Amps decrease with PV8?

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Amps decrease with PV8?

Postby Califoregonian on Sun Apr 19, 2015 12:34 pm

Hi, I'm fairly new to PV, so hopefully I won't sound too dumb. I just got the PV8 combiner box, and have 5 100w panels connected to it. I have two strings of two panels and the fifth panel is on its own. The PV8 seems to have cost me 10 amps somewhere along the way and I can't figure out where.
The background: I'm an RVer, and I started out with one panel and then added two more as I slowly grew. When I had three panels, I used a three to one connecter to reduce the panels to one pair of cables, and it worked fine. Each panel makes about 5 amps and as expected the three panel string made about 15 amps total. Later I added another pair of panels, connected as a string, and combined those cables with the 3-panel string to make one pair of cables going into the controller. All was well, and as expected I could make about 25 amps, with the FM80 cranking out up to 35 charging amps. I knew that the combiner box was kind of required, so I got it.
I connected the two panel string as normal, but the change I did make was to make the 3-panel string into a two-panel string, leaving the extra panel on its own breaker, as I mentioned above. The problem is very apparent and very immediate: I can only make about 20 amps total, and only about 22 charging amps into the bank. Somewhere I've lost up to 10 amps of power! What did I do wrong?
Thanks for any advice, it is truly appreciated!
Califoregonian: what you get when you cross a Californian and an Oregonian.
Califoregonian
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My RE system: FM80, 6x100w Renogy panels, 3x125 ah AGM Vmax bank, 2000w Samlex PST, Flexware PV8. 12v system installed in an RV.

Re: Amps decrease with PV8?

Postby Kent Osterberg on Sun Apr 19, 2015 5:51 pm

Two modules connected to a parallel connector isn't a two module string. A two module string is two modules connected in series. You'd have a terrible voltage mismatch trying to wire the array with modules in series.

The combiner isn't responsible for the problem. You probably have a bad connection someplace. Disconnect one module at a time to find out which one it is.

With five modules you shouldn't be using the parallel connectors at all; each module should be a home run to a breaker in the combiner. The PV modules require over current protection (a fuse or breaker) so that the current that can feed back into the module is no more than the fuse rating on the module, typically 15 amps. With two or three modules, back feed current usually isn't an issue because the maximum current from the modules is less than the module fuse requirement. The parallel connectors are safe for that application. With four other modules in parallel, your system could backfeed 20 amps, or a bit more, into a shorted module. The breakers in the combiner box prevent that from happening. So ditch the parallel connectors, they are only intended for two or three PV modules in parallel.
Kent Osterberg
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Re: Amps decrease with PV8?

Postby Califoregonian on Sun Apr 19, 2015 8:03 pm

Thank you, that helps clarify a fair bit for me. I see I have more to learn about what to call things! I was ordering some things online and the sales person called my two-module parallels "strings" which I wasn't sure was correct but I did not know better. From what you say, what I have is simply two sets of two modules paralleled-- so as to maintain voltage but increase amperage-- but not in a "string", correct?
Each set of two paralleled modules, is run through the PV8 in a 15a 150v Midnite breaker. 15 amps is the max fuse rating for the modules and also the PV8 according to the specs. That's why I reduced my set of 3 modules paralleled to 2, because the Imp of each module is 5.25, meaning it would be possible for the 3 modules to trip the breaker/ go over their rated amps. I know now I shouldn't have paralleled 3 in the first place but I'm still learning, and in some cases learning the hard way.
Anyway, I went about testing the pairs of paralleled modules during peak solar by covering them with a dark blanket and checking the meter, and I'm sorry to say I may see the issue. When covered up, the sets of paralleled modules dropped 10 amps each as expected, but the extra single module seems to be making only about 2 amps at best. (a brief background-- I was very, very exhausted from a long day when I set about installing the PV8 but I wanted to be sure the modules were not producing so I waited until well past dark. I had to use a headlamp and caffeine to get it all done and was not at my best :roll:) I see today that on the single module I accidentally used a fatter wire on the positive lead and on the negative lead a pair of smaller wires connected by an MC4. I suppose that may have something to do with it?
Thanks again!
Califoregonian: what you get when you cross a Californian and an Oregonian.
Califoregonian
Junior Member
 
Posts: 3
Joined: Sat Apr 18, 2015 11:32 am
Location: North Central Oregon
My RE system: FM80, 6x100w Renogy panels, 3x125 ah AGM Vmax bank, 2000w Samlex PST, Flexware PV8. 12v system installed in an RV.

