EVCCON 2012, Charging, and a Watchdog

There's no denying it, this is a long over due update.  Since I last wrote about the charger blowing up, there have been a few events worth noting, and a change in the charging system worth mentioning.  Let's get to it.

EVCCON 2012

You may remember that my father and I took the Z3 out to Missouri last year for the inaugural EVCCON.  It was a fantastic event and before it even ended, I decided that Dad and I would return to EVCCON 2012.  There was a big difference this year in that we didn't take the car along with us.  Having the car out there last year was terrific, but trailer-ing it out there was stressful, expensive, and it took three days each way.  So this year the car waited back in the garage while we went to Missouri.

There has been plenty written of the convention on some very well written blogs, particularly on Mike Brown's blog about his Porsche 914 conversion, ( day 1, day 2 and day 3), and of course on EVTV.  What I was most taken back by was the quality of the builds this year.  I've been told by a number of people that they think I did a great job on the Z3.  Compared to most conversions I've seen, it is great.  Virtually all of the people that brought cars to this year's convention attended last year's and had a chance to see all of the cars that were brought at that time.  There were a handful of car's at last years convention that made the Z3 look like a kindergarten project.  It was evident by everyone that saw them, that they were clearly a different animal.  In fact, it's clear that the community has decided those cars are the new standard.  If you were going to convert a car, they were the benchmark that you need to aim for.  A challenge that all took seriously.

The quality of the cars this year was simply outstanding.  Everyone had all the components laid out and organized better than you'd expect an OEM to do.  All of the wiring was routed perfectly and protected in looms.  The connectors all neat and orderly, everything labeled.  Looking in to these cars was like looking in jewelry boxes.  Just astounding.  Here's a sampling of a few.  I wish I'd grabbed more photos.

Fred Behning and his MGTD

Jeff Greeson's 914.  Take away that blue cord and it's looks like a show piece.

John Allen's Celica.  A beautiful job in every respect.

Kevin Heath and his RX8.  He has every reason to be proud of this build.

Jason Horack's Daytona.  Well laid out, neat and tidy.

Dale Friedhoff's Ranger.  It won best wiring/layout award.

It's inevitable that a fair number of people are going to look at any conversion.  The better they look, the more professional they appear, the more likely people are to take them seriously and not view them as a science project, or worse a rolling death trap that is bound to electrocute someone.  I personally think that producing fine cars like this pushes the cause of EVs forward a bit faster.

If I'm not mistaken, last year Dad and I were the only father/son team at the convention.  Well apparently that inspired a few others.  Several decided they wanted to share the experience with their fathers as well.  I was thrilled to see that list grow to 5 teams.  We took a moment to pose in front of Jack Rickard's original Speedster, along with Jack.

Left to Right, Me, my dad Bill, John Allen and his father, Nabil Hanke , John Hanke, Jack Rickard, Fred Behning and his dad Fred,  Brandon Hollinger and his father on the end.  

After a public car show in the park, the EVs went on parade through town and back to a local hotel were many of the attendees were staying.  They rounded up all the EVs that were in the parade for a photo op.

I think there are 33 cars in the photo, and I know of 5 others that didn't make it.  So that brings the total to 38 EVs at the convention by my count.  Not a bad turnout.  If you have the means to attend, I encourage you not to miss EVCCON 2013.  They are only going to get better from here on out.

Charger News

You may remember from my last post that my charger up and exploded on me.  It went back to Manzanita and they repaired it in a couple days and had it back to me right quick.  I think the charger was out of the car for less than a week.  All seemed well until a week after the install I noticed the charger behaving very erratically.  Though I'd dialed in 20 amps of current, I saw the meter bounce all around from 18 to 2 then 10 then 3 then 5 amps.  It was clear that it wasn't healthy. 

I contacted Manzanita again and explained what it was doing.  They asked me to take notes for a while to see if we could see a pattern to help them determine a cause.  If there was a pattern somewhere buried in the data I gave them, it escaped me.  After a couple weeks, we decided they needed it back to fix it.  I took it out and mailed it the day before Dad and I left for EVCCON.  

As it happens, Rich Rudman owner Manzanita Micro was one of the featured speakers at EVCCON, so I got to talk to him about the charger.  I offered to let him pick my brain about it's behavior hoping that he might have some insight into why it was doing what it was doing.  Instead it turned into a very short conversation.  Rich asked me if it was behaving erratically, and listed off a few of the key characteristics of the behavior.  I said "Yes! Exactly!"  He said "Yeah... we don't know what's causing that."  Apparently they've seen this a few times.  They suspect a specific chip on the power board is causing it.  When they come across this, they replace a few key components and that resolves the problem.

I got it back last Wednesday, they had it for about 2 weeks, and so far, I'd say they nailed it.  It has been rock solid reliable.  Boy, do I like that.  They really are a first rate shop.  

A Watchdog Circuit

It's happened twice now, which isn't a lot, but enough to make me a bit nervous.  The charger which usually cuts off when the pack reaches 164.5 volts has error-ed during the constant voltage portion of the charge cycle.  Instead of cutting off the charge in 10 minutes I set it for, it was well past 15 minutes, and I turned it off manually because the battery was going too high.  I was present on both occasions to catch it and prevent it from over charging the batteries.  But that begs the question, how many times did I not catch it because I wasn't there to watch? 

