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Old 02-11-2018, 19:48   #16
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Re: Circuit Breaker on Solar system

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Originally Posted by noelex 77 View Post
For those interested, I found this article that is a nice blend of a technical disussion and something that can be read by the average person:

http://ep-ru.mersen.com/fileadmin/ca...Tech-Topic.pdf
That applies to large land based systems. If you had four panels in parallel
on a boat you'd need 4 fuses to meet those specs. Not the single fuse that was proposed here.
I have 4 panels in two banks. So 2 parallel to a controller, with two controllers. So even using the specs you referred to it would not require fuses on the panel side.
You always need one on the battery side.
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Old 02-11-2018, 20:12   #17
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Re: Circuit Breaker on Solar system

Fuses are specified to protect the wiring, not the devices attached to the wires,
Fuses are sized in accordance with the current carrying capacity of the wire.
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Old 02-11-2018, 20:29   #18
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Re: Circuit Breaker on Solar system

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Morningstar and victron instructions for their PWM controllers say that the controller should be installed as close as possible to the battery with a fuse installed within 7 inches of the battery. They do not advise the installation of another fuse (or circuit breaker) between controller and panels with at least one I have read actually advising against it. [...]
Before anyone gets confused even more, can you confirm that you retract post #5 please? The one above and post #5 seemed to state the complete opposite.

And yes, we have discussed that many times in the past, there is no need to have a fuse or breaker between the panels and the SCC as the cables have to be able to carry the maximum panel output. Now, you can put one in, of course, and you can put two in series at either end if that makes whatever you have in mind easier.


This applies to typical boat applications though and not to large multi-kW roof installations that run at more than 100V DC! No need to quote some National Electric Code in this context.
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Old 02-11-2018, 20:49   #19
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Re: Circuit Breaker on Solar system

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This advice is actually contrary to that offered from morningstar (the manufacturer of the controller that I use) and other reputable suppliers and installers of this type of equipment.
This was refering to a prior post advising the install of a fuse as close as possible to the panels.

Quote:
Originally Posted by Uncle Bob View Post
Morningstar and victron instructions for their PWM controllers say that the controller should be installed as close as possible to the battery with a fuse installed within 7 inches of the battery. They do not advise the installation of another fuse (or circuit breaker) between controller and panels with at least one I have read actually advising against it. If the need is felt that there should be a switch to enable the disconnect of the panels ( I can't imagine why ) then I would guess that a double pole switch of the required amperage or above would do the job.
I am of the belief that when one properly installs a suitable solar system sized to do the job then it should be left to do that job without undue interference. Done properly they operate for years without interference.
This references the install of a fuse between the controller and the battery, absolutely mandatory. Perhaps I could have added an emphasis that the fuse was in fact after the controller but before the battery.


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Originally Posted by hzcruiser View Post
Before anyone gets confused even more, can you confirm that you retract post #5 please? The one above and post #5 seemed to state the complete opposite.

And yes, we have discussed that many times in the past, there is no need to have a fuse or breaker between the panels and the SCC as the cables have to be able to carry the maximum panel output. Now, you can put one in, of course, and you can put two in series at either end if that makes whatever you have in mind easier.


This applies to typical boat applications though and not to large multi-kW roof installations that run at more than 100V DC! No need to quote some National Electric Code in this context.
Now you have me confused, how can anyone suggest that these are stating the complete opposite?
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Old 02-11-2018, 22:02   #20
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Re: Circuit Breaker on Solar system

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Originally Posted by tanglewood View Post

ABYC creates a similar puzzle. For a battery charger, ABYC requires fusing at both the charger and battery since both are power sources. By extension, this applies to solar as well. The more complete installations I have are do all the fusing. There is little down side to it other than cost.
This is incorrect. ABYC doesn't require fusing at the charger end but always at the battery end of the positive wire.

With a charger connected to a battery the battery is the source to protect with a fuse. The wire's ampacity must greater than the charger's output, as with all current carrying wiring.

The same applies to an alternator or any other charge source - they are current limited whereas a battery can produce a thousand or more amps in a dead short.
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Old 03-11-2018, 00:01   #21
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Re: Circuit Breaker on Solar system

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This was refering to a prior post advising the install of a fuse as close as possible to the panels.

