Monday, April 5, 2010

Motor Controller: Current Sensor Modifications

So because I'm putting this controller in a motorcycle, size is an issue. I tried to fit it in the bike with the case that was in the kit, however it was slightly to large; about 1/16" away from one of the battery terminals. Because of this, I've been trying to figure out ways to make the physical size of the controller smaller. I've determined that the smallest I can make the case - without redoing the controller entirely - is approximately 3 1/2" tall, by 6 1/2" wide, by 8 3/4" long. I designed the new metal case using Google Sketchup, and was planning on making it this past weekend, however a few friends at the local EV club pointed out that it might be best to make the entire case out of lexan. Being non-conductive AND cool, this changed my decision to make it out of lexan; that way I can show people the circuits of the controller without taking the cover off.

One of the other things I've wanted to do for a while was 'flip' the current sensor. Doing so would save me a good 3/4" of space which was only taken up by the connector for the LEM; not a good use of space. After talking to Adam for a while, he figured out that software wise, it was an easy switch; however the hardware current protection would need to be redone. I emailed LEM (the manufacture of the current sensor) and asked if they had a similar product except the pins came out the opposite side; all that they had was a similar product that was to be mounted on PCB board; I could have used that, had the max current not have been 600A. I decided to try to see if I could 'mod' the LEM sensor that Ben fried when he messed up his control board.

Taking apart the LEM was very easy; small screw driver to pry the front cover off, and then just two screws to get the Hall Effect sensor board off the plastic cover. The coil was glued to the other plastic piece, with very little space. I was lucky, however, as there was just enough space to get 4 wires to fit through a small hole in the upper corner - opposite of where the 4 pins were originally.

Heres the PCB that is inside of the LEM current sensor. The small board that is sticking out is the hall effect sensor; thats the magical part! The four pins on the left were what I needed to solder the wires to.

Heres the hole that I had to drill to get the wires through to the four pins above.

Here I soldered the four wires to the PCB board. This was my second time doing this, the first time the bare wire was slightly longer (not by much though); when trying to put the LEM back together, it was struggling to get back into the proper place. I ended up having to cut the wires off and re-solder to the pins.

I then bent the wires to conform to how the curve of the inner coil was, and test fit it again. I made sure to see if any of the wires were touching the coil at all; none were, so I snapped the cover back into place.

I then put the LEM back onto the M- bus bar, using silicon to hold it in place. You can see the black rectangle is where the pins used to stick out. I simply clipped them off, stuck a piece of electrical tape over it, and screwed the PCB back into place to hold it tight. Also, the wire across the B- and B+ bars is simply there to hold the sensor down while the silicon glue set.

Heres another 'mod' I also did, simply drilled two holes in the PCB that separates the control board from the power board, then clip so the thermistor and LEM sensor wires can be totally within the controller and have the siding of the cover even closer to the boards.