What is the cheapest way to fuse panels? How and where do I install circuit protection?

nobody928

Right now I have 3x 140 watt panels. Ran together at 12 volts. I have a 50 amp fuse from the positive cable going from the Charge controller to the battery bank. I also have a fuse on the inverter its self.

If I buy inline fuses where do I need to run them to protect the solar panels? Is it necesary with such a small system
with 7.6 amps per panel?

Vic

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Each string of PVs needs to have a fuse or circuit breaker. when there are three or more strings in parallel -- YES, strings of one do count as strings.

They should be placed in the lead from each PV or string, at the point where they come together -- this is called a Combiner.

Some will say that this important safety measure is best done with quality devices, and cheapness is not as important as reliability and safety.

Would recommend against Automotive ATC type fuses/holders for PV, as these can overheat over extended periods, required for charging batteries.

MidNite Solar has a good line of Combiners, fuses, and circuit breakers used with the Combiners:

http://www.solar-electric.com/pvarco.html

If the combiner needs to be outside, it should be in a NEMA 3R, Rain-tight enclosure. The MidNite combiners are made for outside use. These are good, inexpensive insurance. Good Luck, Vic

vtmaps

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

nobody928 wrote: »

If I buy inline fuses where do I need to run them to protect the solar panels? Is it necesary with such a small system
with 7.6 amps per panel?

Generally (but not always) you need fuses whenever you have 3 or more panels in parallel. Do your panels have a series fuse rating?

The purpose of the fuses is to prevent a fire if one panel shorts out and the other panels are feeding into the shorted panel. If the series fuse rating of your panels is more than 2 times their Isc, you do not need the fuses for just 3 panels.

--vtMaps

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

First, sorry for hijacking this thread. But, since it hasn't been replied to, I figured I would continue it on due to my system being somewhat similar.

I am about to purchase more panels. I need to make sure I have this correct. Although I have read it a number of times, in a number of different threads, I am still a bit confused. Okay, so I am a bit on the thick side. Sorry. But, hopefully you good folks will help me make sure I get this correct.

Vic wrote: »

Each string of PVs needs to have a fuse or circuit breaker. when there are three or more strings in parallel -- YES, strings of one do count as strings.

They should be placed in the lead from each PV or string, at the point where they come together -- this is called a Combiner.

Currently, I have 3 panels in parallel. However, they were wired together on the roof. One 4 awg cable comes down and goes to the combiner, where it is attached to a 30amp fuse. Then, a 6 awg wire continues on to the controller.

vtmaps wrote: »

Generally (but not always) you need fuses whenever you have 3 or more panels in parallel. Do your panels have a series fuse rating?

The purpose of the fuses is to prevent a fire if one panel shorts out and the other panels are feeding into the shorted panel. If the series fuse rating of your panels is more than 2 times their Isc, you do not need the fuses for just 3 panels.

My panels have a maximum series fuse rating of 15 amps. (see attached image) But, the Isc is only 5.69 amps. So, does this mean just one (30 amp) fuse is fine, between the array and the controller? I am going to add more panels, just not sure how many as yet. Probably 3, though.


Attachment not found.

westbranch

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Simply you want circuit protection between the PV's and the Charge Controller and between the Cc and the battery.
This will allow you to work on the CC connections safely. You do not want power to flow from either the PV or battery when you are checking or changing wiring etc. Make sense?

You also want protection between strings of PV once > 2 so that they do not back feed a faulty string and start a fire or? The protection is based on the Amp rating rating of your panels and the manufacturer will state the protection needed in Amps, usually 10 A per sting of 12 v panels

Cariboocoot

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Just a not about series fuse ratings for panels.

See that the term used is "maximum series fuse". This does not mean you should only use the rated fuse/breaker but that you should not use one of greater current carrying ability. In the case of panels whose Isc is around 5 Amps you would be better off with a 10 Amp fuse if possible. Otherwise by the time it blows/trips the current may be well over 15 Amps (depending on how many parallel connections are involved) and the fire already started. Most over-current devices need to be above their trip point by a certain amount for a certain period of time before they actually do their job.

