HELP with breaker size and wiring things safely.

[getvrtcl]

I am trying to be as safe as possible with my setup.  One problem for me is the breakers needed in a system and where they should be placed.  I am starting the system with the following components:
12 Photowatt 205 panels (205 watts 24 volts)  Wired 3 in series with 4 paralleled,   All to a combiner box, then sent to the Outback MPPT 80 with #6 wire 18 feet long.  Then it is sent to the 8 batteries which are NAPA 8146 wired for 24 volts with a disconnect switch.  Then to a Prosine 2.5 24 volt.
I would like a breaker in the panel feed before coming into the charge controller but do not understand what amp fuse would be proper.  12 panels @ 8.0 Isc= 96 amps RIGHT?  BUT when I put a meter on it I only see 48.1 amps.  I don't know if I need a 100 amp breaker or a 50 amp breaker??   How many amps should I see???
Same thing for the battery side??
I have searched here for wiring diagrams but couldn't find anything that made sense of this.
So if anyone can help me with a simple solution I would really appreciate it.
THANK YOU !!!!

[wdyasq]

A lot of wiring depends on more than just the number of panels and what Voltages/Amps they produce. If you are going 'Grid-Tie' or 'Grid-Interactive' there are NEC codes to be followed. If you are just going 'Off-grid' only there are still NEC codes some governing authorities require one to follow.

There are also regulations on the AC side of the electricity game.

Ron

[wpowokal]

All of what Ron said but I would bring each string in on a separate wire to a breaker then combined to the MPPT, the breaker is to protect the cable so that is the rating you need, but 205W @ 24V is around 8.5 amps per string, so a DC rated MCB of 20A (depending on cable) would sound reasonable to me.

The battery side needs fuses rated again for cable size which will be well above inverter maximum current, surges will not blow the correct type of fuse. I take it a Prosine 2.5 is 2.5Kw so max amps are around 100. depending on cable size around 200 Amp fuses would be suitable.

Over to the experts.....

Allan of the jungle

[getvrtcl]

OK now we are getting somewhere.  So if I series wire 3 panels to say 10 ga wire to the combiner , and run each set to a 20 amp breaker, 4  20 amp breakers and I can then combine all of those after the breaker and run 6 ga wire to the charge controller.  Or will I need 6 ga to go to the combiner it will be about 14 ft away from the breaker box/combiner?

Thanks

[thirteen]

Could a person use a regular breaker box and back feed the main breaker from the smaller breakers then go to the MPPT. the main breaker would protect the the system plus you would be able to isolate each panel. I don't know is this an off grid system .  Just a thought.

[wpowokal]

getvrtcl
           Still understand any code you may have to comply with, but talking in gauge is not my first language we went metric in 1966 but from reference material 6G is good for 65A, 10G 30A.

The distances you speak of are not very much, there are plenty of tables out there on the net that tell you this amp capability info. 6G should suffice after the breakers, combined (it's all DC) into one wire to the MPPT. separate breakers allows flexibility, and is just good practice.

Allan in OZ who speaks metric

[rossw]

OK now we are getting somewhere.  So if I series wire 3 panels to say 10 ga wire to the combiner , and run each set to a 20 amp breaker, 4  20 amp breakers and I can then combine all of those after the breaker and run 6 ga wire to the charge controller.  Or will I need 6 ga to go to the combiner it will be about 14 ft away from the breaker box/combiner?

As has been said a number of times - your local code requirements may vary, so check them to be sure your install is legal.

That said, what I did with my modest system was to configure each array (each array is 6 x 100W panels) on their own tracker frames and brought each one in on its OWN 10AWG (4 sq mm) cable, each through its OWN  suitable DC-rated double-pole breaker and then each through their OWN DC current metering, and each with their OWN suitably rated schottky diode (prevents any module being back-fed from the others), to a COMMON set of decent copper bars and then via one common (and much larger) pair of cables to the MPPT controller.

Breakers (upper box, cover off for the photo, and amp meters (lower box)


And here you can see the cables to the meters, the common bar, diodes etc.

[wpowokal]

Something to aspire to Ross, define suitable breakers, what current? And as a reminder series is the same current as a single panel just adds the volts. I am not sure that two pole is necessary although would not hurt for DC in this application, definitely for AC 240v application switch only the active.

