Outback V+A limits

adas

Aloha, I am going to add 28 more Sun 205W blems and trying to learn the V+A ratings I should use.
I will use a total of 4 FM80 outbacks that rate at 80amps and 150V max.

I see the specs for the panels "STC" and "NOCT". and each has Two amperage and Two Voltage ratings. What do I use so not to void Outback warranty? I am assuming the listed 18.4 Vp and 11.15 Imp and not the other voltages in the chart??
So I am making 4 banks of 18.4V x 7 panels in series to give me 128.8 V @ 11.15Imp and that should convert a max out amperage of about 55 amps at 26V.

But the most important question is to I have to use Voc as the theroretical imput Voltage? to keep Outback happy?
Here is the link to the Sun panel 205 chart

http://sunelec.com/index.php?main_page=product_info&cPath=5&products_id=60

thanks
Frank

crewzer

Re: Outback V+A limits

Frank,

You need to use STC Voc specs and the NEC 690.7 "maximum voltage" temperature correction factor for your location to determine NEC-compliant voltage.

Where in Hawaii?

You need to use STC Isc specs and the NEC 690.8 "circuit sizing and current" to determine NEC-compliant current.

What is your planned nominal battery voltage for the new equipment -- still 24 V?

I'll be in Baltimore today doing training for a SunWize event, and I'll be at a family dinner tonight.I'll (try to remember to) follow up with you tomorrow.

Regards,
Jim / crewzer

Solar Guppy

Re: Outback V+A limits

The Outback and Xantrex have similar Voltage ranges ... so you can use this online tool to see what your maximum number of panels in series is allowable. For Current the FM80 can handle 80 vs 60 amps on the XW, but that is just how many parallel strings you can connect to the controller.

Select your panel model, select you min/max temperatures and the tool will show you how many panels you can use in series

http://www.xantrex.com/support/xwsizing/Default.aspx

crewzer

Re: Outback V+A limits

Frank,

NEC 690.7 compliant “maximum voltage” for a series PV string is the product of the module’s STC Voc, the number of modules, and the NEC 690.7 temperature correction factor (TCF). The TCF is based on record low temp for the system’s location.

The 2005 NEC TCF for Honolulu’s record low temp of 11 C is 106%. The temperature corrected Voc for six modules in series would be 22.8 Voc x 6 x 106% = 145.008 V. This is just under the FM80’s 150 V absolute limit, and right at the controller’s operational limit.

So, you could do six modules in series. However, this basic string configuration would be problematic. The FM80 is limited to a 2000 W STC array for 24 V applications, and, since each six-module string would be rated at 1230 W, you’d be limited to one string per controller. Additionally, the controller’s efficiency (~95.5%) would suffer due to the wide difference between the array’s voltage and the nominal battery voltage.

Another solution to consider would be series strings of three modules. Three of these “~36 V” strings could be wired in parallel for a nine-module array rated at 1,845 W STC, which is within the controller’s 24 V power limit. The controller would operate at higher efficiency (~97.5%) due to the lower input voltage.

You’d need more and/or bigger wire from the arrays to the controllers. However, this latter approach would allow you to use just 27 modules and only three controllers.

HTH,
Jim / crewzer

mike95490

Re: Outback V+A limits

crewzer wrote: »

However, this latter approach would allow you to use just 27 modules and only three controllers.

Hey - that hurts sales to make customers happy !


--

"Be a Good Citizen and Turn in a Friend"
- Brazil

crewzer

Re: Outback V+A limits

Right!

Regards,
Jim / crewzer

adas

Re: Outback V+A limits

Aloha My internet and fones have been down for 3 days so I could not reply only suffer withdraw pains. Anyway a cupla followup questions:

1: Using high input voltage you would lower the controller effeciency (95.5) vs (97.5) or so for a lower input voltage?.... so is it better to keep voltage in as close to voltage out numbers?
Then I am faced with high amperage from panels to controller. I understand for longer runs (about 50 feet in my case) I would have to almost exponentially choose massive wire and even then it would be hard to NOT justify the 2% controller loss of high vs lower input voltage by keeping the amps low.

2: If I do load up the controller to a possible 90amps out (under full sunshine, hi noon, cold temps, flat batteries, perfect conditions), would not the controller just throttle down the amperage to 80amp and "waste" it? With no side effects?

3: A thot: if I were to use 1/2" copper pipe shielded in pvc pipe for my high amperage runs, it seems much more economical than say 2 ought or so. (I counted the diameter and number of the strands and 1/2" pipe is even thicker.

thanks, Inquiring minds want to know

Frank

mike95490

Re: Outback V+A limits

adas wrote: »

3: A thot: if I were to use 1/2" copper pipe shielded in pvc pipe for my high amperage runs, it seems much more economical than say 2 ought or so. (I counted the diameter and number of the strands and 1/2" pipe is even thicker.

