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Wiring Multiplus 12/3000 (Check My Math)

HRTKD

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I have a Victron Multiplus 12/3000 on order that will be installed in my RV trailer that already has Victron MPPT controllers and a BMV-712. The Multiplus specification says it's 93% efficient, so I'm using 1.07 in my calculations. I'm conservatively using 12 volts in my calculations even though my battery bank is unlikely to ever go below 13 volts. I have two 280 Ah 12v LiFePO4 batteries wired in parallel. These have been in place for a year and have worked great.

Since the AC output of the Multiplus is 2400 watts, that should be 2568 watts on the DC side (2400 * 1.07) and 214 amps (2568 / 12). The Multiplus manual calls for 400 amps of overcurrent protection on the DC side. That seems to be a bit much, but maybe that takes into the surge?

The Multiplus has two connections for each DC pole (2 pos, 2 neg). I have 2/0 cable to use, which is overkill if I use two cable for each pole. But it's what I have on hand, so I'll use it. To get that 400 amps of overcurrent protection, should I use a single 400 amp breaker/fuse or should I go with one 200 amp breaker/fuse on each cable? Below is a drawing of the latter.

1638203270705.png
My fuse immediately downstream of the battery is a Class T 225 amp. My biggest AC load would be the air conditioner (2300 watts AC) if I used it much, which I don't. So I'm not worried about sizing for the air conditioning. I'll fire up the generator for that if I need air conditioning. The next largest load, and the main reason for the inverter upgrade, is the microwave at 1500 AC watts. The DC current for that should be 133 amps (1500 * 1.07 / 12). That's well within the Class T's rating of 225 amps.

Should I make a change to my Class T fuse? The next higher fuses that the Blue Sea fuse holder supports are 250 and 300 amps. My two batteries with 120 amp Overkill Solar BMS support 240 amps of continuous output, so 300 amps seems way too high to me.
 
Since the AC output of the Multiplus is 2400 watts, that should be 2568 watts on the DC side (2400 * 1.07) and 214 amps (2568 / 12). The Multiplus manual calls for 400 amps of overcurrent protection on the DC side. That seems to be a bit much, but maybe that takes into the surge?

They're probably following some DIN standard vs. U.S. The 2X 50mm^2 is close to 4/0, and some of that stuff is rated for above 300A depending on insulation temp. 400A is within reason for 300A conductors + surge.


The Multiplus has two connections for each DC pole (2 pos, 2 neg). I have 2/0 cable to use, which is overkill if I use two cable for each pole. But it's what I have on hand, so I'll use it. To get that 400 amps of overcurrent protection, should I use a single 400 amp breaker/fuse or should I go with one 200 amp breaker/fuse on each cable? Below is a drawing of the latter.

View attachment 73868

For U.S. standards, each conductor gets over current protection.

My fuse immediately downstream of the battery is a Class T 225 amp. My biggest AC load would be the air conditioner (2300 watts AC) if I used it much, which I don't. So I'm not worried about sizing for the air conditioning. I'll fire up the generator for that if I need air conditioning. The next largest load, and the main reason for the inverter upgrade, is the microwave at 1500 AC watts. The DC current for that should be 133 amps (1500 * 1.07 / 12). That's well within the Class T's rating of 225 amps.

Should I make a change to my Class T fuse? The next higher fuses that the Blue Sea fuse holder supports are 250 and 300 amps. My two batteries with 120 amp Overkill Solar BMS support 240 amps of continuous output, so 300 amps seems way too high to me.

225A between battery and bus bar is fine as long as your conductor is rated for 180A or higher.

While they recommend a given size, there's nothing stopping you from tailoring a conductor to your installation and only using one of the terminals.
 
I installed my Multi according to Victron ( two - 1/0 cables to a 400A fuse) manual. There's only 2' of cable between the bus bar and fuse.

Accroding to ABYC each cable needs to have the appropriate protection. The 2/0 cable will handle 300 amps so a 200A fuse on each would be acceptable.
 
Is that 1 fuse on your 2 batteries or are they fused individually?
 
Yup it was you HRTKD!
Your inverter circuit will be protected by that fuse, there is no need to follow it with bigger ones. If the 2/0 is rated for 300a (I didn't look it up) there is no need for additional inverter fusing-even on your double 2/0....
 
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