More Driving Stats

I've had the car registered for almost 2 weeks now and have racked up 90 miles of driving. I had some clients from Boeing in for a review at work this week and I got to impress them with the car.

Efficiency tends to be in the range of 210-240 Wh/mile depending on how many times I have to stop. I've got RTD explorer working and tracked the temperature of the controller. On a 103 °F day it got up to a peak of 129 °F at the end of an acceleration from 0-50 mph and quickly drops down to 124 °F. If I coast to a stop at a light, it's down to 117-120 °F within a few seconds and seems to stabilize there. So I'm guessing the temperature of the coolant in the system stabilizes to around 117 °F or less (<15 above ambient?) since it's no different after 11 miles of driving.

I've been experimenting with charging. I don't have a heavy duty extension cord yet, so I have to string two regular (probably 16 awg) extension cords together. Originally I had an old computer cable pigtailed to the inlet wires in the loop too. That was bad because that wire was 18 awg and it got hot! All the internal wiring is 10 AWG in anticipation of wanting to charge at 20 amps or higher. If I charge the car at 5.0 amps, the clamp meter reads 14.5 or so Amps rms in from the house 120v line, and a 15 amp circuit breaker would eventually trip. So I've either had to drop down to 4.0 amps or run a third extension cord through my garage door and plug into the 20 amp outlet in the laundry room. Not great for charging when it's 118 °F outside. At 4 amps it takes about 5.5 hours to charge 22 miles (around 21 Ah). At 5.3 amps it's down to around 3 hrs 50 min. When I get a 240v 30 amp outlet installed and am brave enough to try it, I should be able to charge it in about an hour if the charger doesn't get too hot.

In the meantime I've been working on the BMS. The head board is complete and one of the slaves is complete. I've been modifying the code Joe sent me and think it's about ready to test. Unfortunately I completely missed a bunch of connectors in my order and have to wait until July 2nd for Mouser to get them here, so I can't do any testing until then.

So with no car work that needs to be done, I'm focusing on a few things I've been neglecting around the house. My wife is really happy that I cleaned out the garage and she can park in there again! I also tried my hand at cleaning the air conditioner to try and make it more efficient. The bozos who installed the unit in my attic put it in backwards so the access panel faces into a wall! I've had problems with it not draining properly because there's a bunch of sludge built up in the drain pan that I've never been able to clean out. Well, we've got a ton of family coming over on Sunday and it's supposed to be around 118 °F out so it needs all the help it can get so I bite the bullet, got up at 5:30 this morning and head up in the attic. After nailing down some boards I can lay down on and an hour and a half of cursing I managed to get the access panel off. Another hour and I've vacuumed all the sludge out and sprayed down the evaporator coils with some cleaner. Hopefully it was worth the effort. It's currently 115 °F outside and 76 °F inside. So far so good but the forecast is for 122 today.

I've only got two more weeks on my temporary permit to test out the car. I'd love to have the BMS functioning by the end of that before I take the 40 mile trip to the MVD, so hopefully I'll have enough time over the 4th of July weekend to make that happen.

Stay cool!

Free Parking

Today was a momentous occasion for me, I finally drove all the way in to work and back!  My employer has  a solar array in the parking lot and they lease shaded parking spaces under there.  But there are a few fortunate people who get free spots for 100% alternative fuel vehicles, carpooling, and hybrid vehicles (in that priority).  I pulled into my spot this morning even though I didn't have a permit yet (they've had one set aside for me for about two months now, but wouldn't give me the permit until I started driving the car) and within 3 hours I already had my first parking ticket!  Luckily there's no substance to the ticket, and I now have my permit so I can park legally from now on.

Here are the stats from today's drive.
According to Google it's 11.2 miles each way, so 22.4 miles total.
Total energy consumed: 4792 Wh
Energy per mile: 214 Wh/mile
Theoretical max capacity of the battery pack = 3.3x70x60 = 13.68 kW-hr
% Battery consumed: 35%
Max battery amps: 162 A
Minimum battery voltage: 216 V

Unfortunately, RTD explorer apparently experienced a user error and I didn't get any data from the trip other than when it first started up.  Mostly I was wondering how hot the controller would get.  It started out at 104 °F and finished hot to the touch, but not so hot you couldn't keep your hand on it.  So maybe 120 °F at least on the outside?  Not too bad.  Now I get to sweat through 4 hours of charging.  Speaking of sweating, pretty soon I'm gonna need to get the AC working!

