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[serpent]

Dear friends,

While replacing the blinkers on my bike, halfway through, testing, the DC/DC converter went belly-up. After the first shock, thinking I caused that to happen, I learned that it's a common fault, so I saw it as a cast of fortune for it to happen while screwing up the bike anyway (pun intended).

I took a number of photos which might be helpful for others going that route.

Part 1 – Disassembly

[serpent]

I think, there's no way around removing the motor controller including the two protective plates front and rear.

[serpent]

Part 2 – New Converter

I followed the recommendation to get a 450W converter by DMC for 320€. Shout-out to Max at this point:



Let's hope it will last longer, the old one didn't have many hours on it...

The bike frame is designed to match the base plate of the Sevcon converter, so I separated that and drilled new countersunk holes to match the DMC.

I considered changing the fuse from 4A to 5A to increase the headroom for auxiliary consumers, but I couldn't easily source a suitable one (6x30 mm doesn't fit to my liking).

[serpent]

Gave the base plate some light sanding to remove all residue and make it look pretty. Used M5 x 16 stainless bolts.

[serpent]

The connector needs to be fully repinned. I had to remove a clip and slightly pry the plastic hooks apart to get the contacts out. Not too difficult. The thick wires are the output, thin wires are input, black is “–” for both pairs, red is enable.

To keep moisture out I applied plain vaseline, hope that will do.

[serpent]

Part 3 – Reassembly

Be careful not to overtorque the motor controller connectors, you might destroy it. When in doubt, better get a torque wrench. I added a drop of Noalox to each bolt. I had to connect the front-most wire going to the motor before reseating the controller (and the other way around during disassembly).

TÜV was happy in the end.

(Just kidding, they don't care about the DC/DC as long as the lights come on.)

Good luck and have fun!

[serpent]

Bonus 1 – Rusty Nuts

The clip nuts holding the trim together were bothering me for quite a while, they should have been stainless steel from the beginning. Could not find proper replacement parts, so I cleaned and blackened them (engine oil, oven, ~500°C, several rounds). Curious myself to see for how long that will do.

[serpent]

Bonus 2 – Sevcon's Guts

No way to repair it with this approach, or even find the fault, I ripped off many components. Acetone softened the potting compound quite well.

[serpent]

Tried to identify the brand of the caps, but to no avail. These are typical “fail early” components, especially the cheaper ones, and can be an indicator of the general component quality the manufacturer is going for.

The converter went from working to dead in an instant, though, which makes a failing semiconductor more likely.