Wiring PV panels in series

[Phssthpok]

Tried searching, but apparently I'm not too good with selecting search parameters to net the results I seek. :/

I have several 12v PV panels (six 15w, two 64w panels, mixed Mfg.) and I just recently lucked into an unused BPSolar 50watt panel (http://www.southwestpv.com/Catalog/PDF/BP_850_840.pdf)  for $100. Unfortunately it's a wired for 48v nominal output.

Is it possible to wire (2)sets of three 15w panels in parralel, then wire each of these sets in series with each of the 64w panels to yield a nominal 48v, and THEN wire all that in paralell with the BP panel without frying my 12v panels?

If so I was thinking about running the output through A DC/DC converter like this one:

http://www.trcelectronics.com/Meanwell/sd-350d-12.shtml

Then run the output from that into my existing 12v Charge controller/battery bank.

Thoughts?

[Nando]

STARTING from the end

The 12 volts converters are designed to have stiff (low impedance) voltage sources.

No good operation if the solar panels are feeding the DC/12 V converter.

So no good for your purpose !!!

NOW SOLAR PANELS

Panels with different power and/or voltage for paralleling or serializing.

You may parallel panels with the same voltage and different current capabilities.

Same voltage = Vmp = Volts at maximum power point.

If they have different Vmp, the ones with lower Vmp will have reduced current capabilities ( This if you are using a good charge controller).

If you are using a general controller, like the C40 the currents will be saturation current at lower voltage as defined by the battery load.

You may place in series panels with the same current capability ( they may have voltage differences).

If you place panels in series with different current capabilities, the string will have the current of the panel with least current capability.

Better think another route

Nando

[craig110]

Wow, nice score on getting that panel for only $100!!!  I'd recommend against doing what you proposed, however, as you'll end up with a lot less useful power than you might think.  Three things to consider:

1 - Right now you have (6 * 15) + (2 * 64) = 218 watts.  Putting 3 of the 15 watt panels and 1 64 watts panel in series will give you 48 volts, but the amperage will be limited by the smallest link in the chain which is the 15 watt panels that can only handle a nominal 1.25A.  That means each string gives you 48 volts at 1.25A, or 60 watts.  Two of those strings gives you 120 watts, so already you have lost almost half of the power.  Paralleling these strings with the 50 watt panel you got gives you 170 watts max which is 48 watts lower than where you started.

2 - That 12vdc converter page doesn't have really detailed specs, so a major question is whether it converts the total power or merely the voltage.  For example, if you give it 48v at 3.54A, does it put out 12v at 14.16A (converting the 170 watts of power) or merely 12v at 3.54A (converting just the voltage)?  If the latter, it sure wouldn't be a good conversion. ;-) Even if it does convert all the power and so converts the input to 12v / 14.16A, that output figure presumes a 100% conversion efficiency which the device won't have.  You can probably figure on a 5-10% loss in this device.

3 - Last (and my apologies if it sounds like I'm piling on at this point), if the 12vdc converter does its job and puts out 12.0 volts, your batteries won't be charged.  12 volt batteries typically take up to 13.5+ volts to fully charge, and the batteries can't charge beyond the voltage that is being given to them.  So, if the converter limits the output to 12.0 volts, the batteries will never charge beyond that point and will top off at about a 50-70% charge (rough number as it depends upon the particular model of batteries).

What might work a lot better is either to sell the panel on eBay (it should go for around $200-250) and pocket the difference or, perhaps, offer to swap someone the 48v panel for an equivalent wattage 12v panel.  (Like me, for example.  I have an extra 40-45watt 12v panel and am switching my whole setup over to 48v...  ;-)

Craig

[Phssthpok]

The DC/DC convertor page DOES have a tiny little link to a PDF Spec sheet:

http://www.trcelectronics.com/Meanwell/pdf/sd350.pdf

This sheet shows the converter as putting out 29.2A max at 12v., with output adjustable from 11-16v (which is why I concidered this particular unit).

I'm not against selling or trading, though I fear shipping would be a logistical nightmare.

[Nando]

I am quite familiar and as well I have designed the in my job.

The DC/12 converters may try to use as much current as possible, within its capability.

What type of charge controller do you have that you want to couple to the DC/12 converter ?.

Nando

[Phssthpok]

It's a Collins & Associated Inc. MREG16 charge controller/system monitor (which I can't seem to find any info on ). All I know is the guy I bought it from (as part of a kit with 2 US64 panels and 2 Trojan T-125's) bought it just before Y2K to outfit his 'bugout buggy'. Since I'm NOT an HTML geek I'll just post a link to a photo (dun wanna incur the wrath of the editors!)

 http://i2.photobucket.com/albums/y32/Phssthpok/trailer012.jpg

It's a really basic unit (the faceplate is screwed onto a square outlet box, like you'd find nailed to a stud inside a wall), but as you can see it has some system monitoring capabilitites and will carry 16amps max.

DOH! ....I just realized that I'm already close to my max amps with my current panels!

I guess this is all moot!

Looks like I'm going to have to start looking for a good MPPT CC now. :/

Oh well...I still learned a few things (like the amperage 'bottleneck of teh 15w panels).

If anyone out there can dig up some info on this C&A controller I'd sure like to have it.

[Nando]

The photo shows a couple of web links not readable, check them and see if you can get enough info.

Nando

[craig110]

How about sending me an email at craig_y <at> pobox <dot> com since in my conversion / expansion it looks like I might have an extra Xantrex C40 as well.

Craig

[who8myrice]

wow, great find for that 50watt panel, $2 a watt! what site did you buy it from? i clicked on the link and it only opened a .pdf file