The truth is, the charger is pretty reliable, but it uses electronic components to process that logic and is subject to the same faults any electronic component is.  How many times does you computer do something unexpected?  The world is an imperfect place.  To that end, I've always thought that it would be worth while to have a separate circuit watching the charge cycle, one that had the ability to cut off the charge if things got out of hand.  Fortunately a couple simple components allow anyone with a Manzanita Micro charger to do just that.  I believe that other chargers have this capability as well, but I don't own any of them, so I can't say.

The Manzanita chargers were built incorporating what Manzanita calls the REG Bus.  I hear it does many things when coupled with other hardware that they sell.  But the truth is, I only need to use one of those functions, and that's the one that allows me to stop the charger.  

Pin 1 on the REG Bus supplies 5 volts DC.  Pin 2 has no voltage on it; however, if pin 2 sees 5 volts, the charger interprets this as an over charge condition and shuts the charging cycle off.  The charger remains on, with the fans cooling it, but the charging cycle terminates.  The bad side is, if you remove that 5 volts from pin 2, the charger immediately starts charging again.  So the trick is to get pin 1 and 2 shorted under the right conditions and leave them connected until the over charge condition goes away.  Enter the JLD 5740 volt meter.  At $37.50, it's a bargain.

The 5740 will measure anything from 0 - 500 Volts, DC or AC should you need it.  It has 2 relays that you can set independently.  You can set a relay to latch closed at one voltage, and open at a different voltage.  In this way, you can build in any logic for on/off you want.  Here's how I set mine up.

When I turn the meter on, the relay is open.  As the charge cycle runs, the voltage rises to the expected 164.5 volts.  If for some reason, the charger misses it's target, the meter is set to close the relay at 165.2 volts.  When the relay closes, the wire from pin 1 is shorted to the wire from pin 2 and the charger stops dead.  That voltage is low enough that no cell in the system will exceed 3.6 volts.  That relay then is latched closed until the voltage should drop below 158 volts.  Since the resting voltage of the system, after a charge is 160, then the meter will never (without intervention) open that relay, and the charger will never restart.  

When I built the car, I positioned a small switch under the charging door.  When that door is open the switch sends 12 volts to the charger, and it's presumed that I'm charging and the car is plugged in.  I run that 12 volt signal to the Zilla, which sees it and disables the car from moving.  I've simply spliced into that line and use that signal to power a separate relay, that then powers the meter.  I've incorporated the whole thing in a project box.  

Notice the neat glowing switch on top of the box.

The switch is depressed and the meter is on.

I've run the power from the switch in the charging port to a second switch in the project box.  If I want to use the meter to watch the charger, I simply press that button and the meter comes on.  When I press the switch again, or if I close the charging port door, the meter is turned off.  I don't need for it to be on when I'm not charging, so there's no reason to have that parasitic load running.  

The only thing I haven't mentioned is that the 12V from the car that powers the meter first runs through a small 3 Watt DC to DC converter that isolates the high voltage on the meter from the car's 12V system.  We don't want the high voltage system leaking back to the chassis.  Pretty slick, and the whole thing cost less than $50 and it works great.  

Heat: Not So Good for Chargers Either

A couple weeks ago, on a Monday morning, we were in off peak hours and I figured it would be a good time to top off the batteries before I ran the day's errands.  You may remember that I recently destroyed my eXpert Pro meter by re-applying the pack voltage to it and not removing 12V power first.  By the way, DON'T DO THAT!  Any way, I'd received a new one, but I hadn't yet installed it.  Without it, I have no idea how much current I'm pushing to the batteries, so I need to keep an eye on them to be sure I'm not over charging them.  The fact is you learn things when you watch what the batteries during charging.  Over time, I've learned quite a bit, and by watching them closely I can pretty much tell what's going on and predict when the charger will terminate.

At any rate, I know which cell will start to rise above 3.45V first, so I put a meter on it and started the charger.  For me, 3.45V is the top of the charge.  There simply isn't enough energy put into the cells above that point to justify the potential risk and damage to the cells by getting them to the manufacturer's 3.6V.  Ten minutes later, I walked out to see the voltage on the cell had climbed from it's initial reading of 3.26V  up to 3.380V.  I know by experience that means I'm about 35 minutes away from 3.45V when the charger should terminate it's charging sequence.  So you can imagine my surprise when I walked out 25 minutes later and found the battery at 3.364V, and the charger still running.  The voltage had dropped, yet the charger was still running.  I stood there for a moment, completely confused, it just didn't compute in my head.  Kind of like walking into your favorite BBQ place and seeing that it's full of vegans.  Not that there's anything wrong with it, but it just doesn't make sense.

Figuring that the charger must have just gotten confused (after all it does have a simple logic board in it), I figured I'd just reboot it.  I turned it off, waited 4 or 5 seconds and turned it back on.  The moment I turned it on, there was a succession of 3 pops, with the last one being quite loud and producing a bright orange flash and rush of hot gas shooting out the charger's vent port.  This was followed by me yelling "Oh shoot!", or something similar but perhaps more colorful.  I turned the charger back on... nothing.  Wasn't too surprised by that.  I checked the breaker on the house and had not tripped, so whatever failed in the charger failed in such a way that it simply consumed all the power coming into it and blew up, rather than shorting.  Or at least that's my take on it.

