Stuck on 24v mpp all-in-one setup

[snielsenjr]

So I jumped in head first...I have one of the 24v MPP all-in-one units (LV2424), eight of the 3.2v 280ah cells that will be connected for 24v 280ah, and six 160w poly pv panels wired 3p2s to run 24v to the MPP. My question is where I need fuses and/or circuit breakers in this setup. From what I've seen it looks like a 50amp fuse just off of the battery? Also, would inline fuses for the individual panels be sufficient?

My first foray into any kind of solar setup, so any and all help is appreciated! Btw, this is for a full-time rv. tia

 

[snielsenjr]

Also already have 4awg to run from unit to batteries

 

[gnubie]

You don't need to protect each individual panel in your setup, only strings of panels. The rule is if you have more than two parallel strings (a string might be a single panel) you should have a fuse between each string and the common wire to protect against faults in one string resulting in it drawing excessive current from the others and starting a fire. If you don't have a combiner box you can use inline MC4 fuse holders.

I also like to use blocking diodes but these are optional. If one string develops a gross fault the blocking diode will prevent any back feeding from the remaining good strings allowing more power out of the array should the power flowing into the failed string not be sufficient to blow its series fuse.

A fuse between the array and MPP won't offer any useful protection since the MPP (80A max) can handle the full current your array can ever produce. If your local regulations state you must use a fuse here though, you should fit one.

A 50 amp fuse between the MPP and the battery is far too small. The MPP can draw at least 100A (2400W / 24V). You probably want a 150A fuse. I think the MPP's manual advises you on the size fuse.

 

[John Frum]

So I jumped in head first...I have one of the 24v MPP all-in-one units (LV2424), eight of the 3.2v 280ah cells that will be connected for 24v 280ah, and six 160w poly pv panels wired 3p2s to run 24v to the MPP. My question is where I need fuses and/or circuit breakers in this setup. From what I've seen it looks like a 50amp fuse just off of the battery? Also, would inline fuses for the individual panels be sufficient?

My first foray into any kind of solar setup, so any and all help is appreciated! Btw, this is for a full-time rv. tia

2400 watts * 1.15 conversion factor / 24 volts low cutoff = 115 dc amps
115 dc amps * 1.5 fuse headroom = 172.5 fuse amps
You need 2 awg minimum and a 175 amp fuse

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[John Frum]

BTW please don't buy cheap "amazon" fuses or breakers.

 

[SolarQueen]

I'm curious why you are doing 3 parallel strings of 2 instead of 2 parallel strings of 3? The max input is 145Voc, so if you aren't in a cold environment, you could even get away with 1 string of 6. Why limit the voltage to nominal 24V? Wiring and fusing and everything is easier with only 2 strings instead of 3.

 

[snielsenjr]

I'm curious why you are doing 3 parallel strings of 2 instead of 2 parallel strings of 3? The max input is 145Voc, so if you aren't in a cold environment, you could even get away with 1 string of 6. Why limit the voltage to nominal 24V? Wiring and fusing and everything is easier with only 2 strings instead of 3.

Sorry yes, I meant 3s2p. And I'll have to double check the manual and see what it says about fuse sizing. So from what I'm hearing is that if I use MC4 inline fuses for the panels and a fuse between the battery and mpp then I'd be good to go?

 

[SolarQueen]

Sorry yes, I meant 3s2p. And I'll have to double check the manual and see what it says about fuse sizing. So from what I'm hearing is that if I use MC4 inline fuses for the panels and a fuse between the battery and mpp then I'd be good to go?

If you are only doing 2 parallel strings, you don't need a fuse between the panels and the charge controller. However, having a 30A breaker can be nice to turn them off for servicing. Then the fuse or breaker after the charge controller output, the manual says 80A, but if you have no plans of adding panels later, for 6 160Ws, 50A is fine.

 

[snielsenjr]

If you are only doing 2 parallel strings, you don't need a fuse between the panels and the charge controller. However, having a 30A breaker can be nice to turn them off for servicing. Then the fuse or breaker after the charge controller output, the manual says 80A, but if you have no plans of adding panels later, for 6 160Ws, 50A is fine.

Would it better better long-term to use fuses or breakers?

 

[Deleted member 1888]

If you are only doing 2 parallel strings, you don't need a fuse between the panels and the charge controller. However, having a 30A breaker can be nice to turn them off for servicing. Then the fuse or breaker after the charge controller output, the manual says 80A, but if you have no plans of adding panels later, for 6 160Ws, 50A is fine.

I can't believe you are on Wills forums that is cool, I shop with you guys.

 

[SolarQueen]

I can't believe you are on Wills forums that is cool, I shop with you guys.

We love Will, he does such a great job.

 

[SolarQueen]

Would it better better long-term to use fuses or breakers?

I prefer breakers, as it lets you turn off the circuit when needed.

 

[bcarpman]

So I jumped in head first...I have one of the 24v MPP all-in-one units (LV2424), eight of the 3.2v 280ah cells that will be connected for 24v 280ah, and six 160w poly pv panels wired 3p2s to run 24v to the MPP. My question is where I need fuses and/or circuit breakers in this setup. From what I've seen it looks like a 50amp fuse just off of the battery? Also, would inline fuses for the individual panels be sufficient?

My first foray into any kind of solar setup, so any and all help is appreciated! Btw, this is for a full-time rv. tia

Did you ever get this system up and operational? I've implemented virtually an identical system, and I've never been able to get my LV2424 to charge properly. It seems it only charges in "Float" mode. It won't "Bulk" charge. No matter what it is set to, it will only charge to whatever "Float" is set to. There are so many setting on the LV2424 that aren't well defined, so maybe I missed something. Have you (or anyone else) run into this?