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Fuse Confused

RandyG

New Member
Joined
Jan 7, 2023
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9
Location
Arizona
My understanding is a T-fuse is best for Lithium, my basic budget system is 3 - 100ah 100a bms in parallel. 2000w inverter/charger (Xantrex) mfg. recommends 2/0 cable and a 250a fuse, so would the main battery fuse also be 250a or 300a ? I believe the 2/0 cable is rated to 300a ? Also understanding the parallel cables need to be the same length, what about the feeds to the busbars, wired per Victron one cable would be longer in length
 
My understanding is a T-fuse is best for Lithium, my basic budget system is 3 - 100ah 100a bms in parallel.
Class t is required for 24 and 48 volt systems but not 12 volt LFP systems.
2000w inverter/charger (Xantrex) mfg. recommends 2/0 cable and a 250a fuse, so would the main battery fuse also be 250a or 300a ?
2000 ac watts / .85 conversion factor / 12 volts low cutoff = 196.078431373 inverter amps
196.078431373 inverter amps / .8 fuse headroom = 245.098039216 fuse amps.
An 250 amp MRBF fuse.
I believe the 2/0 cable is rated to 300a ? Also understanding the parallel cables need to be the same length, what about the feeds to the busbars, wired per Victron one cable would be longer in length
Victron has suggests a bunch of different wiring methods.
I suggest you use aggregate all the batteries and the inverter/charge to the same busbar.
Fuse each battery at the positive terminal with an 150 amp MRBF fuse and use 4 awg pure copper wire.
Fuse the inverter/charger at the busbar witha 250 amp mega fuse.
Use this video to find out how to fuse the inverter/charger branch circuit

Will you have any other components in your system?
For instance solar charge controller or secondary dc distribution?
 
My understanding is a T-fuse is best for Lithium, my basic budget system is 3 - 100ah 100a bms in parallel. 2000w inverter/charger (Xantrex) mfg. recommends 2/0 cable and a 250a fuse, so would the main battery fuse also be 250a or 300a ?
The fuse on the battery should be selected based on the max current to the loads or the max current from the chargers, whichever is larger. In most systems, the max current to the loads will be larger. I will assume that is the case for the described setup.

We don't know if there are other loads on the system (such as DC loads), but xantrex is most often used on stationary installs, so I will assume it is the only load. I will also assume the xantrex does not have a built in solar charge controller. With all of those assumptions.... you can use a single 250A fuse.

1674162381153.png

I believe the 2/0 cable is rated to 300a ?
Yes, but only if you are using the ABYC boating standards. For the NEC standard the wire size for 250A would be much larger.

ABYC
1674162680159.png
NEC-Ampacity-table.jpg


Also understanding the parallel cables need to be the same length, what about the feeds to the busbars, wired per Victron one cable would be longer in length
In the diagram above the wires from the battery to the busbars should all be the same length. The wires from the battery busbars to the rest of the system do not have to be the same length.
 
Class t is required for 24 and 48 volt systems but not 12 volt LFP systems.

2000 ac watts / .85 conversion factor / 12 volts low cutoff = 196.078431373 inverter amps
196.078431373 inverter amps / .8 fuse headroom = 245.098039216 fuse amps.
An 250 amp MRBF fuse.

Victron has suggests a bunch of different wiring methods.
I suggest you use aggregate all the batteries and the inverter/charge to the same busbar.
Fuse each battery at the positive terminal with an 150 amp MRBF fuse and use 4 awg pure copper wire.
Fuse the inverter/charger at the busbar witha 250 amp mega fuse.
Use this video to find out how to fuse the inverter/charger branch circuit

Will you have any other components in your system?
For instance solar charge controller or secondary dc distribution?
Yes there is secondary dc loads other than the Inverter/Charger this system is in a Small travel trailer with 400 watts solar on top and 100w portable if needed I also use a generator. So the other DC loads is DC side of the trailer load center, and yes I was planning on the modded Victron Power In , actually I'm kinda following Nate's budget system but no Renogy. To be honest I'm getting blown away on costs to run a microwave a few minutes a day and a Starlink system. I was hoping to use the Diagonal parallel as in the attached photo
 

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The fuse on the battery should be selected based on the max current to the loads or the max current from the chargers, whichever is larger. In most systems, the max current to the loads will be larger. I will assume that is the case for the described setup.

We don't know if there are other loads on the system (such as DC loads), but xantrex is most often used on stationary installs, so I will assume it is the only load. I will also assume the xantrex does not have a built in solar charge controller. With all of those assumptions.... you can use a single 250A fuse.

View attachment 130517


Yes, but only if you are using the ABYC boating standards. For the NEC standard the wire size for 250A would be much larger.

ABYC
View attachment 130519
NEC-Ampacity-table.jpg



In the diagram above the wires from the battery to the busbars should all be the same length. The wires from the battery busbars to the rest of the system do not have to be the same length.
It seemed to me Victron case design was for more of a stationery install vs Xantrex ie: marine, police,ambulance type installs. But what do I know, I'm in the Noob section ;) your help I appreciated!
 
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