Another important point about current protection is that the protection should be sized for the conductor, and always the conductor must be capable of handling more current than the CP.

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

westbranch wrote: »

Simply you want circuit protection between the PV's and the Charge Controller and between the Cc and the battery.
This will allow you to work on the CC connections safely. You do not want power to flow from either the PV or battery when you are checking or changing wiring etc. Make sense?

You also want protection between strings of PV once > 2 so that they do not back feed a faulty string and start a fire or? The protection is based on the Amp rating rating of your panels and the manufacturer will state the protection needed in Amps, usually 10 A per sting of 12 v panels

Yes, I want it as safe as possible, of course. But, if my Isc is 5.69 amps, just add that together with each panel in series for the appropriately sized fuse?
What confuses me here is, advising a 10 amp fuse. If I go with a 10 amp fuse for two panels in series, for example, would it not burn that fuse up in good sun?
Or, would the (roughly) 25% estimated drop in output, due to efficiency, be calculated in here?

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Cariboocoot wrote: »

Just a not about series fuse ratings for panels.

See that the term used is "maximum series fuse". This does not mean you should only use the rated fuse/breaker but that you should not use one of greater current carrying ability. In the case of panels whose Isc is around 5 Amps you would be better off with a 10 Amp fuse if possible. Otherwise by the time it blows/trips the current may be well over 15 Amps (depending on how many parallel connections are involved) and the fire already started. Most over-current devices need to be above their trip point by a certain amount for a certain period of time before they actually do their job.

We were replying at the same time, I see.

Okay. So, 10 amp fusing per panel. I misunderstood westbranch.

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Cariboocoot wrote: »

Another important point about current protection is that the protection should be sized for the conductor, and always the conductor must be capable of handling more current than the CP.

Yes. 6 AWG is what I have been using for all runs so far. Combiner to controller is 200 cm. Controller to battery bank is 1.5 meters. When the installers first put the panels up, they ran 4 AWG from the panels (in parallel) to the combiner. I want to get that sorted while adding the additional panels.

Cariboocoot

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

ILFE wrote: »

Yes. 6 AWG is what I have been using for all runs so far. Combiner to controller is 200 cm. Controller to battery bank is 1.5 meters. When the installers first put the panels up, they ran 4 AWG from the panels (in parallel) to the combiner. I want to get that sorted while adding the additional panels.

See now here's the thing. 6 AWG can handle >50 Amps no problem. But if one of the panels shorts it can only handle 15 Amps at best. So in these circumstances you have to think of the circuit having mixed conductor sizes as the panel will be acting as a conductor, not a power source. It is in fact like a piece of 16 AWG wire stuck in the circuit. If the fuse/breaker is rated to protect 6 AWG wire it is not going to protect that 16 AWG equivalent segment to the circuit.

This is something that comes up and is often ignored. Wire sizes are sometimes larger than necessary for the expected current in order to reduce the Voltage drop over distance. Usually this is after the combiner, in which case it has no bearing on a shorted panel in an array. But when you think that the wires usually used to connect panels are 10 AWG (and therefor capable of 30 Amps continuous) you see the problem is there anyway. Hence the series fuse rating.

Sometimes the Voltage drop requirements can trip you up on the current protection.

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Cariboocoot wrote: »

See now here's the thing. 6 AWG can handle >50 Amps no problem. But if one of the panels shorts it can only handle 15 Amps at best. So in these circumstances you have to think of the circuit having mixed conductor sizes as the panel will be acting as a conductor, not a power source. It is in fact like a piece of 16 AWG wire stuck in the circuit. If the fuse/breaker is rated to protect 6 AWG wire it is not going to protect that 16 AWG equivalent segment to the circuit.

This is something that comes up and is often ignored. Wire sizes are sometimes larger than necessary for the expected current in order to reduce the Voltage drop over distance. Usually this is after the combiner, in which case it has no bearing on a shorted panel in an array. But when you think that the wires usually used to connect panels are 10 AWG (and therefor capable of 30 Amps continuous) you see the problem is there anyway. Hence the series fuse rating.

