125VDC max

Discussion about the Power System PV Combiner (PSPV)

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TNHunter
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125VDC max

Post by TNHunter » Tue Apr 06, 2004 5:36 am

I was wanting to use the PSPV combiner box in my off grid system. I will be using 6 -BP3160 panels wired 2 sets of 3 in series for a 72 volt array. The open circuit voltage of these panels is 44.2 so three in series would equal 132.6 volts @ 4.55 amps. I read that the PSPV is rated only for 125VDC max open circuit voltage.

Can the PSPV be used for this system or should I wire the panels 3 sets of 2 in series? (88.4 VOC @ 4.55 amps) If not, should I use the touch safe fuses?

What does Outback recommend for this system? [img]images/smiles/icon_confused.gif[/img]

wd8cdh
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125VDC max

Post by wd8cdh » Tue Apr 06, 2004 11:44 am

Hi,

The legal way would be to use the touch safe fuses.

If you calculate the 125% for cold temps, you will be over 150V.

How far are you from the panels to the MX60?

Ron

TNHunter
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125VDC max

Post by TNHunter » Wed Apr 07, 2004 1:45 am

I am ~ 100 feet from the MX60. I do want the system to be safe and compliant.

wd8cdh
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125VDC max

Post by wd8cdh » Wed Apr 07, 2004 4:31 am

I would lean toward 3 strings of 2 panels. Of course you would need one more run of wire but it would be code compliant at the coldest temperatures.

The added loss from wiring at the lower voltage would not be much. If you use #6 you would be losing only 2.14 Watts more with 3 strings instead of 2. If you use #8 you would be losing only 3.37 Watts more. If you use #10 you would be losing only 5.35 Watts more.

Ron

<small>[ April 07, 2004, 08:00 AM: Message edited by: Ron Schroeder ]</small>

boB

125VDC max

Post by boB » Wed Apr 07, 2004 8:48 am

Are your batteries 24 V or 48 Volt ?
If they are 24 Volts, then definately go for the 48 Volt array (2 in series) for the 100 foot run.

I see that you are in Tennessee... How cold is it going to get there on average ? Maybe it won't even get to freezing very often. Usually, about 0 degrees F will be required before the Voc gets to about 140 Volts.

Many people use 125 Volt breakers even though the Voc might go to 130 or 135 Volts. Of course many people use 120 Volt AC breakers when their AC line voltage may go up to 130 volts or higher.

boB
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TNHunter
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125VDC max

Post by TNHunter » Wed Apr 07, 2004 9:07 am

I have a 48 volt battery bank. I was wanting to wire these for a 72 volt array to cut down on wire size. I calculated that 2 sets of three in series would have required #6 wire for 100 feet. I guess I will have to go with 3 sets of 2 in series and bump up the wire size to #4 awg and use three of the 15amp breakers.

Are my calculations correct? Any suggestions?

wd8cdh
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125VDC max

Post by wd8cdh » Thu Apr 08, 2004 6:06 am

To calculate typical voltage drop, you have to use typical current (Not Isc x 1.56). Minimum breaker size and wire ampacity at operating temperature is calculated at 1.56 Isc.

I think the panels you are using are 4.55A at the max power point. At 100 feet, that will give you .47 volts drop or about .67% of 70 volts with #6 CU wire. That's only 6.4 watts lost in the wires with 3 strings at 4.55 amps each. I think wires larger than #6 would be a waste of money.

Ron

dgsalkeld

125VDC max

Post by dgsalkeld » Thu Apr 08, 2004 2:17 pm

I am not clear on where you are doing tthe combining, at the house or at the array?
If you are combining at the source then two #1 Cu or two 1/O Al would yield less than 1% V drop, calculated at 13.65 amps and 60 volts. Combining at the house would require 6 # 6 Cu conductors to yield similar V drop as you already know.
#1 Cu THHN costs app 70 cents per foot, # 1/O Al XHHW 41 cents and # 6 Cu THHN 23 cents.
Using Al will require converting (using butt splices) to short lenghts of Cu at terminations that are not AL rated.
Aluminum wire properly installed has a good service life.
If I did my calcs properly, it appears that combining at the source with two 1/O Al conductors would be the most economical method.
I hope this makes sense.
Doug

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125VDC max

Post by Kent Osterberg » Sun May 09, 2004 3:57 pm

The open circuit voltage will reach 140 volts with the cells operating at 50F. In full sun with a light breeze the ambient temperature would need to be around 10F for this to happen. There are other times it could happen to: If it is overcast or windy, the 140 volt limit will be reached at higher ambient temperature. Or, first thing in the morning when the cells are still cool and the sun hits them, the open circuit voltage could go over 140 volts. It's probably best to wire the array for 48 volts and avoid any possibility of exceeding 140 volts.

I agree with using #4 copper wire after the combiner for the 48-volt configuration. At full power, you'll loose about 9 watts and 0.8 volts. The 72-volt configuration with #6 copper wire is more efficient and cost less. That would be very attractive if not for the difficulty with 140 volts.

Robin Gudgel

125VDC max

Post by Robin Gudgel » Tue May 18, 2004 8:04 pm

There have been numerous questions regarding the use of our OBPV breakers and the associated ratings. They are UL listed for 10,000 amps interrupt at up to 80 volts DC. They are IEC rated for 3000 amps interrupt at up to 125 volts DC. UL is going to re-test them for 125 volts DC in July. ETL is going to test them at 150 volts DC next week. Our favorite code fundamentalist that writes for Home Power lodged a complaint with ETL about the breaker ratings. This has caused ETL to re-look at the PSPV and the breakers. They are now requireng all sorts of testing and even listing to a new UL spec that I have never heard of. The end result of all of this will probably be the same box and breakers we have been shipping for 2 years, but with new stickers. There will also be a price increase due to all this activity. I don't feel that we have made any real advances here, but we are all going to pay for it!

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