# BBear with me I have another solar panel questi



## steff bugielski (Nov 10, 2003)

Some of you were kind enough to answer all my dumb questions before.
Can I ask some more?

OK I have 8 solar panels-Siemens SP75
They say max volts 17.5
75 watts

I Had them hooked up I guess in series parallel, that's how they were when I got them.
But we were getting almost 50 volts but only 200-300 watts.
As i understand in series / parallel I should have increased the volts and the watts.

So we went back up and wired each bank of 4 panels in parallel then the two banks in series. 
We were getting 20 volts from each bank of 4 and 40 + volts from the two of them.

If the panels are rated for 12 volts, max 17 why are they giving off 20. I thought they would put out 6 v, 12 v or max 17.5 . I can see if they are putting out 24 then I have added the 6 volts 4 times, series, right?
or parallel, 12 volt reading max 17.5 not 20.

The two banks giving 40+ means I do have them wired in series, but where is the 20 volts coming from.
Sorry for the dumb questions but nobody else knows anything about them.


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## no1cowboy (May 2, 2004)

your panels are 12v the 17.5 is open voltage and it is possible to read a higher voltage
when you wire in series your multiplying the voltage, when you wire parallel your multiplying the amps but the voltage stays the same, if you have a 12v battery bank and 12v regulator than wire your panels parallel and your good to go


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## 12vman (Feb 17, 2004)

Not all vom's (volt/ohm meter) are the same. Another volt meter may give you a different reading. The open circuit voltage (Voc) can go as high as 21.7 volts @ the 12 volt configuration.

http://solaralberta.ca/SOCIETY/TRAILER/Siemens_SP75_pvpanel_ds.pdf


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## steff bugielski (Nov 10, 2003)

OK. I am trying real hard to get this right. The only person willing to help us is my friend the plumber. So you are it.
I have hooked up the panels, 4 of them, in series parallel. i am getting 8A-34V and around 250W.
Now how can I double the watts and amps with out increasing the volts. That is what I want to do right? i have a total of 8 panels and 8 batteries.
Also got a link for the three different wiring methods?


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## steff bugielski (Nov 10, 2003)

The 20V is not enough to charge the 24V batteries correct?


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## 12vman (Feb 17, 2004)

Take two of the panels and make a series circuit. Do this with all 8 of them seperately. You should end up with 4 pairs of panels. (connected in series) Each series "circuit" or pair of panels should have a positive and negative lead coming from them. Now you want to "parallel" all 4 pairs of panels. Connect all of the positive leads together to one point and do the same with all of the negative leads also. This should give you the required voltage to charge a 24 volt battery.

To series 2 panels, take some wire and go between the two and connect the wire to a positive connection on one panel and connect that same wire to the negative of the other panel. This will series the panels. The positive and negative connections that are left unused (positive on one panel and negative on the other panel) is now going to be your output to the charge controller.

When you series panels, the voltage doubles but the current remains the same as one. When you parallel panels, the voltage remains the same as one but the current doubles.
When connecting in series, you will be charging a 24 volt system. When connecting in parallel, you will be charging a 12 volt system.

You mention 8 batteries.. Are they 6 volt batteries or 12 volt batteries? What is your goal.. a 12 volt system or a 24 volt system? Do you have a charge controller? What voltage does it operate at? We need more info..


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## steff bugielski (Nov 10, 2003)

Sorry, I have 8- 6volt batteries. Goal is 24V system. Yes charge controller is 12 or 24, set on 24.

One more question. Specific gravity.
Does the specific gravity go down as the battery is discharged?


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## idahodave (Jan 20, 2005)

As you wire the panels it would be a good idea to check each one. 

Measure the voltage with no load, should be about 21v and then the current. Hook up an amp meter that can read to around 10 amps (most do) and you should read about 4 amps. Each panel should read the same. 

Make your measurements with the same sun conditions or the results will change.

The 17.5v max is the voltage at which the panel delivers maximum power, not the maximum voltage out of the panel.

