Wednesday, February 4, 2009

Thoughts on the Kit and Belktronix System

With 350 EV miles on the car, I'm ramping down on fixing things and ramping up on commuting. Before I forget all the stuff I've learned, I'd like to capture some thoughts about the Open-Source kit and my experience with the Belktronix system.

Good points about the open-source Civic-Kit:
  • I really appreciate keeping the clutch. It makes shifting much easier and makes the car feel like a regular vehicle
  • Choosing AGM batteries was a great idea. No hassle with plastic boxes and they put out a punch of current. No acid spill either.
  • The kit involves no welding (metal or plastic)
  • There's no cutting of the chassis to attach parts or install batteries, only drilling holes
  • The kit keeps the spare tire and quite a bit of trunk space while still seating four people
  • Choosing the 5th generation Civic was a good choice for curb and gross vehicle weight. It is also simple to tap into the gauges and electrical system since it's before the advent of complex CAN-bus based systems
  • The use of coil-overs with custom springs makes modifying the suspension so much easier than trying to put stock springs from a different car on the Civic struts. It costs a bit more, but allows for variances between Civic models and battery choices.
  • Picking a standard group-31 size of AGM battery makes the kit flexible and upgradeable
Improvements for the Kit
  • As with many engineering projects, documentation is rather sparse at this point. I think I captured quite a bit of stuff in pictures on the blog, but the official document is only about a third done and not reviewed.
  • The trickiest part of mounting the batteries was desigining the firewall rack. The tolerance between the motor adapter and the underside of the hood is very tight. Too low and you put lots of weight on the motor adapter. Too high and the hood won't close, even with denting in part of the support struts.
  • The vacuum pump is loud. period. I still haven't figured out a good valve pressure switch so that it maintains the right pressure at all times, but it's accepatble so far
  • For my car, I would have liked to get a white car to handle the heat in the summer better. Last summer, the dark blue car heated up quite a bit. Maybe I'll opt for a sunroof
Positive notes about Belktronix controller system:
  • I appreciate the holistic package that Belktronix provides with all the needed parts for a reasonable price
  • Documentation is excellent with lots of diagrams and troubleshooting hints
  • Support is excellent and prompt. You get to talk directly with the designer and don't have to escalate issues to get someone who knows how the system works
  • The vehicle Integrator module is great at telling you the status of the system through LEDs. The precharge sequence for the contactor works well.
  • I like the optical potbox. It mounts easily right under the accelerator pedal and will never suffer from mechanical degradation.
  • The controller seems very smooth and puts out good power. I haven't driven with something similar like a Curtis 1231C, but it accelerates smoothly
  • The battery shunt balancing system puts the shunt resistors off-board to prevent heat buildup near the battery. This also allows placement of the shunt resistors near a fan or other vent.
  • The external thermistor on the BatMon boards allows measuring battery temperature where it is most accurate. I've heard that putting it right on the battery terminal offers the least thermal resistance to the actuall internal battery temperature.
  • The Batmon boards offer individual low-voltage protection (LVP). The controller shuts down when the lowest battery reaches 10.8V instead of just monitoring the whole pack voltage. This prevents killing the lowest battery even though other batteries are okay
Improvements to the Belktronix system:
  • My biggest beef with the Belktronix system is the lack of programmability. It's an analog system where one needs to tweak resistor values to change any parameter. I can't argue that much since most other controllers are also analog in nature, but it would have been nice to change the acceleration curve or LVP cutoff voltage through a laptop.
  • I still need to figure out the LVP circuit. When the battery reaches 50% DOD, I lose all power and can barely creep along at 20mph. I have a bypass switch to get around this, but that disables any LVP protection I might have had.
  • The Batmon boards require quite a bit of wiring which makes the engine compartment look much like spaghetti. It also lends itself to reversed wires or shorts with the wrong terminal leading to blown BatMon boards or a blown Charge Detector. One company added two RJ-45 connectors to their battery boards and just used ethernet cable to wire everything up. No hassle with accidentally swapping or shorting wires and a much cleaner install.
  • I'm concerned that the Belktronix system taps off the main traction pack to power the contactor and the controller, where many others use the 12V accessory battery. This exacerbates pack imbalance and puts a higher load on a subset of the pack. I'm concerned this will cause the pack to degrade more quickly (or diverge more quickly).
  • The BatMon boards are just bare boards (with a protective coating). In the trunk, that's not a big issue, but in the front engine comparment, I've already had issues with fluids like the windshield washer fluid causing intermittent OVP faults. These definitely need to be enclosed.
  • One minor issue is that the controller system doesn't have an over-rev input on it. Bryan at Belktronix worked with me to make an interface that plugs into the back of the tach to create this function, but it's a bit messy. I realize this is problematic since it's hard to set the RPM limit without programmability. Many other systems don't have this feature either.
Overall, I think the controller is fine but the charging system needs some big improvements, especially the wiring spaghetti and bare BatMon boards.

Onward to more commuting!

1 comment:

Carlo said...

To solve your imbalance issue, put one of these across your 144V pack, then tie the - to the pack -, and the + to the 24V tap input on the Belktronix. This is a circuit they could have simply replicated to keep the batteries balanced.

http://www.bb-elec.com/product_multi_family.asp?MultiFamilyId=40&TrailType=Sub&Trail=695