Massive update

A lot has happened since June 8th, when I wrote the last post- Let’s get all that out of the way and move move on to what’s new-

I visited ohio and drove my great-uncle Cal’s tractor on the old family farm:

DSCN0729The semester ended, I got good grades.

As I have hinted, I drove the car- three times now. I still haven’t edited the video from the first drive, maybe I’ll do that tonight. The second time was to the DMV to get the car “verified” and registered, and the third time was just last Sunday, down to the autocross event at Golden Gate Fields. I have been working hard on the BMS/automatic charge balancing system, I think it’s almost working. In fact, that ‘s what I’m working on right now. I’m doing the first run of the charging system with a very basic charge profile set up, just getting a feel for how (if) it works. I’m babysitting it here in the car right now, I figured I might as well use this time to write about what has transpired… as you can imagine I’ve been putting it off.

So, what first-

I am feeling more and more confident about the powertrain of the car, now having driven it three times, I have not detected any issues with the clutch, adapter plate/hub, motor mount, batttery mounts, battery cables or other electrics. The DC/DC converter (IOTA DLS 55) works just fine and quite unobtrusively once I upped the HV fuse for it (it instantly blows 6a fuses, works fine with a 17a fuse) I have a class J fuseblock and fuses installed presently, that’s what was selling at the time I was buying- now they’re selling smaller circular fuses and blocks, I may need to change to this new type of fuse- it’s surprisingly hard to source DC rated class J fuses for reasonable prices. Of course that’s another good $100 bucks on the table, so I’ll hold off for now.

I drove the car to the DMV with my Dad following me with a tow rope, just in case. The drive there and back was mechanically straightforward, and pretty fun. The inspection went fine, they verified the VIN and the electric-ness of it then took the old title, gave us a new registration sticker and sent us on our way. Unfortunately, as is described on the Wikipedia page on EV conversions, I came away with a Q motive power code as opposed to the rightful E power code- apparently that’s the default behavior of the computer system. Q designates hybrid power- as of now hybrids are not subject to smog checks, so this problem is not an imminent issue for me, but it is kind of dumb. I have heard that this is generally a pain and that one way to tackle it is to complain to the governor’s office. I have higher priorities on my list now but this is something I may take on later.



On the way back from the DMV Dad and I stopped by our mechanic’s shop to show off the car, they’ve heard about it plenty of times over the last two years and have been interested in seeing it. I wasn’t expecting all the mechanics from Steve’s Auto Care and the neighboring Albany Tire to come out onto the street and check out my car, but it sure was neat.


Then last Sunday I took the car down to the autocross at Golden Gate Fields parking lot- (1.5 miles away) I had heard they would have scales there, I have been quite curious how much weight the car gained and how my gut-feel engineering worked out for the weight balance-

IMG_79252705 lbs, very evenly distributed- could be worse. I was hoping it wouldn’t weigh quite so much, but all in all it’s pretty good and I’m quite pleased about the weight balance. I definitely need to install stiffer suspension components- either OEM style shocks and custom heavy springs or fancy ground control coil-overs, depending on what sort of advice I get and what the budget is.

I gave one or two people rides through the parking lot although I didn’t attract that much attention as I was not officially part of the event- that’ll come another time. I think the car has potential to be a pretty competent autocrosser. When I arrived back home I tried the speedy launch technique with the clutch a couple times- it really is a rush to wind up the revs and then feather the clutch out. 0-40mph is stupid fast. Just for the heck of it I tried letting the clutch out a bit faster and did a tidy little burnout-


I boosted the contrast a bit to enhance visibility, the super crummy tires on the car now don’t really leave much behind. The tracks are about 15ft long and pretty even, I think it confirms the car has an LSD. It was super loud and pretty fun. I’ll have to refrain from being so obnoxious on my street in the future…

As for the BMS system, I haven’t got a lot of photos, but it is coming along well. Like I said, I am as I type watching the character VFD (vacuum fluorescent display) I programmed to display battery related data from the BMS bus as the PFC 20 charger is cranking about 13 amps into the battery pack. The battery voltages are within about .6v of each other, the top one is about 14.2 right now. At 14.7 the shunt resistor is supposed to start kicking in and the master node is supposed to start slowing the charger down via the REGBUS port. Since we haven’t hit 14.7 yet I’m not sure if all that is going to work… but I’m hopeful. Some things are already looking good, despite the charger generating an insane amount of EMI- it destroyed the radio reception here in the garage- the BMS data bus does not seem to be having any issues- now the PakTrakr is also not having issues, and it consistantly has problems whenever the Zilla is powering the motor. I feel hopeful for the bus though, it uses the differential-signaled CAN transcievers and operates completely over twisted pair wire. I was able to get the system to crash by cycling power to my old school flourescent desk lamp, but I already knew that it generates some pretty nasty EMI pops- it’ll make loud pops in headphones attached to the computer. Hopefully the system will be able to take it OK, it would be neat to have the individual battery volt readouts while driving.

The first battery has hit 14.7 and the shunt resistor duty cycle is about 1/5 right now, drifting up and down, but successfully clamping the battery voltage to 14.7. The real test will be when the duty cycle hits 245/255 and the master node tries to slow the charger down… so far so good at least.

Good news- good good news- most of the batteries have hit 14.7 now and all the shunt resistors seem to be working perfectly. Even better, some of them have reached high enough duty cycle to make the master crank the charger down some, which seems to be working just fine. In fact, everything seems to be working exactly as it’s supposed to. I wish I had my camera out here… and I don’t want to leave this unattended.

Well I can use the iSight camera:

Photo 2As you can see in that photo there are two batteries that seem to be lagging significantly. I’m not sure about them but I’m going to give it some more time.

Ah, well. So here’s the weird part- I noticed two batteries venting very slightly- number 10, which seemed to charge and act just like all the other batteries was hissing slightly from the (-) side vent. Number 6 which was the laggiest battery, its voltage would rise then fall then rise but I don’t think the shunt ever turned on for it was hissing more noticably from the seam where the top meets the casing. Pressing down on the seam would stop the hiss. I know for a fact that the datasheet figures were not exceeded, in addition to my BMS system which is reasonably consistantly accurate to .1v I checked all the batteries and these ones in particular several times with my fluke meter and found the voltages to be well within the expected range, 14.6-14.8v usually exactly 14.7v. I did not even attempt the Optima specified finish cycle (2 amps, constant current) where the battery voltage would certainly excede 14.8v. Hmmmmm. I’ll need to check these voltages tomorrow to get a good SOC approximation and call up the experts. During the previous two times I charged this pack, using the Husky brand 2/10/20 amp digital charger I never noticed these hissing noises, however the Husky charger fan is very noisy- although the hissing noises persist after removal of charge current and I never noticed it before.

I still count this test as a success, my BMS system performed exactly as I expected and intended. I have heard about how touchy these optima batteries can be, I hope I can figure out what exactly is going on here.

… so that’s the massvie update. I will attempt to keep more consistantly up to date in the future. It’s been a stressful and busy last few weeks though, believe me.

Posted on July 2, 2009 at 1:11 am by Henry · Permalink
In: Battery Regulator, EV Miata

Leave a Reply