Wiring up a Multiplus 24/2000

[pda1]

My Multiplus 24/2000 arrived today and I'm preparing to wire it up.
Our off-grid PV system is a 2kW into two BB batteries in series for a 24v.

No grid back feeding will be done but I'll take advantage of the incoming AC to provide an uninterruptible AC supply hopefully with solar priority.

After reading the Multiplus manual and understanding some of it my immediate concern is sizing the cables and disconnects (breakers) and fuses.

Tell me if this is wrong and suggest the correction;

Cable size- batteries to Multiplus= #2 copper welding cables about 2 feet long...maybe 3 feet.

Multiplus grounding cable to earth ground= #2 copper welding cable about 2 or 3 feet.

AC- in to the Multiplus= 14/2 with ground
Breaker before AC input= 15A (breaking the hot wire only)

AC- out of the Multiplus to the load subpanel= 12/2 with ground
Breaker(s) sub panel for output= 2- 15A breakers

The Multiplus has an internal fuse on the battery + input.

Am I missing details or proper requirements?
Any recommendations? (I want this to be a safe installation)

 

[sunshine_eggo]

My Multiplus 24/2000 arrived today and I'm preparing to wire it up.
Our off-grid PV system is a 2kW into two BB batteries in series for a 24v.

Make sure you charge the two 12V individually to 14.4V and then again in parallel to 14.4V for a couple hours. You want to make sure they're both at true 100% when you put them in series.

No grid back feeding will be done but I'll take advantage of the incoming AC to provide an uninterruptible AC supply hopefully with solar priority.

Anytime you use the word "hopefully" you're setting yourself up for disappointment. All "hopefully" items should be resolved before $ is spent.

Default behavior is not like this at all. Inverter/chargers are both, but only one at a time. When AC is live, it is being passed through to the loads. The big transformer is able to be used as an AC to DC charger, but it can't invert and charge at the same time as inversion uses the transformer to inverter DC to AC. Can't have both. Victrons have an uncommon feature for an off-grid inverter where they can boost incoming AC much like a grid tie inverter does, but without backfeeding (except as mentioned in my other response). This happens when the loads exceed the AC input current limit you have specified.

Concerning your description of desired operation, this can mostly be accomplished in a couple ways, but it is not simple. You will also need a Cerbo and the ESS assistant to get full functionality.

Out of the box, it can be set to pass through loads, act as a UPS and favor battery charging from Solar.

After reading the Multiplus manual and understanding some of it my immediate concern is sizing the cables and disconnects (breakers) and fuses.

The manual clearly states cable sizes for DC and AC connections. You simply need to convert metric to awg.

Tell me if this is wrong and suggest the correction;

Cable size- batteries to Multiplus= #2 copper welding cables about 2 feet long...maybe 3 feet.

Copper welding cables are high quality, but their absurdly high current rating is for welding applications where high current is used for short duration at a reduced duty cycle.

Multiplus grounding cable to earth ground= #2 copper welding cable about 2 or 3 feet.

That's more than adequate.

AC- in to the Multiplus= 14/2 with ground
Breaker before AC input= 15A (breaking the hot wire only)

15A * 120V = 1800W

AC- out of the Multiplus to the load subpanel= 12/2 with ground
Breaker(s) sub panel for output= 2- 15A breakers

The manual discusses minimum wiring requirements. The MP can passthrough far more than its 2kW rating, so the output wires are sized to handle the maximum input current + powerassist boost. This is described in the manual.

12 can only handle 20A. You're feeding two 15A breakers (30A total) with only 20A.

The Multiplus has an internal fuse on the battery + input.

This is news to me. I own two Quattros, and I have never heard of this. You might be thinking of the automatic transfer switch (ATS) relay. That is not a fuse. That's the device that passes through the incoming AC to loads.

Am I missing details or proper requirements?
Any recommendations? (I want this to be a safe installation)

Read the Multiplus manual.

Consult link #5 in my signature.

Explore ESS: https://www.victronenergy.com/live/ess:start

 

[pda1]

Just an initial reply;

I opened the MP and at the incoming battery + terminal is a fuse which looks similar to this picture (not the same from my MP). But, as the poster says, if it's blown the inverter can be "considered damaged". The manual says essentially the same thing- see page 17 of this manual;
Multiplus 24-2000/Manual-MultiPlus-Compact-2000-120V-REV-09-EN(1).pdf

Internal DC fuse MultiPlus Compact 12/2000/80 - Victron Community

community.victronenergy.com

Yes, I'll be using a Rsp with Venus to monitor the system.