I am planning to install 3 200 watt panels on the roof of my RV. The factory installed #8 wire and the length is about 30 ft to the controller. The Voc of the panels is 24.3 so in series the wires would be carrying 8.2 amps at 72.9 volts. What I am struggling to find is a breaker that would work in this situation. I would need at least a 75 volt 10 amp breaker. Is this correct? Or should I install these in parallel? If in parallel, I am thinking the wire size is too small.
Fuse size
- Thread starter davwalt
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gnubie
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You are right for the maths regarding the breaker.
https://www.ebay.com.au/itm/Cooper-Bussman-DC-Circuit-Breaker-MRCB-200-amp-CB187F-200-B007P5UNNW-187200F/371343768004?epid=1839012980 (massive overkill)
https://www.ebay.com.au/itm/32A-DC-...2P-2-Pole-Solar-Isolator-C65H-DC/281752330119 (not sure if its genuine)
Try to get a genuine name brand breaker. There's abundant fakes out there, and even more straight crappy ones. The breaker in this case would just be used for isolation. There is no breaker or fuse that you can put inline with your array's output that will offer any useful protection that won't also limit your system's power generation.
Looks like you have '12volt' panels, so you could wire them in parallel and use a cheapie PWM controller but that will need cable and plugs capable of 30 amps. Series connected with a suitable MPPT controller is the better option IMO.
https://www.ebay.com.au/itm/32A-DC-...2P-2-Pole-Solar-Isolator-C65H-DC/281752330119 (not sure if its genuine)
Try to get a genuine name brand breaker. There's abundant fakes out there, and even more straight crappy ones. The breaker in this case would just be used for isolation. There is no breaker or fuse that you can put inline with your array's output that will offer any useful protection that won't also limit your system's power generation.
Looks like you have '12volt' panels, so you could wire them in parallel and use a cheapie PWM controller but that will need cable and plugs capable of 30 amps. Series connected with a suitable MPPT controller is the better option IMO.
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Thanks, I was afraid of that. I want to use a Victron 100 / 50 controller. I understand that the 100 means 100 volts max input. The 50 means 50 apps output. I don’t see any specs on the input amps. What size breaker or fuse should I put between the panels and the controller? In my case the amperage is small but I should size the fuse/ breaker to protect the controller - right?
gnubie
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Yes, the 100 means VoC from the panels must never exceed 100v. 50 amps applies to the input and output, regardless of voltage on those terminals. The Victron will limit the current to 50 amps even if the array can provide more, so in practice there is no fuse/breaker you can put in that will not limit the capabilities of your system that would offer any protection to the controller. The breaker would be used soley as a disconnect / isolation device to let you safely turn the input to the controller off for maintenance etc.
TCgreg
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Isn't voltage max 48v on this circuit breaker? OP would have 70 or so?
TCgreg
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I'm sure others will disagree but a breaker or fuse between panels and SCC isn't required. I installed a circuit breaker instead of a switch since it works as a switch but solar panels don't cause concern by over current of the conductor if it is sized correctly. Fusing is to protect the conductor. If you install a fuse and a switch you are certainly covered.
I have been doing some more studying on the issue and I think I will put in a fuse followed by a breaker which will be used as a switch. Here are the items I plan to use:
Fuse: https://www.amazon.com/dp/B000PS7Y9...colid=1MZJL59TG6FC&psc=1&ref_=lv_ov_lig_dp_it
Breaker: https://www.amazon.com/dp/B07DJ6TSJ...colid=1MZJL59TG6FC&psc=1&ref_=lv_ov_lig_dp_it
The breaker is rated for 72 volts and 70 amps. It think 70 amps is too high to protect the wire? Hence the 35 amp fuse. Comments?
Fuse: https://www.amazon.com/dp/B000PS7Y9...colid=1MZJL59TG6FC&psc=1&ref_=lv_ov_lig_dp_it
Breaker: https://www.amazon.com/dp/B07DJ6TSJ...colid=1MZJL59TG6FC&psc=1&ref_=lv_ov_lig_dp_it
The breaker is rated for 72 volts and 70 amps. It think 70 amps is too high to protect the wire? Hence the 35 amp fuse. Comments?
gnubie
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davwalt, as has been pointed out above there's really no breaker or fuse that you can put between the panels and the charge controller that will be able to offer any protection without limiting the amount of power your system can produce. The cable between the panels and controller should already be spec'd to handle the full current of the system continuously, because your charge controller will be trying to get to that full current point as part of its normal operation. During MPPT searches it will approach short circuit current too, if the load on its output can absorb all the power that it is making available.
The breaker must be rated to carry all that current, and must be rated to break that current at the appropriate voltage too. In cases like this where the breaker is not being used to open the circuit on over-current it's always a good idea to over spec it since pushing the maximum current through a thing will lead to increased temperatures. Those temperatures won't reach harmful levels but keeping things cool when you are throwing current around is always a good idea.
The 70amp rating of the breaker is excessive but only from a cost point of view. If your VoC is 72.9 volts a 75 volt breaker is sailing too close to the wind for my liking. On the breaker itself, don't buy it. It's almost certainly crap, one of the millions of knock offs of a Bussmann breaker.
The breaker must be rated to carry all that current, and must be rated to break that current at the appropriate voltage too. In cases like this where the breaker is not being used to open the circuit on over-current it's always a good idea to over spec it since pushing the maximum current through a thing will lead to increased temperatures. Those temperatures won't reach harmful levels but keeping things cool when you are throwing current around is always a good idea.
The 70amp rating of the breaker is excessive but only from a cost point of view. If your VoC is 72.9 volts a 75 volt breaker is sailing too close to the wind for my liking. On the breaker itself, don't buy it. It's almost certainly crap, one of the millions of knock offs of a Bussmann breaker.
Thanks for the info. My goal is to protect the controller and the wiring but struggling to find a suitable breaker at th voltage I want. By the way, I may be incorrect when I stated the voltage in my original post. Should I use the Vmp or Voc for the voltage? The Vmp for those panels is 21.052 so the array should be at 63.2 volts I think. I will look for a better breaker.
gnubie
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When disconnecting the panels the VoC applies as the array will immediately rise to VoC without a load. The breaker has to be able to open the contacts far enough to not allow that voltage to spontaneously form an arc across the contacts, and the arc trap in the breaker needs to be able to cope with the voltages in order to quickly quench any arc that may occur during switching.
