Questions about Siemen panels

Aug 20, 2009 06:44 am
Questions about Siemen panels

Hi all, great site.

I have two Siemens M75 48W panels wired in parallel. � 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. � You can see the solar panels and the label below.�  Am I getting about the right output from them?

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?�  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. � The propane heater draws a lot at night also.�  This is in the middle of winter in the southwest(Yuma, AZ) with temps from 35-80°. � I don't know what my watt hours are, but the solar panels rarely charge the batteries fully during the day. � 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: Aug 20, 2009 09:00 pm by Mike Beatty »
46 Posts
Aug 20, 2009 06:57 pm
Re: Questions about Siemen panels

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!
Aug 20, 2009 08:47 pm
Re: Questions about Siemen panels

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.
46 Posts
Aug 20, 2009 09:12 pm
Re: Questions about Siemen panels

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. Smiley
Aug 20, 2009 09:52 pm
Re: Questions about Siemen panels

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?
46 Posts
Aug 20, 2009 10:39 pm
Re: Questions about Siemen panels

sorry. thats a sharp 224 watt module. a pair of those with a tracker and a roll of 00 wire would only set you back 5 grand or so. mostly just joking. mostly.
Aug 21, 2009 12:02 am
Re: Questions about Siemen panels

Aug 23, 2009 09:12 am
Re: Questions about Siemen panels

It would appear that you are reading open circuit. But it looks good.
Typically speaking, ones power usage is the starting point and the PV array and battery storage are factored from there.
If you go here and choose; Average, Annual, Flat Plate Tilted South at Latitude, you will see that the area you mention receives the equivalent of 6 to 7 kW hrs. per square meter, per day, based on those parameters.
This is a fair assessment, in my opinion, of the the number of hours of equivalent full rated power from a PV module if the lower value, in this case 6, is used based on those same parameters listed above. So -
2 x 48 x 6 = 576 watt hours or .576 kW hrs.
In terms of battery storage that would be -
576 / 12 = 48 amp hours
I like to multiply that by a factor of no less than 5. This would help to keep what is used from the battery over night in the top 20% of discharge and maybe give a few nights of reserve power.
48 x 5 = 240 amps hours of battery storage.
For example: Trojan T-105's are advertised as having 220 amp hours of capacity at the 20 hour rate.
I agree with Michael B that a charge controller is essential and that a battery monitor such as the Bogart 2020 is very helpful in understanding the "ebbing and flooding" tide (metaphorically speaking) of power flow within your system.
Plan for the future.
Oh, there is lightning surge protection to consider as well!
« Last Edit: Aug 23, 2009 03:00 pm by Thomas Allen Schmidt »
Aug 24, 2009 12:58 am
Re: Questions about Siemen panels

I was wondering if you were going to show up.  Smiley

Yes, that was 18V open ckt with the panels pointing almost directly at the sun at 3pm.

I uses my toy hauler about 12 - 4 day weekends between Oct an May.

I just fired up my trailer and these are my ~amp draws with different appliances turned on.

Fridge + two air sensors  =  .5A
+ Inverter                      =  .8A
+ 1 light                        = 1.7A
+ Heater, no inverter       = 5.0A
Heater, + Inverter           = 6.0A
Heater, Inverter, +1 light = 7.0A

I'm sure it would go over 10 amps with the heater and TV on.
I guess it would be hard to figure my amp-hours with the heater coming on and off during the night.

When camping, I have been leaving my trailer plugged into my truck with two 12V batteries and it does draw down the truck batteries, but there have been times when the solar panels did bring it up to full charge as shown by the lights on my battery test panel.

Tomorrow, I will try it with the fridge, inverter, and TV on to see if the panels keep it at full charge.

Where would be a typical place to mount the Bogart 2020?  The plastic battery box is on the driver's side so I'd have to find a way to access where ever I mounted it.  Are there less expensive monitors.  These solar panels were given to me several years ago.

So, aside from this meter, would I also need a charge controller.  Are the $30 ones good enough for my 96W solar panels?

Thanks for the reply.

Mike B.
« Last Edit: Aug 24, 2009 04:55 am by Mike Beatty »
Sep 3, 2009 10:35 am
Re: Questions about Siemen panels

Being someone who likes to know what is
happening all the time, I ordered the Trimetric
for my two 48W panels that are wired in parallel.
I do not have any plans to expand my setup.
Just trying to run the trailer genny as little as possible.

