48vdc and 12vdc from same pv array

icarus · November 2007

OK Guys here's one to ponder.

I have 2 small pv systems. I am currently doing some upgrades There are 2 battery banks in two different buildings ~200' apart, each serving different loads. What I want to do is this: I want to connect 5 12vdc panels in series/parallel and send 48vdc to a MX60 ~150' apart. I want to pull 12vdc off of two of these panels to a simple pwm controller. The idea behind this is that all 5 panels would contribute to the big loads on the MX 60 as long as the smaller bank was fully charged. I made up a drawing to show how I would wire it. (Apologies in advance for the crudeness, I am not very computer litterate!)

Any input would be appreciated.

(I just discovered that my file is to big as pdf. I'll have to figure out how to reformat it into something else. 'told ya I wasn't very good at this)

Icarus

mike95490 · November 2007

Re: 48vdc and 12vdc from same pv array

1) attachments, a simple line drawing, scanned at 100 DPI, saved as a JPG with 40% quality (60% compression) will be pretty small, likely small enough to attach.

2) Parallel : Must have identical strings to be paralleled. 6 panels would work, 2 strings of 3, but that's not quite 48V yet. 1 String of 4 or 5 in series could feed the MX60 (if you are still below the max input voltage. As I understand, to reduce internal losses you want to be running at lower voltages, but still within the max input Voltage.

You can't sneak power off 2 panels and send it somewhere else, it will starve the other controller. Possibly look into a 48V -> 15V DC-DC converter, run off your 48V bank, to power your PWM controller. You will have conversion losses, but will maintain a fully charged 12V battery. example: http://www.vicr.com/ 48V -> 16V, 200W converter :
VI-200 (full size): VI-2N2-EW
http://cdn.vicorpower.com/documents/datasheets/ds_vi-200.pdf $125
or this option on ebay:
QTY2 Vicor DC Converter in 48V 116.2W out 17V 100W Item number: 170171610183 $25 and only 2 hours left, with 0 bids.

PM:

Have attached your photo, after compressing it to 40%

You can't sneak power off 2 panels and send it somewhere else, it will starve the other controller.

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

I will figure out how to post the line dwg. We (Susan) drew it as a word file then I tried to post it as a PDF. She will have to turn it into a J-peg. (I don't have a clue as to what that s#^&t is. I am under the miguided notion that when you push a computer button it should DO what you want. ERGG!

Will post later.

T

mike95490 · November 2007

Re: 48vdc and 12vdc from same pv array

JPG is a picture format, as is GIF or PNG Print your paper, and scan it.

Valid file extensions: bmp doc gif jpe jpeg jpg pdf png psd txt zip

found under
Reply,
Advanced Reply
Attach Files

westbranch · November 2007

Re: 48vdc and 12vdc from same pv array

try opening your doc in Word and do a 'save as', then choose from the types of file types available on the bottom line.

PDF's are usually used for files you do not want anyone to make changes to.. requires Adobe acrobat reader to open usually ...

Eric

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

Eric,

Tried it last night. Still too big. I'm not sure I understand as it is a simple line drawing. I suffer from a severe luddite syndrome when it comes to this technology. I don't assume it can do anything and therefore I'm seldom disapointed when it doesn't. On the other hand I'm surprised and pleased when I can. Susan on the other hand has a Masters Degree in Comp Sci. (She gave it up in 1985 to become a book binder) Because of her experiance she EXPECTS the machine to do something and is disapointed when it doesn't! She then spends hours making it work, when 2 minutes doing it by hand would solve the problem. My windows 2.0 machine did everything I wanted it to do and never crashed! I did all th same things on my last pc, only this time it could do it in Swahili!. Except it crashed all the time. I'm not using a Mac and all I do (can do!) is write, surf and do keep my pictures! God help me if you want to see them however.

I'll get is somethime.

Icarus

n3qik · November 2007

Re: 48vdc and 12vdc from same pv array

If you want, email me the file. I can host it on my Comcast account and link it from here.

n3qik at XXXXXXXXX

sub @ for at and . for dot

This is to keep the spam bot working OT:p

Edit: received the file.

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

I sent it to Eric who was going to reformat it. (Boy, do I feel like a doofus!)

I'll send you a copy. (I'm note sure this is worth everyones trouble, but my thanks are there.

Icarus

n3qik · November 2007

Re: 48vdc and 12vdc from same pv array

You ask for help. The members of this form are going to try our best.

Here it is: http://home.comcast.net/~n3qik/Solar/solar_panel_design.pdf

As a jpeg: http://home.comcast.net/~n3qik/Solar/solar_panel_design.jpg

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

With thanks to all,, the link is in the previous post. It doesn't seem to work if I link it here. (I told you all I was a doofus!)

Here is the original post so you don't have to go to the bottom,

48vdc and 12vdc from same pv array
OK Guys here's one to ponder.

I have 2 small pv systems. I am currently doing some upgrades There are 2 battery banks in two different buildings ~200' apart, each serving different loads. What I want to do is this: I want to connect 5 12vdc panels in series/parallel and send 48vdc to a MX60 ~150' apart. I want to pull 12vdc off of two of these panels to a simple pwm controller. The idea behind this is that all 5 panels would contribute to the big loads on the MX 60 as long as the smaller bank was fully charged. I made up a drawing to show how I would wire it. (Apologies in advance for the crudeness, I am not very computer litterate!)