In either case, there was no doubt that I was going to need to remove the charger and send it back to Manzanita Micro for repair.  This was the second time I've had to do this.  The first was entirely self inflicted when I mistakenly shorted one of the batteries to the chassis with my multi-meter probe, while the car was charging.  That blew up the AC rectifier and melted the end of my probe.  I had no idea what happened here, but I boxed it up, got an RMA number and away it went to Washington.

It arrived in their shop on Friday and they sent me a note Monday afternoon that it was repaired, tested and ready for shipment.  Remarkably fast turn-around.  I called and spoke with Clarice, their office manager, to ask if they knew what caused the failure.  Clarice has seen enough repairs that she can recognize the likely cause of the failure just by looking at the parts that were replaced.  In this circumstance, both IGBTs failed as well as a capacitor.  She said she'd honestly never seen anything like it, but she'd ask Rich when he got it.  Rich thinks that one of the IGBTs failed and when it did, it took the other with it.  He thinks heat may have been a contributing factor.  This is where things get interesting and where there may be a lesson that all of you can learn at my expense.

As regular readers of this blog are aware, I live in Phoenix Arizona, which is slightly north of, and roughly rock throwing distance from Hell.  It's not uncommon for the inside of my garage to be 105°F.  If my wife pulls her car in after getting home from work, as it ticks itself cool, all the heat that was happily stored in all of that steel, gradually works it's way into the garage raising the temperature well over 110°F.  It's lovely.

Here's the thing.  Two years ago the car lived through it's first summer as an EV.  A significant portion of that summer saw the car dis-assembled because I had sent the motor back to Netgain because the balancing putty had fallen off.  Plus I took the opportunity to redo the battery layout.  So when it was back on the road in late July and I was charging it on a regular basis, I would come out to find the charger's yellow light flashing at me.  I went back to read the manual to find out what that meant, and I couldn't find a reference to what that was all about anywhere.  I figured it was just an oddity with this charger.  What it really was, was the charger warning me it was over heating.  I blissfully ignored this warning for the remaining portion of the summer.

As it happens, the car was taken apart for a good portion of the following summer to again fix a balancing putty issue on the motor, and to add air conditioning to the car.  In fact, I didn't get it back on the road until the first week of September, just in time to tow it out to EVCCON 2011.  But even then I would see the flashing yellow when charging, but by then I'd figured out what it was so I would dial the current back until the light stopped flashing.

That's been my modus operandi this summer.  I'd turn the charger on and dial in between 21 and 22 amps.  I'd poke my head back into the garage in 20 minutes or so and if the charger was over heating, I'd turn it down.  About 90% of the time, it was over heating.  I'd turn it down to 16 amps or so.  In retrospect, I think this behavior, and the initial instances of ignoring the warning, damaged the charger over time.  Heat is the enemy of all circuitry and when the charger was overheating, it felt quite literally like a blow drier firing out of that little vent port.  So my advice to you is don't to this.  I realize that most of you don't live in such hot climates, but for the few that do, pay attention to your charger.  Heat kills.

At this point, I intend to charge at 16 amps or so during the hotter months to protect the charger.  It's remarkable how much cooler the unit runs at that current level.  The problem is the charger was configured at a higher current level.  That means if I charge at a lower current level, there's a risk that the charger will overshoot the voltage I've set and consequently over charge the batteries.  Re-tuning the charger for a lower level is possible, but such a huge pain in the butt that I don't want to do it for the 1 month it's necessary before cooler weather arrives.  But I would like to be able to charge at any level I like and not risk over charging the cells.  I do have a solution in the works which I will be implementing and writing about soon, so stay tuned for that.  In the mean time, I'm going to have to watch the end of the charging curve very carefully to protect the batteries.

A Look at the Bottom

Juvenile jokes aside, at the end of the last post I alluded to the fact that I was interested in seeing how the batteries were doing since I bottom balanced them in February of 2011.  Quite a lot has happened with the car since then.  The batteries have been through 353 cycles.  They've put out 2209 kWhs of electricity and then had it stuffed back in.  I've driven a total of 6324 miles.  The car has been out of commission twice for motor problems, and off the road for a grand total of 7 months.  During those occasions, the battery pack was partially disassembled with half of the cells out and laying on the floor of my garage, while the other half remained connected together in the car.   That last point has concerned me a bit.  I've wondered all along if having them apart might have introduced some variable that may have caused cell drift.  I kind of doubt it, but I simply wasn't sure.  So, I set out to find out. 

Last Sunday I had a chance to drive down to the brand new Tesla store in Scottsdale and take a first hand look at the Model S.  I even passed someone that was out for a test drive in one of the demo cars.  I don't believe I've seen a bigger grin on someone's face while they were driving.  It was a great trip, but I'll write about that later.  At any rate, with a round trip to Scottsdale, and a couple errands thrown in, I'd used about 95 amp/hours out of the pack's 120 amp/hours available.  I decided to make a quick trip out to run the batteries down a bit more.  I figured I'd get up to 115 amp/hours or so and then run the rest down by running the heater in the car.

