First up was Tom Brunka from Helwig Carbon Products. Jack thought this session was going to be a bit of a sleeper, so he scheduled it for first thing in the morning. In fact this was, by large measure, one of the most interesting sessions of the weekend. Of course it helps to be deeply interested in how DC electric motors work - carbon brushes are the unsung hero.
Tom is the senior tech for Helwig, with 35 years of experience and he's doing his own electric conversion project too. Helwig is the only 100% US motor carbon brush company. Their brushes offer increased performance, higher efficiency and longer life. Brushes go in every electric motor application you can imagine.
Most EVs use an Electro-Graphite compound. These brushes have a design life of 2000 hours. At 40 mph that's 80K miles and at 60 mph, that's 120K miles, so brushes are not a constant maintenance issue. Brushes this hard take a long time to "seat" themselves on the commutator. Tom believes the motor should run for 7 days at low current. Unfortunately the motor companies don't want to spend this time or electricity in the factory, so it falls to the customer who probably installs it and runs it at full speed. Brushes are machined with an arc-shaped contact patch at the factory to try to get them as close to the diameter of the commutator.
Metal-Graphite brushes are used in system with voltages less than 48, while standard graphite brushes can handle up to 90 volts.
Brushes are rated in Amps per square inch of contact area. H49 compound of Electro-Graphite is 100A/sq in. H60 Electro-Graphite is 80A/sq in, while H254 Graphite is less than 80A/sq in.
The armature is coated with a dry lubricant film - do not clean this off thinking that it's worn-off brush dust! The thickness and color of the film tells how the motor is running. Black is too thick and causing arcing. Gray signifies contamination. Medium dark chocolate color is perfect.
Brush resistance goes down as temperature goes up, and brushes like moderate humidity. High resistance helps extinguish the arc between the brush and the motor during the break and make of the circuit during rotation. The resistance of H49 is 0.0025 ohms / square inch cube. This is extremely small, but is considered "high resistance" in the world of brushes. One thing to remember - don't remove brushes to "check" them for wear. This will shorten their life by 50%!
Tamping material is the connecting material between the brush and the wire that delivers the current. It can be carbon or copper powder. The factory drills a hole in the brush with a rifling patter, inserts the wire and powder, then tamps it down into place. This shunt wire should be as large as possible to handle the enormous current expected.
EV motor usage is so severe that Helwig is moving to a multi-wafer brush design with a pad across the top. This cuts the voltage drop in half. The shunt wire size is balanced against the spring pressure. The spring is designed to deliver constant force over the life of the brush. This is tricky because the brush gets shorter as it ages. The direction of the carbon grain in the brush makes a big difference too.
There is a sensor wire drilled to the "wear" depth, which triggers a warning by delivering full pack voltage. This is similar to the "screetch" noise made by worn brake pads.
Wear factors for brushes include mechanical wear, arcing, weak spring force and commutator wear. Improper spring pressure can overheat the motor windings by heat soaking the commutator. This is a bad thing. Arcing occurs between the bars in the commutator in the "neutral zone", bouncing across the gap.
A revelation to the crowd was the wearing of the motor bearings due to electrical discharge. The bearings create a ground path for current which causes minute pitting, increasing friction and heat. Helwig sells a grounding brush kit, which is made of 50% silver, to act as a sacrificial path for that current. This is like the sacrificial anode in water heaters. Tom wouldn't tell us what it cost, so I'm sure it's pretty expensive, but if you're interested in the longest life possible, then it's worth investigating.
To maintain your motor, blow out any dust with compressed air and keep it well-ventilated. This can be passive ventilation via the motor's cooling blades or active ventilation like Jack's used turbocharger units. Do not use silicon spray or glue near the motor , as the fumes attack brushes and commutators. If you do need to install new brushes and springs, clean the commutator with garnet sandpaper only, in 80, 100 and 220 grits. Then use a razor blade and a 90 degree micro file to clean out debris between the copper bars in the commutator, then finally sand with 220 again. Only use polyurethane caulk to seal ducts.
The last organized session was George Hamstra again, a wrap-up talk called "Future Transportation Challenges".
