# How to calculate capacitor size?

I'll apologize in advance as I'm sure this answer is already somewhere on the site. I don't have enough of an electrical background to know the proper terms to search for so I came up empty. I'm looking to install a diesel heater that draws 15A at 12V for about 2 minutes before dropping to 2A. The power pack I was hoping to use can supply 10A at 12V. I was wondering if a big audio capacitor could handle the startup but I have no idea how to calculate what I'd need or how to go about wiring it. I'm guessing the capacitor would need to be stupid big but now that I'm thinking about it I'd really like to know how stupid big it would need to be. Thanks in advance.

• you're right, it would need to be stupid big. and you would need other active parts to make it work, likely a boost+buck DC-DC converter. Capacitors lose voltage as they lose charge, so it will only hold 12.0v for an instant. If you could convert the whole of the charge to 12v with a magical perfect converter, you're looking at a 300 farad capacitor at 12v (21,600 joules). Get a bigger power pack, or get another power pack and connect it in parallel. Dec 5, 2023 at 6:17