How do I add another string?

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How do I add another string?

Postby mhoybook on Wed May 17, 2017 8:15 am

I currently have an off grid system using 2 12 panel arrays providing up to 6140 watts, 2 FM 80 charge controllers, one GSLC175PV load center and a GS8048 invertor. My only issue is that this is just not quite enough solar input to charge my 48 volt 1500 amp hour battery bank while I run a house at the same time. I would like to add one more 12 panel array and one more FM 80 charge controller but my question is how do I connect this to the load center. The load center seems to be designed for only 2 charge controller inputs. Surely I don't need another load center to do this?
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Re: How do I add another string?

Postby Mike Curran on Wed May 17, 2017 12:22 pm

For sure you'll need another 80 amp breaker between your FM80 and your battery, and another breaker(s) (sized appropriately for the new array's short circuit current) between your new array and the new FM80. If your current load center doesn't have spaces for these additional breakers then you'll have to figure out a way to work around it. Perhaps a separate enclosure for the added breakers?
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Re: How do I add another string?

Postby mhoybook on Wed May 17, 2017 4:20 pm

Mike Curran wrote:For sure you'll need another 80 amp breaker between your FM80 and your battery, and another breaker(s) (sized appropriately for the new array's short circuit current) between your new array and the new FM80. If your current load center doesn't have spaces for these additional breakers then you'll have to figure out a way to work around it. Perhaps a separate enclosure for the added breakers?


Thanks, but I'm hoping there's a way to add it into the load center using one of the included shunts so I can monitor it with my Mate3 like my other panels?
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Re: How do I add another string?

Postby blackswan555 on Wed May 17, 2017 9:06 pm

as Mike said
Perhaps a separate enclosure for the added breakers?
on the side of what you have now, You can still run the cables inside to the shunt/ busbar,

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: How do I add another string?

Postby pss on Thu Jul 27, 2017 11:29 am

Well lets do the math on this: My battery bank capacity is 900 amps at 48 volts and I have three Flexmax 60's. In full sun, they put about 2400 watts at 55 volts into the batteries plus load. That's 43.6 amps per hour. That is the amount of power the batteries can safely absorb to charge. In 5.5 hours, that is 242 amps into the battery bank. If my battery bank is drawn down to 60%, that is a deficit of 900 x .4 of 360 amps. But I just told you my daily charge capacity with 3 Flexmax controllers is 242 amps. Notice that I am nowhere near the rated capacity of each charge controller of 60 amps maximum. My three strings have a face value of just over 7800 watts. In your case, you have a 1500 amp battery bank. Say your battery bank is charged at the same rate as mine, but it is 600 amps larger or 66%. If you discharge to 60%, that deficit becomes 600 amps. 600 amps divided by 5.5 hours of sun on a good day is 110 amps per hour into your battery bank plus the load. 110 amps x 55 volts means you would need to produce 6050 watts to charge the batteries in one day for 5.5 hours plus capacity to power your load. You currently have 6140 watts in 2 strings. In the heat of summer and with losses for wiring distance, say you actually put out a peak power output of 80% or 4912 watts in total now. You see the problem, you need 6050 watts just to charge the batteries on a full sun day of 5.5 hours from an SOC of 60% Each array at 80% is giving you 2456 watts. Multiply this by 3 = 7368 watts. Subtract 6050 watts to charge the batteries and this leaves you just 1318 watts to power the load. EXCEPT, the system will power the loads first, draining the batteries and only the leftover solar production goes to charging the batteries, so you may still not be fully charged.
In my case, I have chosen to place my system in gridzero for 20 hours and in minigrid for 4 hours from 7-11 PM. While in minigrid, my Radian inverter charger is turned on and charges the batteries from the grid to top them off so they are never low. I wind up having to charge from the grid about every 2-3 days on very hot summer days, but my battery bank (32 Trojan T105-RE stays healthier). You could charge from a generator also. You have to weigh the cost of adding a third string and all the wiring and hardware vs. just charging to top off with a generator or grid as needed and using that as your backup source.

Now, if you really want to add that third string, you will need to add an 80 amp DC breaker for each charge controller and change out our PV array ground fault detector breaker to a quad pole model (Outback has this part). In this way, you can use up to 4 Flexmax charge controllers and integrate all the wiring into the GLSC load center and into the shunts so Flexmax DC works.

