.

Roberto and I are waiting on this information to determine the State of Charge (SOC) so that we know where the batteries are, if there are problems, and if they are charged at any point. We don't know how balanced the pack is, and if we might do damage by doing anything to them.

I also looked at the EV specific fuse box, which runs some of the electronic systems and should also run the center touchscreen which we have been having problems with. All (4) the 15A automotive fuses were questionable, and I don't know why. The modes of failure were interesting too. I wish I had a photo of them. The first had melted plastic, but the filament was still intact.The second had a hole in the plastic melted around the filament, but the filament was still intact. The third was no longer conducting and was so brittle that the process of grabbing it and pulling on the plastic caused it to fall to pieces. The fourth's filament was broken. I'm still puzzled by what we found there.

abrajam giving the Porsche a little love!
As a quick note, if they failed, they should have failed from the filament only, like the picture below. The left has a broken filament, and the right is intact. The discoloration on the left may also hint at some sort of thermal stress, which makes sense due to the fact that the filament breaks via a current induced heat stress.

A melted fuse itself might indicate that something is drawing not quite the rated capacity of the fuse, but close to it, causing the filament to heat up and melt the plastic before breaking the filament. Food for thought.

Monday, July 8, 2013

Dusting off the Porsche

Hello there, I'm John and I'm a rising senior in course 2A with a focus in Energy Conversion. I'm one of the senior EVT members at the moment, and I'm spearheading the effort to get our 1976 Porsche 914-e back on the road.

The Porsche was mothballed about a year and a half ago, and put into covered storage in one of the graduate dorms here at MIT. That shielded it from the elements, but certainly not from dust and the effects of humidity.

Nick and I had worked with another alum, Radu, to run the vehicle during January, but we were unable to find the time to get the vehicle back to the shop and to start the process of getting it legal again. The downside was that in the process of running the vehicle around storage, we broke the transmission linkage and the car was stuck in second gear.

This past weekend, Erick (a former EVT who is returning for grad school) and I went to storage and spent some time getting the car back into the shop. We knew the electronics worked, but we still weren't able to get it to roll. As it turned out, the brakes had bound to the rotors since the handbrake was on, and we had to break the pads free. This effectively meant we put one foot against the wall and pushed really hard, after that it rolled with relative ease. Fortunately, Erick and I rowed together and we put all those hours of pushing on a foot board into pushing on a concrete wall.

The next challenge was getting the car up the ramp that leads out of the garage. That's easier said than done when there isn't much room to get a running start, or a method to get the electric motor into a sufficient torque range. Stuck in second gear, we were barely able to get up the ramp with 500 rpm, when the motor is most efficient around 5,000 or so. In the end, we got the car up the ramp and drove it back to the shop. With the signals and brake lights not responding, it was back to arm signals. Unfortunately though, Cambridge drivers are not accustomed to driving with arm signals, and honking ensued while I was waiting to turn left at a light.

At the end of the day though, the car is now in the shop and we can start going through the systems to learn from it, teach with it, and have some fun with it.

Sunday, July 7, 2013

Visit from WTP

The girls from the Women's Technology Program visited us today!

We had fun teaching them the basics about EVs and why they are the future of transportation! Yay for outreach!

credit for Dr.  Barbara Hughey for the photo!