Allan of the jungle

[rossw]

Something to aspire to Ross, define suitable breakers, what current?

In this case, my panels have a Isc of 6.2A, and running 6 in series has a nominal Voc of 132V.

And as a reminder series is the same current as a single panel just adds the volts.

Absolutely. (Until you then parallel series connected modules, then you start adding amps again!)

I am not sure that two pole is necessary although would not hurt for DC in this application, definitely for AC 240v application switch only the active.

Like I said above - check your local code.
In order to comply *HERE* they need to be double pole. While I'm not grid-connected, and never likely to be, I adopted:
 * Safest practice, wherever legal
 * Best practice wherever possible
 * Code compliant where practical as long as it was consistent with the previous two points


Edit:  Found one of my old working block diagrams....

[wpowokal]

Bugger Ross while I hate to admit it you are right, I braved the cane toads, pythons gooles etc to confirm your statement.



Allan of FNQ grumbling at RossW for proving him wrong, bloody smart #@**^% If you were close enough I would throw rocks on your roof, ops its dirt bugger. Xpole are you sure those Chinese breakers will work? snigger.
  

[wpowokal]

For anybody who does not know this is RossW's house   http://g.co/maps/6z9ee

Allan of FNQ sulking in the corner with a python wrapped around his neck, bar humbug.

[thirteen]

ROSSWW why the smaller wire from the breaker to the buss bar or is it just plain copper wire? I'm not followwing things what is the heavy red wire from?

[rossw]

ROSSWW why the smaller wire from the breaker to the buss bar or is it just plain copper wire? I'm not followwing things what is the heavy red wire from?

Twofold.

1. It provides a "fusable link" - the smallest wire in the whole installation SHOULD be the one to go in the event of some catastrophic failure.
2. The legs of the diodes are quite thin and running thick wire to them was problematic - bending the wires during installation stood a good chance of breaking the pin off.

It's a short length, the loss is negligable, but the resistance might go some way towards helping balance the modules.

[rossw]

Bugger Ross while I hate to admit it you are right, I braved the cane toads, pythons gooles etc to confirm your statement.

lol.

Xpole are you sure those Chinese breakers will work? snigger.

Well, given the maximum the panels are supposed to make is barely 60% of the trip current of the breakers, I doubt they will trip.

The only circumstance I could imagine where they would trip would be if someone shorted a line back at one of the parallel-connected arrays, then the output of the other 5 arrays (30+ amps) could flow back through the feeder cable and then yes, the breakers should trip....

*EXCEPT*.... (I need to re-check the regs) - that stipulate the connection of the breakers IIRC, means that they almost certainly won't trip because the current flow will be BACKWARDS to the way they're designed to operate, in such circumstances!

It doesn't bother me greatly, because I have those big schottky diodes in series with each array, so there is no backflow potential (beyond a few microamps).

So to answer your question: I seriously doubt they will ever go off except when I manually isolate them (as I do sometimes in the worst thunderstorms).

[B529]

What is your MX80's display showing you for max Amps In and Amps Out?

[rossw]

What is your MX80's display showing you for max Amps In and Amps Out?

I can't find any menu to show me the maximum current.
Peak voltage: yes.
Total KWH: yes.
Peak batt volts: yes.
Nothing at all for current except instantaneous values. (I've seen it at 78A out and 36A in though)

[B529]

Where do you live?

[getvrtcl]

Millerton, NY

[B529]

Millerton, NY

Reason I ask is you are at the edge of the max wattage @ 2410 of the MX80. Outback max is 2500 watts @ 24v, the conservative NEC max for the MX80 is 2000 watts.

At your location you'll probably be OK. Keep on eye on your amps out on sunny, cold days. If you start seeing output near or at 80 amps, would be a good idea to shut off one of your strings at your combiner box.

80 amp breaker for your MX80 output. What is your MX80 displaying for amps in?

[B529]

What is your MX80's display showing you for max Amps In and Amps Out?

I can't find any menu to show me the maximum current.
Peak voltage: yes.
Total KWH: yes.
Peak batt volts: yes.
Nothing at all for current except instantaneous values. (I've seen it at 78A out and 36A in though)

You have a single MX80?

