How to easily and quickly know when a series fuse opens on a string of panels?

BilljustBill · May 2014

In what will be a second phase of a 5kw system, I'll be using a dozen Kyocera 135w panels in three strings of 4 panels. This array will have its own Outback 80amp controller.

If I understand it, there needs to be three series in between the 4 panels. If the panels are up on a roof or at the top of a large tracker, routinely checking them would be somewhat of a quest.

My question: How do you quickly know if one of those string fuses has opened? Is there a way or an L.E.D. item that could be installed in the combiner box that would show if there was a string that is dead?

Thanks.
Bill

ButchDeal · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

BilljustBill wrote: »

In what will be a second phase of a 5kw system, I'll be using a dozen Kyocera 135w panels in three strings of 4 panels. This array will have its own Outback 80amp controller.

If I understand it, there needs to be three series in between the 4 panels. If the panels are up on a roof or at the top of a large tracker, routinely checking them would be somewhat of a quest.

My question: How do you quickly know if one of those string fuses has opened? Is there a way or an L.E.D. item that could be installed in the combiner box that would show if there was a string that is dead?

Thanks.
Bill

you would have a drop in the kW that the charge is seeing.

Cariboocoot · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

BilljustBill wrote: »

In what will be a second phase of a 5kw system, I'll be using a dozen Kyocera 135w panels in three strings of 4 panels. This array will have its own Outback 80amp controller.

If I understand it, there needs to be three series in between the 4 panels. If the panels are up on a roof or at the top of a large tracker, routinely checking them would be somewhat of a quest.

My question: How do you quickly know if one of those string fuses has opened? Is there a way or an L.E.D. item that could be installed in the combiner box that would show if there was a string that is dead?

Thanks.
Bill

I think you may misunderstand the wiring: there will be one fuse or breaker per string. If you use breakers you'll know because you'll see it tripped. Fuses aren't so easy to examine.

As ButchDeal said the drop in output by 1/3 is a really good indicator something has gone wrong. Fortunately it rarely ever happens.

BilljustBill · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

Cariboocoot wrote: »

I think you may misunderstand the wiring: there will be one fuse or breaker per string. If you use breakers you'll know because you'll see it tripped. Fuses aren't so easy to examine.

As ButchDeal said the drop in output by 1/3 is a really good indicator something has gone wrong. Fortunately it rarely ever happens.

Thanks Cariboocoot. I guess I am misunderstanding the fusing issue. What I thought was that each string had to have those series fuses to prevent one defective/damaged panel from starting an electrical issue and that the new NEC required them.....

So, the only breaker/fuse for each string is at the combiner box?

For the series string of 4 Kyocera panels, rated at 135 watts and 12v each, what size breaker would you use?

Since it's 48v per string, will the QO line of Square D work as a combiner box breaker?

Cariboocoot · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

BilljustBill wrote: »

Thanks Cariboocoot. I guess I am misunderstanding the fusing issue. What I thought was that each string had to have those series fuses to prevent one defective/damaged panel from starting an electrical issue and that the new NEC required them.....

So, the only breaker/fuse for each string is at the combiner box?

Yes, it is one fuse or breaker per string in parallel - even if it is "a string of one".

For the series string of 4 Kyocera panels, rated at 135 watts and 12v each, what size breaker would you use?

These panels have a maximum series fuse rating of 15 Amps. They produce a little over 8 Amps Isc so you could use 10 Amp breakers/fuses.

Since it's 48v per string, will the QO line of Square D work as a combiner box breaker?

No, because the fuse/breaker has to interrupt the Voc which will be much higher than 48 Volts. In fact the Vmp of a string of four of these will be (17.5 * 4) 70. There are no shortcuts for 48 Volt systems; buy the MidNite breakers.

SkiDoo55 · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

You can also, get and use the USM1I fuse holder if you are already set up with DIN rail mounting in your combiner box if you want fuse's. It has a blown fuse indicator built in. You can use the DC breakers that will also, indicate a tripped condition.

zoneblue · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

I think you misunderstand string fusing. The string breakers are rated above the max output of the string, so a normally functioning string can never trip its own breaker. So why are they there? Its in case one of the strings suffers a catastrophic short circuit, in which case the shorted string gets all the other strings output dumped into it. This can start a fire, as the current exceeds the ampacity of the pv interconnections. As you can imagine this is reasonably rare provided that your gear is top quality.

BB. · May 2014

Re: How to easily and quickly know when a series fuse opens on a string of panels?

Watch the peak output from the array... And use a DC current clamp meter anytime the sun is up (and the charge controller is pulling current) to measure the current in each string--Do it once a month when you check out the battery bank connections with the clamp meter.

-Bill

How to easily and quickly know when a series fuse opens on a string of panels?

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