Good luck.
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Re: How do I add another string?

Postby mhoybook on Thu Jul 27, 2017 12:00 pm

Wow, very timely and educational reply. As a matter of fact, I had already decided one more array of 12 panels would still not be enough so I ordered 24 more 280 watt panels and two Outback FM-80s. I have almost all of the parts needed onsite now but I did not realize about the four pole ground fault circuit interrupter. Thanks for that information and I will get busy and get one ordered today. Thanks again.
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Re: How do I add another string?

Postby blackswan555 on Thu Jul 27, 2017 8:28 pm

PSS, I do not understand which way you mean your comment?
In full sun, they put about 2400 watts at 55 volts into the batteries plus load. That's 43.6 amps per hour. That is the amount of power the batteries can safely absorb to charge.

Most manufacturers recommend 5 to 15 % of 20hr rated capacity as charge current, In your case at 900ah you only have just under 5% with 43.6ah, So I am presuming you are talking about the lowest safe charge current for your batteries, Not the highest ? (FLAs)

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: How do I add another string?

Postby pss on Thu Jul 27, 2017 10:11 pm

This is how I meant my comment:
Battery banks are limited in how fast they can charge. If your batteries need 10 Kw of power to be fully charged, it is not possible to do this in 1 hour, but it can be done in say 5 hours. So what I was illustrating is that with a large battery bank (mine 900 and his 1500) there is not enough hours of daylight to fully recharge the battery bank with 2 Flexmax 80's for his bank and three Flexmax 60's for mine. The 60 or 80 designation is the maximum flow of current safely through the device. But the Flemax controller outputs current based on the load drawn and the size of the battery bank and voltage parameters set for charging. It is then that the software contents of the Flexmax take over to run a three step charge algorithm. The problem is the Flexmax knows when it work up, but doesn't really know how much sunlight it will receive all day or when the sun will set. Therefore, the operator sets the absorb time, or if they prefer the absorb end amps and voltages to be reached. On the Flexnet parameter input form, you can specify the amp hours of the bank, the charged voltage, the charged return amps and the charge factor, but this is used by the Flexnet monitor hardware to calculate the SOC and estimate battery parameters. It does not override the battery charging algorithm programmed into the Flexnet controller.

In my case, the amperage I receive to charge my batteries is a function of the charge controller software and the ambient temperature of the panels. Most recently, I get about 2200 - 2400 watts of power at usually about 55 volts (as determined by the Flexmax MPPT bulk algorithm) above my load. That is how I determined the amperage I receive to charge the batteries. There is no parameter I can find to change to increase the charge current provided to my battery bank. It would be nice to have a dial to simply turn up amperage put into my batteries, but the Flexmax does not have one. As for our original poster, I simply extrapolated my data to his size battery bank to tell him that one string and one controller would not charge his batteries, two more strings may do the trick, but even then he may want to protect his battery bank from chronic depletion by charging from the grid if he is connected or a generator if he cannot charge the bank up to near max daily. I also intimated it may be more cost effective to install a generator rather than 2 more strings and all the hardware, especially since the purpose is not for load during the day, but to charge the batteries for night time load. I hope this makes things somewhat clearer and appreciate any comment on errors I may have made.
pss
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Re: How do I add another string?

Postby blackswan555 on Fri Jul 28, 2017 12:14 am

Sorry to the original poster, Maybe worth starting a new thread PSS, But I am wondering why you are only seeing 1/3 or your rated STC ? Also your mention of 55v, On the FM display what is that? the incoming voltage or outgoing ? ( what are both? )
I presume you are using an FNDC ? Is it controlling charge ? Have you checked your SGs lately ? What settings have you changed from defaults and to what ?

Tim

PS where in the world are you ?
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: How do I add another string?

Postby SandyP on Fri Jul 28, 2017 12:19 am

blackswan555 wrote:Sorry to the original poster, Maybe worth starting a new thread PSS, But I am wondering why you are only seeing 1/3 or your rated STC ? Also your mention of 55v, On the FM display what is that? the incoming voltage or outgoing ? ( what are both? )
I presume you are using an FNDC ? Is it controlling charge ? Have you checked your SGs lately ? What settings have you changed from defaults and to what ?

Tim

PS where in the world are you ?


