Questions about Siemen panels

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Posted by The other Michael B on August 20, 2009, 06:44:25 AM

Hi all, great site.

I have two Siemens M75 48W panels wired in parallel. Ā Aimed directly at the center of our solar system, I get over 6 amps and over 18 volts at the end of a female connector that plugs into an amp meter panel on my 5th wheel trailer. Ā You can see the solar panels and the label below.Ā Am I getting about the right output from them?

http://www.members.cox.net/mcb56/SolarPair.jpg
http://www.members.cox.net/mcb56/SolarLabel.jpg

Inside the J-boxes, there are factory diodes in both the + and - boxes.

The amp meter panel is wired directly to two 6V Trojan batteries wired in series. On a good day the home built panel gauge shows 5+ amps. I calibrated it using several amp meters.

Do I need a blocking diode on the wire going to my meter panel?Ā I am not using a CC as the propane refrigerator, and water heater control modules and all the air sensors are on all the time. At night, I use an inverter to run my LCD TV, and laptop. Ā The propane heater draws a lot at night also.Ā This is in the middle of winter in the southwest(Yuma, AZ) with temps from 35-80Ā°. Ā I don't know what my watt hours are, but the solar panels rarely charge the batteries fully during the day. Ā Without solar, I had to run my generator several times during the evening/night.

I lean the panels against the trailer and try to keep them aimed at old Sol. The cable from the panels to the trailer is a 15' 12/2 extension cord.

Is there any way to improve or anything wrong with this setup?

« Last Edit: August 20, 2009, 09:00:04 PM by Mike Beatty »

Posted by Michael B on August 20, 2009, 06:57:06 PM

Re: Questions about Siemen panels (Reply #1)

Wow. I guess the first thing i would look to do would be to get a charge controller. This can be very important. Helps to not only charge batteries, but charge them correctly.
18v looks a bit high as per the specs on these modules, but if that is what the meter reads then happy bonus volts to you!
What do the amps read at the end of your wire run? my guess is that the next big upgrade would be to go with a larger wire. extension cord... probably 16g, maybe as big as 14g. at 14g you should start to experience significant losses after about six or seven feet! try like a 10g wire. fatter the better.
what angle do you prop them at? the photo looks pretty steep. this time of year in AZ i would be putting them nearly flat probably not much more than 25* or 30* in the dead of winter. you'd have to check what is recommended for your area. Only other thing is not to let your batteries get too low, and dont let them stay too low. trojans are pretty nice, give 'em lots of love. good luck!

Posted by The other Michael B on August 20, 2009, 08:47:33 PM

Re: Questions about Siemen panels (Reply #2)

Thanks for the reply. I'm also a Michael B.

Did you see the 2nd picture of the label on the back of the panel. It shows 19.8 open ckt volts, so I am actually below that with no load on the panel. The extension cord is 12g and 15' long, not 15". My bad. The panel was just leaning on a bench for the picture.

At the end of the extension cord that plugs into my trailer, I get slightly over 6 amps with the panel pointed directly at the sun. I cut off the male end of the 12/2 cord and hard wired it to the panel junction box. From where I plug into the trailer, there is about 18" of 14g going to the battery terminal on my generator. From there, it is like 0g to the batteries.

It was 3 pm when I measured the amps and volts, and the panels were pointing directly at the sun. When I'm camping, I try to keep the panels pointed as directly towards the sun as possible.

I baby the batteries and keep them in a cooled garage during the summer.

My question is, do I need a blocking diode anywhere going to the trailer? Inside the J-boxes, there are factory diodes in both the + and - boxes.

Posted by Michael B on August 20, 2009, 09:12:14 PM

Re: Questions about Siemen panels (Reply #3)

Hey, i did'nt even notice you were an m b too. right on.
as far as any additional diodes, i dont see why you should need them. stock ones should work fine.
12g wire on a 12v system will be losing more than 2% @ 11'.
15', you'll be at a loss, but probably not a lot.
ever consider upgrading to a tracker with some sharp 224 s or something like that? maybe string it all together with some 00 wire.

Posted by The other Michael B on August 20, 2009, 09:52:08 PM

Re: Questions about Siemen panels (Reply #4)

Based on the 19.8 spec, I would lose about .4V, or about .3V on the 15.9 spec.

I use this with my 5th wheel trailer, so it might get complicated adding a tracker. I've been toying with a way to mount it on the roof and have it pivot so I can aim it at the sun, but I may just end up with a ground base that pivots. I have to consider storing it while in transit also.

What's a 224?

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