Fuses

[RolfP]

I saw a boat this winter being repaired from a fire on the coachroof at the mast from incorrectly installed solar panels, so . . . I would tend to over fuse.

[Wotname]

Originally Posted by wingless

It sounds like SOMEBODY stayed at a Holiday Inn Express last night...

Interesting comment; presumably it has meaning in North America but alas it is lost on us downunder - well at least on me

Originally Posted by CharlieJ

........
There are caveats that allow > 7" of unprotected conductor. An OCPD is not required at the output of a current limited device (alternator, solar panel) but is required at the other end of the conductor where it is connected to the DC system B+...........

This makes good sense assuming the wire gauge from the current limited device is large enough to carry the maximum current. In all normal circumstances, this would be the case.

Originally Posted by foggysail

I installed a fuse between my solar panels and the battery. Sure, solar cannot provide enoughI energy to do harm but that is only half of the story. If somehow a short occurs in the panel wiring or the panels themselves, then my battery bank will see it.

And yes, I have my batteries fused but the fuses are in the 250-300 amp sizes! So if a panel or wiring shorted, it is chancy that the high current would be enough to blow the battery's fuse because of wire resistance. Without over current protection, the damage risks just become greater.

Again presumably this will be close to the battery end of the circuit and not the solar panel end.


Lets just make this simple - fusing first principles are straightforward.

Put a fuse near the source of energy and rate it below the safe current carrying capacity of the wire gauge used assuming the source of energy can deliver this amount of current. If it can't, then a fuse is not required.

In the case of a solar panel connected directly to a battery, a fuse almost certainly required near the battery and almost never near the solar panel.

In the unusual case of a large capacity solar panel and small(ish) gauge wiring, a fuse would be required at both ends of the wiring run as both ends are energy sources and could potentially deliver more current than the wiring can accommodate. I repeat however, this would be an unusual set up.

It's not rocket science

[Lake-Effect]

Originally Posted by foggysail

I installed a fuse between my solar panels and the battery. Sure, solar cannot provide enough energy to do harm but that is only half of the story. If somehow a short occurs in the panel wiring or the panels themselves, then my battery bank will see it.

And yes, I have my batteries fused but the fuses are in the 250-300 amp sizes! So if a panel or wiring shorted, it is chancy that the high current would be enough to blow the battery's fuse because of wire resistance. Without over current protection, the damage risks just become greater.

This.

And as also mentioned earlier, what needs protecting is the WIRING.

Because of high internal resistance, a solar array can't produce current beyond a usually low maximum. So if, for example, your solar wiring is rated for 10 A, but your solar system cannot produce more than 3 A, and there's a dead short at the end of the run (assuming for the moment there's no battery bank attached!), there's no danger to the solar wiring.

Add the batteries, which can produce hundreds of amps into a dead short... now you need to protect the solar wiring with a 10 A fuse or breaker, as close to the DC panel or the batteries as possible.

[on preview, wotname has covered the point more completely. While I agree it's not rocket science, it does require some time invested in understanding basic electrical circuits and/or a willingness to learn and follow standards]

[wingless]

Originally Posted by Wotname

Don't know!
But I do know how to analyse an electrical circuit and to calculate resistance, volts, amps, watts, power dissipation and so forth.

Originally Posted by wingless

It sounds like SOMEBODY stayed at a Holiday Inn Express last night...

Originally Posted by Wotname

Interesting comment; presumably it has meaning in North America but alas it is lost on us downunder - well at least on me

It is difficult to always remember that there are people outside the world's cultural epicenter...

FYI

Equation

Originally Posted by wingless

The 40W solar panel will provide ~12V at ~3A.

A fault like a short will have lots of heat dissipated somewhere w/o a fuse.

IMO, ABYC should be followed w/ having a fuse to protect the wiring.

Originally Posted by wingless

It would be better if the OP provided the model number of the solar panel.

