Maximum Series Fuse Rating

[TheGriz]

Folks, I need some help understanding "maximum series fuse rating", and how this rating applies to my solar setup. I attached an excerpt from the spec sheet for my panels below. I will be putting three of these panels in series 3S1P (for now...may expand to 3S2P) going into an EPever Tracer 30A/100V MPPT controller. So, what I think I understand is each panel is internally protected to 10A in event of reverse current resulting from a damaged panel. Do I need to provide for an additional 10A fuse (or other rating) at the end of the series?

 

[schmism]

your mixing current and voltage. Max panel voltage (the largest number you can put in series) is because the blocking diodes can only work up to a certain voltage. Over that voltage you can "push past" them and damage a pannel. (voltage is like water pressure, to much pressure and you can leak past a valve that is shut)

A fuse is designed to interrupt an over current event once. (send to many amps - it blows/melts and disconnects the circuit)

A fuse does not protect against over voltage

 

[tictag]

So, what I think I understand is each panel is internally protected to 10A in event of reverse current resulting from a damaged panel.

Incorrect. No PV panels I am aware of, and certainly not these ones, have fuse protection, internal or otherwise.

Do I need to provide for an additional 10A fuse (or other rating) at the end of the series?

No.


Further information...

Firstly, these panels do not have blocking diodes, they have bypass diodes. Bypass diodes allow panel current to bypass a section of cells if either one of those cells is damaged or, more likely, one of those sections is partially shaded. Bypass diodes offer no protection from reverse currents from, for example, a battery at night. This is what your SCC is there to do. A typical 100W panel would have two bypass diodes splitting the cells up into three distinct series-connected sections/strings. You could if you wish add blocking diodes but this is unnecessary these days and will just waste power.

The 'Maximum Series Fuse Rating' is a bit of an enigma and is only really relevant for big PV arrays e.g. >1,000W.

Under normal operation a PV panel can only generate Isc, that's it, even if you short the output terminals together and shout at the Gods for more sunlight, only Isc will flow ... no more. Therefore, so long as you spec your PV cable ampacity for more than Isc, what does it matter if there is a short circuit? It doesn't, and that's why I never bother fusing smaller PV arrays i.e. <1,000W. Yes, of course, you're not going to get any power out of your array if there is a short ... but, critically, it won't be unsafe.

Now there is a small possibility of certain fault conditions causing a back-feeding effect when you have a large PV array e.g. >1,000W so in that case, yes, I would connect all my panels into a combiner box and, yes, under those specific circumstances, I would ensure a fuse was fitted that was below this 'Maximum Series Fuse Rating'.

Aside from that, this specification can be largely ignored, imho.

Edit: Corrected typo.

 

[SolarQueen]

Since it is wired in series, the amps don't increase for the string. The max fuse size is needed if you have multiple parallel strings. Generally, the internal wires to the solar panel have a maximum current that can flow through them. The max fuse size it to make sure you never go above that without protection from other strings.

 

[Hedges]

Maximum series fuse rating 10A means, if the panel suffers a short, it can safely handle no more than 10A getting dumped into it, otherwise could overheat a wire/trace and present a fire hazard.
If you configure as 3S2P, on shorted panel would only get the 6.10A (more or less) that the other string could generate, so no problem.
If you wire 3 strings in parallel e.g. 2S3P, then each string should have its own 10A fuse. Not much smaller, don't want it to trip from its own current, so stick with 10A. I'm used to seeing max fuse > 2x Isc, not < 2x.

Going unfused with only two strings, we have to hope the charge controller isn't capable of a fault that would backfeed more than 10A.
My first string inverter had one string of panels for which max fuse was 20A, and inverter had a 15A AC breaker, so no problem in that case.
I wonder if your Epever is designed so it can't possibly ever under any circumstances backfeed, at least not more than 10A??
Not knowing what's inside it, I would think a 10A fuse for ever PV string and a fuse for the combined wire (located at the charge controller) would be necessary for safety.
(These musings about charge controller are more for others here to respond to; I'm curious if things have been made fail-safe.)

