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Solar MC4 Junction Boxes
#1
What are you guys using as junction boxes on your roofs? I know Peter mentioned having breakers on his roof too. What kind of enclosure did you use? All I can find is small ones on eBay that cost like $100. I'm looking to join 3 strings of panels with breakers, possibly more in the future then run one big cable down to my shed. Should I leave it as individual cables to the shed?

Just curious what others are doing...
David Pesce likes this post
Solar Setup: 9x 320w panels, PCM60X charge controller
Battery Setup: 14x 120 cell 18650 packs, 48v configuration

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#2
I dont use any. I use MC4 junctions when needed and then all down to the cabinet.

But if i would do i woult go with IP65. Ie outdor cabinets that are made for outdoor use. Not sure what the equivallent is in your area.
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#3
Aren't you supposed to have each string on a circuit breaker in case one string shorts it doesn't short out the entire system?
Solar Setup: 9x 320w panels, PCM60X charge controller
Battery Setup: 14x 120 cell 18650 packs, 48v configuration

Recommended Items:
Opus BT-C3100, Cell Heat Shrink, 4-Cell Holders
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#4
Does this even work? Shorted solar panels will go up in voltage with very little current going through the short, if any, won't they? I would have thought the breakers consequently never would actually break the circuit.
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#5
The circuit breaker wont do much good for a normal setup where you tie 2 paralell strings together since in real life the max current will be 1 string if the other is shorted due to diode issues. And the breaker should be able to withstand the full current from 1 string Smile So the breaker will only work if you have 3 or more strings together and I dont have that. Only 2 per wire going down and then breaker panel at the inverter side.

In sweden low voltage systems are not common at all. Normal is 300-800V Smile And those are generally 1 string down and not combined.

Im not sure of the requirement though. There is nothing in the manuals I have followed regarding the junction more than it need to be weather proof.

Note that there are short-diodes in each panel and they should take out most cases if there are issues.
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#6
In Australia we have to have a disconnect on the roof by law
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#7
(09-08-2017, 06:14 AM)daromer Wrote: In sweden low voltage systems are not common at all. Normal is 300-800V Smile And those are generally 1 string down and not combined.

Aren't you using the PCM60X? How are you handling such a large voltage? Those voltages are pretty standard in the US too for grid-tie systems, not for off-grid systems that charge batteries.
Solar Setup: 9x 320w panels, PCM60X charge controller
Battery Setup: 14x 120 cell 18650 packs, 48v configuration

Recommended Items:
Opus BT-C3100, Cell Heat Shrink, 4-Cell Holders
Reply
#8
The pcm have 2p3s. Mc4 junction on the roof under the panels. 20A 2p dc breakers close to the charger. Then combined after the breakers.
Follow me! >> YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcomming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#9
(09-08-2017, 12:32 PM)daromer Wrote: The pcm have 2p3s. Mc4 junction on the roof under the panels. 20A 2p dc  breakers close to the charger.  Then combined after the breakers.

Is this the kind of MC4 junction you're talking about?
https://www.amazon.com/gp/product/B01MQWPBAG/

I guess I need to look up what the regulations/codes are to start.
Solar Setup: 9x 320w panels, PCM60X charge controller
Battery Setup: 14x 120 cell 18650 packs, 48v configuration

Recommended Items:
Opus BT-C3100, Cell Heat Shrink, 4-Cell Holders
Reply
#10
Kind of but only for 2. They arent made for to high current so i guess those cheap ones are no good. For 100w panels it should be fine. Yes check ur area. They are fine here for non high volt.
Follow me! >> YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcomming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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