Saturday, June 29, 2013

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!

Monday, June 17, 2013

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!

Sunday, June 16, 2013

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...

Tuesday, June 4, 2013

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!