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Question: I have the main fuse of 400Amp. Do I need auxiliary fuses?  

GWL/Team always reminds the need for proper fusing and protection against the short circuit. 

Using a proper fuse is a must! ????

However, one main fuse is not enough. The one main fuse is designed for the high-current rated protection of the main power-lines. In case there are auxiliary circuits that are powered from the battery, these need a separate DC protection.

All auxiliary relays and circuits powered from the battery pack must be fused separately. It is suggested to use a small DC 2 Amp fuse. For most application (12V to 48V), the automotive fuses can work fine for this purpose.

If the short-circuit is on a narrow diameter wire (e.g. 0.75 mm2), or on the printed circuit board, the current will never be high enough to “burn” a 400Amp fuse. Perhaps the current will be some 50 / 80 / 100 Amp — too little for a 400Amp fuse but certainly enough to make the equipment burn or cause some other issues.

The fuses are connected always to the plus pole and they should be connected as close to pole as possible. For the protection of the control electronics the 2 Amp fuses are typically sufficient.

Note: some of the ordinary DC fuses are designed only for 12V — not for 60V (48V)! This means the fuse will not work properly with the higher DC voltage. With the improper fuse, the short circuit will cause the arc that will remain conducting the current, not burning the fuse. Use only properly rated DC fuses.