I set off for a quick 10 mile lap that would do it, when I had a second thought.  I remembered that the last time I'd charged the batteries, the charge had cut off a bit early with the top cell being about 3.40 volts.  That equates to the pack starting off about 7 to 10 amp/hours down, so I decided to cut my trip short.  Turns out that was a good thing.

As I was driving adjacent to my neighborhood heading for a specific entrance, I noticed the car was not really accelerating any more.  A half mile before that I'd accelerated to 40 mph with no problem but now, it was acting dead.  I turned into the neighborhood quickly and headed for home nursing the car the whole way.  I'd brought my multi-meter along but I was afraid if I stopped, I wouldn't get going, so I coasted (running a couple stop signs along the way) and turned the final corner to my house.  As I was heading up to the garage, I was hoping the door made it open in time because if I had to stop, there was no way I was going to get it up the hill of my driveway into my garage.   I made it in, but the car was dead.  It would barely move the 6 more inches I wanted to go.  I quickly jumped out and measured the cell I know to have the lowest capacity and it was at 2.043 volts.  I started measuring others and they were in the 2.5 to 2.7 volt neighborhood.  Well, that doesn't seem balanced to me!  I decided to let the batteries rest for an hour or so and come back to measure them.

By the way, when I pulled into the garage, I'd used 113 amp/hours (for those of you keeping score at home.)

Now, I'll elaborate on this more in a moment, but take note.  The lowest cell was 2.043 volts right after it had had a load on it, which is just above what CALB considers dead.  The car would barely move.  Yet no cell was below 2.0 volts and no cell was ruined.

I came back an hour later and measured the cells and found that the gaps, or differences I'd seen in the voltages had closed up dramatically.  The lowest cell that was 2.043 volts had bounced back and was now 2.684 volts; the highest cell was 2.937 volts.   I should let the numbers speak for themselves.

You can see that the cells were mostly between the 2.700 and 2.800 range, with a few just 1/100 off in either direction.  But there were 4 that were more than 5/100's of a volt off, with the spread from the lowest to the highest cell at 0.253 volts.  Three things come to mind looking at this data.  First, they aren't balanced.  Second, the amount by which the are out of balance is quite small.  At that end of the discharge curve, the difference between 2.684 volts and 2.937 volts is a fraction of an amp hour.  The third thing is that I think I simply wasn't patient enough when I performed the bottom balance.  You may have heard this elsewhere, or experienced it yourself if you've ever bottom balanced a pack of batteries, but it is an extremely boring, tedious, and lengthy endeavor.  Or to put it another way, it sucks big time.

On that first attempt at bottom balancing, it wasn't until after I was sick of the whole process and charged the batteries back up that I realized the proper thing to do would have been to let them rest for several hours to be sure they remained balanced.  I had them all within 1/200ths of a volt when I charged them, but I now know that if I'd waited, I would have seen them settle, and found they were likely a bit further off.  I think that inaccuracy is reflected in the variations in this data. 

In spite of my ineptness demonstrated here, I must have balanced them well enough to be, what I consider, successful.  The car would not have moved another 10 feet if I needed it to, yet no cell went below 2.00 volts let alone reversed itself and died a horrible death.  Something a top balanced pack simply can't do.

Now, I know what you're thinking.  "But Tim, you brought on this situation yourself.  This was completely and utterly self inflicted!  There was no need what-so-ever to discharge the pack this much.  I never intend to take my pack that low and expose them to this peril.  Consequently I'll never face the jagged, rocky bottom of the discharge curve, risking one or any cells in the process."   In part, you're right.   But consider this.  These cells, like any other, lose capacity over time.  How much and how fast is determined by how you treat them.  The problem is, the dangerous, jagged bottom of the curve sneaks up with every charge.  In other words, a pack that started out as a 120 amp/hour pack eventually becomes a 110 amp/hour pack, and then 100 amp/hour pack.  If you don't know where the bottom is, you risk hitting it and running a cell or 10 into reversal.  Since mine are bottom balanced, I "see" that imbalance at the top.  The charger cuts off at a preset voltage and the batteries will eventually reach that voltage regardless of how many amp hours they can actually hold.  The difference is, if I hit bottom the car stops moving and the batteries are fine.

So what's a fella to do at this point?  Best try to balance them again and do it properly.  This was monumentally difficult.  Not because the job is hard, and not because the batteries put up a fight or anything.  Rather because it's miserably hot and humid in AZ at the moment and spending 3 days in the garage balancing the batteries was not my idea of a good time.  One of those days was 18 hours long!  Suffice it to say, I got them all between 2.757 and 2.761, 4/1000ths of a volt, and that was with letting them rest for 4 hours at the end, before I put the charger on them.

One of the key pieces of information I wanted to get and was eager to share with you was the total number of amp/hours that went back into the pack.  That really is a measure of how the batteries have held up to the 545 cycles they've seen.  Sadly because of another, yet different stupid mistake, I'm not able to share that with you.  In may haste to get the pack balanced and the car back on the road, and my zeal to get it done right, I forgot something very important.  When ever you disconnect the main battery pack from an e-xpert pro meter, you MUST remove power from the meter.  I forgot to do this.  I opened the car and saw the following...

