Jon R
Senior Member
We have a lot of posts and discussions about circuit protective device (fuse or circuit breaker) location and sizing for the truck charging wires, the camper battery wire, and branch circuits, but I don’t think i have seen in the few years since I joined the following issue discussed: specific protection of the wire from the camper main positive bus bar or terminal to the camper fuse panel positive bus connection due to multiple sources of fault current.
I sized my camper battery external fuse with the size of that particular wire in mind (6 awg, 80 amp fuse), but recently I was thinking about the fact that, if there’s a short to ground of that wire (really any wire connected to the positive bus, but all the other wires are short, secured well, and entirely located and visible in the battery compartment) while I’m driving on a sunny day, the fault current will initially be the couple of hundred amps the battery delivers plus the 30 amps each outputs of my DC to DC charger and the solar charger. The battery fuse would blow quickly, but then I would potentially have 50 to 60 amps flowing steady-state into the short from the chargers. That could be a fire hazard.
I decided to check the Victron manuals to see if my Orion or Smart MPPT charger have any kind of output short protection. The MPPT manual says it has output short protection, but doesn’t describe the nature of that protection. The Orion 12/12-30 does not say it has output short protection, and instead says its output short current is 60 amps. That would require its input side to receive 70 amps from the truck. My 6 awg wires and 80 amp fuse at the truck battery would allow that.
So, while it sounds as though the solar charger won’t just sit there putting 30 amps into the short, the Orion apparently will make up for it and put 60 amps for a prolonged period into the short until something internally acts or fails and reduces the current. Does anybody know that not to be the case?
I can’t reduce my camper battery fuse size because I want it to be able to charge at up to 60 amps from the two chargers simultaneously. The wires are sized for that. However, I’m thinking of doing two changes:
1) Adding a 40 amp fuse in the wire from the positive bus bar to the camper fuse panel located near the bus bar. That will allow the normal load currents and allow the Iota DLS-30 to charge the battery if it ever decides to grace my lithium battery with 30 amps. It would blow if that wire shorted to ground either from the huge initial battery fault current or from the 60 amp output short current of the Orion.
2) Reducing the size of my fuse at the truck battery to 40 amps so it would hopefully blow if the output of the Orion shorts and the input current rises significantly.
Arguably I don’t need to do both, but I probably should have fused the truck end of the Orion input wire at 40 amps in the first place. I used an 80 amp fuse because it was there and available on the OEM battery fuse block and it was adequate protection for that wire.
Thoughts on this, anyone? Thanks.
Oh, and “spend the money on beer instead” is still being considered as a possible alternative.
I sized my camper battery external fuse with the size of that particular wire in mind (6 awg, 80 amp fuse), but recently I was thinking about the fact that, if there’s a short to ground of that wire (really any wire connected to the positive bus, but all the other wires are short, secured well, and entirely located and visible in the battery compartment) while I’m driving on a sunny day, the fault current will initially be the couple of hundred amps the battery delivers plus the 30 amps each outputs of my DC to DC charger and the solar charger. The battery fuse would blow quickly, but then I would potentially have 50 to 60 amps flowing steady-state into the short from the chargers. That could be a fire hazard.
I decided to check the Victron manuals to see if my Orion or Smart MPPT charger have any kind of output short protection. The MPPT manual says it has output short protection, but doesn’t describe the nature of that protection. The Orion 12/12-30 does not say it has output short protection, and instead says its output short current is 60 amps. That would require its input side to receive 70 amps from the truck. My 6 awg wires and 80 amp fuse at the truck battery would allow that.
So, while it sounds as though the solar charger won’t just sit there putting 30 amps into the short, the Orion apparently will make up for it and put 60 amps for a prolonged period into the short until something internally acts or fails and reduces the current. Does anybody know that not to be the case?
I can’t reduce my camper battery fuse size because I want it to be able to charge at up to 60 amps from the two chargers simultaneously. The wires are sized for that. However, I’m thinking of doing two changes:
1) Adding a 40 amp fuse in the wire from the positive bus bar to the camper fuse panel located near the bus bar. That will allow the normal load currents and allow the Iota DLS-30 to charge the battery if it ever decides to grace my lithium battery with 30 amps. It would blow if that wire shorted to ground either from the huge initial battery fault current or from the 60 amp output short current of the Orion.
2) Reducing the size of my fuse at the truck battery to 40 amps so it would hopefully blow if the output of the Orion shorts and the input current rises significantly.
Arguably I don’t need to do both, but I probably should have fused the truck end of the Orion input wire at 40 amps in the first place. I used an 80 amp fuse because it was there and available on the OEM battery fuse block and it was adequate protection for that wire.
Thoughts on this, anyone? Thanks.
Oh, and “spend the money on beer instead” is still being considered as a possible alternative.
