February 2011

The 312v (405v max) AC motor control system in my truck is very energy
efficient. It’s only 70kw right now. But it will be 90kw here shortly. It has
the capacity to handle way over 100kw.

I don’t have to cram very much of a pack into this vehicle to get excellent
range. If I put in a 160ah set of Thundersky cells, my range would be 256 miles.
But then I have to put up with all of the cold voltage sag as well as the sheer
volume that this pack would take up. Works for some, just not for me.

Speed is electronically limited to 72mph. That also assumes I leave the
transmission locked in 2nd gear. It’s a 5 speed manual with overdrive. Adding a
shifter makes the top speed math go to some insane top speed. Or as ACP does,
remove all of the unused spinning mass in the form of gears and syncros for yet
more of an increase in efficiency.

Something I keep forgetting to explain. The cells themselves will only weight
154lbs. They completely fit in well under 1/2 the battery box.

The 7.36 kwh pack I’m building will take my truck 36 miles at it’s current
efficiency of 200wh/mi at 4000lbs. My estimate of a 15% increase in efficiency
from losing 600 lbs, will put the range at 42 miles at 175wh/mi at 3400lbs. On
only 50 amps the truck goes 60mph. There is an owner of a truck just like mine
with a 19.2kwh Thundersky pack. He went 112 miles on a charge. That’s about 171
wh/mi. But his cells weigh 550 lbs. That’s 400 lbs more than my A123 cells. It’s
feasible that my truck could end up with a 50 miles range off of the tiny A123
pack. Since the camber on the front end was finally just now set to zero, there
could be some additional increase in efficiency. I have yet to block the grille
and add the coroplast to the chassis underside to clean up some of the
aerodynamics. Those are standard features on all ACP vehicles, old and new. All
I need for my driving requirements is 15 miles of range. With 36+ miles of range
my cycle life will be close to forever.

I will pick up some cobalt 18650 cells for spot welding and testing. After all,
since the safest chemistry available can currently be set on fire so easily, it
just makes sense to try them. Their smaller size would make for an even lighter
pack. It’s just takes some mechanical and thermal engineering to make this work.
It’s just not that difficult.

I wonder if the laser welder I used back in 80’s is available surplus somewhere?
I use to spot weld nickel ‘flags’ to stainless wire. Not unlike materials for
cell module construction.

Gasoline is $3.79/gal down the street! Wow! We’re on our way to $4/gal and it’s not even close to Memorial day. Oil today was down to 96.50/barrel. Man am I glad this truck runs. The timing for making the A123 modules is pretty good.

The truck turned over 23k miles tonight. So in 765 more miles I will have put 20k miles on the truck myself. Everyone of them without using a drop of gasoline.

I wonder if it’s even possible to spot weld aluminum with my spot welder? It is not as conductive as copper, but is far less expensive. Copper has at least tripled in the last couple of years. So I will start with trying to spot weld some aluminum foil from the kitchen and see how that goes. It’s cheap and easy to use for proving the concept, one way or the other. I will still be trying to spot weld braid as well.

Today I found a shop that actually could handle the shims on my front end. My normal alignment shop sent me to them.

I had the service writer write down what I wanted. Zero toe and zero camber. When they were done it was R+.125 L+.50. with me in the truck. The manager told me my body weight will change the camber .25 degrees. I didn’t buy it. When he took the measurements with me in and out, they changed .125 degrees. Which made more sense. Then I mentioned that +.5 is a far cry from zero. So they did the left side again. Now it’s R+.125 and Lzero with me not in the truck. With me in the truck it’s Rzero and L+.125. Much better! Splitting .125 degrees is very fine, but I wanted zero camber while rolling down the road. They started out at +1 and +1.25. It’s raining like mad here. When it’s clear I’ll see how it feels. Initially it’s fine and stops dead straight without using any regen. $100 however. But after the wear I found on my front tires, it would have worth doing it 16k miles ago. I did have it aligned back then, but the previous shop didn’t want to go after the hard to get shims. They accessed the shims today from the tire opening. So the Dolphin didn’t really matter.