I was confused as well, however it appears (I am assuming) his loads are using the other 2/3 rds of the solar panel / FM output amps.
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Re: How do I add another string?

Postby pss on Fri Jul 28, 2017 10:08 am

Yes, I am using 55 volts (output voltage on Flexmax display) because in MPPT bulk mode, the input voltage from the panels is converted by the MPPT software to provide maximum power to the batteries and load. Power is watts. And power is moving, from the panels into the batteries and through the batteries into the inverter to supply the load requirement. Power from the charge controllers does not flow directly to the inverter. The inverter derives all of its power from the batteries, and the batteries receive all of their power from the charge controllers. As the load increases, the power passed through the charge controllers will go up to the maximum output of the panels for the solar condition at that moment. At at moment in time, under load, the panels may be able to supply the load and charge the batteries, but if they cannot, then even in the daytime, the batteries will discharge to supply the load. If the panels can output power greater than the load, the excess, up to the limits of the MPPT software program will flow into the batteries and be absorbed, increasing their voltage.
I mentioned 55 volts, because when I monitor my charge controllers, in MPPT bulk mode, most consistently the input voltage from the panels is stepped down to about 55.1 volts and the corresponding amperage is then increased, resulting in more power being delivered to the batteries (MPPT = maximum power point tracking).
In my case, when I observe my charge controllers in the daytime, under full sun, my panels and charge controllers push about 2200-2400 watts above load into my battery bank. My absorb time is 5.5 hours. Under my usual full loads, the load is about 5.0 - 5.5 kW. I have directly observed short loads to 8.1 kW. The highest solar panel output I have directly observed is 6.8 kWh, but when I look at the lifetime maximum output of each of the three strings and add them all together, it would total over 9 kW, exceeding the rated output of my strings.
Also, under the best solar conditions all three of my Flexmax controllers in MPPT bulk mode are within 0.1 volt of each other and almost identical amperage output, so they work together in a coordinated fashion.

Now, I think this is where a lot of the confusion comes into play. The software intelligence to provide power to the loads and charge the batteries lies in the Flexmax charge controllers and the inverter. The Mate3 is a programming interface as well as a web server and DHCP server to the HUB 10.3 and interface to the outside world internet. In fact, if you power down your Mate3 in the daytime, your charge controllers and inverter will function just fine! The FNDC is a device to use the installed shunts and information told to it to ESTIMATE the status of charge of the battery bank, report the measured voltage and provide information on amps into and out of the battery bank on a daily and lifetime basis. But, IT DOES NOT PROGRAM OR CONTROL THE CHARGE CONTROLLERS. In fact, the FNDC is optional, a convenience for the human need to see pretty information.

I have not turned off all of my load circuit breakers at the panel, but if I did, then all of the solar output available to me would be strictly for charging the batteries and operating the inverter and Mate3, Hub 10, etc. That condition would tell you exactly how much power the Flexmax charge controller software is allowing to go into your battery bank to charge the batteries and how much time it would take to complete. then you would know by determining if you are down 200 amp hours or 500 amp hours to a full charge how many hours of good solar output you need to restore to full charge.

Again, I am not a Ph.D in solar, but am trying to illustrate how the Outback technology works in the real world. I have read and researched many topics and articles for many hours and often do not see the information people really need to create the system that meets their expectations.

Adding battery capacity to increase the time of power without solar input is nice, but then you have to figure out if you have the solar power to charge the increased size of the bank or would be better off with a bank that works for maybe 24-36 hours under load and using a support generator after that to charge the batteries and maintain power to the load. In general, batteries cost more than a generator and the life expectancy of a decent generator is probably longer than the battery bank. Also the location of the system and total costs and budget of the owner all need to be considered.

Please, any questions and comments are encouraged because I do not know it all.
pss
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Re: How do I add another string?

Postby mhoybook on Fri Jul 28, 2017 11:01 am

Again, this is all timely and useful information and much appreciated. Most of it makes perfect sense to me now since I am living this condition. We are truly off grid so we only have a generator to make up for the charge deficiency during the day at this time. One more hardware question for you: I realized today that my Outback Load Center has only two shunts and each one is currently connected to an array of 12 panels. When I add my additional 24 panels, can I double up on the shunts? For example, put the first 24 panels on one shunt and the second 24 on the second shunt? They are 500 amp shunts.
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Re: How do I add another string?

