AcuteAero

Sunset in Southern Oregon (firefox kind of sucks the life out of this picture, unfortunately. Imagine it much more saturated...)

I’ve got three big areas that need work on the car:

1. Overloaded suspension
2. Plug-n-Play chargability
3. Amp-hour/range remaining instrumentation

Starting with #1

I’ve been researching and pondering suspension options. I was thinking about sticking some off the shelf eibach springs and nice shocks on it, but there are no aftermarket off the shelf springs that I have found for the Miata that have a higher spring rate but aren’t lowering springs. I don’t particularly want the car much lower than stock. I just think that option wouldn’t achieve what I’m trying to achieve. I thought about threaded coilovers, but was advised against the cheaper ones, the good ones are very expensive. So then, thinking about maybe combining custom heavy duty springs with OEM style shocks, I contacted Valley Spring Works and was quoted $328/pr for custom springs- nearly $700 just for springs all the way around. I also have been checking out air-shocks, and have found a couple packages- which are ~1500 and up. Similar cost to high end threaded coilovers. I’m not sure about the performance characteristics of the air springs, it seems like their primary purpose is for easily adjustable ride height. Seeing the price of air springs make the custom steel springs seem cheap… which they are not really.

And it just today occurred to me to check the GVWR of the miata- 2770, if you recall, dry it weighs about 2700 now. So it’s definitely over. Damn. Oh well.

#2

I have been planning modifications to the BMS master to allow the landline cord to be attached, the system to start charging then stop when it’s finished- I’ve picked up a few parts for that purpose. I will house the master board in an aluminum box with an AC solid state relay to provide/cut power to the charger. By default the charger will be unpowered, so in the case of a system failure or problem it will just be disconnected. I think I will set it up so that the master board can detect if itself or any of the slaves has crashed on account of software failure or EMI, and reset. There will also be a built in 12v supply to power the BMS off the landline-power, and circuitry for switching the power from landline to car’s power to entirely off. I have decided what sort of connector the charge inlet will use, and will be used in the in-car wiring and on the out-of-car cords and adapters- Neutrik PowerCon 32 amp:

Neutrik PowerCon 32

Power-in will use the chassis mount connector, Power-out will use the cable-mount. Unlike the PowerCon 20, there is no alternate style for power-in and power-out. So, on the long 10/3 cord I have to use with the car I will need to have both a cable mount and chassis mount connector on the ends of the cord- I think I will try making a round sleeve/strain relief on the lathe to mount the chassis mount connector on the cord instead of using a box- on the less prominent connectors inside the car trunk I will just use boxes. These connectors are expensive (best prices I found: here and here) and aren’t supposed to be used to break under load- but they are of very high quality and I feel better about using them than mis-using some NEMA twist lock that is actually supposed to be used with some particular H/N/G 120/240 circuit instead of this more flexible voltage input. These connectors also have a really high quality look and feel that I like. Note- if you screw the strain relief ring on a Neutrik connector down, then unscrew it again with great force, don’t expect the ratcheting action to be nearly as good subsequently- try to avoid taking these connectors apart after you’ve assembled them once!

#3

I ordered a 1000 amp shunt and an Albright SW-200 contactor to replace the Kilovac one on Otmar’s recommendation- in line with what I observed at UC Davis (four welded-shut kilovac contactors kicking around in the hybrid car lab), apparently the Kilovac contactors have an alarmingly high likelyhood of welding shut in break-under-load situations as compared to the Albright ones. Bonus with the Albright- you can inspect and clean the contacts if you’re worried about them. So, I’m going to rework the high-power wiring center in the front of the car to incorporate these new parts. I think I’m going to make interconnects out of copper busbar material instead of welding cable as well… Anyways, I’m working on figuring out how to amplify and detect the +/-50mv signal from that shunt in such a way that it can be used for peukert-corrected coulomb-counting. Which of course opens the door to some useful instrumentation. More on that as I get it working.

