Truck #1 (Nicad)


Yesterday Mike Bennett and I worked on a load tester for my nicad pack in my shop. It loads each cell one at a time with around 40 amps. Which is 1C. The goal is to find bad or failing cells when the pack is discharged down to the first drop in pack voltage. This occurs around the 5 mile mark. So I know many cells are croaking at that point.

We bought a 100 amp, 12v lead acid load tester from Harbor Freight for $25 on sale. We ended up using bailing wire as an additional load element. I’ve used bailing wire before for discharging cells. It works fine. It’s a soft wire that when it turns red, it still soft. So it stays consistent. We did some empirical testing to see how much bailing wire we would need to add to get 40 amps at around .6 volts. We came up with two 11″ pieces in parallel. We crimped on 1/4″ yellow lugs and bolted them to the large copper crimps already in the load tester. That worked great!

The meter ranges from 0-16v. As it turns out it was fairly accurate around the .5-1.5 volt range. But that was too small of a needle swing for me. So at a later date I will recalibrate the meter by 10x. It will then read 0-1.6v. Perfect for nicad testing. It has a 51 ohm 1/8 watt resistor across the meter movement. So that needs to be changed to a 470 ohm pot so it can be calibrated nicely.

We load tested a couple of cells continuously to see if the bailing wire would fail. It got hot, but never glowed. So I think the only weak link is the rocker switch moving 40 amps through it. Since having a rocker switch would require 2 hands to operate the load tester, I may very well bypass the switch. Then the load tester can just be rocked only the 2 cell terminals and that will activate the load tester. There are 250 cells to test. So speed is everything!!

This load tester could be tweaked for use on lithium too.

Ooops. Overshot a bit. Hit 107.00kw today.

Pavement dried out. The acceleration is stretching the front suspension upward
nicely.

98.44kw so far. Getting there. I bet any sagging is caused by the pack.

I’ve got the pack doing better. But now it’s raining. Anywhere from 0-10 mph I
can spin the tires right up in the rain! More testing on dry pavement will force
more current from the system. That will let me know how close to 100kw I am.

Some prototyping netted 91kw of output from my truck recently. The acceleration was unbelievable. That’s still an 80% improvement. The pack is sagging more than normal right now. So I’m correcting that as of now. I suspect that would be worth a few more kw. Looking forward to 100kw soon as the pack gets updated and the R & D progresses.

The data sheets say the factory igbt’s are rated at 400 amps. Almost there now. If I can keep the pack above 250vdc at 400 amps, then I’ll be at 100kw.

I have had an igbt/hv buss redesign going. Might have to put more priority into that since the factory igbt’s are nearly at their max current rating. Although for maybe only 10-15 seconds at a time, 400 amps may not be a threat to their longevity.

With the A123 prototype modules doing fine, a full pack would have such low impedance that 100kw would be easy to hit. Maybe too easy. Going to build about 12 more A123 modules soon.

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.

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.

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