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.
6 comments:
Wow Tim, that's some saga! Glad to hear you're back on the road. It's interesting that Warfield considers a small voltage leak acceptable. Perhaps it's impossible to completely isolate the case from the rotor when it's all made of metal?
Not to make you second-guess your decision to keep the 9" brushes, but I wonder if the difference in size would affect how many comm bars the brushes can contact at once. In other words, if the 9" brushes are narrower (on the shortest dimension), they would contact slightly fewer comm bars, and perform at a slightly lower level due simply to a smaller surface area in contact with the commutator. What do you think?
Alex
Alex,
Actually, the brushes for the 9" and 11" motor are the same in all respects except the radius that's pressed into the end that rests on the commutator. The width, breadth, height and material are all identical. So it does cover the same number of bars on the commutator.
I read in the EVDL archive that some leak is inevitable, but once the resistance gets low enough, they blow the motor out real well. In all cases, it's caused by the accumulation of carbon dust. Makes AC systems seem a bit more attractive.
Tim, First thanks for the warning on the grease on the transmission shaft. I’m hoping to mate my motor to transmission in the next couple weeks.
I’m in the process of running my Warp9 with 12 volts to seat the brushes. I took a resistance measurement before I started and I get greater than 10 MOhms to the motor body. I’ll check again after 20 hours of run time.
Your comment about noise and vibration is interesting. It had to be due to the radius on the brush as you mentioned. I placed an accelerometer on my motor the first time I powered up, and measured 10 mili g’s of acceleration at 2100 RPM. It will be interesting to see if this number changes as the brushes form during run-in.
Here’s to hoping your motor issues are in the rear view.
Joey,
What would really be interesting is to take a reading of resistance after you seat the brushes, then blow the dust out with some compressed air and take the reading again. I highly doubt your brushes are going to dust as much as mine simply because of the circumstances. But still, it would be interesting to see if there's a difference.
I'd be surprised if you see much of a difference in performance after the brushes are seated as from before. But if you could look into the motor and see the surface of the commutator, you'd likely see a little less arcing.
By the way, in the two days the Z3 has been back on the road, I've put about 70 miles on it, and I've found that it's using less power than before. Before, the average was about 330 Watts/mile, but these last two days it's been 300. And that's while running the AC system the whole time. It makes me wonder if either the old racing brushes were some how less efficient at transmitting power, or there was some other problem with the motor. Can't say for sure, but I'll be keeping an eye on that.
Your conversion is shaping up to be a real beauty. I'll be eagerly following your progress.
Whenever possible, the airflow
through the motor should be in
the direction of the brushes to blow all the coal dust out of the motor.
The fan is on the correct side,
that should be ok as it is, but i dont know what happens when you are driving faster and there is a lot of
air flowing from all directions
around the motor
Franz,
My thought is the more air, the better. Right now I'm concerned that the 105 cfm that fan puts out may not be enough. I may look for a better fan. These new, harder brushes are supposed to produce a lot lest dust, but we shall see.
Post a Comment