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I want to make a DIY Power PUC to put led's on my motorcycle. I plan to use 5050 RGB strips. Power supply to these LED's will be in the form of a carbon brush - aluminium ring assembly. But since the wheel will be rotating there will be fluctuations in the current reaching the LED on the wheel through the carbon brush. Hence I was thinking of using capacitors to tide over the current drops. These capacitors would be attached between the aluminium ring and the LED wire.

I would like to know how I should calculate the capacitor required and how to connect it - in series/parallel, and whether any other components will be required for this purpose.

Thanks in advance. Attaching a rough sketch of the connections

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  • \$\begingroup\$ Capacitors maintain voltage, not current. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 25, 2015 at 19:04

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You want to connect it in parallel and you don't need any additional components.

To compute the value you need you just have to use the formula C = (i * dt)/dV, where dV is the value of voltage variation you want and i the current that will be flowing through your LEDs. From that you should get an approximate value that you can try. Try to get the biggest possible value, but be aware that the bigger a capacitor, the bigger the delays.

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  • \$\begingroup\$ That formula is wrong. There is a missing "dt". \$\endgroup\$
    – LorenzoDonati4Ukraine-OnStrike
    Commented Jul 25, 2015 at 21:50
  • \$\begingroup\$ 1) I don't want voltage variation. I basically want a constant power supply to the LED, because fluctuations in power supply(which will occur as the brush is stationary and pushed into contact with the rotating aluminium ring by a spring) will cause them to flicker thus reducing their life. So should the formula be C = i/V 2) Capacitor charge delay will occur only initially when the power is switched on right? and not constantly as it is running? \$\endgroup\$
    – Anxx
    Commented Jul 26, 2015 at 8:24
  • \$\begingroup\$ 3) Do i need to use a separate capacitor for each colour (3 wires for R G & B on the LED strip) as each colour will be getting power from its own separate ring (total 4 rings R G B & negative) Specs on my strip mention a current draw of 1.2amp/m so for each colour it should be 1.2/3 = 0.4amp per colour. Hence capacitor required is 0.4/12 = 0.033farad? \$\endgroup\$
    – Anxx
    Commented Jul 26, 2015 at 9:02
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    \$\begingroup\$ @Anxx: Flickering won't reduce the lifespan of an LED. Most LEDs around you already are flickering, simply at a rate too high to be noticed normally. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 26, 2015 at 18:03
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    \$\begingroup\$ It's going to be very hard estimating the duration of the interruptions before you build the system. I'd just get an assortment of electrolytic capacitors, and try various values as needed, and if needed. Just be mindful of the voltage rating. \$\endgroup\$
    – DamienWontContributeToAITheft
    Commented Aug 28, 2015 at 18:25

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