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Saturday, 12 October 2013

Harnesses

I had an inspired thought, and I've soldered up two new "foolproof" wiring harnesses. One for charging, and one for driving.

The "foolproof" aspect happens as follows. If, with a lead-acid car battery, you connect the positive to the negative, you get a flash and a bang as hundreds of amps make their way across, and much damage is done. A Lipo is ten times worse. These batteries are as dangerous as a can of petrol. Meaning, if you treat them right, you won't have a problem, but if you do something foolish, you can have a very big problem.

So I've used kettle plugs (IEC 60320) connectors. Female to the battery, because with a female kettle plug, it's pretty much impossible to cause a short unless you really try hard, so the batteries get the females. The male plugs are pretty easy to short if you drop a bit of metal into the plug, so the males will be on the other end, where there isn't any power until the male is plugged into the female, and therefore safe.

And then for charging, four males to a pair of bananas (which is a lovely phrase). The bananas plug into a watt meter (which tells me the number of amp-hours charged), that plugs into the iMax charger, which plugs into a PC power supply, which is connected to the mains electricity.

For driving the bike, four males to a female (which also is a lovely phrase) via a fuse set to blow at 25 amps, because if 25 amps is coming out of the battery pack, something's gone very wrong, the maximum should be 20 amps, I think. And the four batteries are each connected to an alarm that sounds off if the voltage of any cell falls below 3.2 volts, so that I know to stop using the battery.

I also wired up a digital voltmeter at the front of the bike, so I know the voltage of the battery pack, which starts at 33.6 and if all the cells fall to 3,2, then that will show 25.6, So between 33.6 (full) and 25.6 (empty), I know how much power I have left, roughly. That uses green LEDs, because I found that the red LEDs are impossible to read in bright sunlight.

I've ordered another wattmeter, that will go on the driving wiring harness, so I'll be able to see how much power I've used at the end of the day (or when a battery is about to be changed).

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