Wednesday, October 1, 2014

Cooling Pump Follow Up

If I had one thing to add to the previous post, one thing I've learned, it's don't send a boy to do a man's job.  Let's recap the story of my attempts at cooling the Zilla controller in the car. 

The first cooling solution I installed in the car was essentially a kit sold by EVSource.  It came with a little 4x8 inch radiator, and a Laing D5 Strong pump.  The car hit the road in March of 2010, when the average daily high temperature is about 75°F.  All was right with the world.  However, by late April, when temperatures are beginning to approach 100°, I noticed the controller starting to over heat, and go into thermal cutback after I'd traveled a couple miles from the house.  It turns out that a radiator from a kit designed for a liquid cooling system for a computer wasn't up to the task of cooling a 1000 Watt controller.  Go figure!

What did I do about that?  I added a couple of 120mm fans to the radiator.  But as the car was off the road that summer while I re-did the battery layout up front, and removed the motor for repairs due to faulty balancing putty, I never got to test this solution in heat of the summer.  When next summer rolled along, I found out that it was only slightly more effective than the previous year when I had no fans. 

Attempt #3 at getting adequate cooling:  I swapped out the little 4"x8" radiator for a nice big 12"x14" that incorporated it's own 10" fan.  I hooked that fan up to a temperature switch on the Zilla so it would spin up if the Zilla got above 122°.  This system was far and away better, but the controller would still go into thermal cutback if I ran it on the freeway for more than 5 miles.  Now, you may notice through all of this, that I never changed out the pump.  The little Laing D5 Strong pump was still in the car spinning away. 

When that pump failed early this summer, I was forced to replace it, and I was fortunate enough to have purchased one of the OEM quality Pierburg water pumps from EVTV.  It would have been far easier to simply swap the bad Laing pump for another, I wouldn't have had to modify anything in the car, but I'm so glad I didn't.

I've run the car in our typical 105° August/September weather, on the freeway for 12 miles at a time, and so far the controller has not complained once about getting too hot.  In fact, I haven't even heard the radiator fan kick on!  If I'm honest, may have come on when I was on the freeway, but I never heard it due to road noise.  The bottom line is that thanks to this Pierburg pump, the controller is finally getting the water supply it needs for proper cooling.  And the properly sized radiator is providing enough cooling area to suck the heat out of that water.  This is a big relief.  Heat is the enemy of electronic components.  The better I can keep them cool, the longer they'll last.

Thursday, September 11, 2014

A Failed Water Pump and Building a Circuit

Sometime in January, I think it was, I was driving the Z3, having a good time, minding my own business, when the  Zilla controller's light started flashing at me, indicating a fault with the controller.  The car kept moving and responding as normal, and shortly afterwards the light stopped.  It's done this in the past, during summer time when cooling system wasn't up to keeping the controller cool.  But this was January, so that couldn't be it.  Right?  This happened a couple more times, completely baffling me.  Each time the fault would clear on its own by the time I got home.  I hooked the laptop up to the controller... No faults.  Hmm.

Shortly after that I took the car off the road for some mechanical upgrades and a few small repairs: new steering rack, and replace the damaged front bumper.  Because I'm careful with my work, and took my time (read lazy), the car was off the road for about 2.5 months.  I got it back on the road in late May.  The first drive back in the car is always glorious.  I love driving the car! 

On that first drive, I was on my way home and the warning light started flasing again.  Then it started flashing faster.  It was at that time I noticed that the car was barely responding to the throttle.  At that point, the light came on in my head and I realized what had been happening all along.  But how could the car be overheating?  A hot day in May, sure I understand, but not to this degree.  And certainly not back in January when it was 60°F outside!  What could possibly be going on?