Notice the haze in the lower corners of the display?  The sharp eyed ones among you may also notice that the meter is not actually displaying any data.  I opened the door and immediately smelled the distinct aroma of a fried circuit board.  NOOOOOOOOOOO!   It gets better.  I took it out this morning, hoping to send it back to Evolve Electrics for repair, and this is what I discovered:

I'm no doctor, but that does not look good.  This meter was a few oxygen atoms away from catching fire.  I'm not sure if the deformation of the cylinder is clear in the photo, but it is not healthy looking.  Don't be like Tim.  Disconnect power from your meter before you work on the battery pack.  Incidentally, it fried the 1:10 prescaler as well.  *Sigh*

So, the end result of that is that I don't have a precise number to give you regarding how much power the batteries were able to accept when I finally charged them.   I can tell you that I turned the charger's dial to what I believe to be the position where it delivers 20 amps, and it took almost exactly 6 hours to charge.  That works out to 120 amp/hours, but it's really no better than a guess at this point. 

10,000 Electric Miles

I pulled into the garage last night and noted the amp/hours I'd used and the mileage on the odometer so that I could record them like I do every time I charge the car.  The mileage read 144,214 which is significant because that marks exactly 10,000 miles since the Z3 was reborn as an EV.  I figured that this would be a good time to go over some of the numbers I've been collecting that last 2 years, 4 months and see what I could glean, and then share them with you. 

530        Number of Charge Cycles

18.9       Mean average miles driven between each charge
34.9%    Mean average depth of discharge
36.0%    Median average depth of discharge (half the data points are above, half below 36.0)


WARNING: Wild numbers and speculation will now commence. 

CALB says that these batteries are good for 2000 cycles at an 80% Depth of Discharge (DOD), and 3000 at 70%.  But how long will they last if I'm averaging roughly 35% DOD?  Of course no one knows.  However, if you use the 50% increase we see going from 80% DOD to 70% DOD as a baseline, and extrapolate that out, we might be able to conclude that we could get 4500 cycles at 60% DOD.  If we keep going and then apply it to my average DOD of ~35%, we come up with something close to 12,500 cycles.  At 18.9 miles per cycle, that works out to 236,250 miles. 

Of course that's all theoretical, but it's likely not too far off from reality.  But let's be conservative and say I only get half that number of cycles out of the batteries, that's still 118,000 miles.  However, we need to keep in mind that the original 2000 and 3000 cycles that CALB states is a bit misleading.  It's not as if the batteries stop working when they get to 2000 cycles.  What they really mean is that after 2000 cycles to 80% DOD, the battery will only hold 80% of it's original capacity, so they will still push the car as far as I need to drive on a daily basis.

</Wild numbers and speculation>

As you can see this whole "cycle life" or "life expectancy" question for the batteries is highly fluid with the real numbers determined by a number of factors all at once which are, for practical purposes, impossible to determine or track.  One thing that is certain is that these batteries will out perform a lead acid pack by at least an order of magnitude.  Seeing as they only cost 4 times as much as a lead acid pack, I call that a good bargain.  And that's not even taking into account the numerous other benefits they offer, like the 60 mile range vs. a lead acid packs 20 miles (at best). 

$1,402    Amount saved not buying gas
3639       Total number of kWhs used to charge the car

That $1,402 figure is derived by taking into account the price of gas when I charged the car and subtracting the cost of the electricity used to charge the car.  I always charge the car at off peak hours, and I add an extra 10% to the amount of electricity consumed to take into account the inefficiencies of the charger as it converts the 240 Volts AC to 160 Volts DC. 

So how has the car performed?  How well has it used that energy?

376        Mean average Watt-hours consumed per mile
388        Mean avg Watt-hours/mile with the old solid brushes
319        Mean avg Watt-hours/mile with the new split brushes

You can see there's been a marked difference in efficiency since replacing the brushes.  The old average of 388 Watt-hours per mile was experienced over 442 charge cycles and 8,184 miles.  The average has dropped to 319, and that has been over 88 charge cycles and 1,816 miles.  I don't know how one could dispute the claim that these Helwig Carbon split Red Top brushes are better. 

That increase in efficiency has moved the car from a 50 mile range using the 388 Watt-hours per mile figure to 61 miles using 319 Watt-hours per mile.  Of course most of you know how much range can fluctuate with an EV depending on how and where you drive.  I've been on 40 mile trips with the car where I saw the energy consumption average drop to 266 Watt-hours per mile, which works out to 73 mile range.  Is that useful data?  I don't know, but it's interesting.

Expanding on that, I found 4 data points that fit together nicely.   These are individual trips with the miles driven, the total kWhs used and the Watt-hours used per mile.

50 miles      17.23 kWhs    345 Watt-hours/mile
51 miles      17.89 kWhs    351 Watt-hours/mile
51 miles      16.49 kWhs    323 Watt-hours/mile
51 miles      14.57 kWhs    286 Watt-hours/mile

Guess which trip occurred after the new brushes were installed in the motor.  By the way, those were all trips to the same destination and back.

The real question at this point is how are the batteries fairing?  For those not familiar with the car and reluctant to go back and read the multitude of tedious posts, I bottom balanced the pack back in February of 2011.  The only way to find out how the batteries are doing now is to draw the pack back down to the bottom and make note of the amp/hours taken out and the state of charge on each battery.  Hmm... sounds like another post.  Stay tuned.

