Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

Wannabesolar

I have 3 -140 watt solar panels that i would like to connect together in parallel . I originally had 2 of these panels connected in parallel through a small midnight baby box going through a 15 amp dc breaker to which i have had no problems . I received another 140 watt solar panel, through a trade with batteries i had . Id like to add that to my system but i was made aware that when you wire 3 -12 volt solar panels in parallel, you must fuse each panel individually ? Is this correct ? I know you can wire 2 -12 volt panels in parallel and you don't have to have them individually fused , as my breaker system with 2 solar panels has worked great with no issues using a 15 amp dc breaker .

The issue i now have is how do i wire these up properly with the addition of the 3rd panes ?

Here are my options i am thinking about?

(A)
http://www.ebay.com/itm/MC4-In-line-Fuse-Connector-15-Amp-1000-VDC-Male-to-Female-PV-Solar-Fuse-Holder-/161178355943?pt=LH_DefaultDomain_0&hash=item2586fa88e7

(b) either buying or making a combiner type of box for 3 -12 volt solar panels .

(c) cutting the mc4 connectors on the solar panels and splicing in a fuse, which i don't want to do .

(d) Adding another breaker 15 amp breaker in baby box (the 30 dollar one) for that 1 -12 volt solar panel and try to figure a way to get 2 wires to fit into the charge controller (since i have 2 panels connected through a 15 amp breaker currently ) ?

(e) Your options and suggestions?

Id like to find the best way to go here without spending a lot of money that is safe .

zoneblue

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

Wannabesolar wrote: »

I have 3 -140 watt solar panels that i would like to connect together in parallel . I originally had 2 of these panels connected in parallel through a small midnight baby box going through a 15 amp dc breaker to which i have had no problems . I received another 140 watt solar panel, through a trade with batteries i had .

Are all three identical panels? If so great, if not are the specs the same or very similar? If not it may not work so well. MAke sure that the Vmp of all three is equal, and enough margin greater than your battery voltage. ie 17V for 12Vbat, 34V for 24Vbat)

Id like to add that to my system but i was made aware that when you wire 3 -12 volt solar panels in parallel, you must fuse each panel individually ? Is this correct ? I know you can wire 2 -12 volt panels in parallel and you don't have to have them individually fused , as my breaker system with 2 solar panels has worked great with no issues using a 15 amp dc breaker .

String fusing is to protect against panel fires when one string shorts internally. The rule is when the combined short circuit current of the number of strings less one, exceeds the sticker "string fuse rating" for the panel, then string fusing is required. Thats law as well as good sense.

The issue i now have is how do i wire these up properly with the addition of the 3rd panes ?

Here are my options i am thinking about?
(A) http://www.ebay.com/itm/MC4-In-line-Fuse-Connector-15-Amp-1000-VDC-Male-to-Female-PV-Solar-Fuse-Holder-/161178355943?pt=LH_DefaultDomain_0&hash=item2586fa88e7
(b) either buying or making a combiner type of box for 3 -12 volt solar panels .
(c) cutting the mc4 connectors on the solar panels and splicing in a fuse, which i don't want to do .
(d) Adding another breaker 15 amp breaker in baby box (the 30 dollar one) for that 1 -12 volt solar panel and try to figure a way to get 2 wires to fit into the charge controller (since i have 2 panels connected through a 15 amp breaker currently ) ?
(e) Your options and suggestions?

Dont mess about with fuses and such. You could add breakers to the baby box, but only if the baby box is located indoors, and not more than say 5m from the array. Most people use midnite solars 3 or 6 string combiners, they have everything you need and are relatively cheap, and are weatherproof. Checks out NAWs shop under combiners.

The other option to consider is if you have an mppt controller to wire in 2 strings of two or one string of three. This can save some money on combiners, however at the end of the day having the ability to shut off each string independently is kind of useful for faultfinding. The combiner also serves as a PV disconnect should you need to work on the dc disconnect, or array wiring indoors.