I did some testing yesterday and came up with:

1:00 PM, 19V and 6.06A with a clear sky and cold panels.

I then fired up the trailer off grid and got these readings.

CO2 + Propane = .18A                       
+ Fridge   ====  .51A
+ 1 Lite  ====  1.46A
+ Inv/w TV === 6.06A
+ Heater   === 11.00A
Got inverter alarm. 11 amps doesn't like going through meter leads.
The inverter is 300W and is enough to run my 15" LCD TV and digital
converter.  I rarely have the heater and light on during the day.

Will my panels keep up if I charge the batteries with the genny in the morning?
I should be pulling < 5A with just the TV and inverter on.  During the day, I am
away from the trailer for an hour or two at a time, so it gets the full charge minus
the fridge, CO2 and propane sensors.

Should I disconnect my truck batteries when I get to camp and run on
the Trojans alone?
« Last Edit: Sep 4, 2009 06:17 am by Mike Beatty »
99 Posts
Sep 11, 2009 02:55 am
Re: Questions about Siemen panels

A couple of suggestions:

1) From my admittedly stereotypical envisioning of AZ, it's probably dusty.  Keep the panels wiped clean as much as possible.  A haze of dust could diminish power significantly.

2) Get yourself a Maximum Power Point Tracking (MPPT) charge controller.  Right now, with no CC, if you have enough solar in the morning or evening to only produce, say, 10V, then it will do nothing for you.  You can't charge your batteries with 10V.  An MPPT CC will do some electronic magic and boost the voltage (by robbing the amperage) so that you have enough voltage even in low-light conditions to charge your batteries.  This may significantly extend the usable period of the day and improve performance on cloudy days.  A CC will also ensure that your batteries are not overcharged or charged too quickly, thus extending their life and providing better safety against fire or explosion.
Sep 11, 2009 04:23 pm
Re: Questions about Siemen panels

I gonna asked if it is a good idea to use Lemon Pledge on them.  We camp at the Imperial Sand Dunes just west of Yuma, AZ and at times, it can get quite dusty.

I am working on installing my Trimetric 2020, but got slowed down with back problems.  I'm gonna see what that shows before I invest a lot more money into this project.  Like I said earlier, these 2 - 48W panels were given to me.

I think my 2/7/05 T-105s are shot.  I charged, equalized and de-sulfated them and after 2 days off the charger and no load, they were down to 9.6V.

Anybody out there have a used MTTP CC for sale?  I only need one that can handle 6 amps.
99 Posts
Sep 11, 2009 09:06 pm
Re: Questions about Siemen panels

I gonna asked if it is a good idea to use Lemon Pledge on them. 

I wouldn't.  Just glass cleaner or soapy water.
46 Posts
Sep 11, 2009 09:10 pm
Re: Questions about Siemen panels

Aahhh! No lemon pledge. Probably wouldn't hurt anything, but mild soap (dish or car) and water is fine.
You should be looking for a cc capable of aprox. 10 amps. A 6 amp one will be a bit to small I think. Mppt is a great suggestion though. Check out the products from Solar Converters Inc. if you cant find something used for cheap. They make some small, simple mppt cc for a reasonable price.
ps. sorry to hear about your Trojans, sounds terminal...
Sep 12, 2009 09:23 am
Re: Questions about Siemen panels

I was thinking the Pledge would help repel dust..  That's what they promote on their newest version.

I bought a new 10A HQRP PWM CC on Ebay for $30 that said it had a digital LCD display.  The same seller had some that didn't have the display for the same price and when I questioned him, he said they didn't send him the ones with the digital display, so I got out of buying it.

I was hoping someone here here might have a spare one laying around, but will check out Solar Converters Inc.

I'll probably get some Sam's Clubs cart batteries for $73 each when the dune season starts.  I'd get some hydro readings, but they are in a 13x15x12 enclosure and I would have to disconnect them and remove them.  My back would not like that at all.
99 Posts
Sep 25, 2009 10:10 pm
Re: Questions about Siemen panels

Re: Pledge.  If there's some residue left behind which is capable of repelling dust, that residue will probably impair the solar collector.  Just use glass cleaner or soapy water to ensure maximum insolation.
Sep 26, 2009 11:20 am
Re: Questions about Siemen panels

What is the "glass" top coat made of on a M75, 48W Siemens?