On Power Steering and a "Normal" Feeling Drive

Anyone who's been reading this blog for a while, knows that I have a Toyota MR2 electric hydraulic pump running the power steering system.  Take the ICE engine out of a car, and chances are your power steering pump goes with it. 

There are a few ways of dealing with this problem.  One is to simply fore-go power steering.  But unless you replace the steering rack with one that's geared for non power steering, that makes turning at low speeds rather like arm wrestling with Lou Ferrigno.   The second is to build some apparatus for holding the old power steering pump onto the front of the electric motor, putting a pulley on the tail shaft of the motor and powering it off that.  Of course, if the motor isn't spinning, you have no power steering.  For me and I'm guessing many others, there simply wasn't enough room to incorporate something like that.  You'd be surprised how many times you run out of room and 1/16th of an inch more was all you needed to make something fit.

The third, and perhaps most popular remedy is to use an electric power steering pump.  There are a few OEM cars out their using such devices and the second generation Toyota MR2 was one of them.  They cost somewhere around $300 to $400, they don't take up much room and its relatively inexpensive to have the custom hoses made to add them to the system. 

On a normal car, they run all the time and you really wouldn't care because the alternator will just produce the energy it needs to work.  But in an EV, you want to try and reduce parasitic loads.  That pump can draw up to 85 amps in a hard lock!  So the idea of having it run all the time was troublesome to me.  To resolve that, I devised a system by where the pump stayed off when driving in a straight line, but would come on as soon as you turned the wheel a few degrees.  I also added an off-delay relay so that it would remain on for 10 seconds after I was going straight.  In this way, it wouldn't cycle on an off while I was going through a parking lot or some other place requiring a lot of turns. 

But it wasn't a perfect solution, and I grew to dislike it for two reasons.  One was that it proved to be dangerous.  As is bound to happen when driving, it became necessary for me to quickly dodge something in the street.  The amount of effort it takes to begin turning is massive.  So when the pump kicks in, you just can't react quick enough to release the pressure.  I ended up nearly steering right into the car next to me.  It left me with a case of the sweats as I pondered the fact that I'd nearly caused an accident and destroyed all my hard work.

The second reason was that when I would have other people drive the car (something I do as frequently as possible) they had a difficult time getting used to that sluggish, stiff steering wheel when heading into a corner.  I thought, "how can I convince people that EV's are fun to drive and just like any other car, only better, when they had to wrestle the steering wheel going into any turn?  This was not the message I want to convey. 

I thought I would simply put a latching switch into the system that would allow me to bypass the proximity switch on the steering column which would then turn the system on and leave it on until I pressed the switch again.  Seemed like the perfect plan and I even had a great place to locate the switch in the cabin.   So, before I took the car apart to work on the last motor problem, I ran a few tests to find out just how much power the pump drew when I was traveling in a straight line.  It turns out that it draws less than 2 amps from the high voltage pack.  That translates into something like 18 to 22 amps on the 12 volt system.  Not trivial, but not too bad.  The system is sized to accommodate it.

The point is, I could let the car sit idle running that pump and it would take over 60 hours for it to deplete the battery pack.  That means in a standard commute to work, which takes 20 minutes, the power steering pump uses an extra... let me think... about, Oh I don't care!!  It's seriously not enough for me to worry about AT ALL!  Since the car has been on the road, I've left that switch engaged the whole time.  My previous post detailed how I've experienced a boost in efficiency seemingly from the new brushes, so the change to the system of having this pump run all the time might have had an adverse impact on that, but it's not enough that I care. 

The car drives like a normal car now, in almost all respects.  I don't have to explain to people that drive it why the steering feels weird at first, and they don't have to experience the sharp jerk when the pump kicks on and they aren't expecting it.  This is definitely the way to go. 

By the way, I have turned it off a couple times.  Sitting, waiting for my daughter to finish her choir practice, I left the car on so I could listen to the radio and enjoy the air conditioning, but I turned the pump off.  Honestly, I'm not sure it was worth the effort of lifting my hand to press the switch. 

Efficiency I Can't Quite Explain

With the exception of the few months the Z3 has been off the road for repairs or upgrades, I've been driving the car for just over 26 months.  During that time, I've kept detailed records of every charge/discharge cycle of the batteries.  Every time I plug in, I note the mileage on the odometer, and the number of amp hours I've drawn out of the pack.  I then take that data and plug it into a spreadsheet that calculates a number of things for me, including how much money I've saved because I wasn't burning gas, how much the electricity I'm using is costing me, and most interestingly, how many Watt-hours per mile the car is using.

I've reported in the past the the car averages about 320 Watt-hours per mile on surface streets.  That's the number I've used to calculate the range of the car: 19,400 Wh / 320 Wh = 60.625.  This is why I've always stated the car has a 60 mile range.  And I've proved that out once, driving 62 miles on a charge once, in preparation for doing a bottom balance on the batteries.

Of course, once I go on the freeway traveling between 65 and 70 mph, that 320 Watt-hours per mile begins to look like a distant dream.  The aerodynamic drag on the car causes energy consumption to quickly rise to around 420 Watt-hours per mile at 65 miles an hour.  That meant that my round trip to work, a 23 mile journey, which includes 7 miles of surface streets and 16 miles of freeway, averaged between 370 and 380 Watt-hours per mile.  I've made this trip a few hundred times, I know the numbers.

