Sunday, January 24, 2010

Fixing the Batmon Resistors

Well it's about time I get the Civic working again now that the weather seems to be getting warmer. The biggest concern I have with my current system is the Batmon balancer resistors. The existing ones seem to be always on the verge of catching fire.

To replace the existing resistors while keeping the same mounting holes, I cut some 2.5"x3" rectangles of aluminum and bolted some beefier power resistors to them.

Here's the rectangle of aluminum with the larger power resistors. I'm hoping this system has much more thermal mass than the last one and can dissipate more power safely. I used a 1/8" drill and 6/32-1/2" self tapping metal screws to hold the resistors on. The two holes in the aluminum on the upper edge have the same size and spacing as the prior holes that held in the previous resistors.

After I was all done, I had four resistor "packs" to replace. There was clearance issue with the resistors just behind the front grille, so I made a different heat-sink block (shown on the bottom in the picture) to fit the two 6mm bolt holes on the driver's side just above the grille.

Here's the heatsink and power resistors installed just in front of the motor over one of the front-most batteries.

Here's the old power resistor setup. Note the discoloration on the bulkhead from the smoke and excessive heat.

Here's the replacement setup. with the larger resistors and aluminum heatsink.

Here is yet another replaced unit on the driver's side in the rear trunk.

In addition to bulking up the resistors, I also increased the resistance from 3 ohms to 5 ohms. This won't have as much balancing effect, but I'm banking that it will dissipate enough to do a reasonable job while lowering the heat generation. If each Batmon board kicks in at 14.6 volts, my heat dissipation (V^2/R) goes from a worst case of 71 watts to 42 watts. Since the Batmon boards are actually switching on and off quickly, I should never reach the worst case situation.

The next step is to get rid of the noise on the PakTrakr lines. My series 100 ohm resistor didn't work, so I'm going to have to try a few other tricks.


KazooPaul said...

Welcome back, Tim; glad to see you're back at the workbench!

David Harrington said...

Great that you are back at it!

I am finally getting around to install cabin heat in my Civic, and I am looking into electric blankets to warm my batteries for better winter useage.