Here is the GANZ 40W Solar Panel Installation Manual.

Originally Posted by foggysail

NO! Solar panels are current sources not voltage sources so there will be little to no heat from a shorted panel....you may get 3 amperes but the voltage will be near zero.

NOw if that panel is connected to a battery and it shorts, it will be the battery that does the damage.
So yes, fuses by all means.

By definition a short is zero volts.

According to the specifications for the 40W panel in the linked datasheet, the open circuit voltage is 21.6V, the maximum output current is 2.30A and the short circuit current is 2.52A.

IMO, that is enough current to cause damage and should be protected.

[Wotname]

Originally Posted by wingless

It is difficult to always remember that there are people outside the world's cultural epicenter...

FYI

Equation

Thanks for the explanation!

[Matt K]

Originally Posted by wingless

It is difficult to always remember that there are people outside the world's cultural epicenter...

FYI

By definition a short is zero volts.

According to the specifications for the 40W panel in the linked datasheet, the open circuit voltage is 21.6V, the maximum output current is 2.30A and the short circuit current is 2.52A.

IMO, that is enough current to cause damage and should be protected.

That makes little sense. What exactly you want to protect and how?

[Wotname]

Originally Posted by wingless

.........
By definition a short is zero volts.

According to the specifications for the 40W panel in the linked datasheet, the open circuit voltage is 21.6V, the maximum output current is 2.30A and the short circuit current is 2.52A.

IMO, that is enough current to cause damage and should be protected.

Let's look at the maths for your scenario.

Power = V*I or R*(I^2)
As R = 0, then power dissipated in the shorted out wiring is 0 watts. However in real life, there will be some resistance in the wire so let's say 0.25 ohms;
Now we have 2.52*2.52*0.252 which is 1.6 watts. IMO, this will not cause damage in the average boat!

OK what happens in the solar panel, there we have 12 volts with a current of 2.52. There is .63 volts dropped in the shorted out wiring (2.52*0.25) so the voltage of the solar panel is 12 -.63 which is 11.37 so the power dissipated inside the solar panel 11.37*2.52 which is 28.65 watts. So the solar panel heats up but then is was designed to do this so again no problem.

[Lake-Effect]

Originally Posted by wingless

By definition a short is zero volts.

Not true. By definition, a short is a very low resistance shortcut across a pair of conductors or a load, where there wasn't supposed to be one.

According to the specifications for the 40W panel in the linked datasheet, the open circuit voltage is 21.6V, the maximum output current is 2.30A and the short circuit current is 2.52A.

IMO, that is enough current to cause damage and should be protected.

If a solar panel can only produce 3A, maximum, and the panel wiring is rated to pass up to 10 A safely, then a dead short at the end of the solar wiring will cause... 3 A. Which will cause... nothing. Nada. Rien.

If the solar wiring is connected to batteries, and then there's a short across the solar wiring, there will be fireworks and smoke, unless the solar wiring is fused near the battery end.

[wingless]

According to the GANZ 40W Solar Panel Installation Manual the specifications for the 40W panel in the linked datasheet, the open circuit voltage is 21.6V, the maximum output voltage is 17.2V, the maximum output current is 2.30A and the short circuit current is 2.52A. They also state that the likely short circuit current and open circuit voltage is 1.25 greater than listed, or 3.15A and 27.0V

According to the GANZ GCC-4.5A Kit Manual that is recommended for this 40W panel, they recommend and provide wire nuts for all the connections.

They show the system wiring diagram w/o fuses either at the battery or at the panel.

IMO, they show a system that does not comply w/ ABYC and is not appropriate for a boat.

IMO, if this were my system then I would put a 5A fuse or circuit breaker, near the solar panel to provide protection if a downstream fault occurred, but to not suffer false fuse failures.

Originally Posted by wingless

It would be better if the OP provided the model number of the solar panel.

This is still a valid request! We should have the OP's equipment identified.


