Knowing how to properly combine capacitors in series and parallel is a great, practical field skill to employ when you need to get a customer up and running and you don’t have the exact size.
Increasing in size is easy. Just connect in parallel and add the two sizes together. For example, if you needed a 70MFD capacitor you could easily connect a 50 and 20 in parallel will add up to 70MFD. Connecting in parallel is as easy as making two jumper wires with connectors and jumping one side of each capacitor to the other and then connecting one side like usual.
Series is a little more tricky, it goes like this
Total Capacitance is 1 ÷ (1÷C + 1÷C) = Total MFD When Wired in Series
The result is that the total capacitance will always be less than the smallest capacitor. Let’s imagine a real-world scenario where you need a 3MFD capacitor and all you have is 5 & 7.5 MFD on your van.
The math would be
1 ÷ (1÷5 + 1÷7.5) = Total MFD
1 ÷ (0.2 +.13) = Total MFD
1 ÷ (0.33) = Total MFD
3.03 = Total MFD
Definitely not something you will run into every day but a nice knowledge tool to have in the noggin toolbox