Making progress on Loose Ends

Sunset in Southern Oregon

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.


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

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!



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.

Posted on August 28, 2009 at 11:39 pm by Henry · Permalink
In: Battery Regulator, EV Miata

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