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Old 03-07-2014, 03:07 PM   #1
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calculating voltage loss re: solar panels

do i use the manufacturer`s rated current and voltage to plug into the voltage loss calculator, and use 2x the one way wire run for length of cable.

I got confused, wondering what exactly I should plug in for source voltage : 12, 13.85 or the mfg`s rated V. Got further confused reading recent posts about how the solar panel output could vary depending on battery charge, etc....
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Old 03-07-2014, 03:27 PM   #2
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A solar charge controller is used between the photovoltaic solar panel and the battery.
A Charge controller is an essential component of your photovoltaic (PV) system. The controller maintains the life of the battery by protecting it from overcharging. When your battery has reached a 100% state of charge, the controller prevents overcharging by limiting the current flowing into the batteries from your solar array.
The lower the battery charge the higher the charge rate is regulated by the controller. 10ga to 8ga wire is generally recomended for solar panel installation.
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Old 03-07-2014, 03:35 PM   #3
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I know the feeling of confusion on all this.

Voltage loss is going to happen in any situation. My take is that the loss is better BEFORE the controller than AFTER the controller. The voltage from the panel to the controller can be quite a bit more than 12v in some sun situations, so voltage loss before the controller can still allow the controller to put out decent charging voltages.

That said, if you have one of the portable panels that has a controller mounted on it, you will have to use what the manufacturer lists as the maximum output voltage from the controller to the battery and however much and what gauge wire you want between it and battery to calculate loss,

And it is just the distance of the run not 2x.
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Old 03-07-2014, 04:28 PM   #4
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It is always good to get that controller that Jubal and Eric mention as close as possible to the batteries. If you are within three feet there is not as much concern with the gauge of wire. When you get further away the gauge between the controller and battery needs to be lower in number as you increase the distance.

Coming from the panel I have used 17 volts but there is a great variation based on time of year, temperature and amount of sun. At the minimum you should have 14.8 coming into the controller, more depending on the absorption rate of the controller. Eric is correct, no need to 2X.

In the calculations I have run I have found 75 ft of 14 gauge wire will work, assuming 17 volts and a reduction of amps from the specs of the solar panel. The problem here is there are variables that cannot be controlled...the sun.
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Old 03-07-2014, 04:32 PM   #5
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Those online voltage calculators generally do not say whether to include the total wire length in the circuit or just the one way distance. They must think we are telepathic! We know that all the wire in the circuit affects voltage drop, and must be included in the calculation. Many of the calculators automatically double the wire, thus use only the one way run length for the number to plug into the calculator. Also some of the calculators don't allow you to plug in exact voltage, say 14.8vdc., and only offer 12 or 24 etc. I just use the closest one. The current draw you want to enter accurately, so enter the maximum the controller can put out.
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Old 03-07-2014, 05:36 PM   #6
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I knew there was a reason I bought a generator.
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Old 03-07-2014, 06:40 PM   #7
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I knew there was a reason I bought a generator.
If we are in a campground where generator use is allowed, my Honda generator is so quiet compared to the ones in the big land whales that when I'm inside Blue I can't hear mine right next to our trailer over the noise theirs make.
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Old 03-07-2014, 11:40 PM   #8
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Fortunately, the voltage loss has nothing to do with the voltage coming out of the solar panel... just the current. Yes, the current does change with voltage, but still, it's only the current.
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