[kennybobby]

The primary purpose for using a fuse is to protect exposed wiring from catching on fire in the event of an accident or accidental short-circuit condition of the wires.

There are various types of fuses with different "blow" characteristics, such as delayed or slow-blow, instant acting, inrush-withstanding, etc. which can be selected to provide the short protection but allow some overloading and not create nuisance fusing.

Also consider that HV DC fuses have different requirements and characteristics than for AC fuses. It's not a one-size-fits-all situation.

Draw up a schematic or sketch of your battery pack with lengths of exposed wiring, that will help you visualize what needs to be protected and where to locate fuses.

 

[Teddy]

Hi,


I am converting a Beetle to run off a Hyper 9 system, 120V pack voltage (5 Tesla modules in series).



The kit I bought includes a meaty 600A 150V fuse.


My question is over best practice - should that fuse be as close to the battery pack as possible, or should it go in the contactor box I have yet to build?

Secondly, I am running a split pack, with two Tesla modules up front and three in the back. Should I have a big fuse for each pack, or is one enough?


Thanks in advance.

Yes, you had the right hunch. The main fuse should indeed be as close as possible to one end of the battery string. Where connections between packs are in protected spaces where they are not likely to be crushed even in a severe accident, I would not place intermediate fuses but make sure that the 2 cables from one battery module are well clear of each other.


Since the traction voltage is not to be earthed, a single insulation fault won't cause a short circuit (but could make touching a conductor dangerous).


In my Beetle I have split the battery into 5 modules, one in the space of the fuel tank, 2 under the back-seat and one on each side of the motor. I have placed the main fuse inside one of the battery containers at the negative end of the battery string and the main contactor at the positive end. This way pulling (or blowing) the main fuse causes both battery poles to be disconnected.


Although I have laid the cables to the front battery module inside the tunnel and given them additional protected with flexible conduit, they could both get crushed in case of a front collision. Therefore I have prevented short-circuit of the front battery module with another fuse inside the container. This fuse is bolted-in and of higher current rating than the main fuse as it is not needed for cable protection, just to prevent the battery module from cooking. The voltage rating of the front fuse has to be just high enough for the voltage of the front pack, that's why it is not as big as the main fuse.


In the wiring schematics it looks as if cables crossed each other, but they don't. The ones going side to side are under the backseat and in the drive bay, the lengthways runs pass under the rear luggage compartment.


Although you'll have to adapt the layout to your battery arrangement, I hope this gives you useful hints. Enjoy the design-phase of your project, time spent now saves you much more during the build

 

[MoonUnit]

Thanks, that's really helpful, and kind of you to post the schematic.