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.
I believe I found the article in question by Rod (@Maine Sail). I’ve run into it before and it’s a great article.
Solar Charge Controller Failures - Professional BoatBuilder Magazine
Solar Charge Controller Failures - Professional BoatBuilder Magazine
Regarding the above link, we are talking about if fuse on the input side of the controller can protect against fire. My answered in the case above is not since there is excessive voltage not excessive current. This write up is from a 2013 magazine not from a technical review. Technology has improved and lessons learned.
The real problem is caused by a want-to-be solar panel installer with just enough knowledge to make trouble.
This is not normal case if installed properly.
I dismiss this writeup as a convincing proof for anything. You can comfortably ignore it.
The real problem is caused by a want-to-be solar panel installer with just enough knowledge to make trouble.
This is not normal case if installed properly.
I dismiss this writeup as a convincing proof for anything. You can comfortably ignore it.
I think you missed the point of the article, which was not about whether or not fuse the panels and controllers, it was about knowing your system, being careful about who you hire to install a system, and even well intentioned people can make mistakes that can cause significant damage. its about who to trust with work on your boat.
ABYC Standard E-11, as amended July 2023:
11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent
protection device(s) within a distance of seven inches (178 mm) of the point at which the conductor is connected to the
source of power measured along the conductor (see FIGURE 8).
EXCEPTIONS:
1. Cranking motor conductors.
2. If the conductor is connected directly to the battery terminal and is contained throughout its entire distance
in a sheath or enclosure such as a conduit, junction box, control box , or enclosed panel, the overcurrent
protection shall be placed as close as practicable to the battery, but not to exceed 72 in (183 cm).
3. If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 in (102 cm).
4.Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 in (102 cm), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.
5. Overcurrent protection is not required at an alternator if the ampacity of the conductor is equal to or greater than the rated output of the alternator.
6.Pigtails less than seven inches (178mm) are exempt from overcurrent protection requirements.
NOTES:
1.Multiple main overcurrent protection devices may be connected to a common busbar connected directly to the source of power.
2.If the DC electrical distribution system is not connected as a grounded system per E-11.5.2.3, then both the positive and the negative DC conductors are ungrounded conductors.
11.10.1.1.2 In addition to the provisions of E.11.10.1.1.1 the ungrounded conductors to a battery charger, alternator, or another charging source shall be provided with overcurrent protection within the charging source, or within seven inches (178 mm) of the charging source, based on the maximum output of the device.
EXCEPTION: Self-limiting devices.
I have questions based on statements made above:
Why should a solar panel or solar controller be considered a self-limiting device? A battery charger is not. Why one and not the other?
Two points I'd like to offer:
1. ABYC excludes alternators from the OCP requirement IF the cable is larger than the rated output. Why is this not acceptable for a battery charger?
2. Assume a 30A MPPT controller. The output is wired to the DC bus with 10AWG and within the distance limits for 3% voltage drop. With the panels providing maximum output, no OCP on the controller output, and a dead short into the wire between the controller and positive busbar, something's going to smoke. smolder, or burst into flame. Could be the wire. Could be the controller. Why take the risk?
My standard practice is to fuse the output of a power source. Convince me it's unnecessary.
11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent
protection device(s) within a distance of seven inches (178 mm) of the point at which the conductor is connected to the
source of power measured along the conductor (see FIGURE 8).
EXCEPTIONS:
1. Cranking motor conductors.
2. If the conductor is connected directly to the battery terminal and is contained throughout its entire distance
in a sheath or enclosure such as a conduit, junction box, control box , or enclosed panel, the overcurrent
protection shall be placed as close as practicable to the battery, but not to exceed 72 in (183 cm).
3. If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 in (102 cm).
4.Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 in (102 cm), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.
5. Overcurrent protection is not required at an alternator if the ampacity of the conductor is equal to or greater than the rated output of the alternator.
6.Pigtails less than seven inches (178mm) are exempt from overcurrent protection requirements.
NOTES:
1.Multiple main overcurrent protection devices may be connected to a common busbar connected directly to the source of power.
2.If the DC electrical distribution system is not connected as a grounded system per E-11.5.2.3, then both the positive and the negative DC conductors are ungrounded conductors.
11.10.1.1.2 In addition to the provisions of E.11.10.1.1.1 the ungrounded conductors to a battery charger, alternator, or another charging source shall be provided with overcurrent protection within the charging source, or within seven inches (178 mm) of the charging source, based on the maximum output of the device.
EXCEPTION: Self-limiting devices.
I have questions based on statements made above:
Why should a solar panel or solar controller be considered a self-limiting device? A battery charger is not. Why one and not the other?
Two points I'd like to offer:
1. ABYC excludes alternators from the OCP requirement IF the cable is larger than the rated output. Why is this not acceptable for a battery charger?
2. Assume a 30A MPPT controller. The output is wired to the DC bus with 10AWG and within the distance limits for 3% voltage drop. With the panels providing maximum output, no OCP on the controller output, and a dead short into the wire between the controller and positive busbar, something's going to smoke. smolder, or burst into flame. Could be the wire. Could be the controller. Why take the risk?
My standard practice is to fuse the output of a power source. Convince me it's unnecessary.
What do you mean by “a dead short into the wire between the controller and the positive busbar “? The controller is already connected to the positive busbar. It will output up to its rated current (30A) as long as the batteries and connected loads will absorb that much. 30A will not burn the wire.