Re: Amps decrease with PV8?

Postby Kent Osterberg on Sun Apr 19, 2015 9:54 pm

From what you say, what I have is simply two sets of two modules paralleled-- so as to maintain voltage but increase amperage-- but not in a "string", correct?
Yes, in parallel the voltage stays the same and the current adds. In series, the current stays the same and the voltage adds.

That's why I reduced my set of 3 modules paralleled to 2, because the Imp of each module is 5.25, meaning it would be possible for the 3 modules to trip the breaker/ go over their rated amps.


Consider a fault in the single module. There are four modules that will provide up to 20 amps that back feed through the 15-amp breaker. In the event of a fault, it will may take a long time but the breaker going to the faulted PV module will eventually open.

Now consider a fault in one of the pairs of paralleled modules. Four modules back feed into the wiring for a single module providing a bit more 20 amps, but the breaker that needs to trip will have just a bit more than 15 amps going through it. And that will only occur under optimal sunlight and time of day conditions. So you have got a circumstance where there is certainly too much current back feeding into the faulted PV module, but the breaker probably won't open.

In small systems, two or three modules, a parallel connection with no breaker or fuse isn't a problem because the current will usually be less than required fuse for the PV module. In this case, you couldn't select a breaker that would ever open either; so it certainly make sense to omit the breaker. In large systems with lots of parallel connections a breaker for every module or series string of modules is essential. In between there are some combinations (often with four modules) where the code, or basic safety, requires a breaker but it may not trip reliably or it takes a really long time.
Kent Osterberg
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Posts: 1494
Joined: Mon Jun 09, 2003 11:01 pm
Location: Cove, Oregon
My RE system: SMA Sunny Boy 2500 with eight Mobil Solar Ra 180 modules

Re: Amps decrease with PV8?

Postby Califoregonian on Mon Apr 20, 2015 10:05 am

That's very interesting, and is also even clearer, thank you again for your detailed reply! Basically I've got more "moving parts" than is necessary for my current setup, is what you're saying. I like the idea of a fuse, but they can't act as an "on/off" switch and cost money every time they blow.
My eventual goal is to have the FM80 maxed out in 12v at 1000w PV input, but for my system and RV's small spaces getting the PV8 instead of the PV12 was necessary. So in order to connect 10 100w modules to the PV8 I'd need to parallel at least two of them-- since the PV8's manual say it can only accept 8 breakers/fuses maximum. In the interest of space for the PV8 and the 18 cables required to run those 10 modules, I decided to combine them into 5 two-module-parallel groups, so there would only be 10 cables running into the RV and the PV8.
I don't have a place to mount the PV8 outdoors on my RV as it would have to be hanging off the "driver's side" and therefore in harm's way/high winds while under motion, as well as would have up to 20 cables out there as well. The only other way to do 20 cables would be to disconnect and reconnect all 20 every time I move the rig, but that much trouble plus the wear and tear on the connectors and cables would not be ideal.
It's tough not having an ideal way to set this up but I guess that's all part of the learning experience, eh? I've been looking around my little town of 250 and other than a person with 5 small modules on a chicken coop/shed, I seem to be the only person using PV, which makes forums like this my only source for learning about using my equipment. Thanks for helping me with my problem, I really appreciate it!
Califoregonian: what you get when you cross a Californian and an Oregonian.
Califoregonian
Junior Member
 
Posts: 3
Joined: Sat Apr 18, 2015 11:32 am
Location: North Central Oregon
My RE system: FM80, 6x100w Renogy panels, 3x125 ah AGM Vmax bank, 2000w Samlex PST, Flexware PV8. 12v system installed in an RV.

Re: Amps decrease with PV8?

Postby Kent Osterberg on Mon Apr 20, 2015 4:01 pm

To reduce the amount of wire you can connect the PV modules in series strings of two modules. Then run a pair of wires to the combiner from each string of two modules. The FM80 will convert the increased PV voltage down to the correct value for charging the 12-volt batteries.
Kent Osterberg
OutBack Emperor
 
Posts: 1494
Joined: Mon Jun 09, 2003 11:01 pm
Location: Cove, Oregon
My RE system: SMA Sunny Boy 2500 with eight Mobil Solar Ra 180 modules


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