Postby pss on Fri Jul 28, 2017 11:27 am

Yes, and you can even add a third shunt to the load center. As long as they are wired correctly, the info will get to the FNDC.
In my case, two strings on one shunt, one string on another shunt.
pss
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Re: How do I add another string?

Postby mhoybook on Fri Jul 28, 2017 12:12 pm

Thanks for the information!
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Smoke from Flexmax 60

Postby Signman on Wed Aug 09, 2017 12:13 am

I have just added another 1.75 Kw of panels to our existing system (7 x 250w panels)
We had 6 x 64w panels and 3 x 190w panels.
My friend, who is supposed to be pretty clued up did the wiring, added them into the 190w panels.
Turned it on and smoke and a black liquid came out of the Flexmax 60 Controller. Liquid display is not reading now.
He disconnected the 1.75 Kw of panels and hooked it back up as it was. Things seem to be still working.
What might the problem be? What have we done wrong?
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Re: How do I add another string?

Postby EMCF on Wed Aug 09, 2017 9:05 am

"For example, put the first 24 panels on one shunt and the second 24 on the second shunt? They are 500 amp shunts."

You technically (and physically) do not add group of panels to a shunt. You electrically connect in series the negative side of a charge controller to a shunt, wherein this charge controller's PV input is from those "24 panels" that you have, or PV array.
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Re: How do I add another string?

Postby pss on Wed Aug 09, 2017 10:56 am

How can a Flexmax 60 or 80 work when a string of panels connected to it contains panels of different wattages and voltages all mixed together? Where would it even begin to function with MPPT?
An MPPT charge controller depends on the voltage and amperage coming in to it and then calculates the optimum voltage and amperage so more amps flow from the controller into the battery bank.
For example, suppose your panels produce 68 volts and 43 amps, but your battery bank is 48 volts, then the charge controller may determine that your maximum power into the battery bank is really 55 volts and 53.16 amps. But this number is always changing in real time as clouds pass and the energy produced from each panel is changed by the environment. The charge controller is constantly monitoring and adjusting the power algorithm. The lowest common denominator usually wins.

I suspect that the new wiring condition either caused an overload of volts, amps or both, probably blew out a capacitor and the LCD display. Maybe an IC too.
I am under the impression that all panels in a string are to be essentially the same for optimal charging results and that just connecting up any king and number of panels in a hodgepodge manner will defeat the purpose of an MPPT charge controller which is the maximum harvest of power from the solar panel array.
pss
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My RE system: 7800 watts in three strings, Flexmax 60 x 3, Radian 8046A, GLSC load center, Mate 3, Hub 10.3 and 900 Amp, 48V Trojan T105-RE battery bank.

Re: How do I add another string?

Postby EMCF on Wed Aug 09, 2017 1:29 pm

Differences in power rating is not a factor in blowing up your charge controller when you connected those additional solar panels. The most important thing is your friend should have configured the total open circuit voltage (Voc) of your additional array to equal or near equal with the existing array. I assume your friend connected them in parallel. It is possible the the total Voc exceeded the designed maximum open circuit voltage of 150vdc. One other thing, the polarity of the new array should have been possibly identified prior to connecting.
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Re: How do I add another string?

Postby Signman on Wed Aug 09, 2017 3:42 pm

All sounds logical if not a bit over my head. Thanks so much for the replies.
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3 x 190w Panels
7 x 250w Panels

Re: How do I add another string?

Postby Signman on Wed Aug 09, 2017 4:16 pm

Another question - Shouldn't the circuit breakers/ fuses have blown before it got to the stage of blowing the Flexmax 60?
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2x300AH 12v sealed valve regulated lead acid AGM Batteries.
6 x 64w Panels
3 x 190w Panels
7 x 250w Panels

Re: How do I add another string?

Postby pss on Wed Aug 09, 2017 4:49 pm

Circuit breakers, if properly installed will trip when the amperage exceeds that of the rated breaker. The circuit breakers really function to protect the wiring from carrying too much of a load (amperage) and then heating up and causing a fire. For the breaker to trip, current in excess of the breaker rating would have to have originated in the panels or be back fed to the panels.
pss
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My RE system: 7800 watts in three strings, Flexmax 60 x 3, Radian 8046A, GLSC load center, Mate 3, Hub 10.3 and 900 Amp, 48V Trojan T105-RE battery bank.


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