On the road

Happy Father's Day to all you fathers out there.  Today I celebrated by driving the car to church!  At 5 miles each way, this is my longest drive to date.  I got a  30 day temporary registration on Friday, so I've got a nice amount of time to test things out before taking the 20 mile (each way) drive into Phoenix to get all the registration stuff sorted out.

I didn't want to get the 30 day tag until I knew I could recharge the batteries, which means I can recharge the batteries now!  Last Wednesday was the first test.  Here you can see the mounting location for the charger.

Of course, mounting the charger means making another bracket.  Man, I've made so many darn brackets.  They look so simple, but to get this charger in took two full evenings of measuring, cutting, and welding.  Thankfully this is the last major fabrication I have to do at least in the foreseeable future.  As you could see in the picture above, I still don't have the charger permanently wired in yet, which is good.  I've had a few minor issues to deal with and reprogrammed it a couple times.  The voltage sensing circuit had to be calibrated, and I keep getting an occasional safety fault that trips and shuts things down.  Here's what it looks like when it's charging.

Set is the current setting.  Out is the actual current going into the battery.  IrmsIN is the RMS current coming in from the wall (not right at the moment). BMS is a signal from the BMS that tells the charger the max current it will let it charge at (currently hard fixed since the BMS isn't finished yet).  Then on the right, the top number is the voltage it will charge to and the one below is the current voltage.  The fourth like is the IGBT temperature, and finally the time it has been charging.

On Thursday night I'd worked out a few bugs and charged all the cells up.  I think 51 °C was the max temp I saw.  Considering it's about 100 degrees F out, that's only a 23 °F rise in temp, which is good.  On Friday, after getting my temp tag I took the Porsche on its first real trip - 1 mile each way to the grocery store.  Then today I put in another 10 miles.

I hooked up some instrumentation that keeps track of the voltage, current, and total energy consumed (among other things), so now it's time for a little post-trip analysis.  For some reason it didn't turn on for the first mile, so I only have data for the proceeding 11 miles or so.  I maxed out at 163 Amps to the batteries.  I have the controller set at 166 Amps max, so that checks out.  The min voltage was 203 volts, so if the nominal voltage was 235 (resting voltage), that's about a 14% sag at 2.7C discharge.  I'm guessing that most of that isn't due to the batteries, and mostly attributed to the 90 or so connections in the string.  If none of the sag were due to the batteries, that's about 2 milliohms per connection.  That's good enough for the aircraft industry, so it's good enough for me.  I consumed 2,345 Watts, so that's 213 W/mile.  Granted 11 miles is only an estimate, but that's really good for an electric car.  Also, I was consuming slightly less than 1 Ah per mile.  The cells are supposed to be 60 Ah, which implies a better range than I was originally expecting.

Soon I'll be hooking up the charger for good, which means I need a fancy plug in place of the gas cap.  I picked one of these up online.  It's a charging port for a boat so it should be fairly weather resistant.  I need a disc of metal to mount it to.  Unfortunately, I don't have 7/8 inch and 3.60 inch hole saws to cut it out with.  Luckily I'm still borrowing my buddy's lathe, so here goes nothing!

I'm making a lot of progress on the BMS.  Hopefully I'll have more to share on that soon...

The Master

I had an evening at home with the kids so I decided to watch a movie with them and put together the BMS master board.  

So, master board, what what's a typical day look like for you?  

Well, I take the battery info and give it to the charger and driver.

So you physically take the battery info and give it to the charger?

Well, no, I have cables that do that for me.

So, what is it that you actually do do?

I've got lots of IO's!  I know how to talk with an LCD!  I've got processing power, can't you understand that?  What the hell is wrong with you people?!

In other news, I finished top charging all the batteries, so now the total pack voltage is around 246 volts.  Time to take it for a spin!

There's a 35 mph zone in the neighborhood, so that's my first stop.  One mile up and back and I've got the need, the need for speed.  Out on the open road (well, Gilbert road at any rate) I do a 2.5 mile loop, max out at 50 mph and return home for a total of around 4 miles!  Now's a good chance to see if any of those connections are a little loose, which you can do by touching each one to see if it's hot (with your other hand in your pocket to avoid a deadly shock of course).  Everything seems in order.  The laptop battery wasn't cooperating, so no data from the controller.