It's no secret that I've had a few problems with the motor in the car.  The balancing putty has come off for a some inexplicable reason, twice.  Just recently it developed a short to the case that no amount of air blown through its guts could resolve.  George Hamstra at Netgain has been a champion through all of this and ultimately had a new motor sent to me.  In addition, we swapped out the brushes from the standard H-49 brushes used for high current applications like drag racing, to H-60 brushes which are better suited for street use.  A cool feature on Helwig H-60 brushes is the split, Red Top design, which helps to ensure better contact on the commutator.

At any rate, I got the new brushes seated in the motor properly, put the car back together and launched it back onto the streets about 3 weeks ago.  The car is my daily driver, so once I began driving it to work and other places, and recording the energy consumption, I was a bit surprised to notice it was more efficient.  At first I thought it was maybe just an anomaly, but it's clear something has caused the car to make much better use of the energy in the batteries.  My round trips to work are now averaging about 280 Watt-hours per mile.  Compare that to the older 370!  That's more than a 25% improvement in efficiency!  I made one trip where the average dropped to 266.

Today I took a bit of a longer trip out to Scottsdale.  A total of 38 miles, with 30 of those miles on the freeway, traveling around 70 mph.  The average consumption for the entire trip was 274 Watt-hours per mile.  In the past, I would have estimated this trip to be a 400+ Watt-hour per mile trip.  But that's not all!  During the entire trip, I had the AC system on (which draws about 9 amps) and of course, I've configured the power steering pump to run all the time now adding another 2 amp continuous draw.  BTW, the change to the power steering is interesting, but that's another post.  So there are more parasitic loads, yet, efficiency is up.

The one thing I haven't done yet is to see what average I would get if I traveled at 40 or 45 mph.   There's no reason to think the gain in efficiency that I'm seeing wouldn't appear there as well, but I simply don't have those numbers yet.

It seems like an obvious conclusion to draw that the increase in efficiency can be attributed to the new motor, or brushes, or a combination of them both.  But I really can't say that with certainty.  Perhaps I'd made some error when installing the drive line in the past which caused some binding or friction that I simply wasn't aware of.  I kind of doubt that, but who knows?  There's no question I've gotten better at disassembling the drive line of the car, but there really isn't much room for error here.  I have no reason to doubt the numbers the meter is giving me; after all, it's the same meeter with the same set up I was using before the motor swap.

What ever the cause, the car does seem to be more efficient.  At an average draw of 280 Watt-hours per mile, it's gone from a 60 mile range to nearly a 70 mile range.  I'll take it.

Update 5/20/2012:

I've continued to see the gains in efficiency I detailed above, but I've realized I've let myself fall victim to insidious creature that is over optimism.  I've always maintained that the Z3 had a 60 mile range.  That was based on the fact that it consumed about 320 - 330 Watt-hours per mile when driving at ~45 mph in normal traffic.  What I really hadn't done is take an average over multiple trips to get a more balanced number, a real world number you can take to the bank.  Well since I've seen this improvement in efficiency, I've gone back  to my spreadsheet to see if I could mine some more useful, accurate data from the numbers.  Here's how it works out...

Since the car was put on the road, up until the motor/brush replacement, it has averaged 376 Watt hours per mile.  That is the real world average.  Sure there were many trips that were better, but there were also many that were worse.  I can't get out of my neighborhood without consuming something like 480 Watt-hours per mile.  It's all about stopping and starting.  With no regenerative braking, stop signs and stop lights really affect your range.  The more of them per mile, the worse your range.  Well, there's 6 stop signs on one of the routes it takes to get from my house to the main streets, so you can imagine what that does to energy consumption.

The average after the motor/brush swap has dropped to 321 Watt-hours per mile.  Compare that to the old 376, and you note a 14.7% improvement.  That is huge!  Interestingly, and I've mentioned this above, virtually all of the trips I've made in the car since putting it back on the road have been on the freeway at 65 - 70 mph.  Meaning, that as more trips on surface streets are recorded I expect that 321 number to drop even further.

The bottom line is that I've been misrepresenting what the car's range really is by skewing the data toward the happier, more optimistic lower numbers.  Not intentionally or maliciously mind you.  The old average was 51.6, the average now seems to be 60.4.  A painful thing to admit, but there you have it.  Just as I could have easily squeezed 60 miles out of the car before, sticking to surface streets and avoiding stops, I expect I could squeeze 70 miles out of it now, doing the same. 

I've brought all this to Jack Rickard's attention at EVTV, and just like me, he was skeptical and ultimately amazed.  He's been doing some tests swapping out the original H49 brushes for the split, Red Top H60's and he's finding the same results.  I have a feeling this is going to be a hot topic in the EV community for a while.

What An Ordeal

The few of you who read this blog have probably wondered what's been going on with the Z3.  When I last left you, I'd received the new motor, had put the new split top, harder brushes in and was seating them by running the motor off of a 12V battery.  Well, quite a lot has happened, and frankly, it wasn't all good.  So sit back and enjoy the saga.