[getvrtcl]

I have not gotten the FM-80 hooked in yet I wanted all the wiring in place first.  But yes I only have one of them.  If I read the manual right I can run 2500 W @ 24 vt out.  My panels will produce 2460 W @ 24 volts.  It seemed like this was the max I could run with one FM-80.

[B529]

I have not gotten the FM-80 hooked in yet I wanted all the wiring in place first.  But yes I only have one of them.  If I read the manual right I can run 2500 W @ 24 vt out.  My panels will produce 2460 W @ 24 volts.  It seemed like this was the max I could run with one FM-80.

A few yrs ago I installed two MX60, 1600 watts each, 4v's (Outback max 1800 watts) here in sunny Colorado @ 9800' for a customer. 1st winter the MX60's shut down due to over current. Swapped them out to MX80's, lesson learned. When sizing arrays for MX80/60's I stay 15% or so below the max.

My location is different than yours, that's why I asked, you'll probably be OK. Just keep an eye on your output during cold sunny days.

[getvrtcl]

Good to know.  I am VERY close to the max.  When they shut down does anything get damaged?

[rossw]

Good to know.  I am VERY close to the max.  When they shut down does anything get damaged?

It's my understanding that they don't "shut down", they just "current limit".
80A *output* - so if you have (say) 10kW PV connected, you'd reach the maximum output quickly, but get no additional benefit from any additional capacity you might have.

[B529]

Good to know.  I am VERY close to the max.  When they shut down does anything get damaged?

It's my understanding that they don't "shut down", they just "current limit".
80A *output* - so if you have (say) 10kW PV connected, you'd reach the maximum output quickly, but get no additional benefit from any additional capacity you might have.

In the case of the two mentioned MX60's, they shut down completely. Would not reset on their own. Nothing damaged, only let it happened a couple times. I turned off a string on each array until upgraded to the MX80's.

Keep an eye on your output current!

[dave ames]

I'd be very interested in any other details about that charge controller overload issue, or any other example of an MPPT charge controller problem caused by an overload of PV watts. The reason I ask is that I've never been able to find an example of overloading caused by too large an array- wattage wise...every example found was an issue of the controller loaded above it's corrected VOC or over it's ISC input limits? curious...

Hi getvrtcl,

We can offer some observations on your pv set up.
The spec sheet for our photowatt modules:

http://www.solardesigntool.com/components/module-panel-solar/Photowatt/PW2050-205/specification-data-sheet.html;jsessionid=9DE61DC68992C77275038A02CEDED3BA

We see an ISC of 8 amps and a VOC of 32.7 volts and a max series fuse rating of 15 amps.

Seems we should use 15 amp breakers for the series strings..the midnight solar PV combiner and breakers are nicely rated at 150 VDC.

The four strings combined come to a corrected array ISC of 49.9 amps (8*4*1.56) so a 50 amp breaker for the combined input breaker/disconnect before the controller seems reasonable... and well below the max controller input rating of 64 amps  ISC

For the controller output DC breaker a continuous duty outback 80 amp or standard duty 100 amp should do (80*1.25)

We ran the modules through some of the string calculators and our corrected VOC at 40 below comes in at 130 VOC so we are good there.

Not sure about your plans with the prosine? I suspect you want to try to use it's internal transfer switch?

Cheers, Dave

[getvrtcl]

I'd be very interested in any other details about that charge controller overload issue, or any other example of an MPPT charge controller problem caused by an overload of PV watts. The reason I ask is that I've never been able to find an example of overloading caused by too large an array- wattage wise...every example found was an issue of the controller loaded above it's corrected VOC or over it's ISC input limits? curious...

Hi getvrtcl,

We can offer some observations on your pv set up.
The spec sheet for our photowatt modules:

http://www.solardesigntool.com/components/module-panel-solar/Photowatt/PW2050-205/specification-data-sheet.html;jsessionid=9DE61DC68992C77275038A02CEDED3BA

We see an ISC of 8 amps and a VOC of 32.7 volts and a max series fuse rating of 15 amps.

Seems we should use 15 amp breakers for the series strings..the midnight solar PV combiner and breakers are nicely rated at 150 VDC.

