Radial Alum. Cap. Substitution

**rayhjr** · 03-11-2023, 07:49 PM

I'm Buildind some BBB16 controller boards and they call for 220uf 50v radial caps and I have a lot of 220uf 25v on hand. Can I substitute 25v for 50v or is that a no no?

**zaker** · 03-11-2023, 07:59 PM

The voltage on a cap is the max rating. You can substitute higher, but depending on how it is in the circuit, lower is not advisable. Is the 50v called for on the BOM, possibly that was the part available and used. Someone with experience building that particular board should be able to tell you if it's ok with the lower voltage. I may be wrong but there shouldn't be possibly more than 12v on that board.

**rayhjr** · 03-11-2023, 09:01 PM

It appears to be for the 5v Regulator

220cap.png

**zaker** · 03-12-2023, 10:24 AM

Rule of thumb is Cap voltage rating should be twice the applied voltage. The regulator has 12v input, and that's where the cap is connected. So 25v is double the 12v input, so you are ok. Never use lower voltage ratings, but you can always substitute a higher one.

**Reddy_Kilowatt** · 03-12-2023, 02:07 PM

(-)cap(+)*(-)cap(+) connect two 25v caps in series and they would be 50v.

-Craig

**rstehle** · 03-12-2023, 04:25 PM

Originally Posted by zaker

Rule of thumb is Cap voltage rating should be twice the applied voltage. The regulator has 12v input, and that's where the cap is connected. So 25v is double the 12v input, so you are ok. Never use lower voltage ratings, but you can always substitute a higher one.

I think you argued both sides of that one.

In reality, a cap rated at 25v will work fine in a 12v circuit.

**P. Short** · 03-12-2023, 04:41 PM

Originally Posted by Reddy_Kilowatt

(-)cap(+)*(-)cap(+) connect two 25v caps in series and they would be 50v.

-Craig

No, not in the world that we live in. It's only true if both capacitors have EXACTLY to same capacitance, otherwise the voltage across one will be larger than 25V and across the other one will be less than 25V.