Once I installed the new brushes and turned the motor on, it made a hell of a racket for the first few hours.  I remember seeing a video John Allen had made when he was breaking in new brushes for his Warp 9, and I was struck by how loud it was, so I wasn't too surprised when mine made similar noises.  I ran the motor for 100 hours and at the end, it sounded as smooth as silk.  Job done!

I mounted the motor up to the transmission and tightened up all the bolts and called it a day, planning to reinstall the motor/transmission back into the car the next day.  During the night, I realized I'd done something kind of stupid.  The manual for the car states that you should put a little grease on the input shaft before you mate it up to the motor.  It already had a film of grease on it, but I thought more is better.  When thinking about it that evening, I realized that I had cleaned off a little grease I'd found on the flywheel.  It was in a pattern that looked like it had been thrown off the shaft.  It was at that point I realized more is not better, and I'd set myself up for a greasy, slip prone clutch.  So I took the tranny off the motor, cleaned the shaft of excess grease and mounted it back up.  It only took 45 minutes or so, so it wasn't that bad.  I'm telling this story so that if anyone out there reading this can learn a lesson from my stupidity, then I've served some purpose on this planet.

Moving on.  The motor/transmission assembly went in to the car later that day without a hitch, and thanks to my dad who came out to help me.  I mounted up the drive line and started the process of re-assembling the car.  It went quite smooth really.   I was making one of the last battery connections when I leaned my elbow on the chassis, and it felt like I got stabbed or cut.  I remember thinking that I didn't remember the bolt I leaned on being particularly sharp.  I touched it again and realized that I didn't get stabbed, I got shocked.  That's right my friends, the leak, which I was trying to get rid of, the one for which I'd been sent a replacement motor, was not gone.

Talk about a kick in the teeth.  I started testing and dis-assembling everything and came to the conclusion that, once again, the source of the leak was in the motor.  How could this be?!!!   I was absolutely gutted and just walked away from the car for what ended up being the whole weekend while I thought about what to do.

I decided what I had to do was figure out, definitively if it was the motor or something else.  I decided the best way to do that was to assemble all of the components completely, but leave the motor out of the assembly process.  In place of the motor, I simply ran a cable from the Motor + terminal on the controller to the Motor - terminal.  This was simply to replicate the existence of "something" in the system at that position in the circuit.  Once it was all back together (minus a few batteries) I found that there was no leak. I added the motor back in, the leak appeared.

I thought perhaps breaking the brushes in had created enough dust to cause the problem, so I decided to blow it out with compressed air.  While some dust did come out, I could still measure the HV pack voltage on the chassis.  Ghaaaa!!

It was time to contact George again.  I can't express to you how much I did not want to darken his inbox with bad news again.  George asked if I would send him and Tom Brunka of Helwig Carbon Brushes a picture of one of the brushes that I broke in.  He wanted a close up of the face and shot of the profile.  Puzzled, and unsure of how that would help, I obliged and sent off the photos.  Tom got back and said that the brushes looked like they were broken in perfectly, so that was good.  But then he apparently noticed something else, and that was the model number printed on the brush indicated it was for a 9" motor.

The pieces started falling into place for George at that point.  The commutator on a 9" motor has a smaller circumference than that of an 11" motor.  That means that the brushes for a 9" motor would be made with a smaller arc to the face.  Aside for that, they are identical in function, composition and structure.  But what that meant was that rather than the brush's surface resting with more or less complete contact on the commutator, it was riding on the very edges.  That explained why they were so loud when I first put them in.  Truthfully, at that time, I even wondered if I might have been sent brushes for a 9" motor, but it was just a passing thought.

So, through an innocent mistake, George had sent me the wrong brushes.  He mentioned that it really was no problem to use them now that they were seated so well, and I would have had to wait another 2 weeks to get 11" brushes anyway.  I was fine with keeping these.  Anyway, because the brushes weren't contoured correctly for the 11" motor, that meant that a bit more material had to wear off of them than would have normally happened.  Couple that with the fact that when running off a 12V battery, the motor doesn't spin fast enough to create enough airflow to vent the dust that does come off the brushes, and you have a recipe for developing and internal path to ground.

I went back and measured the resistance of the path from the motor terminal to the chassis and found that it was .880 mega Ohms.  Don't ask me why I didn't measure that after I blew the motor out the first time, but I didn't think to.  I saw that I could measure voltage on the chassis and felt that was enough of a problem that I didn't think to measure resistance.  But what I found was that after I had blown it out, it had made a difference.  .880 mega Ohms can only pass 0.13 milliamps at 160 volts.  I could touch the terminal of the battery and the chassis and felt nothing.

George added that once I got the motor back on the road and spun it up to 3000 RPM, it would blow the rest of that dust out.  he also mentioned that Warfield Electric consider a leak to chassis acceptable as long as it won't light up a light bulb.  Well, .13 milliamps isn't enough to light a light bulb, and it's also not enough to cause my charger to complain.

Today I got everything back together, tested the systems, and flipped the charger on with fingers crossed.  It came right on and dutifully charged the batteries back up to full.  All systems go!  I took the car down from the jack stands drove it out of the garage and put 20 miles on it this afternoon.  It seemed like everyday since the car has been out of commission, I came across either a Nissan Leaf, or a Chevy Volt, while out driving and I would just grumble in envy.  Today I saw Leaf  while I was driving the Z3, and I simply felt joy.