1994 US Electricar Repair Blog by Mike

Nical Cell Load Tester Prototype

Administrator — Mon, 16 Jan 2012 15:36:01 +0000

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.

Fellow Techie gets a hand

Administrator — Fri, 16 Dec 2011 01:20:43 +0000

Yin wrote me today to let me know that I saved him $1230 in repair bills on his THS720 scope. He had the same problem that mind had back in 2009. He found this blog with the repair entry through Google. It felt great to hear that my work helped someone else!

THS730 for sale!!

Administrator — Fri, 16 Dec 2011 01:13:53 +0000

I am selling a great Tektronix THS730 scope. It’s here on Ebay.

EV Race in the UK!!

Administrator — Thu, 15 Dec 2011 15:14:29 +0000

Here is an EV race in the UK with so many different brands of vehicles. The energy consumption was listed over a 60 mile course for each car. There is a pdf file do download that has all of the great data!

107.00kw Today!!

Administrator — Sat, 03 Dec 2011 00:31:20 +0000

Ooops. Overshot a bit. Hit 107.00kw today.

Closer Still….

Administrator — Wed, 30 Nov 2011 20:46:13 +0000

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.

Closer….

Administrator — Wed, 30 Nov 2011 20:20:24 +0000

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.

Fluke 83 display repaired with polymer pencil eraser

Administrator — Tue, 29 Nov 2011 15:45:46 +0000

My old faithful Fluke 83 from the mid 1990′s had a display problem that is sometimes described as ghosting. It was much lighter in color than normal. Some segments were nearly faded completely away. I found this thread. All I did was take a polymer eraser, the white ones from many mfr’s, and cut it to a more pointed shape. Then carefully cleaned the places on the circuit board where the lcd makes contact. These contacts were made visibly brighter by the eraser. I then cleaned up the contacts for the push buttons as well. They were never a problem, but worth the cleaning since I was in there anyway. I cleaned the carbon tips of the buttons gently with the eraser as well. I never took the old original pink elastomer off of the lcd nor did I clean the lcd. Just gently cleaning with the polymer type eraser of the pcb contacts was all that was needed. The display has never looked so bright and crisp!! We will see how long this repair lasts!

There is a replacement kit on Ebay from a vendor named A-fluke. The kit these days is about $24USD. It supplies instructions and the newer gray elastomeric parts for the 80 series of Fluke meters.

Almost at 100kw!

Administrator — Tue, 29 Nov 2011 00:39:42 +0000

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.

A123 Modules Stress Tested!!

Administrator — Thu, 10 Nov 2011 03:28:37 +0000

My A123 modules got a beating at a combat robotics contest recently. They held
up fine. They were charged with a BMS on each cell. Discharge rates overlapped
my truck. These cells saw far more G-forces than normal. But I needed some
testing on the structural side of the design to make sure nothing stupid
occurred. The spot welds were of particular interest. The owner uses A123′s in
his robot. Now he’s sending 100 more for more packs to be made. Sweet. This time
however he has a different module layout he wants to try.

I used nickel as the conductor since copper is apparently next to impossible to
weld with a CD welder. I was told this and didn’t believe it. Then I tried to
for 3 days. Nope. Even as fancy as my CD welder is. Nickel is universal for cell
assembly. But not only is copper cheaper, it also is a better high current
conductor. That’s also what makes it harder to weld. It basically has no
resistance. Since I’m making over 70kw now, I have to make sure a module can
pass 100kw for the future (fingers crossed). If copper ever gets used, I’ll have
to buy/make an inverter type welder.

I just won’t be satisfied until I can spin tires on dry pavement at will!