Re: [electricboats] 48V system cirucuit breakers? Vs. Fuses?

For voltage issues you put the fuses in series, not parallel.

I've actually seen DC circuits with the fuses in series to get the isolating voltage required.

Fuses (and circuit breakers) have a break voltage rating (and fault current interruption ratings) that are sometimes a little difficult to find. Every one thinks about the trip current and forgets the rest.

The voltage and fault current ratings are rather important for DC. Probably not so much an issue with 48v, but once to get into the 100v plus region you have to pay attention.

DC arcs will not self extinguish and resulting plasma conduit can have a very low resistance and sustain quite a significant current flow indefinitely.

I recently took apart a 750v volt 400amp fuse that had blown. It was full of sand. The idea being when the fuse element burns through the sand fills the gap and stops the current flowing across the gap in a plasma tunnel.

The DC circuit breakers in the same machine have magnetic quench / arch chute mechanisms to quench the arc. (The magnetic field pushes the arc up the chute). A breaker designed for AC of the same rating would probably self-destruct (and take much other equipment with it) if mistakenly used the same location.

On 6/5/20 1:37 pm, sw via groups.io wrote:

Maybe u can use two parallel fuses?

On Tuesday, May 5, 2020, 08:34:04 PM PDT, john via groups.io <oak_box=yahoo.com@groups.io> wrote:

Ric,

I've been thinking about your response.

The original plan is to put a fuse or breaker near the battery that would blow or trip at about 30 amps - well below the rated current drain of the battery of 50A, and far below the peak battery current of 100A.  The intention of this was to make sure the BMS of the battery never tripped (as I don't know what the BMS will do - if it has an internal fuse, will self reset, or will blow FETs and "brick" the battery).

I had found an inline fuse holder on Amazon that came with a 30A fuse.  But the wire on the fuse holder is only 12AWG.  I found one online reference that said 12AWG wire could handle up to 41A for "chassis wiring", but it wasn't clear that this was for STRANDED wire, and not SOLID wire.

Makes me wonder if the wire on the fuse holder might get rather warm if I ran at 20A for an extended period of time.

The other BIG concern that I have is whether a 30A blade fuse can be used for a 48V system.   Most seem to be rated for automotive use, generally 12V systems, with some fuses marked at 32V.

John

On Monday, May 4, 2020, 09:06:01 AM CDT, Ric Sanders <rsandersemail@gmail.com> wrote:

Hi John,

Unless the device has a specific fuse called for, the main purpose for the fuse or breaker is to protect the wire. You do not want to use a device that calls for a fuse or breaker of 25 or 30 amps If using 14 ga wire as the wire max is 15 amps or thereabouts. A device wired with that same wire however may call for an in line 5 amp fuse at the specific device, and there may be multiple devices connected to the same wire and breaker but the fuse or breaker at the start of the run must be sized for the wire. Look at your device maximum draw in amps and size the wire and matching breaker/fuse size for that amperage. There are many charts available on the internet that specify wire size for various amperage.

Cheers,

Ric Sanders

Ric Sanders

Rsandersemail@gmail.com