I am hoping someone can help me with this. I am upgrading from AGM batteries to lithium batteries in my fifth wheel camper. I will be adding 600 watts of solar panels. I will be adding a 50 amp Victron solar controller. My camper already has a 2000w inverter. There is a 300w Class T fuse from the batteries to the inverter. I do not know what size of bolt on fuse I need for the new batteries. There will be 2 206 amp hour lithium batteries. If I understand this correctly I need to put a fuse on each battery. I just don't know what size of fuse. The wire is 2/0 gauge. Thanks in advance for the help.
Help with Bolt on fuse at Battery
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Tomthumb62
Solar Wizard
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Pictures will help you get better answers.
If only two batteries in parallel, you only need one fuse, between battery positive and your inverter (or the bus bar if you use one).
Your size the fuse to the cable. What is the temperature rating of your 2/0 cable? Usually 90C or 105C. 2/0 90C is rated for 195A so ideally you’d use a 175A fuse, but I think a 200A one will work since it’s so close.
If you don’t know the temperature rating, then assume 60C. 2/0 60C is only rated for 145A.
Now your 2000W inverter can pull as much as much as 185A, so keep in mind that if you fuse lower than that due to your wire’s amp rating, and you max out your inverter, you’ll be blowing fuses. You could upgrade to 2/0 105C and a 200A fuse to avoid that.
If only two batteries in parallel, you only need one fuse, between battery positive and your inverter (or the bus bar if you use one).
Your size the fuse to the cable. What is the temperature rating of your 2/0 cable? Usually 90C or 105C. 2/0 90C is rated for 195A so ideally you’d use a 175A fuse, but I think a 200A one will work since it’s so close.
If you don’t know the temperature rating, then assume 60C. 2/0 60C is only rated for 145A.
Now your 2000W inverter can pull as much as much as 185A, so keep in mind that if you fuse lower than that due to your wire’s amp rating, and you max out your inverter, you’ll be blowing fuses. You could upgrade to 2/0 105C and a 200A fuse to avoid that.
DIYrich
Solar Wizard
2/0 wire in conduit is 175 amps at 75c. Chassis wiring is around 280 amps. I have 3 racks of batteries, so each rack should draw 90 amps max continuous (inverter limited to 275 amps). But at low SOC, one or two racks could reach low voltage cutoff, and put all the load on one rack until it cuts off a few minutes later. Hopefully I'm watching at that point and turn off the high drain devices (ac, dryer), and not test the wire.
Last edited:
JK14
New Member
Building on @mikefitz comment - the important class T fuse with its very high AIC is ONLY protecting the inverter and if you get a dead short (dropped wrench?) anywhere on the positive bus bar, or any other positive lead leaving the battery, they are not protected from a high amp discharge event.
My vote would be to wire the Class T fuse between the battery and positive bus bar. Using the 300A version you have (I am guessing that's what you meant by "300W") is OK if the 2/0 cables are in free air and rated 90 Deg C minimum (and the bus bar is rated at ≥300A which it might not be).
Then everything else gets wired from the bus bar - and each wire needs a fuse that protects that particular wire gauge.
The additional downstream fuses/breakers don't have to be class T. A 200A fuse/breaker to the inverter makes sense as @Tomthumb62 noted. If the batteries are down to 11 volts and the inverter is maxed out to 2000W and 90% efficient, it would pull 202A.
My vote would be to wire the Class T fuse between the battery and positive bus bar. Using the 300A version you have (I am guessing that's what you meant by "300W") is OK if the 2/0 cables are in free air and rated 90 Deg C minimum (and the bus bar is rated at ≥300A which it might not be).
Then everything else gets wired from the bus bar - and each wire needs a fuse that protects that particular wire gauge.
The additional downstream fuses/breakers don't have to be class T. A 200A fuse/breaker to the inverter makes sense as @Tomthumb62 noted. If the batteries are down to 11 volts and the inverter is maxed out to 2000W and 90% efficient, it would pull 202A.