Automotive growth explosion outside the US is staggering - up 300% between 1995 and 2020. As for carbon emissions, the US is now the highest per capita, but China has the largest total. Worldwide electric production comes from 1/3 oil, 1/4 natural gas and 1/4 coal, with other minor inputs.
As the price of oil increases, more reserves become economically viable that are now hard and expensive to get to: tar sands, deep-water drilling, etc. The cost of gasoline is 68% oil cost, 15% refining cost, 6% distribution and marketing and 11% taxes. A single 44 gallon barrel of oil produces 19-21 gallons of gasoline. The profit is generally in the other 50% of that barrel of oil - quarts of lubricating oil, fertilizer, kerosene, thick goop for asphalt and roof shingles, etc.
Post World War II baby boomers have consumed 70% of the US oil reserves in one generation. This is not sustainable. Wikileaks says the Saudis are over-estimating their reserves by 40%.
GM, Ford, Chrysler, the US Department of Energy and several oil companies came together to form the PNGV - Partnership for Next Generation Vehicles. The goal was to create the Freedom Car, using "leapfrog technology". The effort died in 2003.
The highest growth in oil consumption is in the light truck segment.
Fuel cells have high energy density, but lower power output in vehicles. They could be viable in houses and commercial buildings.
Lithium air batteries are on the horizon and claim 20% more power than current Lithium ion models.
Tom wrapped up by telling us oil companies are the largest users of coal-generated electricity to actually run the oil refineries. It takes 7KW of electricity to refine 1 gallon of gasoline to go 30 miles. That same 7KW of electricity in an electric car will take you 30 miles down the road directly, so why go to all of the trouble of refining and using gasoline just to burn it to go the same distance?
With the official sessions complete, we all drove over to a local town park for an electric car show, open to the public. I was lucky enough to get a ride over to the park in David Hrivak's Tesla Roadster. I made a video of the trip, but someone called me in the middle, which cut off the video, so I had to start a second one. It looks like I've run into an upload limit, so I'll work on getting the video up later.
As we pulled into the park's parking lot, they directed David to park right in the middle as the Tesla was going to draw a big crowd. We were barely out of the car when it was surrounded.
The townsfolk quickly piled into the park.
Close-up of the dragster. It has dual motors and dual controllers. The racing team has announced plans to upgrade nearly everything in the car soon to make it even more awesome..
And a great shot of the guts of Fred's Sprite.
Following the show in the park, we had a police-escorted parade through town back to the hotel. It was probably the quietest auto parade the town has ever seen. I rode with Fred in the Sprite and we got a lot of stares and waves from people as we rolled down the street.
I shot a video of the parade but it's far too long to upload. I'll have to figure that out later.
After we got back to the hotel, we worked to arrange all of the cars, builders and drivers for a group shot. I was standing in the bed of a pickup truck holding my camera over my head trying to get a decent shot.
Here's a quick video of Brian trying to arrange all of the cars for the shot.
After the picture, we all went to the hotel to clean up and get ready for the closing banquet. Unfortunately Fred and I missed the memo where it said we should get dressed up. We were the only two people still wearing the EVTV t-shirt. The banquet had fantastic food and wine and there were a small number of speeches, the best thanking Brian for being the brains and the hard work behind the show being such a success. Here's Jack in all his glory and white suit.
Below is Jack announcing Brandon Hollinger of ampRevolt as the winner of the EVTV Build Your Dream Contest with his proposal to convert a 1971 Austin FX4, more commonly known as a London Taxi. Brandon promised to take videos throughout his build.
Jack also announced the date of the 2012 EVCCON as September 26-30. Many of the events will again be held at the hangar at the Cape Girardeau Airport, but the sessions and vendor floor will be in Cape's own 32,000 square foot Show-Me Center Arena. Jack and Brian are making provisions for as many as 800 attendees and 100 cars. After our goodbyes, we headed back to the hotels to get some sleep before our trips home on Sunday.
My 914 conversion will be complete for the show next year, but it's a logistical problem to get the car there. It's 2003 miles and pulling the car on the trailer for that distance there and back is going to be brutal. I may hire a car shipping company to transport it for me. Several of the attendees did this - it's not cheap but it does the job. I may be able to get a discount by sharing a trailer with someone else, possibly Richard from San Diego. We'll see, lots of time to plan for next September.