The next day I can't help but boost the current to the motor.  Previously I'd had the motor current set to a value of 3, which corresponds to 3 / 8 x 500 x 5 / 3 = 312.5 amps of course.  This time around I toggle it up to 4, or 416.7 amps max to the motor.  The battery limit is still set to a value of 100, which anyone knows corresponds to 166.7 amps, right?  I take a spin around a 4 mile block and check the stats.  Controller temp has reached 102 °F (39 °C), both the motor and battery currents maxed out, I consumed an approximate 1 kWh, and I've got a huge grin on my face!  The battery current limit is actually limiting me to around 55 Hp, so I'll have to bump that up next time around.  Booya!

Motor Controller Part 5: The controller strikes back

Last time I was working on doing wiring on all the batteries.  I'd run out of time to finish it before our friends Toni and Warren visited us from Germany.  But between beers and while the girls were playing video games, Warren and I snuck out to get a little work done.  We started by finishing the routing of the 2/0 cables.  I got the cables securely tied up under the car so there's no chance of a stray stick snagging it.  Warren is sitting here with a phone in his hand.  He punched in 9-1, and if the car falls on me he'll just have to hit 1 again.

After finishing the large cables, it was time to finish the small wires.  You can see all the BMS wires are hooked up in the front and we got all the connectors pinned out.  I also wired up the the B- contactor and the vacuum pump.

Here's a close up of those connectors I keep mentioning.  There are three that plug into the BMS boards.  I'm also using them to initially top charge the batteries.

Here are the two clusters of wires coming out the back end of the car.  Finally the spaghetti of wires are neatly bundled into wire looms and all fitted into connectors.  Now I just need to drill a hole into the cargo cubby hole that's behind the wheel well  and stuff the wires in there.

Alright, what's next?  Hmm, can't think of anything else that needs to be done...I guess it's time to test out that controller again!  Just a reminder, I've driven the car about 3 miles on 1/3 of the battery pack.  That's about 80 volts.  Well, a lot of the reason for the custom controller is that I wanted to run higher voltage than 150v, so I really haven't proven anything yet.  An 80v 300 amp controller is pretty common out there, but a 230v nominal controller, that's special and seems to cost $2400-$3800.

Well, no more lollygagging, let's see what happens.  I flip the manual disconnect and that connects the positive side through the precharge resistor.  Next I flip the ignition to engage the B- contactor and that closes the loop and allows the capacitors to charge up.  If something blows, the voltage here probably will be less than the pack voltage, but since the 1k ohm precharge resistor is the only path for current to flow, the current is limited to 1/4 amp and the damage can be minimized.  Once that's bypassed by closing the contactor, the controller determines the amount of current, and if that fails closed it'll be a couple thousand amps.  Booya, 235 volts!

Okay, don't get too excited, it's possible that something still hasn't surfaced yet.  I opened up the manual disconnect and discharge the capacitors by pushing the pedal.  0 volts, so that checks out.  I decide to redo that cycle a couple times just to make sure there's no problem with the caps charging and discharging with no problems.  In the pic below I had opened the manual switch for a while and the voltage reading actually drained the charge a bit to 231 volts.  So now for the real test.  At this point I also hit the "start" button to close the B+ contactor and remove any limitations on battery pack current other than what the controller does.  I put the car in neutral to avoid a runaway and push the pedal...

Aaaahhhhhhhh!  Oh the humanity!  At least I've got insurance now.

 

Just kidding...the motor just spun like it's supposed to.  Though the picture above represents some of the nightmares I've been having over the last couple weeks.  Here's what the car really looks like now.  After slowly working my way up to it, I drove a whopping 0.1 miles to pick up my daughter from a friend's house and successfully made it home!  Woo hoo!

Next up, time to start installing instrumentation and get ready to take it to the DMV!

Wires, wires, and more wires

The batteries are all finally mounted in the car.  To get here I spent months designing, fabricating, fitting, modifying, refitting, and finally bolting in the battery racks.  It was a lot more difficult than I imagined it would be, but I guess that's par for the course for such a custom car.  Now that the batteries are strapped in place it's time to wire them all up.  Each of the rear battery clusters has 23 batteries, 46 bolts, 92 washers, 1 fuse, 2-4 copper bars, 22 bus bars, 3 twisted pair wires, and 24 BMS wires.  The next step in wiring these all up is to build the BMS wires.

