Finishing up

A project log for Bicycle Regenerative Braking System

Turn excess kinetic energy into electrical energy rather than waste all it as heat. Built from commonly available and recycled parts.

recyclojunkrecyclojunk 01/23/2015 at 14:560 Comments

(I had written this up earlier but somehow forgot to post it! The actual camp happened on 140914)

Everything had to fit into a Clipsal weatherproof electrical box. The two capacitor banks were sized and shaped to make the most of available room. There was only room enough for one LC filter, which I placed on the output (as a boost-converter's input current is relatively smooth even without any filtering). Soon everything was fitted in and I gave it a test. It didn't work anymore. After alot of probing around (a long BNC cable comes in handy when riding the bike while tethered to the o-scope) the MAX44284 current-sense amplifier was found to be fried. I ensured it's 5V supply (78L05 regulator) was as normal and replaced the amplifier, only to find that the replacement was also fried. Must have been an electrostatic-discharge on it's sense pins; this isn't the first time I've had Maxim parts die for seemingly no reason. So it was replaced with a LTS25-NP hall current sensor (hacked to also output it's 2.5V reference, which it's output was amplified against by a 4x gain differential amplifier). And it finally worked again!

(yes the wire colours on the mosfet pins are mixed up. Also, they're all in parallel (yeah, overkill alright))

It was now Saturday and the trip was scheduled for Sunday, and I hadn't even started packing. As the forcast for the week was mostly sunny, there was no need for it to be waterproof just yet so I glued three voltage-displays to a piece of aluminium that I had attached to the handlebars, to display the input voltage and current, and the battery voltage. The controller was also modified to only power up the BRBS when the dynamo was spinning.

(Not many pictures were taken in the mad rush to get it done at 0300 sunday morning, hence the picture from the camp)

Now the BRBS itself was complete, but it still had to charge my camera batteries. I hacked together a quick charging rig built out of some 0.5mm pin-pitch TQFN Li-ion charging chips and a 5V switching pre-regulator I got off ebay, and put it in a nifty little project box I found screwed to a brick wall outside.

Last step was to connect two more of those cheap switching regulators, one for the LED torch and one for the GPS. It was now early Sunday morning, so it was time to start organising what food and camping gear I was going to bring.

Stay tuned for a writeup of the actual camp itself, and whether the BRBS a success or failure