Oh, and the vacuum pump is getting to really annoy me. Every time I switch the car on it makes a huge noise, for a way long time. I think I might just get fed up with it- I’ve seen the YT STABLE product in person, I was pretty impressed- it’s powerful enough to replenish the vacuum fast and it’s not a diaphragm pump so you get much less vibration and noise. EV Source is carrying it now. It’s a little expensive but jeez that diaphragm pump is getting on my nerves. I turn the key and invariably whoever is around says- what’s that NOISE- man!?

Much more in the works. Stay tuned.

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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:

The 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 EVSource.com 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-

2705 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:

As 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.

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This is a work in progress- I am working on planning how the battery regulators for the car are going to work. One key part of that process is deciding on the actual optimal charging procedure for the Optima-type AGM battery.

One often-seen charging procedure is the “three-stage charging” process. It consists of three distinct phases:

1. Bulk, constant current. The charger puts out its maximum possible current until the battery voltage reaches a certain setpoint (usually 14-15v for 12v nom. batteries.
2. Absorption, constant voltage. The charger then holds the battery at that setpoint as the current declines, either for a certain amount of time or or until the current drops below a certain setpoint.
3. Float, constant voltage/current. The battery voltage is kept at a lower voltage (usually around 13.8v) where there is little change in the current.

This process is recommended for its speed and efficiency. It would be reasonably possible to implement with the battery regulators.

The Optima documents specify a different regimen, however, for cyclic applications (applications like in the car where the batteries are cycled significantly, often- as opposed to starting or UPS use)

Cyclic Applications:

• 14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour.

This is a bit different, and a bit strange seeming. I found the Exide Orbital tech sheet a little more descriptive and useful to clarify and reinforce this different idea:

2. IUI or Constant Voltage/Constant Current/Constant Voltage Recharge: Appropriate for more continuous
cyclic discharge/recharge applications
o Step 1: Maximum current limit of 20% of nominal capacity (approx: 15 amps) and voltage limit of 14.4 volts (A)
o Step 2: Hold at 14.4 volts until recharge current reaches 2% of nominal capacity (1.5 amps for most Orbital sizes)
o Step 3: Hold current at 2% of nominal capacity (1.5 amps) for 2 hours
o Discontinue charge if battery reaches 50oC (122oF)

Taken from Exide Orbital Technical Information PDF

While the numbers Exide chose for the Orbital charging recommendations are a bit different, the concept is very much the same. It’s definitely useful to see this kind of consistancy.

So, how will this work?

• At first, all the regulators will not shunt, voltage will be under 14.7 volts at all batteries and current at all batteries will be the same, up to 20 amps (charger limit)
• As some batteries start to approach 14.7v the regulators will start regulating, up to their maximum shunt current, at which point the master regulator will start scaling back the charger current. Batteries that have not reached 14.7v yet will continue to charge at the lesser amperage.  Charger current will continue to decrease to avoid pushing the strongest batteries over 14.7v.
• The charger output will go as low as 3.5 amps, since the regulators sink about 2.5 amps at wide open, that will allow the strongest batteries to reach 1 amp at 14.7v while the weaker ones continue to charge at up to 3.5 amps
• Once the strongest batteries have reached 1 amp at 14.7v the regulators can go into “extended absorbtion” phase for those batteries, with the charger still at 3.5 amp output can hold those batteries at 2 amp constant current for an hour, while the weaker batteries continue to do whatever they need to do.
• Once the strongest batteries have been charging at 2 amps for an hour, the charger will reduce to 2.5 amps to allow those batteries to stop charging entirely or 2 amps if all the other batteries have reached “extended absorption” phase. The regulators on those batteries that have completed an hour will shunt all the charge current.
• A low current float phase could be implemented after all batteries have completed an hour at 2 amps.

The individual regulators can be aware of the voltage of the battery they’re regulating and the current they’re sinking in the shunt by way of ohm’s law and the duty cycle the shunt is running at. The regulators must be able to be aware of the current the charger is putting out for a constant current mode. Temperature compensation capability would be desirable. The master charger regulator must be aware of the duty cycle of the regulators and the voltage they’re sensing to decide how to scale back the charge current. Alternately the regulators could ask the master to reduce current, although the latter setup could be less versatile.

I think that accounts for all the provisions laid out by the Optima charging specs, and this hardware setup. I’m sure I will continue to think about it and how it’s going to work though– of course!

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