From what I know about super caps, you apply a voltage to them to charge them up. If a supercap is rated to 10v, then when the voltage reaches 10v, it's charged. Is there a circuit or board to stop charging the super cap when a predefined voltage is reached? I assume the circuit would be different for different super caps rated at 2.7v, 5v, 10v, 100v, etc.

Most off the shelf boards I've seen are for 18650 lithium batteries and stop charging at about 4.2vdc.

 

Basically, only connect the cap to a voltage lower than the rated capacity of the cap. It depends on the type of capacitor, but I don't use a cap unless it has a voltage rating twice the capacitor's rating. That is, don't use a 10V cap in a circuit whose supply voltage is greater than 5V.

 

So if I have a 10v capacitor and charge it with 5vdc from a USB port, will the capacitor only charge to 5v?

I want to charge a super cap via USB and use it to light an LED for a few minutes.

 

So if I have a 10v capacitor and charge it with 5vdc from a USB port, will the capacitor only charge to 5v?

I want to charge a super cap via USB and use it to light an LED for a few minutes.

Yes, it will only charge to the supply voltage.