Battery Testing

I got the Big Red Van back from the shop last week and it seems to be running fine. So... with that I'm putting it back into daily use and have started pulling batteries out of the Saturn.  My plan is to cycle every cell to determine their actual amp-hour (ah) capacity and internal resistance (ir).  I bought a little charger that is really made for remote control car/airplane type batteries, designed to quick charge them, but it will work very well for what I need as well.  It's called the Powerlab 6 from Revolectrix, and it will discharge and charge the cells at up to 40a, and create cool looking graphs.  Fairly unique is it's ability to calculate the cells internal resistance, which is a strong indicator of health. Each cell will take 7-8 hours to cycle.

Yes, this will take me a few weeks to do since there are 48 cells, I figure I'll be lucky if I can get 2-3 done per day. But I am also going to pull the motor/trans out and re-do some things in the car so it's not just lost time. 

As of now, I've got 14 cells done.  It's not stellar news in that quite a few cells are below spec, but it's about what I expected based on the voltage sag I've recorded while driving.  What is interesting is that there are some cells that are excellent, some that are normal, and some that are weak, but there is no pattern to where they are in the series string of batteries.  A good cell will be right next to a weak cell, quite randomly.  It makes it hard to believe that any kind of mistreatment caused the cells to degrade, perhaps they were just mismatched from the factory?  Typically not the case, but I'm not sure how to explain such a wide variance.  Some cells are testing over 135ah, others are below 125ah.  Internal resistance numbers are varying from 0.5mohm to 1.2mohm.  

Below is a picture of the setup, there is a 12v deep cycle battery connected to the Powerlab 6, connected to the battery cell. I've got a power supply on standby in case it needs it on the charging side, and the laptop is connected to the PL6 via USB and logs all the data. The fan is there to keep everything cool.

It's really cool to do these tests, I've seen all the battery charts before, but it's a whole different understanding of the cells to actually create the charts.  Here are two volts vs. time files for cells.  The top one is a good cell (139ah, 0.5mohm) and the bottom one is a weak cell (124ah, 1.2mohm). Notice the differences:

1. sharpness of curve at end of discharge/charge cycles. The weak cell is much more gradual.

2. Difference in voltage between the two shelves. The good cell holds a higher voltage on discharge, and charges at a lower voltage on the charge side.

3. Length of time at CV. The good cell gets full in about 20 minutes after hitting 3.60v, the weak cell sits there for over 45 minutes.

dead battery

just back from a week's vacation, despite disconnecting the 12v battery, and despite charging it up a few hours right before leaving, it was down to 5v when I returned...  Not a problem with the car, just a weak battery.  It should be able to sit disconnected for a week without going dead.  Anyway, I've found I can easily jump-start it by touching a quarter across the DC/DC contactor, which sends 13v from the 160v main pack to the aux battery and gets everything up and running.

In other news, I've begun tearing the upper motor mounts a little bit.  A redesign has already happened in my head, just need to make it happen in the car now...  Basically I want to replace the upper mounts which are simple cylindrical rubber vibration isolation mounts with the original beefy rubber engine mount that was in the car.  I've ordered the parts I need, but it will require fabricating a new end plate to connect the motor to the new mount.  And will require pulling the motor/trans out again.  That's ok, there's a few other things I want to do in there too that will be a lot easier with it all out.

Next update will probably be in a few weeks, I'm not going to tear it apart until after the new year, and after I have a chance to get the Big Red Van's transmission looked at (it's slipping a bit).  In the meantime, I've lowered the motor amps to 350a to save from doing more damage to the upper mount.

a few little updates...  It's been running well, the heater has been fine even in the cold 30 degree mornings lately.  And that's just with one element switched on.  I can't imagine needing the second one!  Though it is garage kept right now, which helps keep it not as cooold overnight.  Less to have to warm up.

Anyway, I've been tracking my ah/mile (amp hours per mile) through the controller lately, and I've noticed about a 10% difference between the 30 degree morning run to school, and the 55 degree afternoon pickup.  All else is pretty equal but the temp.  Not too surprising, batteries don't really like cold weather.  Even worse case usage, I've still got an easy 45 mile range without flattening the batteries (you really aren't supposed to take them further than 80% discharged) which is plenty for my daily routine.  Best case in the summer should be closer to 60 or so miles.

yesterday I wired the brake vacuum pump through a toggle switch so I can shut it off in parking lots for that cool 'silent EV effect' and for those times when the pump sticks on...  I plan to do the same to the motor blower, but it's not nearly as noisy so I'm not feeling quite as urgent about it.

it's getting driven between 20-40 miles every day right now, charging up for what I calculate to be the equivalent of ~$1.30/gallon when normalized against the Honda Odyssey it replaced.  And working just fine as my main kid transporter!  And this is paying a pretty high $.24/kWh with PG&E, should be able to pretty easily cut this in at least half with either solar, or a dedicated E9 rate meter, or both.  Down the road a bit for those...

New stereo

I did a little 'fun' work on the car last night, installed a new stereo and put on a few decals. It had an am/fm cassette, but since installing the new controller, the radio had so much interference I couldn't use it while driving. I tried a Droidx to cassette adapter, but the radio ate the adapter... I pulled the radio out and destroyed it to retrieve my adapter (which works fine in my van, so I wanted to keep it). The new stereo came from Crutchfield, basically just a cheap-ish unit that allows bluetooth. I don't so much care about the phone, I never really have a need to talk on the phone while driving, but I wanted to be able to stream Pandora over bluetooth from the Droidx.

As it turns out, I now have no interference on FM, and only a little bit on AM. I took great care in getting good chassis grounds (instead of grounding through the factory harness), maybe that helped? Anyway, I'm super happy about having radio reception again!

