Thursday, February 12, 2009

Fixing the Charging System...Again

After doing another fix to the Charge Detector box on Monday, I enclosed all the BatMon boxes to prevent them from shorting out due to grime and automotive fluids.

Here are the plastic boxes I talked about in a prior post. They are held in place with velcro adhesive tape and the box lids are held together with red electrical tape. I don't seem to be having any trouble with overheating (yet...) and the clear plastic lets me see the OVP/LVP lights.

This has been my third week of commuting and I've got 550 miles on the car. It's been fun to drive and show off. I sold my other EV (Porsche 914 at last Sunday, so I'm glad to not have three cars to deal with and the associated insurance.

I'm going to take a break now and just enjoy driving the car, hopefully without too many charging issues. About a month from now, things are going to get interesting again because I'll be trying out a beta test controller from Sykromotive. It's much more programmable, so we'll see how it goes.

Have a great week, everyone.

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!

Battery Imbalances

I've been somewhat concerned with how imbalanced my pack has been lately. Given that the charging system has been blown for a few days, I'm not too surprised.

Here are some observations. The front two batteries behind the radiator grille are the lowest voltage in the pack. They tend to be the coldest because they get lots of air while I'm driving. They also get more drain then other batteries because they supply 24V to the controller and to the contactor. Furthermore, one of the front batteries is tied to the IsoBatMon unit. The IsoBatMon pulls no power when there is no LVP/OVP signal activity; however, when charging, it pulls 10mA when the OVP signal is on. I think the voltage drop across the zener diodes on that BatMon board is just a few tenths of a volt higher than the other BatMon boards (home fix job).

Thus, we have a perfect storm happening on the front-center battery that gets the highest load, and equalizes last due to a slightly different zener drop on the BatMon board. I think I'll swap boards with another battery to see if that lets the green light come on earlier.

In the end, the pack imbalance isn't horrible. If I take no-load voltage measurements on the batteries after they sit for an hour, the voltage difference is less than 150mV, so maybe my expectations are too high for what kind of balancing to expect.

Anyway, I'm just sharing these thoughts so they don't get lost in time. Cheers.

Tuesday, February 3, 2009

Aligning Suspension and Fixing Charging System

Last Friday, I took the Civic into the suspension shop to replace the passenger-side axle (CV joint boot was broken), replace a brake line (those are important) and get a full alignment. The mechanic just couldn't get over how he could come to a full stop and not stall the motor without pushing in the clutch. The electrical specialist mechanic up the street took my card and vowed to come to the next OEVA meeting. I'm really glad I had the over-rev protection on the motor via the tach shift-light output. The mechanic revved the motor quite a few times while trying to shift like a gasoline car.

With the Charge Detector unit not working, I've been using my timer-on-a-cord to charge the batteries at night. For the past few days, I've been trying to figure out why the charge detector blew up. Many folks would have just sent it back, but with my EE skills and stubbornness, I chose to figure out the problem myself.

After taking a few days to study the circuit, I found a few blown components. I replaced the blown components and tweaked some resistor values and we'll give it another try with a full charge cycle tonight.

I'm not going to post any details of the circuit here for two reasons. First, Belktronix is moving to the Gen2 version of the charging system which doesn't use a charge controller and, second and more importantly, it's a proprietary design and I don't want to cause any ill will with Belktronix. I suppose I voided my warranty anyway by tinkering with it, so I'd better live with my decision.

The first two days of commuting this week went well. The outside temperature is warming up a bit (we're above 50 degrees F now) and the batteries are getting broken in, albeit somewhat jarringly.

Let's hope the rest of the week goes well...