I discovered that "copper pipe" is only about 80% copper, and the rest some alloy materials, so it's not as conductive as it could be. Maybe 3/4" thick wall copper pipe?

niel

Re: Outback V+A limits

a pipe is hollow and not solid or filled in the middle like wire is so the diameter is irrelevant. there are also differences in pipe like m hard or l hard for example. different mixes of metals and even different wall thicknesses. you're better off with wire unless you had no choice at the time for wire handles more current, often comes with insulation, and is more flexible. now i didn't figure it all out cost wise, but i'll bet the wire is cheaper given both with the same voltage drops.

adas

Re: Outback V+A limits

Aloha, yeah, probably will stick with wire, But, flattened copper pipe make great buss bars! And heat up the copper pipe and insert into a PVC "T" and you have a great insulated Buss bar.


frank

tallgirl

Re: Outback V+A limits

adas wrote: »

Aloha, yeah, probably will stick with wire, But, flattened copper pipe make great buss bars! And heat up the copper pipe and insert into a PVC "T" and you have a great insulated Buss bar.


frank

Not sure what you're planning to do with that sort of buss bar, but I'd use Polaris connectors before I used a flattened piece of pipe. Polaris connectors (Crewzer will be along with a link shortly ) are insulated and can be bought in large sizes. Much safer, and code compliant.

adas

Re: Outback V+A limits

Aloha, all. I have a question on the FX80. I know that the limit is 150V and it is advisable to use lower input voltages for greater effeciency But is the 2000W also a limit? Will the FX80 not just trim any Amperage output over 80? I think the reality is that you will never see 200w on a 200w panel running at 24V. So why can you not go to say 2300-2400W string array, because even if you get ideal cloudless conditions at High-Noon when you may get 2400W, you will be putting 27-28V into your batteries which will bring the amperage well under 80 amps. Will you cause damage to the FX80 or is it that you could be potentially wasting wattage? thanks
Frank


BTW I settled on using 36x200 watt panels. 3 banks of 4 series would be nice (90V input)

BB.

Re: Outback V+A limits

As far as I know (which is not much), a good quality MPPT Charge Controller will limit its output based on current and temperature.

So, adding solar panels to the input can lead to some lost energy collection on cool days/edge of cloud effects.

My Xantex GT 3kWatt system has 3.5 kWatts of roof mounted panels (20 miles south of San Francisco, CA).... Only a few times a year does it come near near to the 3,000 watt GT inverter limit... The rest of the time it is around 2,500 to 2,700 watts peak--and I would not have been worried to add another 500 watts (4,000 watt total) to my system on the existing 3kW inverter. There would only be a few times a year where I would appear to lose significant amounts of energy.

The only "limit" would be (that I could see) is if you exceed the PV array input current by a whole bunch, you may need to add a protective fuse/breaker on the panel input of the MPPT charge controller.

Given that you are in a "warm" climate--you too can probably add significant extra panel capacity to your existing MPPT controllers. Monitor their output (when in bulk charge) and see how much more panel you can add to hit the output limit.

Of course, monitor the heat sink temperatures too... It is possible that you get the unit so hot (warm weather/poor air circulation) that the MPPT Controller may limit it maximum output current to less than 80 amps (FM 80) because of its temperature.

-Bill

crewzer

Re: Outback V+A limits

Frank,

I've been away, and also working on a few other projects.

I know that the limit is 150V and it is advisable to use lower input voltages for greater effeciency

The operational limit is actually 145 V.

As the FM80 graphs indicate, “lower” input voltage results in higher controller operating efficiency. This feature may or may not be useful to you, depending on wire length between the array and the controller.

“Fatter” wire does cost more. However, the efficiency gain in the controller may allow for a smaller and less costly PV array. IOW, I recommend you consider this issue from a system perspective, and not just from the cost of wire.

Also note that while the wire should be sized per the NEC (ampacity, conditions of use, etc.) for design and code-compliance purposes, you may want to consider calculating operational voltage drop (and resulting power loss) based on 80% of STC rated Imp array current (i.e., module NOCT specs), as the array will rarely deliver more power.

But is the 2000W also a limit? Will the FX80 not just trim any Amperage output over 80? I think the reality is that you will never see 200w on a 200w panel running at 24V. So why can you not go to say 2300-2400W string array, because even if you get ideal cloudless conditions at High-Noon when you may get 2400W, you will be putting 27-28V into your batteries which will bring the amperage well under 80 amps. Will you cause damage to the FX80 or is it that you could be potentially wasting wattage?

OutBack provides two sets of power limit specs for the FM80: “Maximum” and “NEC Recommended”. The latter set is applicable to code-compliant systems that will be inspected, and is based on OutBack’s interpretation of NEC Article 690.8, Circuit Sizing and Current.

See: http://www.outbackpower.com/pdf/specs/flexmax.pdf

The derating from "Maximum" to "NEC Recommended" is common practice in the industry and in product manuals, although the associated wording can sometimes be somewhat vague.

Article 690.8 requires a 125% STC Isc multiplier to allow for occasional instances where the array operates under conditions that exceed “ideal cloudless conditions at High-Noon”, such as edge-of-cloud events, or reflections from water, ice, or snow, any of which can mean higher than STC-rated current. The 125% multiplier is intended to accommodate these occasional PV circuit current excursions, and PV circuit current calculated per 690.8 are considered continuous per NEC 690.8(B).

An array and controller delivering 2,400 W at 27 V-28 V will deliver 85.7 A – 88.9 A, not including losses in the controller and wiring. I’m not sure that I would agree that these values are “well under 80 amps.” If the batteries are deeply discharged, then 2,400 W at 24 V would mean 100 A.

The FM80 is designed to limit charge current to approximately 80 A. Also, note that the FM80 utilizes a two-stage active cooling algorithm, and the fan operates more aggressively (on/off at lower temps) when the output current exceeds ~50 A.

HTH,
Jim / crewzer

P.S. Link to Polaris Connectors: http://www.polarisconnectors.com/