Circuit breaker for Solar Panels

Dr. Dickie

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I am just curious how many folks have circuit breakers on there solar panels.
I am going to be getting 6 350 watt VOC 40.73 v (running two in series for 48 V system 3 parallel), so I am figuring a 10-15 amp breaker on each of the parallels.
If you are using them, which ones would you recommend?
 
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floydR

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How many amps is each panel? 10-15 amps sounds low for a 3p setup
Later floyd
 

OffGridInTheCity

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Yes, I have circuit breakers on all strings. Its natural to design / feed PV into a combiner box. This box is
- Physical terminus between array and the charge controller(s) - e.g. minimum set of wires between array and charge controllers.
- A place to put circuit breakers for quick disconnect code requirements - the Midnite Solar combiner boxes (shown here) have a 'red handle' the toggles the circuit breakers behind the cover in 1 swoop.
- debug various strings / control the amount of power being combined
- A place to put a lightning arrestor

1614711092125.png
 
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Dr. Dickie

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How many amps is each panel? 10-15 amps sounds low for a 3p setup
Later floyd
They do not list an amperage, but I figure they are 350 watt panels with a VOC of 40.73 V so amperage of 8.6 amps. The 15 amps would be for each two panels hooked in series. So a total of 45 amps for the 3p.
They will be these panels.
Q cells
 
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Dr. Dickie

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Yes, I have circuit breakers on all strings. Its natural to design / feed PV into a combiner box. This box is
- Physical terminus between array and the charge controller(s) - e.g. minimum set of wires between array and charge controllers.
- A place to put circuit breakers for quick disconnect code requirements - the Midnite Solar combiner boxes (shown here) have a 'red handle' the toggles the circuit breakers behind the cover in 1 swoop.
- debug various strings / control the amount of power being combined
- A place to put a lightning arrestor

View attachment 24075
Looks good, and midnight solar makes 15 Amp breakers for that box!!
Excellent, thanks!
 
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OffGridInTheCity

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Looks good, and midnight solar makes 15 Amp breakers for that box!!
Excellent, thanks!
Exactly. A typically 300w solar panel delivers 9'ish amps. So if you have a string as in 1p - then 15a circuit breakers as they are quite common. If you parallel strings on the physical array as 2p then you're up to 19-20a - so a 25-30a breaker type of thing.

If you try to do 3p with 9a panels then you're at 27a. 10awg wire coming out of a panel and mc4 connectors max at 30a. 27a is bit close to 30a for me personally, so I limited myself to 2p and had a couple of extra wires coming into the combiner box.
 
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italianuser

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Feb 25, 2020
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I'm choosing my new panels, I can mount up to 6 but I'll probably start off with less.

They are 285W, VOC ~39V, 8.64A each. Supposing to mount two in parallel I will leave some margin on the MCB, so 8.64A x 2 = 17.28A, so I'll choose a 20A or 25A 1000V DC MCB.

Can't wait to share my small project and get some of your points of view:)love learning new stuff!

EDIT: yes, I have MCB and fuses even on my current small 4x50W system
 
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floydR

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They do not list an amperage, but I figure they are 350 watt panels with a VOC of 40.73 V so amperage of 8.6 amps. The 15 amps would be for each two panels hooked in series. So a total of 45 amps for the 3p.
They will be these panels.
Q cells
Watts (STC) 350 W
Max Power Voltage (VMPP) 34.07 V
Max Power Current (IMPP) 10.27 A
Open Circuit Voltage (VOC) 40.73 V
Short Circuit Current (ISC) 10.79 A
Max System Voltage (UL) DC 1000
 

Dr. Dickie

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Watts (STC) 350 W
Max Power Voltage (VMPP) 34.07 V
Max Power Current (IMPP) 10.27 A
Open Circuit Voltage (VOC) 40.73 V
Short Circuit Current (ISC) 10.79 A
Max System Voltage (UL) DC 1000
Thanks, that wasn't in the link was it? I looked for amps every where on there.
Still think 15 Amp should be okay, right?
 

Dr. Dickie

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Exactly. A typically 300w solar panel delivers 9'ish amps. So if you have a string as in 1p - then 15a circuit breakers as they are quite common. If you parallel strings on the physical array as 2p then you're up to 19-20a - so a 25-30a breaker type of thing.

If you try to do 3p with 9a panels then you're at 27a. 10awg wire coming out of a panel and mc4 connectors max at 30a. 27a is bit close to 30a for me personally, so I limited myself to 2p and had a couple of extra wires coming into the combiner box.
I am only going to parallel them after the 15 amp circuit breakers. Will put a 50 amp breaker before the solar charge controller.
 

Roland W

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Thanks, that wasn't in the link was it? I looked for amps every where on there.
Still think 15 Amp should be okay, right?
15A is correct.
I personally use fuses for PV strings. Then the common line would be a 2-pole breaker. But that is just a personal preference...
 

Dr. Dickie

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15A is correct.
I personally use fuses for PV strings. Then the common line would be a 2-pole breaker. But that is just a personal preference...
Yeah, I am going to put a breaker on the common line in the shack.
I would just like to be able to take out the panels if needed, so breaker on each set.
Like you said, personal preference.
 

OffGridInTheCity

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I find breakers (switches) very useful to work on the system. The combiner box (and individual string breakers) is an end point. I have 3 of these. They feed into a charge controller 'end point box'. This box has 3 separate 80a breakers - 1 for each charge controller.

When I first started on all this, I just didn't get the purpose of things like this - but believe me, it add safety and lets me turn OFF the PV input for 1 or all charge controllers at the charge controller area - to work on them. This has proven very helpful / safe.
 
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