The BMS wires serve two purposes.  When the BMS functions, a very small amount of current is flowing through the wires while the circuit board monitors the voltage across each cell.  The current flowing out of one cell is not exactly the same as all the other cells in the cluster, and I'm estimating after 3 months, some will be around 1.5% more discharged than others (about 1 Ah).  Eventually, this will cause the charger to stop charging prematurely and the cells will need to be re-balanced.  The BMS boards each have three balance charging ports, and a balance charger will send current through those little BMS wires to do just that.

Each wire comprises a ring terminal where it is bolted to the battery, a 4 amp fuse, and the wire.  To put these wires together I had to crimp the terminal to the fuse and solder it in place.  Without the solder joint, there's a chance that the crimp could come loose and cause some faults.  How do I know this you ask?  Well, I'll just say that Joe highly advised the solder joint.  So clip the fuse to size, crimp on the ring terminal, solder the fuse lead, solder the wire to the fuse, cut the wire to length, heat shrink over the fuse connections.  That should be too bad right?  Only a couple minutes and you're done.  If you add it all up, that took about six and a half minutes.  Multiply by 73 and that's how long it took to make all these dang wires!

Ok, the next step is to hook it all up.  One of the terminals on each battery is aluminum.  When you put aluminum and copper together you have the potential for galvanic corrosion.  To get around this, you put a little conductive anti-corrosion paste and rub it in with a wire brush.  After I got everything installed, this is what it looks like:

To keep things straight I got some sticker number flags and put one on both ends of each wire.  Amazingly some places want to charge you $20 for a sheet of these stickers, but luckily I found some on Amazon for just a couple bucks.

Yeah yeah yeah, I know I'm missing one wire and I forgot to put the fuse in (if you look two pics up).  And no, I swear I didn't do the exact same thing to the battery pack on the other side...I was up until 12:30 last night getting this done, so cut me some slack!  So far, so good.  Now I bundled all the wires together, zip tied them about 700 times, and collected all the ends.  They're not all the same length anymore, so I have to retag them and cut them all down to the right length.  I've gotta be really careful though because each of these are live wires!  If I'm unlucky enough to touch two wire tips together I'll have to spend another 13 minutes making new wires plus another 30 minutes swapping them out.  That also means don't clip more than one wire at once!  So I clip, strip, then crimp a connector pin onto the end of each and now I've got three plugs to go into the plugs of the BMS circuit boards.  I've got all the wires mounted on the batteries, but only 1/3rd of those connectors have been pinned out so far.  Oh yeah, and I'm missing one wire.

I also got all the large 2/0 cables measured, cut, and crimped with lugs, so theoretically I'm all set to test out the controller on 230v.  I just have to screw it all together.  I'm a little battery weary and we've got friends visiting this weekend, so I'm not gonna push it an do something stupid in the testing phase.  So after a weekend of R&R I'll be back next week to see if I can keep the magic smoke in the controller!

Need more volts

Previously I've been driving the car around on just 1/3 of the batteries, or about 80v, but now it's time to put the rest of the batteries in there.  In the back of the car below the floor I have two battery racks that hold 23 cells.  Actually, they're big enough for 23 each, but I only bought enough for 23.  I guess if later on I want 2/70ths more range I can buy two more cells.  At any rate, the way the batteries are tied down, I can't just leave that empty space open so I need a battery "blank" to fill it in.  My father in law has a ton of scrap wood and woodworking tools, so he helped me put a pair of these together.

As part of the battery monitoring system I added the capability to monitor the temperature of the cells, three spots in each cluster of batteries.  To do that I've got some thermistors, which are resistors that vary resistance as a function of temperature.  Here's one of them soldered onto a wire.

Apparently there's a lot of debate of how to "properly" monitor the temp of your cells.  Some people attach the thermistor to the posts on the cell since they're wetted in the electrolyte.  Other people using lead acid batteries will actually put the thermistor inside the battery so it's directly touching the electrolyte.  I'm going simple and just taping it to the side of the battery like this.

Then I loaded all the batteries in those nice racks in the back and clamped and strapped them down the same way I did with the front batteries. 

Pretty clean look from underneath.  You can see the threads on the four eyebolts that are really easy to access here.  Too bad the aluminum clamps are super difficult to get to, but oh well.

Well that's it for now.  This weekend I'll start wiring it all up!