In this pic you can see the bluetooth dongle (it's not integrated directly into the unit) on the left side of the photo. Once again I'm super happy with Crutchfield, and their installation kits. Pretty much plug and play, just had to solder the wires from the supplied car adapter to the radio pigtail. The plastic bezel and little pocket above the radio fit great, and the texture even matches the stock panels.

From 2011-11-29 stereo

the following pic shows a more overall shot. I've temporarily removed the pack volt and amp gauges (they used to be where the Droid mount is) because I didn't like them there. I'll either re-install them on the A-pillar (that's where they are on my van, I'm used to it...) or go with a 'virtual' display over the Droid.  I'm still investigating my options there, but in the meantime I can either use a laptop on the passenger seat connected to the Synkromotive, or just drive blind (which is what I've been doing for the last few days). There's plenty of safety systems in place to keep the pack safe, I don't really NEED the gauges. But I do like having them.

From 2011-11-29 stereo

And here's the new decals. The 'high voltage' and symbols on the left side are basically there to cover up a decal from the original selling dealer. The 'electric' emblem looks pretty good, I think! Still pretty subtle.

From 2011-11-29 stereo

It's been about a week, not much to really update... Car's been running great, I've been driving it every day. Between 20-40 miles/day, charging overnight. I did do a few small things; moved the motor blower to an isolated mount, removed the radio (it ate my ipod tape adapter, so I forcibly removed it!), and installed a shoulder harness for the middle backseat seatbelt so I can now carpool 4 kids to school.

I am having a little problem with the vacuum pump (the pump keeps the vacuum for the power brakes up), it sometimes doesn't shut off. I've found that a sharp 'whack' to the side of the pump does it, so it must just be a sticky pressure switch (the pump has an internal pressure switch). I want to move the pump to the same isolated mount that the motor blower is on, I'll pull it apart and see if I can clean up the switch while I've got it out.

range update

just a little range update here... last night I did 27 miles up to a meeting and back, Most of those miles were at 65 mph on the freeway. It was about 40 degrees F out, and I used the heater about 1/2 the time (1500w electric element). It re-charged for ~10 hours at 5.8a last night, about 60ah.

If I assume I don't want to go below 80% dod (depth of discharge, which would be 104ah of my 130ah pack) then I have a freeway range of about 46 miles. A bit more if I don't need the heater. I'll round it up to 50 miles and call it good. It should do even better in warmer weather.

As an aside, for a 15 year old car with over 130k on the chassis, this thing rides smooth! It's nice and quiet on the freeway at 65 in 4th gear, no vibes or anything.

more pictures

Things are looking good! I installed the Evnetics TPS and the Netgain speed sensor, and rewired the vacuum pump to be on a relay. All went well, I went for a 10 mile or so test drive and had no cutouts or faults. I did lots of experimenting with settings, I’ve settled (at least for now) on 400a battery side and 750a motor side. I’ll just rely on my judgement and right foot control to keep from spinning tires or breaking CV joints… Anyway, with only 400a from the battery I’m not able to get 750a for long at all off the line, but it starts high, then holds over 600a for a while (up to about 2000rpm or so). With these settings it’s pretty quick off the line, and certainly fast enough for daily driving with a little fun when desired. I will still hit a low voltage alarm on the MiniBMS if I try to sustain more than 300ish amps for too long, so I set the low voltage ‘soft’ limit to 135 volts in the Synkromotive software. This lets me use up to 400a briefly, and the controller will taper it back for me when needed. It seems to work well, I did some intentionally hard pulls and never heard the alarm after setting this limit. I never felt any kind of cutback, the controller handles it smoothly. I’ll have to go back to my test road soon and re-test the 0-60.

here's a bunch of photo's from the weekend:

the old potbox

From 2011-11-06 synkro

the custom cable holder. just a simple piece of sheetmetal bent and drilled to hold the nub on the end of the cable. the holes in the TPS bracket are already the perfect size for this, so the cable is sandwiched between the arm and this little bracket. each side holds the nub, and it's free to rotate. simple and effective.

From 2011-11-06 synkro

here is the arm with the cable attached

From 2011-11-06 synkro

here's the whole throttle assembly attached. it is truly a piece of beauty! I'm not sure my car is worthy of such a nice part. it certainly deserves a nicer mounting bracket...

From 2011-11-06 synkro

here is the Netgain speed sensor. Very easy to install, the only challenging part was that my motor endshaft had just enough surface rust on it to keep the collar from sliding on. i had to remove the wheel to get better access, then lightly sand the shaft with some 600 grit paper to smooth it up enough to install the collar. although looking at this photo, i can see that I accidentally lined up one of the set screws with the keyway. dang, I'll have to get back in there and rotate it a bit.

From 2011-11-06 synkro

here's the controller! the small terminal block right in front of it holds the connections to the speed sensor and the throttle. The bundle of wires on my heater controls box are the extra wires not needed for my installation (reversing contactor controls, various outputs, etc). Not sure what to do with those yet... all the wires plug into the controller with a nice waterproof connector, which seems a little odd since the controller itself is obviously not waterproof. Anyway, the wires were all nice and long, easy to route and connect up.

From 2011-11-06 synkro

here's the backside. Yes, I'm using a second EV200 contactor for my high voltage accessories. Yes, it's overkill.

From 2011-11-06 synkro

and the overall shot. this is pretty much finished up. You can see the 12v relay next to the terminal strips, that's for the vacuum pump. The loose wires heading down in the front of the photo are going to the motor blower. I still need to clean up and re-route those wires.

From 2011-11-06 synkro

That's it for now. Hopefully it will stay this way for a little while. I do need to put on some of the plastic bits back on up front to get it ready for the rain, but it's basically ready to be my daily driver now.