I popped the hood and immediately notice a small bubble in the line that leads from the Zilla to the radiator.  It pains me to say it, but that is the high point in the system.  Anyway, I notice it's barely moving.  When I'd filled the system, the pump was able to push all that air through the system down to the radiator where I bled it out.  I climbed under the car, touch the little pump and I found it was cool to the touch, and didn't seem to be running.  I tapped it, and it started running, but it didn't sound right.  After much testing and what not, I was able to determine that my little Laing D5 Strong pump had given up the ghost.  That was a big surprise; these things are known to last forever.  Fortunately I had a replacement pump waiting in the wings, but not the same make or model.

Sometime last February, Jack Rickard at EVTV announced that they had some Pierburg water pumps for sale that they'd acquired in the Azure Dynamics bankruptcy.  These are the same pumps used by multiple OEMs including BMW.  They normally retail for nearly $500, and he was selling them for $100.  What a deal!  Maybe it was premonition, but I decided to buy one in case I needed it.  Truthfully, it was probably a stupid purchase at the time, but fate intervened to make me look like a genius. 

The only thing is this pump puts out 8 gallons of water a minutes, but he Zilla only requires 2.  The thing is, more water is not better.  Your first thought might be that more water will likely cool the system better (I know that was mine).  But it turns out that if you push water through a heat transfer system too fast, it simply doesn't have the necessary amount of time when it's in contact with the surfaces to transfer heat efficiently.  Fortunately, this pump has a PWM input signal line that you can use to control the pump, dialing it from 10% duty cycle up to 100%.  The problem is, I know nothing about circuits other than if pressed I can identify a circuit versus say a can of fruit. 

I decided to do a little Googling to see what I could find, and wouldn't you know it, I found a YouTube video (since taken down) posted by a man named Klaus Wolter about how to control the pump.  He subsequently posted a design for a PWM circuit he'd designed to control the pump.  I'm reprinting the circuit here, though I have no way to contact Klaus for permission.  Klaus, post a comment if you object.

For those of you who don't know, a PWM signal, or Pulse Width Modulated signal, is simply a series of On-Off signals used to control a motor.  Now some PWM controllers actually send current to a motor to control it's speed, like for instance the Zilla controller in Z3.  Others simply produce a PWM signal with no current.  That's what this pump requires.  It reads that signal and the circuitry in the motor interprets it and then controls the motor's speed, meaning that this circuit doesn't directly control the motor.  It became clear that I was going to need that circuit if I was going to make this pump work in my car, so I decided to give it a go and try and build it.

I found a couple electronic component stores near by and went and collected all the parts I'd need. I bought at least two of each figuring that I was sure to foul up the first attempt.  Next, a friend encouraged me to buy a bread board so that I could build it out first without soldering any of it.  The only problem is that there were a couple aspects of the circuit that I didn't understand, particularly how that diode fit in.  Fortunately my bother-in-law Mark is an EE and he talked me through it, showing a great deal of patience I might add.  I put the circuit together on the bread board and sat there staring quite proudly at my accomplishment.  It was at that time that I realized I had no way to test it.  I don't own an oscilloscope.  But, I had an idea.  I know that motors controlled by a PWM circuit see an average voltage depending on duty cycle.  If you have a 100 volt system, and you're driving the motor with a 50% duty PWM signal, the motor "sees" 50 volts.  OK, really it sees 100 volts for 50% of the time, but since it's switching on and off so fast it averages out to 50 volts.  I'm sure every EE reading this is going to be shaking his head for some reason, but that's how I understand it.

With that understanding, I thought I might be able to throw my multi meter on the circuit's output and I should be able to measure a difference as I twisted the potentiometer.  Sure enough, I could!  OK, time to solder it up.  Here's what I ended up with.

Not terrible for a first ever attempt.  But would it work?  I hooked it up to the pump, ran some hoses to a bucket of water and turned it on.  Nothing.  I could feel the pump was on, but it felt like it was barely running.  If I twisted the pot I could tell the motor spun a bit faster, but still the pump moved no water.  Well, time to troubleshoot the circuit.  I spent hours going over it, checking and re-checking, but it all looked good.  I finally decided I was going to EVCCON in a week or two, I would take it there and ask some friends there if they could take a look at it. 

