Archive for July 2010

Buttoning Up

July 25, 2010

This past week I completed the rear portion of the Fastback.  The BMS is fully functional for the back 60 batteries and the battery covers are  installed.  All that remains is replacing three dead cells in the front bank and installing that cover.  Then the project will be finished!  Except for a heater.

I took photos of the finished portions so you can see how it looks in the end.  First, the wiring under the back seat:

Wiring under back seat - driver's side

This rat’s nest is wiring for the BMS and control relays.  It actually looks a lot nicer now than a few days ago, as I coiled and tied down everything.  In the center is the BMS controller with 12 wires to the battery banks and one wire to the current detector, plus six wires for control (2 power, 2 ground, 1 for charger shutoff and 1 for motor shutoff).  At the top, bottom and right sides are the control relays.  These include two original relays for turn signals and brake lights, plus six others for the EV function (2 for charger interlock to prevent driving with the car plugged in, 1 for the key switch which starts everything when you turn the key, 1 for regeneration which turns the brake lights on while regenerating even without using the brakes, 1 for BMS charger interlock and 1 for BMS motor controller interface which turns the motor off if the batteries are being over-discharged).

Back seat wiring - passenger side

The other wiring is under the passenger side, shown above.  Here we have the small 12 volt battery to the left and the current detector to the right h(ard to see – sorry).  At the bottom is the DC/DC converter.  Not visible is a small relay for which kicks up the DC output to 14.3 volts when driving so the headlights don’t get dim.  To the upper right is a white bar – this is the 12 volt distribution block.  In both pictures you can see wiring coming through the original heater ducts, and maybe you can make out the foam I sprayed in there to seal it up.  This cut down the road noise dramatically.  The foam is standard window insulation, but the type that won’t make toxic fumes if burned (DAP Tex-Plus).

Engine Compartment - Driver's Side

Here is the motor, controller and rear-most battery bank, with a cover on it.  The red block is the service disconnect mentioned in an earlier posting.  The throttle cable and spring are visible to the right of the controller.

Engine Compartment - Passenger Side

The right-hand upper battery bank contains 18 batteries.  There is now a plastic cover over it to protect against dropped tools, etc.  To the right is the rear-most bank with its cover.  This bank has six batteries.  Two of them died due to bad wiring of the BMS.  I could not remove them, so simply added two more batteries and wired around the dead ones.  Better to carry around an extra 11 pounds of dead weight than spend 8+ hours dismantling the car to get them out.  The two replacements are laying on their side with the terminals facing away.  It turned out to be pretty simple to get them in there and wired.  LiFePO4 batteries can be mounted in any orientation, which made this possible.

Lower Battery Box - Passenger Side

Lower Battery Box - Driver's Side

Motor Mount and Transaxle

The three pictures above show the underside of the rear-end as finally installed.

One more battery box to go and it’s done!  On the cost front, I have spent another $1,550 buying replacement boards for the BMS and cells that the BMS destroyed.  And another $100 for professional assistance with the last wiring issues.  This brings the total for the EV portion to almost exactly $30,000 before tax credits.

Public Debut…and more lessons learned

July 13, 2010

On Saturday, July 10 was the Portland EV Awareness Day at Pioneer Square in the heart of Portland.  I took the Fastback and showed it to the world.  There were lots of cool cars to see, but still many people stopped and asked about our car.  One of the OEVA (Oregon Electric Vehicle Association) members took a bunch of pictures:  It was a hot sunny day and I wish I’d worn sunscreen and a hat…

I cleaned the car really carefully (with a toothbrush in spots) and put a nice wax on it so it would look pretty.  Jeanette came by and took some pictures.

At the OEVA Show

At the OEVA Show

I also got to take a close look at the other conversion that people had done, and talk to them about their experiences.  I learned a few things about how to properly mount batteries, and other sources for parts and systems.

My design for the battery boxes has a few flaws.  If you are considering a conversion, please think hard about access to the components after installation.  In my case, I should have done two major things differently.

Mount the batteries on shelves, not in boxes.  The batteries come with clamps for locking them into compressed blocks.  I tossed these and put the batteries into boxes instead.  In hindsight, this was dumb because: (1) it’s very hard to get a single battery out; (2) it forces you to do your battery wiring with the batteries in the boxes; and (3) the boxes are heavy.  What I should have done was use shelves with a 1″ lip.  I then could have bound the batteries into blocks of four or five and simply dropped them onto the shelves once they were wired.  A simple hold-down bracket would complete the job.

Use a modular design. In the upper rear engine compartment, my design has one big box/shelf combination that holds 24 batteries and the controller.  I should have designed this as three smaller units.  Having it in one piece caused two big issues: (1) I cannot work on a drive-train component such as the clutch or transmission without removing the entire rear setup; (2) that single piece is so heavy that I cannot easily handle it.  To give an example, to replace one battery in my rear-most bank, I would have to remove all the rear battery boxes, the motor mount, the motor and transmission (as a unit) and the motor controller – and then pull out the very heavy one-piece box/shelf combination.  This would literally take all day, involve using several jacks, and risk damaging things that are working fine.  It’s such a daunting task that I might rather leave a bad battery installed and simply wire around it.

When you design your conversion, keep everything small and manageable.  Your design should allow you to remove any battery block without removing anything else.  If no more than five batteries are treated as single unit, your heaviest component will be only 40 pounds.  If it’s easy to access the motor, you’ll then be able to work on your clutch without disassembling half the car.  Trust me – you’ll be glad.

As an update, my replacement BMS components have arrived.  With luck, I may be able to complete the installation next weekend.