How about de-natured alcohol, acetone or M.E.K?
« Last Edit: Sep 26, 2009 11:23 am by Mike Beatty »
46 Posts
Sep 26, 2009 01:19 pm
Re: Questions about Siemen panels

Tempered glass.
Cleaning agents are getting worse, not better. Try a garden hose. Unless they are totally caked with thick dirt, the derate factor will be less than your wire losses.
Sep 28, 2009 12:55 pm
Re: Questions about Siemen panels

Last week, I desulfated x 5, charged and equalized my Trojan T-105s.  Friday, I bought a hydrometer and it took several times filling and draining the hydrometer in each cell to get a good, consistent reading. I couldn't believe it, they all came out 1.275. I equalized it over a week ago.  Does stratification happen that soon?

Trojan says 1.277 +/- .007 @80° and to add .004 for every 10° above 80°. Electrolyte temperature was around 89°.
So, 1.277 + .004 = 1.281 +/- .007 = 1.274 to 1.288. At 1.275, I'm borderline full charge.

A week ago Friday, I took the BatteryMinder off.  The voltage after I took it off was:
3:00 PM 13.31V
3:30 PM 12.86V
7:30 PM 12.70V
9:30 AM 12.66V

This Saturday, it still read 12.66, so I put the BM back on.

I realize that these readings don't show the true load capacity, but at least all the cells appear to be charged the same. There may be hope for these batteries yet.
220 Posts
Sep 28, 2009 02:55 pm
Re: Questions about Siemen panels

 Hi Tomb,

 yep, those batteries sure sound healthy to me. did we ever figure out how/why they got down to that 9.6v level?

 don't be alarmed with that overnight voltage drop from 13.31 to 12.66 that would have been just a surface charge and not counted as our voltage.

 "Should I disconnect my truck batteries when I get to camp and run on the Trojans alone? "
 we did not see this issue addressed. i would recommend that you have your RE system totally separate from your truck batteries. always.

 "Lemon Pledge" just the rain works for my area. otherwise just mild soap and water.

good luck, dave

*Tomb..The other Michael B  .sorry couldn't help it, all in good fun:)
Sep 28, 2009 09:48 pm
Re: Questions about Siemen panels

TOMB...  Took me a couple seconds to figure that out.  Smiley

Don't know where I came up with the 9.7V  Musta had my head where the sun don't shine.

I took the BM off 4 hours ago and it still shows 12.75V. Smiley

I will try running without the truck hooked up, one day off and one day on the next trip to see what Mr. Bogart says.

Just fired up the 5er to see what it draws overnight with the fridge, propane and CO2 sensors running.  It shows -.42 right now.  I just found out that the propane water heater draws ~.60A when fired up.  I only use it just before a shower, and don't know what it draws after the water is hot.  This is not a good test as I use the inverter and TV for several hours during the day and evening/night.

If the panels put out ~4A during the day, the batteries should be charged when the sun goes down and should also keep the truck batteries charged.  There have been times when the trailer battery test panel showed a full charge with the array and truck connected.

Here's a trick I recently learned.  If you have some old glasses with fine scratches, Pledge them.  I tried it on some I use in the shop and the scratches all but disappeared.  Wouldn't this also improve the insolation on a PV panel?  Try it on some old glasses and try to tell me it doesn't help.


Disclaimer and Disclosure

The Alternative Energy Store, Inc reserves the right, within its sole discretion, to refuse or delete any posting or portion thereof, or terminate or block the access to this forum.

The opinions and statements posted on this forum are the opinions and statements of the person posting same, and do not constitute the opinion or act of the Alternative Energy Store, Inc (AltE). The Alternative Energy Store, Inc does not endorse or subscribe to any particular posting. No posting shall be construed as the act or opinion of the Alternative Energy Store, Inc.

Click here for BBB Business Review

McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams
Desktop Website | Mobile Website


Click on an icon to share! If you don't see the method you want, hover over the orange "+".


What can we do to help you?

Please enter a summary
Sorry, the copyright must be in the template.
Please notify this forum's administrator that this site is using an ILLEGAL copy of SMF!
Copyright removed!!