I explained the situation to a friend, one of the attendees, Doug Ingraham and he happily offered to help.  We borrowed Jack's oscilloscope, hooked it up, and to my great surprise, the circuit worked perfectly!  I was thrilled, but puzzled as to what could have been the problem when I was testing it.  It took a quick conversation with Jack to discover the problem.  Once again, it was my surprisingly great ability to assume that was my downfall.  I had assumed that if there was a problem, it MUST be the circuit I'd just built.  In my defense, that was more than 99% likely.  In this case however, it was the fact that these pumps are not self priming.  There was no way the pump was ever going to suck water up out of a bucket.  *Hand on forehead, shakes head slowly.*

I got back from EVCCON, and the next day tested the pump with a gravity fed system and it worked perfectly.  But it was a good thing I spoke with a number of people about this while at EVCCON because I learned I was going to need to make a couple other modifications to the car to accommodate the larger diameter inlet and outlet from the pump.  Particularly I was going to need to make sure that the pump had enough water feeding to it, or the pump would cavitate, ultimately ruining the pump.  The old pump had a 3/8" input, but new one, 3/4".  The tiny reservoir that supplied coolant to the old pump, with its 1.5 cup capacity and 3/8" outlet would not do.  I replaced it with a 1 quart model that has a full 3/4" outlet and inlet. 

I had the whole system together a couple days later, and the car was back on the road running cooler and better than ever.  That is until I turned on the A/C for the first time and found that it had lost it's charge.  I think I might have hit a hose or something while working in there, perhaps I broke a seal and allowed the gas to escape.  *Sigh*  It never ends.  But winter is coming.  I don't need to attend to that right away. 

Monday, May 12, 2014

Wheel Alignment

Recently I had to replace the steering rack in the Z3.  This was a completely new experience for me as I've never messed with any car's steering components.  As it turns out, it wasn't that difficult.  As a friend accurately stated, "It's all a mystery until you've done it once, then it's just work."  The plan was that after I got the new rack on, I'd drive it a couple miles to the nearest Costco to get new tires, and then a mile from there to have the front end aligned.

Of course, I needed to try to get the tires as properly aligned as possible for those two short trips between the house and those two places, otherwise I risked scrubbing the remaining rubber off my tires (at best) or losing control and getting into an accident (at worst).  But how?!  I don't have any fancy alignment systems.  Then I came up with a clever plan.  I still have two 5 foot pieces of 1" angle aluminum laying around.  I clamped one to each of the brake disks on the front end, with them sticking out in front of the car.  I pointed the steering wheel straight forward, and then took a measurement of the distance between the brake disks where the angle aluminum was clamped.  I then adjusted the toe-in, toe-out until the measurement between the end of the angle aluminum was the same as it was at the disks.  So how did I do?  I needed to wait for the shop's initial measurement to find out.

I got the new tires on and dropped the car off at the shop.  I told them when they aligned the car, I wanted it set so that the tires had no toe-in.  In other words, I wanted the wheels aligned for 0° toe-in.  After all, this is what I'd had done before, and is generally accepted by EV enthusiasts as a great way of reducing rolling resistance.  Ultimately every degree you have dialed into the toe-in is more energy that gets scrubbed off your forward momentum.  Of course, we've all come to accept the fact that having the car aligned with 0° toe-in means that the car tends to wander a bit when you head down the road.  You get used to the car sort of following the grooves in the road, requiring you to work the steering wheel a little more to keep the car in a straight line.  Not a big hassle by any means, but certainly not what most people are used to when driving a car.

When I made this request, the owner of the shop stopped and said "Why would you want that?"  I explained that I wanted 0° toe-in for efficiency reasons.  He considered what I said and replied "That won't get you what you want."  "Why?" I asked.  He explained that as any road car moves forward, there is a certain amount of force pushing all the tires back.  OK, that makes sense.  He went on to explain that this force will inevitably cause a certain amount of deflection, or flex in the rubber bushings that make up the steering/suspension, causing the tires to lose some of the toe-in that's dialed in when they are aligned.  He stated that if I started at 0°, once the car was moving forward, and the tires were experiencing that road resistance, that pushes them back ever so slightly, I would end up with a slight bit of toe-out.  He continued saying that in such a case, you'd likely find the car wanting to wander a bit as you went down the road.  That got my attention.

