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First, my apologies if I am using this site inappropriately. I am looking for information on DC breakers and fuses and with a 3 1/2 month summer season where I live, time is running short: Maybe I can connect with a few tribe members who could guide me over the next few weeks as I put the final touches to my PV system (robere@sympatico.ca).
Here is a question i recently asked an acquaintence and I am still awaiting a reply:
"if my premise is correct that the fuse between the solar panels and the charge controller is to prevent the unlikely event of a "backflow" from the system damaging the panels in the event that the charge controller fails, and if DC current travels ia a given direction, and if I am using a DC breaker instead of a fuse, is the direction of the current flow relevant to the functioning of the DC breaker i.e. if protecting the panels from the system should the breaker be put in the reverse of the position that it would have been in tof protect the charge controler from an overflow from the panels.
To review my understanding of the DC breaker: a wire goes in at either end, in both ends the wire is from the positive terminal: i.e. positive from charge controller goes in one end, positive from panel goes in the other end; however, the breaker actually itself has one end marked with a positive (+). My assumption would be that if I am protecting from a possible current from from the batteries through a faulty charge controller and into my panels, resulting in their demise....then the positive from the charge controller should go into the breaker on the side marked (+).
Would you concur or am I going off on some irrelevant tangent as is my occasional modus operandi?
Here is a question i recently asked an acquaintence and I am still awaiting a reply:
"if my premise is correct that the fuse between the solar panels and the charge controller is to prevent the unlikely event of a "backflow" from the system damaging the panels in the event that the charge controller fails, and if DC current travels ia a given direction, and if I am using a DC breaker instead of a fuse, is the direction of the current flow relevant to the functioning of the DC breaker i.e. if protecting the panels from the system should the breaker be put in the reverse of the position that it would have been in tof protect the charge controler from an overflow from the panels.
To review my understanding of the DC breaker: a wire goes in at either end, in both ends the wire is from the positive terminal: i.e. positive from charge controller goes in one end, positive from panel goes in the other end; however, the breaker actually itself has one end marked with a positive (+). My assumption would be that if I am protecting from a possible current from from the batteries through a faulty charge controller and into my panels, resulting in their demise....then the positive from the charge controller should go into the breaker on the side marked (+).
Would you concur or am I going off on some irrelevant tangent as is my occasional modus operandi?
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Re: DC breakers between solar panels and charge controllers
Sat, May 30, 2009 - 1:36 PMif you only have one string you dont even need overcurrent protection. it is to prevent backflow between parallel strings in the case that a panel breaks and there is more current than the series fuse rating of the panel. in that case the broken panel would become a resistor and all the current would flow to the broken panel. look on the back of your panel and you will see series fuse rating which is usually enough to put 2 strings in parallel with no risk. many battery systems would have lots of stings (3, 5, 8) and in that case you need fusing.
as for the direction of the breaker, positive would be off the panel and you would put the other side into some kind of bussing before you sent a thicker wire to the charge controler.
i think you are alright if you put the cb in the wrong direction. you can always check it out with the documentation of the cb, but in general, the current will flow from panel to charge controller.
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Re: DC breakers between solar panels and charge controllers
Sun, May 31, 2009 - 4:21 AMThe main point, on the breaker polarity, is that the positive needs to face a positive charge, and the negative needs to face a negative charge. Charges come from the power source (the panels). Putting the positive from the panels to the positive on the breaker has the positive end of the breaker facing the positive charge, and the negative end of the breaker then faces the load, which, through a roundabout path, puts it facing the negative side of the charge.
I would point out a couple of things though. I think fuses to be preferable in these situations for a few reasons.
First, fuses aren't as bad as they are often made out to be: they only pop when things go wrong.
Second, AC breakers rely on the zero-crossing of the power to assist in quenching the arc. DC has no zero crossing, hence it is far more difficult to build a circuit breaker that can properly quench an arc. This makes them more expensive and less reliable than their AC counterparts.
Thirdly, fuses are far cheaper than DC breakers, and also provide you an additional incentive (if they start costing you) to fix whatever is not right rather than putting up with it. -
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Re: DC breakers between solar panels and charge controllers
Sun, May 31, 2009 - 8:38 AMGlenn's post was the tipping point and I will go with a fuse as he suggested.
Thanks to all, more questions are sure to follow. -
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Re: DC breakers between solar panels and charge controllers
Sun, May 31, 2009 - 2:32 PMhow many strings is your system?
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