Thursday, March 12, 2009

Charge Detector Blown Again

A few days ago, something funny happened to the vehicle. I drove home and my LVP light came on earlier than I expected. When I got home, the front battery was rather lower than the others in the pack. I attributed this to being just behind the front grille where a lot of cold air is blowing in. to remedy the problem a bit, I slide a large sheet of foam-core board between the batteries and the radiator grille which gives a bit of insulation and forces the air go around the side.

After measuring my batteries for several days after that, they seemed much better, but still didn't seem to get fully charged when sitting at work. Again, I attributed that to the low temperature around here (mid 30's).

Today, I drove home, plugged in the charger and just checked to see if the charge detector was working. Sad to say, the FET has probably blown open again since the OVP lights were not on and lots of current was dumping through the large external 3-ohm charging resistor, making it really hot. This would definitely explain the slow charging.

After trying to fix this device several times, I have a few options:

- fix it again (and wait for it to blow again)
- send the charging system back to Belktronix to get upgraded to a Gen2 system without the charge controller for about $400
- dump the Belktronix system altogether and go with something else, like individual Soneil chargers (Rob Connelly did this and is happy with the results)

I'm not sure what I'm going to do. The existing charger works, but it's just a bit slow. I'll ponder this over the weekend. I have an OEVA meeting to lead this evening.


Saturday, March 7, 2009

1000 Miles and Still Going...

There's not too much to report on the Civic. I just passed 1000 miles yesterday and it still seems to work fine. I've definitely noticed over the past several weeks of commuting that my range is highly dependent on my speed. Even driving at 55mph instead of 60mph on the freeway gives me a few extra percent of battery life on the Link-10 E-meter.

I've ended up driving with the LVP protection disconnected from the Belktronix controller because it tends to make my speed go way down even though I have plenty of battery left. The LVP circuit is still attached to the battery light on the dash, so I know when to start being very careful of my driving habits.

The charging system seems to be working fine now that I have the BatMon boards inside boxes, protected from the elements. I've driven in a hard-driving rain several times without any problems. The final voltage on the batteries differs slightly from battery to battery due to the analog nature of the Batmon circuits. The BatMon boards rely on the calibration and tolerances of analog components to activate the shunt resistors at 14.5 volts or so.

I'm starting an experiment with several prototype digital battery monitoring boards from Synkromotive. I'm going to see if I can determine which battery is causing the LVP fault earliest with this monitoring system. For you circuit geeks out there, the Synkromotive system (prototype only at this phase) has a 12-bit A2D converter which makes it more accurate than the PakTrakr system used in many EVs today. Those extra bits can make a big difference when your batteries are close to the end of charge and the balancing system needs to compensate for small differences like 50mV. The digital nature of the system (each battery gets an 8051 microprocessor) allows for easy adjustment of calibration values in case things drift over time.

I'll report back when I get some more results.


EV Driven Link

A few weeks ago, I added an "EV Driven" link to the right menu bar of this blog. EV Driven is a group of folks trying to spread the word about EVs and are behind the upcoming movie Revenge of the Electric Car. It contains several searching features for this blog as well as many other blogs related to electric vehicles. Please check it out when you get the chance.