Sometimes the Voltage drop requirements can trip you up on the current protection.

I see what you are saying. That's why I realized this needs to be sorted. At the moment, three panels are connected, without fuses and in parallel, to one length of #4 wire. This length of wire is then run to the combiner.

Cariboocoot

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

ILFE wrote: »

I see what you are saying. That's why I realized this needs to be sorted. At the moment, three panels are connected, without fuses and in parallel, to one length of #4 wire. This length of wire is then run to the combiner.

Normally the panels would each have their own 10 AWG wires running to the combiner where they'd go through fuses/breakers and then connect together to larger gauge wire to make the 'home run' to the charge controller (or inverter).

Just for clarification to anyone else reading this thread.

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

I also have to order some MC4 cables and Multibranch connectors. Got a bit of work to do.

Thanks for helping me clear things up in my mind about this.

vtmaps

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

ILFE wrote: »

At the moment, three panels are connected, without fuses and in parallel, to one length of #4 wire. This length of wire is then run to the combiner.

I don't understand this... what is your combiner being used for? The panels are already combined before they get to the combiner?

The combiner is usually an outdoor rated box with circuit breakers for each string. The combiner is also an excellent place to put a lightning arrester. If you install an outdoor combiner with a lightning arrester, you may avoid bringing lightning into your house (or power shed, or where ever).

--vtMaps

hemmjo

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

If I may ask a follow-up question along these lines. I am going pick up 4 panels in the Dominican Republic in a couple of weeks of this project I have been working on. The only specifications I have so far are; 265 watts, 36 volts, "around 4' x 5'." This information was relayed to me by a non-technical person who I asked to get me specifications from the supplier down there.

Looking at what is available in the US, I find 265 watts panels in the range of -
1) Pmax: 265 Watts , Voc: 38.1 Volts, Vmp: 31.9 Volts, Isc: 8.82 Amps, Imp: 8.33 Amps, Max reverse current 16 amps
2) another with Voc: 38.3 Volts, Vmp: 30.7 Volts, Isc: 9.12 Amps, Imp: 8.64 Amps, Max reverse current not given
30 another with Voc: 39.0 Volts, Vmp: 30.8 Volts, Isc: 9.31 Amps, Imp: 8.69 Amps, Max reverse current 16 Amps

Interesting #'s 1 and 3 are for the same panel on different sites.

Is it safe to assume these 265 watt "36 volt" panels will be close to these values? I was planning to make 2 series pairs of 2 panels on the roof and make 2 ≈ 72 volt, 10 ga. runs the 15 feet to the combiner box. Would a pair of 10 amp DC breakers be correct to protect these panels?

Last question, for now, which direction to put the breaker? Is the + side toward the battery, since the panels cannot make over 10 amps to trip the breaker, the excess current would have to come from the batteries due to some system failure or wiring error?

As always, Thanks,

John
http://villagemountainmission.org/

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

vtmaps wrote: »

I don't understand this... what is your combiner being used for? The panels are already combined before they get to the combiner?

The combiner is usually an outdoor rated box with circuit breakers for each string. The combiner is also an excellent place to put a lightning arrester. If you install an outdoor combiner with a lightning arrester, you may avoid bringing lightning into your house (or power shed, or where ever).

Yeah. Well, that's why I don't trust Cambodian installers. The cable from the panels goes into the box, through the circuit protection, and to the controller. The negative side goes straight to the controller, not in the combiner.

Cariboocoot

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

hemmjo wrote: »

If I may ask a follow-up question along these lines. I am going pick up 4 panels in the Dominican Republic in a couple of weeks of this project I have been working on. The only specifications I have so far are; 265 watts, 36 volts, "around 4' x 5'." This information was relayed to me by a non-technical person who I asked to get me specifications from the supplier down there.

