Help with capacitor voltage rating needed

[pcb rookie]

Alright ... 1st attempt at calculate the voltage needed for a capacitor on a diagram. Let me know if I got this right ...

I'm trying to evaluate the minimum voltage rating for the C6 (470u) cap on the attached diagram (Derailer)

- 9V through D1 (IN5817) diode as a forward voltage drop of 0.450 witch is roughly 8.6v
- 8.6v through R2 (10R) .... (8.6v x 10) / (10+10) = 4.3v
- 4.3v through R8 (10k) .... (4.3 x 10000) / (10000+10000) = 2.15v

If my calculations are right, I would be fine with a 6.3v electrolitic cap ...

Does this make sense?
Are my calculations accurate?

Thanks in advance for your help!

 

[BuddytheReow]

You’ve got 9v going in. Right there you need a 10v capacitor at a minimum. My general rule of thumb is to double the in voltage and round up to the next capacitor level. In this case it would be 25v.
2 reasons for this. One, you’ve got some wiggle room in case your power supply goes wonky. Two, certain circuits will work/sound differently with 18v rather than 9v. A little advanced beyond your initial question, but this allows the opportunity down the road if you decide to travel it.

obviously if there’s a charge pump in a circuit you would have to take that voltage and double it. The schematic should show if there’s a voltage bump.

on a side note I appreciate the math.

 

[pcb rookie]

You’ve got 9v going in. Right there you need a 10v capacitor at a minimum. My general rule of thumb is to double the in voltage and round up to the next capacitor level. In this case it would be 25v.
2 reasons for this. One, you’ve got some wiggle room in case your power supply goes wonky. Two, certain circuits will work/sound differently with 18v rather than 9v. A little advanced beyond your initial question, but this allows the opportunity down the road if you decide to travel it.

obviously if there’s a charge pump in a circuit you would have to take that voltage and double it. The schematic should show if there’s a voltage bump.

on a side note I appreciate the math.

Thanks for your explanation. This is usually the way I go (35v when available and 25v if I have to). It this case what got me going on this voltage calculation is that for 470uF electrolytic caps, at 25v, the dimensions are 8mm diameter which doesn't fit on the layout with the other components around. The easy fix is to let it float above the other components with shrink tube on the cap legs just to be safe but it got me wondering if I could actually get away with a 10v cap (6.3mm) that fits perfect. From your explanation, it wouldn't be a safe route ....

 

[spi]

I use a minimum of 16 V rated for any pedal that runs on 9V, and a minimum of 25 V for any that can run on 18V.
I usually only try to buy 25V-35V now, but I still have some stash of 16V, so I still use them.
I've even used 50V (but the 50V ones can be too large to fit in some boards so I stopped buying them).