Fuse goes POP

Fuse goes POP – ooops.   This was fun when I was at university, making the lab technicians jump, but on my boat – well not what I wanted at all.  No satisfying POP in this case, not even a sound or a flash.  At university the fuses were loud when we deliberately made them pop; louder than any firecracker I have ever heard a really sharp bang – VERY satisfying.  Ok what amused me at 18 is less than amusing when over 50 and on my own boat, and where I have to figure out why and find a solution.

I tried a larger fuse 16A instead of 10A – well who doesn’t and to be fair the higher rated fuse was still more than adequate to protect the cable.  Well my 16A fuse also blew instantly on a circuit that had no load where it should have only used 0.05A at most. Ok, time to start to think what is going on, especially when these fuses are £5 a pop, literally per pop.

Our boat has a 48v propulsion battery that connects to the motor and Victron Quattro inverter via 225A and 400A fuses.  It also supplies the 24V DC system for the lights, water pump etc. via DC/DC converters that turn the 48V battery supply to 24V.  So far so good; this saves having a separate 24V house battery and battery charging system.

Under normal canal cruising conditions our batteries need to supply about 50A and when cooking less than 100A (yes we have an electric oven and electric induction hob like one would normally use in  a house).  Even our 3KW Electric kettle only requires 60A.  But, our batteries can deliver over 2,000 amps as a continuous load, around 5,000 amps for many minutes and perhaps 20,000A for tens of seconds into a fault.

The fuses I had selected are capable of interrupting a 200,000A fault current without rupturing or creating a source of ignition, but now I know will blow instantly when it should only draw 50ma (0.05A). Oh!

Time to get back home and let the boat builder do the final fettling before we move on board later in the month, while I consider what to do next.