Looking at what is available in the US, I find 265 watts panels in the range of -
1) Pmax: 265 Watts , Voc: 38.1 Volts, Vmp: 31.9 Volts, Isc: 8.82 Amps, Imp: 8.33 Amps, Max reverse current 16 amps
2) another with Voc: 38.3 Volts, Vmp: 30.7 Volts, Isc: 9.12 Amps, Imp: 8.64 Amps, Max reverse current not given
30 another with Voc: 39.0 Volts, Vmp: 30.8 Volts, Isc: 9.31 Amps, Imp: 8.69 Amps, Max reverse current 16 Amps

Interesting #'s 1 and 3 are for the same panel on different sites.

Is it safe to assume these 265 watt "36 volt" panels will be close to these values? I was planning to make 2 series pairs of 2 panels on the roof and make 2 ≈ 72 volt, 10 ga. runs the 15 feet to the combiner box. Would a pair of 10 amp DC breakers be correct to protect these panels?

Last question, for now, which direction to put the breaker? Is the + side toward the battery, since the panels cannot make over 10 amps to trip the breaker, the excess current would have to come from the batteries due to some system failure or wiring error?

As always, Thanks,

John
http://villagemountainmission.org/

What you get is the fact the Wattage of the panel is based on Vmp * Imp, so if you have two of the numbers you can work out the third. 265 / 30.7 = 8.63 which is close enough. Some slight variations in the individual cells make one panel slightly higher/lower in Voltage than another. It is not a big difference; you could use these two interchangeably. Isc tends to be about 8% higher than Imp so you can estimate that as well: 8.63 * 1.08 = 9.32 A bit higher than reality, but close enough. So same type/size/Voltage panels will have specs pretty close to one another.

These panels would probably be rated for 15 Amp series fuse, not 10, as their Isc is so close to 10 Amps.

As for breaker alignment, the battery doesn't enter in to this because the purpose of the breakers on panels is to protect from overloading a shorted panel by the other panels. Oddly enough it works out the same, though: the power source will be the other panels and the side of the breaker designated for that goes away from the panel (because when it shorts you are expecting current to come from that direction).

Excess current from the batteries would have to travel through the charge controller, which should be able to block reverse current flow by its internal circuitry. If that fails you have the over-current protection between the controller and batteries (installed just as you say). This is even more important than panel fuses in my opinion as batteries have huge current potential compared to the capacity of the wiring used to connect the controller.

Brewgonia

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

I haven't gotten around to building my system yet so pardon the seemingly simple question. What kind of fuses and holders do you use for such large conductor wire? I'm used to the small gauge ATC kind used on cars and motorcycles which use #10/12/14 wire. Where do you find something that takes #2/3/4 wire?

Cariboocoot

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Big wire = big current = big fuses: http://www.solar-electric.com/infubr.html
There's other variations on the theme too.

ILFE

Re: What is the cheapest way to fuse panels? How and where do I install circuit protecti

Brewgonia wrote: »

I haven't gotten around to building my system yet so pardon the seemingly simple question. What kind of fuses and holders do you use for such large conductor wire? I'm used to the small gauge ATC kind used on cars and motorcycles which use #10/12/14 wire. Where do you find something that takes #2/3/4 wire?

I am using ANL and Mini-ANL fuse holders. They will handle most of the cable / fuse sizes I need. They are also considerably cheaper than most others I have found online.


Mini-ANL Fuse Holder
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ANL Fuse Holder
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The mini-ANL holder has dual o-rings on either side of the holder, as well as rubber bushings included, to make them rain / splash and insect resistant. they work perfectly for #6 wire. I would have no problem installing them in a location where they could get wet. However, mine are wired inline only in dry, covered areas. You can buy fuses rated from about 15 amperes to about 200 amperes for the mini holder.

The ANL holders have lugs with dual nuts on them and - I believe, 5/16" lugs on which to attach cable terminals. This holder isn't as beefy as the mini, but considering all the power goes through the fuse, it isn't an issue for me. It is sturdy enough to mount to my power board. You can buy fuses rated from about 30 amperes to about 300 amperes for the ANL holder.