Sensing that this could be very important I replied, "Go on."  He said "We normally dial in a total of 16, or 8 for each wheel.  I would suggest that we halve that to 4, or perhaps 3 on each wheel.  That way, when you're going down the road, you're more likely to be at 0° or just a bit less.  That should get you the efficiency you want, and the car will track truer."   I asked him exactly what measurement 16 was.  What was the increment used?  Is it degrees, tenths of a degree, furlongs, what?  It turns out that it was 1/100ths of a degree.  That means that normal toe-in would be set at .08° for each wheel, and he was proposing .03°.   I told him to do it, .03° it is!

The fact that the increment used for aligning the car was 1/100th of a degree seemed to me to make his claims that much more plausible.  The reason I say that is because if the standard increment used for aligning the car had been higher, say like 1/10th of a degree, he would have been asserting that the deflection in the steering geometry was in excess of .6°, which seems a bit extreme to me.  But with the measurement's increment being 1/100th of a degree, the total deflection in the steering geometry is more like .06°.  A more plausible prospect. I have no way of knowing if what he says is true, but it certainly sounded reasonable.

So the ultimate question is was he right?  To know the answer to that, I'd have to be able to see either no loss of efficiency in the car, or even better, a slight gain in efficiency.  Plus I should see the handling improve as the car should track down the road better.

Unfortunately I'm unable to say with any certainty whether the car is more or less efficient in rolling now.  The only measurement I have at my disposal to determine this is the average watt hours/mile.  As most of you know I've been collecting that data with every trip the car makes since it hit the road.  Doing so was what helped me discover that the Helwig Split H60 brushes were more efficient than the standard H-49 brushes that came on the Netgain motors.  But the value, or worth of that number is dependent on all other things in the car remaining the same.  If you change two things at once, there is no way to tell what's responsible for the change in readings.  Well having just put a brand new set of tires on the car, I've completely negated the relevancy of any efficiency numbers I've gathered since those changes.  That said, the car is using a bit more energy per mile.  It had been averaging 320 Watt hours/mile, but it looks like we're up to about 350.  Is it the tires?  Is it the alignment?  Impossible to say.

What I can say is that the car drives great.  It tracks down the road beautifully and is better to drive than ever.  In that regard, the service shop owner seems to have been correct.  I'm calling that a win.

Truth be told, I'm much less interested in the minor increase in efficiency that might be on the table, than in gaining what most people would refer to as "normal" driving car.  Not unlike when I abandoned the nifty little proximity cut off switch I'd designed for the power steering pump.  It worked just fine, and saved a bit of energy, but you had to turn the steering wheel a couple inches before the power steering kicked in, which meant for those first few inches there was no power steering.  It wasn't all that difficult, but it was strange, and I had to explain it to anyone that drove the car.  I don't want a car that drives oddly, and neither does anyone else for that matter!  But for me it's probably for a slightly different reason.  I don't want anyone who allow to drive the car saying "It's great, except for this one strange thing..."  I don't want anyone's first EV experience tarnished by having to work the steering wheel like a saw as the car meanders around the road.

The point is, if you're having your car aligned with 0° toe-in, thinking that it's remaining that way when you're moving down the road, and you're enjoying a lower rolling resistance, you might be wrong.  Your car might be rolling down the road with a slight toe-out.  What would be great is if someone else with a 0° toe-in set on their car could gather a lot of efficiency data, and then have their car re-aligned to .03 or .04° toe-in per wheel and then report back.  Any takers!?

Oh, and incidentally, the alignment I did in the garage was .63°.  Not bad for a guy with a couple of sticks and a measuring tape.