Wannabesolar

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

The 3 solar panels are and about equal in specs . When you mention string fusing, Excuse me if this sounds dumb, im a newbie, but do you mean you can have 1 string, made up of 3 solar panels wired in parallel to just 1 breaker (example : each solar panel is rated for 15 amps each , so would 3 of these solar panels equal a single 45 amp breaker for 1 string ? ) . I am using a morningstar pro 30m charge controller , it is not a mttp . My baby box is located indoors . I do have room to add another dc breaker in baby box but my problem is how do i wire the current 2 solar panel connection from one current breaker and then add the other breaker and connect the 3rd solar panel to the same charge controller ? Im hoping i can just switch out the breaker to 45 amp one , wire up the 3 solar panels in parallel and be done without having to buy a bigger combiner . With 3 -140 watt solar panels, Im at in general 420 watts overall (probably 320 watts in actual ) , maximum watts with charge controller at 12 volts is 500 watts so i am withen its limitations .

BB.

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

We are talking about "series strings" of panels... In your case, you have three single panel strings in parallel (for higher voltage arrays, there may be 2-10 panels in series--Still one string).

So, we are suggesting three fuses/breakers. One fuse/breaker in series with each panel.

In general, the series fuse ratings for a panel may be 15 amps, and each panel can output around 8 amps (as an example). The two "good panels" can output 16 amps into the one shorted panel-The 15 amp fuse on that one panel will blow and help to prevent a fire because of the other two panels feeding the shorted third panel.

For two panels in parallel--The one panel cannot "over current" a second panel. Three panels are (typically) just over the series fuse rating and there should be fuses to protect.

Arrays with more than three panels in parallel, definitely need a series fuse per parallel panel/string connection.

-Bill

unyalli

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

Not arguing here...

String fusing is to protect against panel fires when one string shorts internally. The rule is when the combined short circuit current of the number of strings less one, exceeds the sticker "string fuse rating" for the panel, then string fusing is required. Thats law as well as good sense.

I've heard this over and over and understand. There are roof top RV combiner boxes out there that are just a couple bus bars in an enclosure. Some will allow 8 panels (strings) to parallel and come down off the roof via #2 wire. If one of the panels shorted it would receive the combined current from the other 7 panels. Ouch?

Attachment not found.

-Jeff

BB.

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

Jeff,

I know you are not arguing--I just want to be sure we have an understanding (no confusion)--So I can get repetitive at times.

-Bill

unyalli

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

The pictured combiner box is installed on hundreds (thousands?) of RV roofs. I bought one to use in my install if the doctors can ever get me back on my feet. I'm now thinking I want an in-line 10 amp fuse inside this box on each string.

Cariboocoot

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

unyalli wrote: »

The pictured combiner box is installed on hundreds (thousands?) of RV roofs. I bought one to use in my install if the doctors can ever get me back on my feet. I'm now thinking I want an in-line 10 amp fuse inside this box on each string.

I'm thinking that's a good idea if there's room for it.
Putting 7X Isc rating to a shorted panel may not be just "ouch" it could be "goodbye RV".

zoneblue

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

unyalli wrote: »

The pictured combiner box is installed on hundreds (thousands?) of RV roofs. I bought one to use in my install if the doctors can ever get me back on my feet. I'm now thinking I want an in-line 10 amp fuse inside this box on each string.

That was how it was done in the bad old days, particularly for small arrays. Google "pv array fires", to see why things changed. Sure 3 x 10 watt panels in parallel are not going to melt much, but as arrays have grown in size, so has the required protection.

Good habits, and best practice is what we are striving for.

BB.

Re: Ideas for newbie on connecting 3 - 12 volt soalr panals in Parallel ?

Not your type of system--But an example of how many things can go wrong even though the home owner thought he was hiring the right people for the job:

Panel Fire Question

-Bill