Any input would be appreciated.

Icarus

n3qik · November 2007

Re: 48vdc and 12vdc from same pv array

I was uploading new file, that maybe why.

Now your problem.

The panels are how far from each building?
How much current load at each building?

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

The load from the smaller bank seldom excedes 7 amps 12vdc, and runs about 2-3 amps, for 3-4 hours a day, but only for a few weeks in the summer. It is ~20' from the panels.

The load on the bigger bank never excedes 10amps 12vdc, ~20amp/hours/day year round. It would be located ~100' from the panels.

My dillemma is I have better sun at the location nearer the smaller batteries. If I run 48vdc from there I get an additional hour or more of sun per day in the winter and several hours in the summer. Additionally being able to use the capacity of the "extra" panels 50 weeks a year on the big system without having to take stuff apart and put it back together to use the smaller system.

Icarus

westbranch · November 2007

Re: 48vdc and 12vdc from same pv array

Tony what about a double throw switch on one panel? summer feeds the small bank, winter it feed the larger bank.

Eric

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

Eric, once again, not a bad idea. If I did that, can I still run the five panels 2 in paralell and the rest in series to make 48vdc?

tony

westbranch · November 2007

Re: 48vdc and 12vdc from same pv array

I'll leave that one to the experts like Crewzer or Niel.

My idea was that you could have all the panels in the best spot and in winter throw the switch and add the 5 th panels' output in series and let the CC figure it out as to input V and output V. All within the equipments limits etc etc...

Eric

n3qik · November 2007

Re: 48vdc and 12vdc from same pv array

Just a off the wall suggestion.

Series all 5 panels, this will give you about 60+ VDC @ the current ratting of the 4 55W panels. Feed this into the MX60 at it current location ( winter loads ). This will charge the 4 L-16's. Now run a new wire ( 10 AWG or 8 AWG )from the L-16's to the summer load. Remove 12v PWM CC and the 2 T105's as they are not needed, as you will get the 12VDC from the L-16's batteries. You could sell the CC and t105's batteries and get 2 more L-16's.

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

The problem with this solution is that the loads are at opposite end of the island. The panels are currently in the center, with the batteries close. The loads then head west to two buildings, 1 ~50' away, a second ~150' away. The distance is already to far if I have more than a 5 amp load.

The new building is 200' further east, making the loads to the west building ~300' I could (should) invert at the central location, but there are some local reasons that I don't want to. I think I will continue to give the t-105's a single panel and CC, and send the 48vdc panel to the MX 60. (At present I don't have a MX 60 but am considering the possibilities.

Icarus

crewzer · November 2007

Re: 48vdc and 12vdc from same pv array

Tony,

I don’t see how the system in your drawing could possibly work.

An alternative might be to build two sub arrays, one 36 V (three modules in series) and the other 12 V/24 V (two modules wired in parallel or series). Using a voltage controlled switch (VCS) or a Morningstar relay driver (MRD), you could have the smaller array send 12 V to the PWM CC and the T-105’s, and the 36 V array would connect to the MX60.

When the T-105 voltage is high enough for long enough, the VCS or MRD could switch the 12 V array to 24 V and insert it in series with the 36 V array to make a 60 V array (all via DC-rated relays).

I suspect this approach would work technically, but it might be a bit clunky. And, the cost of the wire, VCS/MDR, and relays might make it worthwhile to just buy a dedicated module to charge the T-105’s.

Stuff to think about…

Regards,
Jim / crewzer

n3qik · November 2007

Re: 48vdc and 12vdc from same pv array

From post #12 I got the impression there was 120' between buildings. Oops. 300' would = a 2 AWG wire. NOT!!

I think crewzer has the right ideal about two sub arrays at each site.

icarus · November 2007

Re: 48vdc and 12vdc from same pv array

Jim,

I was wondering whether you were going to weigh in on this. (I'm glad to hear from you).

The fact of the matter is what I am looking for is a solution in search of a problem. While I like the elegance of your solution it is way more technology than I need for this situation. If the buildings were closer together I could eliminate the smaller bank. I should just invert and send 120vac to the other buildings. The problem is I have 12vdc loads in both locations. (The other problem is that the users of the smaller bank is NOT me and therefore creates some other dynamics if you understand).

I think I will go back to my original plan. 2 basic systems, 1 for me with 220 watts of panel and the l-16' and the 1 55 watt system for the T-105's. We have been using the t-105's for 10 years so I guess if it aint broke, don't fix it!

Thanks one and all for your input. I'll keep looking at these ideas.

Tony

westbranch · November 2007

Re: 48vdc and 12vdc from same pv array

tony, I guess all you need to calculate is ANY benefit from moving the panels to the sunnier location vs the work you have to do to benefit form the change... Clear ? as Mud?... volts/amps vs time/effort....VS peace and harmony among the masses...

cheers,
Eric

48vdc and 12vdc from same pv array

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