The four strings combined come to a corrected array ISC of 49.9 amps (8*4*1.56) so a 50 amp breaker for the combined input breaker/disconnect before the controller seems reasonable... and well below the max controller input rating of 64 amps  ISC

For the controller output DC breaker a continuous duty outback 80 amp or standard duty 100 amp should do (80*1.25)

We ran the modules through some of the string calculators and our corrected VOC at 40 below comes in at 130 VOC so we are good there.

Not sure about your plans with the prosine? I suspect you want to try to use it's internal transfer switch?

Cheers, Dave

Dave thanks so much.

The one change I think is that I have 3 panels wired in series and the are 4 groups of 3 going to the CC.  If I read your math right I should figure 8 amps X 3 panels X 1.56 = 37.4 amp breaker or 40 amps??  Now that tells me that the 4 groups together would be 149.6 amps which should be 150 amp breaker before the CC  RIGHT??    Does the amps stay the same no matter how many panels I have tied together.  I guess I am over thinking it.  The more I try to make sense of this the worse it gets.
Thanks for the help

[getvrtcl]

I'd be very interested in any other details about that charge controller overload issue, or any other example of an MPPT charge controller problem caused by an overload of PV watts. The reason I ask is that I've never been able to find an example of overloading caused by too large an array- wattage wise...every example found was an issue of the controller loaded above it's corrected VOC or over it's ISC input limits? curious...

Hi getvrtcl,

We can offer some observations on your pv set up.
The spec sheet for our photowatt modules:

http://www.solardesigntool.com/components/module-panel-solar/Photowatt/PW2050-205/specification-data-sheet.html;jsessionid=9DE61DC68992C77275038A02CEDED3BA

We see an ISC of 8 amps and a VOC of 32.7 volts and a max series fuse rating of 15 amps.

Seems we should use 15 amp breakers for the series strings..the midnight solar PV combiner and breakers are nicely rated at 150 VDC.

The four strings combined come to a corrected array ISC of 49.9 amps (8*4*1.56) so a 50 amp breaker for the combined input breaker/disconnect before the controller seems reasonable... and well below the max controller input rating of 64 amps  ISC

For the controller output DC breaker a continuous duty outback 80 amp or standard duty 100 amp should do (80*1.25)

We ran the modules through some of the string calculators and our corrected VOC at 40 below comes in at 130 VOC so we are good there.

Not sure about your plans with the prosine? I suspect you want to try to use it's internal transfer switch?

Cheers, Dave

Dave thanks so much.

The one change I think is that I have 3 panels wired in series and the are 4 groups of 3 going to the CC.  If I read your math right I should figure 8 amps X 3 panels X 1.56 = 37.4 amp breaker or 40 amps??  Now that tells me that the 4 groups together would be 149.6 amps which should be 150 amp breaker before the CC  RIGHT??    Does the amps stay the same no matter how many panels I have tied together.  I guess I am over thinking it.  The more I try to make sense of this the worse it gets.
Thanks for the help

I think I might understand now, after an afternoon of research.  The 3 panels in series will produce a higher voltage BUT the amps stay the same.  So 8 amps per each group of 3 times 4 groups =32 amps
 total
Now the voltage  The 4 groups paralleled   Voltage is per group of 3 = 98.1 volts.  times 4 groups = 98.1 volts
Am I understanding how this works or am I  AFU?
Thanks

[dave ames]

Cheers getvrtcl,

A very productive day of reading there! This stuff can have some levels of a learning curve..So well done.

What's not so obvious sometimes is the constant derating everytime we turn around..where else does 8 X 4 = 49.9  or how 98.1 volts equals 130 volts in cold temperatures? crazy but fun stuff.

Keep at it!
Kind regards, Dave

[getvrtcl]

Hard to teach old dogs new tricks.

The small system I put together to run our greenhouse and woodfurnace finally got a chance to be tested last night.  I had 4 Evergreen 120 panels stored for 4 years and decided it was time to put them to use.  I wired them in parallel  when I mounted them and then purchased an Outback FM-60 after the fact.  Probably  would get more out of them if I rewire for series.  I have that running 4 NAPA 8146 batteries and then to the Prosine 1000.  It ran a constant load or 4.36 amps for 9 hours last night and performed well.  I am impressed that it all works the way I had hoped.  Now on to tackle the bigger system for the house to see what I can do there.
Thanks for the help, I really do appreciate it

Dan