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High Current PV Isolator Required

T

TheCarltonKid

New Member
Joined
Nov 10, 2024
Messages
15
Location
Nottingham UK
I have a Victron MPPT 250/100 which will be fed from 12 Longi solar panels in a 4s3p arrangement. These panels have an output of just over 13A so the 3 strings in parallel will provide an output of 39 amps at 180v. These panels will be at the top of my garden so all on one cable run. The problem I am having is finding a suitable rotary isolator switch, all these available have a rating of 32 amps. There are plenty of DC circuit breakers of over 40A but I don't know or think it a good idea to be switching this amount of DC current with one of these devices. Also, I want to install inline DIN rail fuses but again these fuse holders are rated at 32A. I have attached a picture of my unfinished DC box, PV in on the left, through fuse, with surge protection, and finally into the isolator switch, then out to the Victron MPPT.

The long and short is I am looking for fuse holders and isolator switch that can safely operate at over 40 amps.
 

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TheCarltonKid said:
I have a Victron MPPT 250/100 which will be fed from 12 Longi solar panels in a 4s3p arrangement. These panels have an output of just over 13A so the 3 strings in parallel will provide an output of 39 amps at 180v. These panels will be at the top of my garden so all on one cable run. The problem I am having is finding a suitable rotary isolator switch, all these available have a rating of 32 amps. There are plenty of DC circuit breakers of over 40A but I don't know or think it a good idea to be switching this amount of DC current with one of these devices. Also, I want to install inline DIN rail fuses but again these fuse holders are rated at 32A. I have attached a picture of my unfinished DC box, PV in on the left, through fuse, with surge protection, and finally into the isolator switch, then out to the Victron MPPT.

The long and short is I am looking for fuse holders and isolator switch that can safely operate at over 40 amps.
Click to expand...
For three parallel strings you need to fuse each string. At 15A. Before combining them. Then to the disconnect and then to the scc. Instead of a disconnect you could use a midnite mnepv dc breaker they are fully rated to operate under load. One of these tandem 600V which is two 300V breakers, you can remove the bridge piece and run both positive and negative into the bottom then out the top to scc.

www.stellavolta.com

MidNite Solar MNEPV40-600-2PP Circuit Breaker 40A 600VDC

Shop now for MidNite Solar MNEPV40-600-2PP Circuit Breaker 40A 600VDC.
www.stellavolta.com www.stellavolta.com
 
What is the voc of the Longis? If you'll be under 250V taking into account record cold temps consider a 5s2p with 10 panels and drop 2. Then your current is manageable, and no need for fusing, easily available 32a imo would work.
 
Brucey said:
For three parallel strings you need to fuse each string. At 15A. Before combining them. Then to the disconnect and then to the scc. Instead of a disconnect you could use a midnite mnepv dc breaker they are fully rated to operate under load. One of these tandem 600V which is two 300V breakers, you can remove the bridge piece and run both positive and negative into the bottom then out the top to scc.

www.stellavolta.com

MidNite Solar MNEPV40-600-2PP Circuit Breaker 40A 600VDC

Shop now for MidNite Solar MNEPV40-600-2PP Circuit Breaker 40A 600VDC.
www.stellavolta.com www.stellavolta.com
Click to expand...
That looks perfect, Cheers
 
Brucey said:
What is the voc of the Longis? If you'll be under 250V taking into account record cold temps consider a 5s2p with 10 panels and drop 2. Then your current is manageable, and no need for fusing, easily available 32a imo would work.
Click to expand...
I did consider 5s2p but the VOC for these is 52.21v so at 261.05 the Victron id likely to smoke. I have also located some suitable 50A fuse carriers and fuses. I wish I could have gone for the 5s2p arrangement which would have been more efficient with less power losses in the cables.
 
TheCarltonKid said:
I did consider 5s2p but the VOC for these is 52.21v so at 261.05 the Victron id likely to smoke. I have also located some suitable 50A fuse carriers and fuses. I wish I could have gone for the 5s2p arrangement which would have been more efficient with less power losses in the cables.
Click to expand...
Yeah too high a voc. Just remember the goal is a 15A fuse on each string to protect from a panel fault causing the other two parallel strings to dump their current into it. I'm planning on using inline mc4 fuses for an eventual 5s3p with vikram 375w bifcials on a 250/100 they have a voc of 41V so there's margin there for 5s.

Sounds like it's not too far from panels to scc?
 
Brucey said:
Yeah too high a voc. Just remember the goal is a 15A fuse on each string to protect from a panel fault causing the other two parallel strings to dump their current into it. I'm planning on using inline mc4 fuses for an eventual 5s3p with vikram 375w bifcials on a 250/100 they have a voc of 41V so there's margin there for 5s.

Sounds like it's not too far from panels to scc?
Click to expand...
Actually it would have been a 6s2p for the 12 panels which would definitely blown the MPPT. I have a second 2s2p of the same panels feeding a Victon 150/45 so no problems with protection for those. The 4s3p block are at the end of about a 35m run of 6mm2 and the 2s2p are about 20m of 6mm2 cable. I'll look into the inline MC4 fuses, will save space in the combiner box. Just ordered a very heavy duty 250v 124A PV breaker that should easily cope with the max 39.5 amp load.
 
Don't forget to calculate using the temperature coefficient for the record low temperature in your area. Or use the nec 20% allowance.

In my case living at altitude I get 22% gain in winter for voltage a wattage output.
 
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