OK, makes sense now and we are on the same page
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Old 03-11-2018, 01:53   #22
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Re: Circuit Breaker on Solar system

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That applies to large land based systems.
Land or sea does not make a difference, although there is perhaps an argument that standards should be stricter for marine installations. There are more serious consequences of fire on a boat (you cannot run away, and there is no fire brigade that is going to help offshore) and this is combined with a greater risk of chafe and corrosion producing a fault situation.

The size of the panels does not change the risk. Smaller panels have smaller internal wires so the fault mechanism remains the same.

The configuration of the panels does affect the risk. More panels in parallel increases the problem. Boats typically wire their panels in parallel.

In short, it is wrong to dismiss fusing of the panel side as a problem that only needs to concern large, land based arrays.

Quote:
Originally Posted by Paul L View Post
I have 4 panels in two banks. So 2 parallel to a controller, with two controllers. So even using the specs you referred to it would not require fuses on the panel side.
The article advises 3 panels (or more) connected in parallel need fusing on the panel side. This is not unusual in a marine installation, but if you have only two panels in parallel you are below the threshold (according to this article).

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Originally Posted by Paul L View Post
on a boat you'd need 4 fuses to meet those specs.
Yes, fuses are needed on each panel. The criterion suggested by the article is 3 panels in parallel, not four.

Quote:
Originally Posted by Paul L View Post
You always need one on the battery side.
Agreed. This is the most important fuse.
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Old 03-11-2018, 03:59   #23
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Re: Circuit Breaker on Solar system

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Originally Posted by tanglewood View Post
... The voltage rating needs to be more than the peak Open circuit voltage of the panels, plus 15%. Under solar edge conditions, that’s what you will see. My guess it that you will be looking at something in the 60V range...
Indeed.
Voltage rating is a function of a circuit breaker's ability to suppress the internal arc that occurs when a circuit breaker's contacts open.

The voltage rating of a circuit breaker must be equal to or greater than the circuit voltage.
The voltage rating of a circuit breaker can be higher than the circuit voltage, but never lower.

In North America, circuit breaker maximum DC voltage ratings generally range from 65 VDC, to 80VDC, to 125VDC.
Maximum AC voltage ratings generally range from 240VAC, to 250VAC, to 277VAC, to 480VAC, to 600VAC.
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Old 03-11-2018, 04:04   #24
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Re: Circuit Breaker on Solar system

Quote:
Originally Posted by noelex 77 View Post
Land or sea does not make a difference, although there is perhaps an argument that standards should be stricter for marine installations. There are more serious consequences of fire on a boat (you cannot run away, and there is no fire brigade that is going to help offshore) and this is combined with a greater risk of chafe and corrosion producing a fault situation.

The size of the panels does not change the risk. Smaller panels have smaller internal wires so the fault mechanism remains the same.

The configuration of the panels does affect the risk. More panels in parallel increases the problem. Boats typically wire their panels in parallel.

In short, it is wrong to dismiss fusing of the panel side as a problem that only needs to concern large, land based arrays.



The article advises 3 panels (or more) connected in parallel need fusing on the panel side. This is not unusual in a marine installation, but if you have only two panels in parallel you are below the threshold (according to this article).


Yes, fuses are needed on each panel. The criterion suggested by the article is 3 panels in parallel, not four.


Agreed. This is the most important fuse.
I want to sort it out a little.

Fuses are Amps only, they blow and must be replaced. There are (marine grade) fuses that are spark protected to prevent explosions of gases when blowing.

Circuit breaker have two means of blowing and can be re-set. there are such for AC and for DC or both. Voltage rating is essential because of the arc, and because of the magnetic coil, that interrupts on short cuts, there is a thermal bi-metal element too that interrupts on light over-loads over a longer period of time as a delay, so short overloads when starting inductive devices like motors does not blow the breaker. There are gas tight CB too for explosion protection, same for relay / solenoids / switches. If you install such devices in the engine compartment, think about it.

A fuse must be installed at the battery only, all other stuff is optional. The battery can provide a lot more Amps than the wire usually can take.

The controller output is rated 20A, your wire is dimensioned for more, the controller cannot overwhelm the wire, no fuse necessary, same for the solar panel. Additionally the controller has an internal fuse to protect the electronics, that will blow or disconnect in case of voltage mismatch, wrong polarity, overheating, shortcut etc. So this fuse is already there.

however you can add a cb or fuse to the panels at any place to protect the wires in case of a lightning strike. The controller will die anyway in such a scenario, the cb is not quick enough to protect the electronics from over-voltage.
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Old 03-11-2018, 04:54   #25
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Re: Circuit Breaker on Solar system

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Fuses are Amps only, they blow and must be replaced. There are (marine grade) fuses that are spark protected to prevent explosions of gases when blowing.
I agree the voltage rating of circuit breakers is much more likely to be a problem, but fuses, and fuse holders have voltage ratings as well. For example, the popular ANL fuses are usually rated at a maximum of 32v DC.


