Unless it's doesn't. Catastrophic failures of solar controllers are not unheard of. @mainsail posted about such events some time ago. Each time the failure resulted in significant damage to wiring and batteries. A power source should have OCP.
Solar Voltage
- Thread starter Project_Mayhem
- Start date
For a power source like a solar panel do you fuse closer to the panel side or closer to the controller side of the wiring run?
Interesting. Can you post a link to that information?
A battery is like a bucket of water. If you tip the bucket over (shorting it), the water comes out all at once. A controller is limited by the power coming into it. It can’t create more power. It doesn’t absorb and hold power like a battery does.
I’m interested though.
Do you have a citation to where @Maine Sail said a controller over-current damaged a wire? I looked but all I can find from him are statements about fusing at the battery side of the controller wires, like this - Solar Panel Breaker. A failed controller certainly could over-volt the battery and damage it by overcharging, but no fuse will stop that.
I'll have to dig through @mainsail's archives. It might have been in Practical Sailor, maybe 2 years ago.
I've got limited internet at the moment but will try to find it. The gist of the article was that the failures sent panel voltage into the 12 VDC bus. Depending on the panel configuration that could be 40 VDC or more.
Generally speaking, the batteries are already fused, right? The solar controller's output is connected to the DC bus, as are the batteries. They both need to have OCP.
Yes - that kind of failure makes sense to me, and yes, the battery side is already fused. Fuses act on overcurrent though, not over voltage. I’m sure that a controller has failed and passed through solar voltage to the batteries but, as was just mentioned by @Davidasailor26, a fuse wouldn’t protect against that kind of event.
I’m still interested in seeing the article if you can pull it up. I’m doubting that whoever wrote it suggested fusing to address this issue. I’m guessing that this falls more in line with “don’t use cheap solar controllers on a boat” thinking.
A solar panel and a controller are both self-limited. You size the wire to handle their maximum current and you generally need no fuse between them.
The exception is when connecting several panels in parallel, where a short in one panel could get fed by the others and exceed its ability to carry that current safely. If you have that many panels in parallel on a boat you should probably be considering splitting them into separate controllers anyway to better handle shading.
ABYC says within 7" of the power source. The distance can be extended when in a sheath or conduit.
QUOTE Davidsailor26
The exception is when connecting several panels in parallel, where a short in one panel could get fed by the others and exceed its ability to carry that current safely.
End Quote
A short in one panel will not effect the other panels when they are connected in parallel since they have diodes on their outputs to keep current going back into them.
The exception is when connecting several panels in parallel, where a short in one panel could get fed by the others and exceed its ability to carry that current safely.
End Quote
A short in one panel will not effect the other panels when they are connected in parallel since they have diodes on their outputs to keep current going back into them.
Here's the ABYC Standard for overcurrent protection. Note the exception for regulated alternators, a solar panel is also a regulated power source and would thus not need OC protection at the controller. The panel is connected to the battery, which is unregulated, and would thus need OC protection at the battery end. Revisions were made to this standard in July, ABYC may have clarified this in the revision. I don't have a copy of the revision.
Hi Joe,
It's my understanding that this is true in most modern solar panels, but that fusing parallel panels is considered good practice for safety.
Fires on boats are just such bad news. I think it's wise to make every effort to avoid them.