KS-14C Power capacitor replacement and better placement

[tudordewolf]

Important part first: Here's how I fit replacement power filter capacitors in a KS-14C. It solves the problem of constantly bending the leads when you have to access the batteries, and shortens the distance between the second capacitor and the circuit board, which increases its ability to do its job.

I came into possession of a faulty KS-14C from electricunicyclereview's closing, along with a new control board and batteries for it. It would turn on and run, but had very low battery and wouldn't accept a charge. When I opened it up I saw that the power filter capacitors were blown. I put the new circuit board in, and it would boot up but not balance or light up the battery indicator. It probably just needs to be configured for the first time, but I figured that since the original board was functional and just needed new capacitors, I'd try to fix it. I realized the replacements I'd gotten were slightly skinnier, enough to fit in the circuit board compartment lying flat. I mounted them as such, put everything back together, and it works! I also replaced the battery with 2 packs, and discovered it had a few bad cells after tearing it apart. The rest are good, so they'll be useful for other EUC-related projects.

In researching the repair, I discovered that the capacitors are less effective the further away they are from the MOSFETS (in terms of electrical path) It has to do with impedance and smoothing the voltage ripple - I suspect the blown capacitors contributed to damaging the battery pack, perhaps being blown during an over-voltage downhill surge that then killed a few cells without the capacitors to smooth the spikes. I also learned that the wires between the batteries and an ESC should be as short as possible, to reduce impedance (which I understand to be a sort of "lag" between the voltage dropping and the batteries providing the amps to restore it, which the capacitors are there to fill in for)

SO, it follows that shortening the battery wires as much as possible and installing larger power filter capacitors would be an overall "upgrade" to unicycle electronics, their robustness and its ability to handle bumps / uneven terrain without as much pedal dip, which is better for the unicycle and the rider. Thoughts? Some designs have up to 6-8" of wire that could be removed, and according to this forum post, that would be worth doing.

[Hunka Hunka Burning Love]

Nice job!  That one cap with the black wire attached looks a little close to the screw.  I wonder if those cap legs would be better shrinktube wrapped to avoid conducting where they shouldn't be conducting.  Are they supposed to be in parallel like that?

[tudordewolf]

13 hours ago, Hunka Hunka Burning Love said:

Nice job!  That one cap with the black wire attached looks a little close to the screw.  I wonder if those cap legs would be better shrinktube wrapped to avoid conducting where they shouldn't be conducting.  Are they supposed to be in parallel like that?

The leg could be insulated, but it was far enough away from the screw that I'm not worried. The capacitors are in parallel, it has the effect of adding up their capacitance (series would add up their voltages, and they're already rated for 80v)

[Hunka Hunka Burning Love]

How is the top capacitor secured?  Considering the amount of vibration these wheels experience it might be good to silicone them to the control board?

[tudordewolf]

 

2 minutes ago, Hunka Hunka Burning Love said:

How is the top capacitor secured?  Considering the amount of vibration these wheels experience it might be good to silicone them to the control board?

In most cases I would think so, however these were such a snug fit that it would have been hard to put the board in without adjust them a bit to maneuver it in. That said, I'm pretty confident it's held tightly enough not to rattle around. The original capacitors weren't mounted any more securely,- then again, those capacitors are fried...