The postulation that the solar panel power source not requiring a fuse at the panel when the system wiring is designed to tolerate greater current than can be provided by the solar panel is a valid argument.


However, the ABYC standards exist to provide fault tolerance, so if a single failure occurs, then bad stuff won't happen.

So, for the bad GANZ GCC-4.5A Kit Operator's Manual documentation, I would recommend no wire nuts and a 5A fuse or circuit breaker near the panel and near the battery. I would also recommend following all the other ABYC standards for the installation.

[wingless]

Originally Posted by Lake-Effect

If a solar panel can only produce 3A, maximum, and the panel wiring is rated to pass up to 10 A safely, then a dead short at the end of the solar wiring will cause... 3 A. Which will cause... nothing. Nada. Rien.

Correct, unless the wiring becomes defective and cannot tolerate the 3A, 40W or 27.0V that the panel can output.

In that case a fuse or breaker would be handy.

[Wotname]

Originally Posted by salticrak

Hello folks, I have a single battery hooked up to solar panels, no engine. My question is do I need a fuse between the battery isolator switch and the fused distribution panel?

thnx.

Hey Salti,

I think we all got sidetracked with the need or otherwise to place a fuse near the output of the solar panel and that doesn't seem to be your question.

You should have circuit protection (ie fuse) on almost all wiring and that fuse should be placed as close as reasonably practicable to the source (ie battery etc).

Presumably you have a simple set up with a battery, a battery isolation switch, a fuse panel and a solar panel.

So ideally a big fuse between the battery and the isolation switch - but a lot of simple set ups don't bother so really it is your call.

Next you should have a small fuse (say 5 amps) in the wiring going to the solar panel and this must be placed as close as possible to the battery.

Hope this helps.

[Wotname]

Originally Posted by Lake-Effect

............

[on preview, wotname has covered the point more completely. While I agree it's not rocket science, it does require some time invested in understanding basic electrical circuits and/or a willingness to learn and follow standards]

Yes, you are quite correct and my "not rocket science" statement was uncalled for and a little over the top. Note to self, don't post late at night.

[salticrak]

I thank you all for your spirited advice. I know this thread has helped me immensely.It's threads like these that have emboldened me to'' have a go'' in the first place.I may place some pics in the order of installation once i have applied what i have learned here.
cheers paul.

[goboatingnow]

Fuse the solar panel of you will , near the panel. But always fuse the solar wire at the battery


Dave

[wingless]

This question was posed to ABYC. The question and the paraphrased reply are provided.

The fuse at the solar panel is not a requirement, but it is prudent to have one at that location.

There must be a fuse / circuit breaker at the battery.


Question to ABYC
What is the appropriate way to uses fuses on a 40W solar panel for battery charging?

The panel specifications are: open circuit voltage is 21.6V; the maximum output voltage is 17.2V; the maximum output current is 2.30A and the short circuit current is 2.52A. They also state that the likely short circuit current and open circuit voltage is 1.25 greater than listed, or 3.15A and 27.0V.

The panel has a controller to provide appropriate battery charging voltage and to prevent back-feeding the solar panel.

The wiring is large enough to tolerate a 24/7/365 dead short to full load output from the panel.


Does the solar panel get treated like a battery, w/ a fuse within 7" of the panel, or should the only fuse or circuit breaker be at the battery end?

Are these solar panel questions / issues specifically addressed in any ABYC standards?


Paraphrased ABYC Reply
Solar panels are a power source. Solar panels must be treated as a power source.

There is an exception in ABYC E-11 to not require over-current protection within 7" of a "self-regulating" power source.

The 7" over-current protection requirement is to protect the conductor, not the device. It is expected that there will be a long conductor run between the solar panel and the charge controller and the battery.

Those conditions make it prudent to have over-current protection at the solar panel. There have been fires stemming from seemingly insignificant wires such as meter shunts, etc.