 

[Zil]

Just to list what I have built with hope it helps you figure what you are doing. I have four panels connected in parallel. Each panel has short circuit amperes equal 7 amps. The 8awg lead wires can handle that with ease. so a fuse is not required. Unless there is a failure in one panel. Then the other three panels can back feed 21 amps into a short, also shutting down the whole dang system. So I have each panel fused at 15 amps before the box they combine into two 4awg into CC. I used this fuse block. https://www.bluesea.com/products/category/16/61/Fuse_Blocks/ST_Blade

 

[Hedges]

Just to list what I have built with hope it helps you figure what you are doing. I have four panels connected in parallel. Each panel has short circuit amperes equal 7 amps. The 8awg lead wires can handle that with ease. so a fuse is not required. Unless there is a failure in one panel. Then the other three panels can back feed 21 amps into a short, also shutting down the whole dang system. So I have each panel fused at 15 amps before the box they combine into two 4awg into CC. I used this fuse block. https://www.bluesea.com/products/category/16/61/Fuse_Blocks/ST_Blade

Sounds perfect.
Just make sure those 15A fuse are actually fuses, and not an excellent "fuse-like device" supplied by the lowest bidder.
Either pay a fair price for a reliable brand, or at least take a 4-wire resistance measurement and compare to published values for good brands.

Now that I've learned about that, I need to go back and screen all the fuses in our cars. I've bought kits from the local auto supply, which is where someone demonstrated he found cr@p. Even Harbor Freight, which had previously supplied bad ones, did a recall and weren't carried any more when he did further testing. But the auto stores continued to carry bad ones. I see Harbor Freight once again carries fuses. Maybe I'll buy and test some.

 

[Zil]

The only fuse on board are by Bussman, maybe from BlueSea.

 

[frodo2222]

Incorrect. No PV panels I am aware of, and certainly not these ones, have fuse protection, internal or otherwise.

No.


Further information...

Firstly, these panels do not have blocking diodes, they have bypass diodes. Bypass diodes allow panel current to bypass a section of cells if either one of those cells is damaged or, more likely, one of those sections is partially shaded. Bypass diodes offer no protection from reverse currents from, for example, a battery at night. This is what your SCC is there to do. A typical 100W panel would have two bypass diodes splitting the cells up into three distinct series-connected sections/strings. You could if you wish add blocking diodes but this is unnecessary these days and will just waste power.

The 'Maximum Series Fuse Rating' is a bit of an enigma and is only really relevant for big PV arrays e.g. >1,000W.

Under normal operation a PV panel can only generate Isc, that's it, even if you short the output terminals together and shout at the Gods for more sunlight, only Isc will flow ... no more. Therefore, so long as you spec your PV cable ampacity for more than Isc, what does it matter if there is a short circuit? It doesn't, and that's why I never bother fusing smaller PV arrays i.e. <1,000W. Yes, of course, you're not going to get any power out of your array if there is a short ... but, critically, it won't be unsafe.

Now there is a small possibility of certain fault conditions causing a back-feeding effect when you have a large PV array e.g. >1,000W so in that case, yes, I would connect all my panels into a combiner box and, yes, under those specific circumstances, I would ensure a fuse was fitted that was below this 'Maximum Series Fuse Rating'.

Aside from that, this specification can be largely ignored, imho.

Edit: Corrected typo.

