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Sunday, November 21, 2010


I'll know I'm doing too much stuff when these posts start coming at more than 1 month intervals.

Anyways, time for another ELB update!
I finished cutting and rough sanding the last 40 polycarbonate inserts for my new hubcaps.

It's INCREDIBLY tedious work to polish these things. The above is after cutting, 220 grit, and 400 grit. There's still 600, 1200, 1500, and 3000 (lapping paste) to go. Anyways, this is the point where I got bored and decided to work on something else.

This is my charger: Turnigy 4x6S . It can charge four 6S packs independently. I figured I could use it to charge my 12S ELB pack (just link two of the ports together). But...
Each charging port is NOT independent, despite what you may have heard about it, or may assume about it, or read about in the description ("All ports work independently of each other."). From the outside, all you see is a single input for 12Vish DC and 4 charging ports. Internally, there are 4 separate chargers. Sounds ok, right? However, all of the chargers' inputs (+ and - ) are linked by traces that go all the way around the board. This wouldn't be a problem if they were high quality (isolated input/output) chargers. But this is a Chinese Cheap Charger (CCC). The negative/ground wire is connected straight through from the input to the output (battery ground). This means that all of the outputs are at the same potential, which in turn means you can't link ports and charge anything over 6S. I need 12S. There goes $100. OR:

Doctorbass to the rescue. Check out his hack for this charger...genius. He made it into a single 24S charger by isolating the four chargers by cutting the traces that link them, and then buying 4 small (cheap) switching power supplies, 1 for each charger. His application is a little different than mine, so he did some other cool modifications, but I'll just show how I did it.

Take it apart

Each charger has two holes like this for wires to go into. It's like they were originally going to manufacture it to run off of four independent power supplies (like it should have been), but they instead just added a trace all they way around to save money.

Cut traces on each side of each set of input holes. Dremel worked well.

Cut the bottom traces, too. Be careful not to cut into other traces, just the power traces.

Back side was easier. Could just slit the board without hitting any components.

The four 12V, 5A power supplies. You can get these on eBay for <$40.

Cut the DC plug off the power supplies and string the wires through the wire hole in top plate of the charger. (De-solder the existing input wires first.)
Solder the new inputs to the circuit board.

Yep, definitely isolated now.

Finish soldering all the input wires. Route them as you see fit.

Semi-finished. They all work!

Removed excess wire. That's better.

Double-stick tape/duct tape the power supplies together. I velcroed the charger to the power supplies, too.
Now I have one big block of a 24S, 200W charger. Not too bad for $130 and 2 hours.

In addition to these things, Shane's been helping me calibrate the motor controllers to my motors (well, he's been doing most of it).

Note the old hubcaps with chunks of missing polycarbonate....why I'm making new ones.
I've got updated data for the motors now, too. Before, using a Turnigy controller and running the motors sensorless, we calculated a top speed of about 30mph. Now, using sensored sinusoidal control and about 15 degree advanced timing, the top speed is around 20mph. Not too bad. The really impressive thing is the torque. I'm looking at getting 50lbs of force at the ground..assuming 200lbs of mass (rider+board), that translates into 1/4G of acceleration, which is nuts...especially for something without a seat or handlebars. I probably should have wound the motors a little less for torque and a little more for speed (less windings, or thinner stator, etc), but I think 20mph is plenty. 

That's all for now.

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