Batteries


This week getting more done on the spot welder has been my goal. There is a lot of details. I got more parts from Halted. The fet board in now tested and fully modified and assembled. I’ve gutted the chassis that the spot welder will be mounted into. It’s going to be a very tight fit. I’ve cut a base plate to mount the electronics onto.

Here is the modification that Fritz has everyone do to their boards. We are suppose to just use a piece of solid wire down each open path. I used copper plate to make it even more robust.

To help keep warmer parts cooler, they get mounted up off of the pcb.

With my experience with motor controllers, it seemed prudent to add a schottky diode and 10 ohm resistor to each fet’s gate pin. There is an issue with ringing on the fets. We are suppose to add a board full of schottky diodes to lower the ringing’s peak value to less than the voltage rating of the fet’s diodes. I used a pointed spiral bit for cut across each gate’s trace. The gap is just wide enough so that an 0805 sized resistor can fit across it. I used a 1/8″ endmill to remove the green solder mask to make solder pads for the new components. A very light touch was required to remove the solder mask without removing any copper. I used my Bridgeport mill for this mod.

Here the parts are mounted next onto the gate’s trace. A perfect fit on the width of the trace.

Here is 1 of 3 heatsinks with fets mounted, ready for pcb installation.

Here they are with the heatsinks mounted. The one row of parts on the right, just clears the heatsink due to the double sided foam tape thickness. I still had to space the heatsink up off of the pcb a little more so that it did not contact the delicate glass diodes. The other two rows of parts were totally clear of the heatsinks.

I’ve been working like a dog on making an electric vehicle system for a guy on the east coast. It’s been assembled for days. Runs too. But it has this kind of miss to it. Almost like it’s got one bad spark plug wire. It just runs rough. I’ve not seen that kind of problem before with an AC electric vehicle system.

Also have the spot welder nearly assembled. It just needs some finishing. I hope to create a process to spot weld braided flat cable to lithium battery cells. The cable allows flexing without breakage. Mostly for our combat robot buddies. For automotive use it’s not really necessary. But it will be a great process to have under my belt.

After this system gets shipped, I have gathered all of my hand drawn individual schematics, and will create one large schematic for the entire Dolphin main board. I have almost every square inch documented. Just a little remains. But even a mostly completed schematic will be helpful in debugging. I’m still deciding what cad package to use.

Yesterday the Insight cell testing was finally completed. I put 4 chargers and 2 constant current power supplies to work individually charging 6 sticks at a time. That way the discharger was always testing a stick of cells. It took about 5 hours to do the remaining 15 or so sticks. The diode balancer didn’t work fast enough. So I just used the shorting clips from the flooded nicads to discharge each cell in a stick on those sticks that looked like it could help equalize. I found 3 sticks out of 20 that were able to sustain 6 minutes at a 50 amp (8C) discharge load. The rest fell under that time. That’s 5ah of capacity. Since nicads have a bit of a Peukert factor, then I think an 8C discharge will show a lower capacity than the nominal 6.5ah that they are rated at. My constant current discharger is so incredibly useful for testing these nicad cells.

The next step is to remove the pack from the Insight and do the same testing to it. I am not sure with 80k miles on the pack where the testing times will fall compared to the used pack. I still have to decide what is more useful, fully charging or discharging the Insight pack before I remove it. In order to duplicate the tests performed on the used cell, I would have to charge the Insight’s cells until very warm like I did the used ones.

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