I am also doing the same thing sort of 2S/2P.....I have 2 250 watt 24 volt panels that are going to be together to give me 75 volts and 8.27 amps then both will be tied in parallel to another 2 panels in series which If I understand correctly will give me the same 75 voltage but 16.54 amps when ll 4 put together, the panels fuse rating of 15 amps so If I fuse them with a 15 amp fuse before I combine them in parallel then they should be fine correct? with a larger fuse/disconnect before the controller... ANY clarification on this is VERY welcome..getting ready to do this but do not want to fry myself...the voltages in the pic was from the actual book NOT my arrays mine are the aforementioned 75 voltage and 16.54 amps.. my controller by the way is a 100/50 MPPT Epever if that makes any difference

 

[Hedges]

Label says 15A fuse, so using one per string is acceptable.
With your 2s2p configuration, no fuse is required. If 2s3p, 2s4p etc. then each string should be fused. Purpose is so a shorted wire is protected against over-current from the other 2, 3, or more string dumping into it.

A breaker to isolate panels from charge controller is convenient.
That could be single pole interrupting positive after strings are combined (should be at least 1.56 x 2 x Isc)
Could be two pole interrupting two positive strings before they are combined (at least 1.56 x Isc)
Could interrupt both positive and negative.

Voc = 37.6 x 2 in series = 75.2V, even if that increased 15% or 25% in cold weather, would still be less than 100V rating of SCC, so that's good.

4 x 250W = 1000W (STC) from array.
What is your battery voltage? If 12V, 1000W/12V = 83A (more or less as battery charges and according to PV performance at the moment.)
A 50A charge controller would only capture part of the energy during middle of the day. We call that "over paneling", and it lets the system sustain 50A charge for more hours and off season.

If you orient one series string toward 9:00 AM sun and the other toward 3:00 PM sun (90 degree angle), peak output will be 0.7x as much, 58A into 12V or 50A into 14V, for more power harvested.

Of course with 24V battery you'll get all the power through that charge controller.

 

[frodo2222]

Label says 15A fuse, so using one per string is acceptable.
With your 2s2p configuration, no fuse is required. If 2s3p, 2s4p etc. then each string should be fused. Purpose is so a shorted wire is protected against over-current from the other 2, 3, or more string dumping into it.

A breaker to isolate panels from charge controller is convenient.
That could be single pole interrupting positive after strings are combined (should be at least 1.56 x 2 x Isc)
Could be two pole interrupting two positive strings before they are combined (at least 1.56 x Isc)
Could interrupt both positive and negative.

Voc = 37.6 x 2 in series = 75.2V, even if that increased 15% or 25% in cold weather, would still be less than 100V rating of SCC, so that's good.

4 x 250W = 1000W (STC) from array.
What is your battery voltage? If 12V, 1000W/12V = 83A (more or less as battery charges and according to PV performance at the moment.)
A 50A charge controller would only capture part of the energy during middle of the day. We call that "over paneling", and it lets the system sustain 50A charge for more hours and off season.

If you orient one series string toward 9:00 AM sun and the other toward 3:00 PM sun (90 degree angle), peak output will be 0.7x as much, 58A into 12V or 50A into 14V, for more power harvested.

Of course with 24V battery you'll get all the power through that charge controller.

I got the cheap 100 amp fuse/breakers so figured id put on the line down to the controller just to be able to totally shut it off...I have 10 trojans T-105 and 2 other controllers that are PMW ar 12 volts and a Aims 2500 inverter/charger that is already 12 volts..if it wasn't for that I would change the whole thing over to 24 but it's another $600-1200 for a new inverter soo...I already get 60 amps trying to get to the 110 am level to be able to RUN my AC all day just on solar so if it is over paneled that's fine as it will get more sun in the am and pm part of the day.

So it sounds like the fuse would not be needed on the single series arrays but I can put in one 15a fuse per string and nothing bad will happen it sounds like and if everything else failed ie chinese fuse/disconnect that would still protect the other serial array....THANKS for the explanation..make it much easier to NOT fry me or the houseRV

 

[prtrc]

What gauge wire should be used from a MPPT solar controller to the battery bank? I will be using 2AWG to wire batteries together in Parallel. Should it be 2AWG from the controller to the batteries or can that be the same gauge wire that runs into the controller from my panels (in my case 10AWG)?

 

[timselectric]

That depends on the output of the charge controller.