If the wire between the bus bar and the controller shorts to ground then it will carry virtually unlimited current from the batteries. That’s why you need the fuse at the battery. If the cable from the bus bar to the controller has lower ampacity than the fuse at the battery then that cable should also be fused near the busbar, to protect the cable from the battery’s current. In any case nothing you can do will get you more than 30A from the controller end.
These are not just my thoughts by the way. Here’s what Nigel Calder says in his Boatowners Mechanical and Electrical Manual:
“We now have to consider an issue that is routinely overlooked and misunderstood. All alternators, battery chargers, DC generators, wind generators, and solar panels are technically a “source of power.” To comply with the standards, the cables connected to them need to be overcurrent protected within 200 mm/7 inches of their connection to the charging device, except that the ABYC (but not the ISO) exempts “self-limiting devices.” This exception covers solar panels, internally regulated alternators (and possibly all alternators, including externally regulated alternators—it’s arguable), and wind generators that are based on alternators (as opposed to those built around electric motors—see Chapter 5). It does not cover most battery chargers, which, as a result, either need internal overcurrent protection (a built-in fuse or breaker) or additional external protection within 200 mm/7 inches of the output terminals.”
At the end of the day if you really want a fuse on the controller output you can do that; there’s certainly no regulation against it. But there are reasons exemptions are written into the rules. The second fuse there becomes two extra splices with additional points of failure, reducing the reliability of the circuit and making troubleshooting more difficult. Installing the extra fuse also means (slightly) more expense and installation time, both of which could be better spent to mitigate other higher risks.
Davidsailor26 usually has the right answer.. I will just add a little.
Check the spec on a solar panel. It will list some open voltage, maximum operating current and short circuit current. You will notice that the operating current and the short circuit current are nearly the same number. You can short circuit a solar panel all day long and it wont hurt a thing. In fact, the original solar charge controllers from many years ago used to actually limit the solar from overcharging by shunting the panel voltage to ground (obsolete now but these were called shunt controller https://www.researchgate.net/figure/Fig-54-Shunt-charge-controller_fig4_316460374 ).
So technically, you dont need a fuse between the panel and the charge controller because the current in this wire cant exceed the panel short circuit spec. You definitely need a fuse near the battery. If the charge controller gets damaged and basically connects input to output, the fuse at the battery still fully protects everything.
There is another aspect and that is if the panel is operating and the charge controller is doing its job, a short on the panel can damage the charge controller electronics. The max current in the wire is never more than the panel short circuit spec but it often will damage the electronics. You may have heard to put a blanket over the panel before messing with the wire to the controller, this is why. A fuse between the panel and the controller may or may not keep the controller from being damaged if the panel is shorted.. There is of course no harm in having the fuse between the panel and the controller, but its the one at the battery that is important.
There was one misconception here. If you have bunch of panels in series that puts out 100 volts but has a operating current (and short circuit current) of 5 amps, if that 100 volt panel is connected directly to a 12 volt battery, by a bad charge controller, it does NOT apply 100 volts to battery. Instead, the voltage of the panel becomes the battery voltage and its still limited to 5 amps. Ie, the panel might be 100 volts open circuit but connect it to a battery and its voltage is the battery voltage. This is actually the way that PM or PWM solar controllers work, they just connect the panel to the battery but modulate the switch. When the switch is closed, the panel voltage is the same as the battery voltage and the current will be somewhat close to the panel short circuit current.
Check the spec on a solar panel. It will list some open voltage, maximum operating current and short circuit current. You will notice that the operating current and the short circuit current are nearly the same number. You can short circuit a solar panel all day long and it wont hurt a thing. In fact, the original solar charge controllers from many years ago used to actually limit the solar from overcharging by shunting the panel voltage to ground (obsolete now but these were called shunt controller https://www.researchgate.net/figure/Fig-54-Shunt-charge-controller_fig4_316460374 ).
So technically, you dont need a fuse between the panel and the charge controller because the current in this wire cant exceed the panel short circuit spec. You definitely need a fuse near the battery. If the charge controller gets damaged and basically connects input to output, the fuse at the battery still fully protects everything.
There is another aspect and that is if the panel is operating and the charge controller is doing its job, a short on the panel can damage the charge controller electronics. The max current in the wire is never more than the panel short circuit spec but it often will damage the electronics. You may have heard to put a blanket over the panel before messing with the wire to the controller, this is why. A fuse between the panel and the controller may or may not keep the controller from being damaged if the panel is shorted.. There is of course no harm in having the fuse between the panel and the controller, but its the one at the battery that is important.
There was one misconception here. If you have bunch of panels in series that puts out 100 volts but has a operating current (and short circuit current) of 5 amps, if that 100 volt panel is connected directly to a 12 volt battery, by a bad charge controller, it does NOT apply 100 volts to battery. Instead, the voltage of the panel becomes the battery voltage and its still limited to 5 amps. Ie, the panel might be 100 volts open circuit but connect it to a battery and its voltage is the battery voltage. This is actually the way that PM or PWM solar controllers work, they just connect the panel to the battery but modulate the switch. When the switch is closed, the panel voltage is the same as the battery voltage and the current will be somewhat close to the panel short circuit current.
How does the math work on this? The panel is producing 500watts (5a at 100v) and supplying 500 watts to the battery. 500 watts at 12v is 42 amps. The equation doesn't balance.