After the test drives they had taken on my truck, it had used 400wh/mi! That’s what I use to get with my 104 Hawker lead pack! It’s usually around 225-250wh/mi.

Starting last night I drove the pack down until it was only around 200v. Then pulled it into the garage for discharge maintenance. I made up a system using six 2000w, 120vac water heater elements to discharge the pack in large groups rather than just two groups.

Here is the pack attached to all of the water heater elements. A 5 gallon bucket of water was used for cooling since an experiment with air cooling caused the elements to glow red, which is an ignition source. The water level dropped about 3/4″ when the pack was done discharging.

I used my cnc to machine 6 holes in these two pieces of 3/8″ thick plywood. They held the heater elements 3″ apart and 3″ from the sides of the plastic bucket.

After the overnight discharge was complete, I put some jumpers across about 5 cells that were still showing some voltage (not shown). Shown here is the 240vac variac and a bridge rectifier mounted to it’s heat sink. It takes me about 45 minutes raising the voltage by hand, to about 320vdc. After that, the on board charger is used to finish up the charging.

Here is the finished spot welder. I sure like the way the LCD display is shining through the smoked acrylic. When it’s off it’s hidden. With the foot switch jack is in the rear and the LCD behind the smoked acrylic, the front bezel is kept very clean. The knobs blend in nicely. I will be this is the smallest chassis this welder has even been built into. The tight confines did create some EMI issues however.

Here is the waveform across the fet source and drain with the probes held firmly against the work, making a good weld.

Notice the 40.8v spike on this waveform. It was caused by the probes not being held tightly against the work. The fets have a 75v internal diode that should protect them. But it has been recommended that a schottky board be installed per the note from the designer, to attenuate these spikes to help better protect the fets.

The spot welder is finally working now! It was the fet driver signal from the processor that was not going back to ground after it sent the dual pulses. I added a couple of different values of resistor and placed them from the fet driver signal on the processor’s pin 27 (terminal block position 17) to ground. I ended up soldering the 2.2k resistor onto the right side of R27 and the left side of R22 for a permanent installation. 2.2k worked the best and draws only an additional 2ma. The I/O pins are rated at 25ma on the processor data sheet.

What also helped a lot was not connecting the ground lead for the fet driver to any of the grounds on the terminal block. When it was attached to any of the terminal block grounds, the spot welder kept sticking on. So I soldered it to the ground pad of C9, which is one of several parts not installed per the manual. It worked far better after that. This fet driver ground lead location was always contributing to the sticking on issue.

I also added a 1k resistor in series with the fet driver input signal so that when the fet driver fails shorted, it won’t take out the processor as well. When the first fet driver failed it was forcing 3.4v into the fet driver input circuit. Which forces pin 27 of the processor to 3.4v when it’s trying to stay at ground.

Now it’s time to get accustomed to using the settings to make good welds! All I have right now is .010″ thick nickel for testing. My aim is to spot weld braided cable for the combat robotics folks.

When I disconnect the fet driver wires from the control board, the fet driver pulse works fine. It no longer locks in the on state. Also when the ground lead for the fet driver output is attached near the grounds where the pots are attached, positions 6 & 7, it causes that pot to wander all over the place. So I soldered it to the ground hole near position 1 on P3. That corrected that wandering issue. Still the output gets stuck on. At least one press of the foot pedal corrects it. It almost looks like a ground loop.

Here is what the fet driver input signal looks like on the control board when the spot welder stays on. Trace #2 shows that it’s just stuck full on at 5vdc. This holds the fets in the on state and that’s why the probes are energized. The power supply is straining to keep up with the constant load instead of the milliseconds long pulses that it normally sees.

This is what the fet driver input signal looks like when operation is normal.

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