As 12vman posted, you will need a charge controller to prevent overcharging the battery bank.

The panels are rated to produce a total of 600 watts, but only on a bright sunny cool clear day with the sun directly overhead. Expect to see less.


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## steff bugielski (Nov 10, 2003)

Thanks guys.
I will do as 12vman says today.
Yes i have a charge controller, I have everything. It was all given to me.
8 panels, 8 batteries, charge controller, Inverter, DC disconnect and all wires and everything.
Now if only that guy had stuck around to show us how to hook it all up.


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## 12vman (Feb 17, 2004)

This is how you should connect your batteries. With 2 banks of 24 volts.

Hope this helps..


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## steff bugielski (Nov 10, 2003)

Yes the battery bank is like you show but I am still having problems with the Watts. I wired as you said. I now have two sets of 4 panels in series. Each 2 panels read 40V. 4 panels together read 40V. All 8 together read 26V 240W, down at the controller.
Is the controller giving a true reading of what is coming in from the panels?(trace C40)
What am I doing wrong?
I get this right I am going to bake you all a virtual apple pie.


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## SouthernLiving (Sep 16, 2008)

Most likely you have a wiring error at the panels, or a bad panel. 

How far are the panels from the controller. You will see voltage drop between the panels and the controller due to wire resistance. The greater the current and the smaller the wire the larger the drop. Wire size may need to be increased.

Also, the wattage is going to remain fairly constant regardless or your wiring scheme (12V or 24V). Power(W) = Voltage x Amperage. The parameters you have to play with are the V and A.

Like Idahodave posted, the chances of you ever seeing 600W from a 600W rated system are low, especially in your region.


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## 12vman (Feb 17, 2004)

If you're seeing 26 volts at the charge controller, I'd say that's almost normal. The resistance of the battery(s) is going to pull the voltage down. You will also find that the voltage you see on the panel side of the controller will be real close to the bulk/float voltage settings that the controller is adjusted to, depending on what mode the controller is in at the time. (after the battery has accomplished a good charge) The controller will shunt the voltage/current down to protect the battery from overcharging and dissipate it into heat or into a diversion load, depending on how the controller is configured. If it's just being used as a controller, the fins at the top will warm up a little. This is normal.

Also, as SouthernLiving stated, if the wiring between the charge controller and the panels is too small, you will have loss, especially under load. (while charging)


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## steff bugielski (Nov 10, 2003)

We are using a mix of #12 , #14 and #10 on the panels themselves. We are using #10 wire, rated for 30A, going from panels to the controller. #6 from the controller to the battery. #04 from the batteries to the disconnect and the inverter. It is about a 30 foot run to the controller.
Should we use bigger wire? we have it on hand.


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## 12vman (Feb 17, 2004)

By using this chart and remembering that it shows a "one way" run, dealing with around 25 amps, you should be using 3ga. wire to keep the losses below 5%. (by doubling the distance on the chart) from the panels and the charge controller.


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## steff bugielski (Nov 10, 2003)

Well we have been watching the watts climb up to 400+ so I am guessing we have it wired right. We might change the wire. 
I am sorry to make you type DH doesn't like doing it either, why you must deal with me.
I thank you so very much for all your help.


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## 12vman (Feb 17, 2004)

Ahhhmm.. Where's our pie?


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## idahodave (Jan 20, 2005)

Great news!

I wouldn't change the wire...at 25 amps the wire is dissipating about 10 watts. Bigger wire will not add this loss to your load with the C40 controller. You need a power point tracking regulator like an Outback MX60 if you want to recover the loss by going to a bigger wire. The panels act as a constant current generator, so as long as you have the excess voltage from the panels, larger wire wont help much (might add a few watts at sun up and down).

400+ watts is a good number.


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## idahodave (Jan 20, 2005)

I got carried away with the wire from the array....the wire that could be bigger is the #4 to the inverter. It needs to be as short and as big as possible, especially if the inverter is a high power one.


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