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The controller output is rated 20A, your wire is dimensioned for more, the controller cannot overwhelm the wire, no fuse necessary, same for the solar panel.
The internal wiring within the solar panel is kept as thin as possible (because on most cells the wire is on the top blocking light from reaching the cell). A rating of only about twice the normal current produced by the solar panel is typical.

It is this wire that needs protection. For example the internal wiring in my Sunpower 335w panels is rated at a maximium of 15A.

The external wires may be able to handle many hundreds of amps, but not the wires within the solar panel.




Traditionally most marine solar installations were modest affairs with low voltage panels. The cheap availability of large, high voltage panels has changed this. At the same time we are seeing much more complex electrical systems with larger battery banks, including battery chemistries such as Lithium that can deliver enormous energy in a short time.

Practices that were fine for 12 and 24v systems can come back to bite us when installing a 60v solar panel. A simple example is ignoring the voltage (and IC) rating of circuit protection devices and switches.
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Old 03-11-2018, 05:29   #26
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Re: Circuit Breaker on Solar system

What Noelex said.
And FWIW: Typically, as DC-rated fuses get larger (Amperage), their rated interrupt Voltage falls. You might find a "small" fuse rated to 85 or 120 VDC, but the high current version, of the same fuse, rated at only 32 VDC (even if not so published).
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Old 03-11-2018, 07:20   #27
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Re: Circuit Breaker on Solar system

It is important that people, especially those doing their own installation of solar power with high voltage panels, understand the difference between interrupting DC and AC voltages. The interruption may be a switch, it may be a circuit breaker or fuse or it may be a break in the wiring from a fault.

These videos are at a higher voltage than boat solar installations. 220v DC for the first, but the current is not high. The second is at 380v DC with a polarised DC circuit breaker installed the wrong way around.





The 60V DC of high voltage solar panel is very different to 220v DC, but it is also very different to 12 or 24v DC or to 220v AC. These videos are not an accurate representation of the effects of 60v DC, but nevertheless I hope they convey the message that higher DC voltages are not easy to interrupt and are good at starting fires when you break the circuit.

Make sure the components you are using are rated for the expected DC voltages.
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Old 03-11-2018, 07:23   #28
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Re: Circuit Breaker on Solar system

In line with my 2-360w sunpower pv panels I first go through a 20a switchable dc breaker, then into my Victron 100/30 controller, then into a 30a switchable dc breaker and then onto the 600a dc positive buss. This is the same for both panels and controllers.
This works great in that I can isolate each part of the system for checks or maintenance. The best part is that when Iím going to pull a big load on the battery bank, such as running the SeawaterPro watermaker, I cycle the breakers from the panels which instantly puts the controllers in bulk mode to get the maximum current output. I do this each day for 20-30 minutes to top off our water tanks when the sun is high.
The 69v output of the panels does well with the Victron mppt controllers.
On my last boat with the same setup but with a single panel I have seen over 375 watts output when the battery bank was low due to a faulty thermostat on the freezer.
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Old 03-11-2018, 09:26   #29
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Re: Circuit Breaker on Solar system

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.......


Yes, fuses are needed on each panel. The criterion suggested by the article is 3 panels in parallel, not four.


......
Which is almost never suggested by the CF crew that posts about the absolute need for a fuse on the upstream solar side of the wiring. A single fuse upstream does nothing practical. Multiple upstream fuses near each panel would require in many cases fuses that are completely weatherproof.
In my opinion this an overkill on cruising boat situation. In the super rare case of a burnt wire at the panel end on my boat it might create some smoke, but it isn't going to burn the boat down or start a fire. I guess I could image a large Cat with a huge array mounted on a flamable hardtop all in parallel as a possible small risk.

In practice we all have to the balance risks individually.
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Old 03-11-2018, 10:39   #30
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Re: Circuit Breaker on Solar system

For parallel panel arrays installation you can use string diodes to protect the panels from reverse curret instead of string fuses.
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