Archive for November 2009

Now the Fun Begins

November 22, 2009

Lots of news this past week.  The car is back from the Fab Shop with all the boxes painted and installed.  Better yet, the motor and controller shipped!  They will be here on Tuesday – one box at 38 pounds, the other 105!  My final 36 batteries have shipped from China but the delivery date is not known – most likely early December.

So, the assembly process began this weekend.  First up – the front battery pack.  This involved several steps, all of them tedious and some of them just flat hard.  Recall that this pack has 30 batteries in it weighing about 165 pounds and mounted forward of the front axle.

I started by inserting the batteries.  This proved to be snug and some judicious use of the hammer was required to get the last battery in place.  Here’s how it looked with them all in.

Batteries in the front box

The blue tape is to prevent accidental shorts.  It would be a shame to drop a tool on the pack and destroy a battery.   Next step is to connect the batteries in series.

Connecting batteries in series

First remove the tape from one battery and use the multimeter to check that it has a 3.3 volt charge.  Every single one did.  Then attach a copper bus bar from the negative terminal of one battery to the positive of the next, as in the photo above.  Repeat 30 times.  After each battery is wired, I checked the voltage across the series by connecting the multimeter to the first positive terminal in the set (the leftmost) to the last wired negative.  The voltage should be the sum of all the batteries in the series.  In the photo below, you may be able to see the multimeter reading 23.2 volts DC which is exactly right at that point.  When I took the picture, there were seven batteries in the series.  At 3.32 volts each, the sum should be 23.2 which is what the meter showed.  There was no measurable loss from the bus bars.

Checking series voltage

Next up was installing the individual cell control boards for the battery management system.  Earlier I had soldered the sets together; now they get mounted.

BMS Cell Boards

Each board has a little LED on it and each one lit as it should when I attached them.  It will be awhile before I can actually connect the BMS controller, so I have to assume they are OK for now.  The battery terminal screws get tightened down and then repeat three times until all thirty are wired.  Below is a picture of the first set of ten.

One set done

Now the pack can be installed in the car.  My neighbor Clint lent a hand (thank you Clint!).  We maneuvered the pack into position only to discover that one of the mounting bolts wouldn’t clear the cutout.  I had to get out my metal cutter and make a few modifications to the cutout.  After resting overnight, we tried again (thanks again Clint!) and got it installed.  The mount is rock-solid.  At one point the battery box was resting on the jack and we realized that the jack stands were no longer touching the axle.  The battery box was carrying the full weight of the front-end of the car!

Closeup from the front

Closeup from the windshield

The red straps are bungees I installed to hold the batteries in place.  Everything fit, but I may have to make some adjustments.  The forwardmost battery is touching the steering column box (left side of the picture above) and this is skewing the entire pack slightly out of line.  Once the car is running, I can check it closely and if there’s a problem it’ll be back to the Fab Shop for some tweaks.  Also, there is not enough clearance to route the cables from the front of the pack to the controller units.  I need to drill some holes for the cables, and make up grommets so they don’t rub.  This can wait until I am doing the final wiring.

When we removed the jacks, the front end of the car sagged down from all the new weight.  Once the rear batteries are installed, it should balance out.  But stronger torsion bars will probably be needed – the car looks like a lowrider now.

I’m stoked to actually be at this stage.  Several months of measuring, planning, ordering, checking, studying, etc. are finally taking concrete form.  We may yet be driving it come Christmas!

First Wiring

November 8, 2009

This weekend I began wiring work.  I cannot yet do any wiring in the car as it’s still at the Fab Shop.  But I did make up the wiring harnesses for the battery management system.

Each battery has its own little circuit board that controls that specific battery’s charge state.  The circuit boards connect back to the main brain – the eLithium BMS.  So I made up the wires for these – 90 of them – and fabricated the first six banks.  These will connect to the 54 batteries I have in hand.

The first step is to measure the distance between battery terminals and cut 90 wires to that length.

90 Little Wires

90 Little Wires

Next each wire has to be stripped at both ends 1/4″.  This is not hard, but it sure is tedious.  It leaves a bunch of “droppings”, as if a hamster had eaten nothing but lemon peels for a week.

Wire Droppings

Wire Droppings

Next step is to “tin” each wire end by applying a drop of solder.  This makes for a better connection when the wires attach to the circuit boards.  Here I am doing one – this is the first time I have soldered in at least 20 years.

Tinning

Tinning

And here is a pile of 90 wires tinned at both ends.  This took me almost four hours, but I bet if I had to do it again it would only take two.  However, I am in no hurry to prove it.

Tinned wires

Tinned wires

Finally, it was time to actually connect the circuit boards in strings.  There is a specific board for the positive end of the string, another specific one for the negative end, and bunch of generic ones for the middle.  I made three strings of 10 for the front set of 30 batteries, two strings of 9 for the upper right rear set of 18, and one string of 6 for the upper center set.  Here’s a picture of the first one I made; one of the strings of ten.

String of 10 Battery Circuit Boards

String of 10 Battery Circuit Boards

Installation of a battery bank will go like this, if I understand correctly:

  1. Put the batteries in the compartment
  2. Connect each battery to its neighbor with copper bus bars
  3. Check that the voltages at the ends are the sum of the batteries.
  4. Connect each BMS circuit board to its battery
  5. Screw it all down tight
  6. Make up a wire with Molex connectors to connect the positive and negative end boards in each bank back to the BMS (under the back seat)
  7. Make up heavy cables to carry the positive and negative voltages from the battery pack to the controller

Repeat for each of the six compartments.  Then connect the BMS to a laptop and run a series of tests.  Then do the rest of the wiring for the controller.  Oh – and the whole time I have to be careful to never touch anything metal across the terminals of any battery.  I think this is going to take a while…