Solar Charger and Panels - Page 5 - Fiberglass RV


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Old 07-19-2007, 09:14 AM   #57
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My 45 watt solar array is up and running baby!

Complete with hinges; you're an inspiration Frederick!

The instructions mention something about not having the controller wired too far away from the battery...is there a max. length of wire one should stay under from the controller to the panels, or is it simply a matter of upping the gauge?
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Old 07-30-2007, 12:56 PM   #58
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Bought the Harbor freight panels 3 weeks ago and went on a trip to fishing rivers of Idaho (will post later) They seem to work well for my needs. I did put a one way plug on each solar panel and have found out that on a very sunny day I run just one panel to keep our battery charged. I did this so I could test each panel and found out it was fun to see the charge rate of 1 2 or 3 panels.
I would recommend these panels and regulator for people who love to boondock like we do to find off beat fishing and camping.
We are back for a few days and will be taking off again.
Dave and Sharon Tharp
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Old 09-04-2007, 12:02 PM   #59
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My 45 watt solar array is up and running baby!

Complete with hinges; you're an inspiration Frederick!

The instructions mention something about not having the controller wired too far away from the battery...is there a max. length of wire one should stay under from the controller to the panels, or is it simply a matter of upping the gauge?

Greg, All you have to do is keep in mind that the 'smaller' the wire the more resistance there is and thus the more voltage you will loose while passing current through it. SO, use the largest diameter and the shortes length you can live with betweem the controller and the battery.
I use the same solar panels for my Ham Radio Station here in Florida and it works wonderfully. (Let's hope i don't have to use it for real this hurricane season".
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Old 09-04-2007, 09:46 PM   #60
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keep in mind that the 'smaller' the wire the more resistance there is and thus the more voltage you will loose while passing current through it. SO, use the largest diameter and the shortes length you can live with betweem the controller and the battery.
Well, yes and no. The voltage lost is related to both the number of amps you run through the wire as well as the wire size and length. At 45 watts under full sun your solar panels generating something like three amps (45 watts divided by 15 volts = 3 amps). If you connected your solar panel to your charge controller with a 50' cable, here's how much voltage you'd loose:

20 Gauge Wire 3.1 Volts (15v to 11.9v)
18 Gauge Wire 1.9 Volts (15v to 13.1v)
16 Gauge Wire 1.3 Volts (15v to 13.7v)
14 Gauge Wire 0.8 Volts (15v to 14.2v)
12 Gauge Wire 0.5 Volts (15v to 14.5v)

And here are the figures for a 25' leash:

20 Gauge Wire 1.6 Volts (15v to 13.4v)
18 Gauge Wire 1.0 Volts (15v to 14.0v)
16 Gauge Wire 0.6 Volts (15v to 14.4v)
14 Gauge Wire 0.4 Volts (15v to 14.6v)

And for 12.5 feet:

20 Gauge Wire 0.8 Volts (15v to 14.2v)
18 Gauge Wire 0.5 Volts (15v to 14.5v)
16 Gauge Wire 0.3 Volts (15v to 14.7v)

Why does this matter? Since most charge controllers limit the charging voltage sent to the battery to 14.5 volts or less, any volts over 14.5v are lost anyway, so buying heavier, more expensive wire won't improve your solar system performance.

--Peter
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Old 09-04-2007, 10:11 PM   #61
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I use a 10g 20ft pigtail.

The solar panels should be spitting money out at me...
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Old 09-04-2007, 11:41 PM   #62
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Well, yes and no. ...
At 45 watts under full sun ...

Why does this matter? Since most charge controllers limit the charging voltage sent to the battery to 14.5 volts or less, any volts over 14.5v are lost anyway, so buying heavier, more expensive wire won't improve your solar system performance.
Is there any difference when one is not under full sun? Not being too knowlegeable in this area, I would think that in less than perfect conditions, one would want to minimize voltage drop to keep the voltage heading into the controller up to 14.5 to facilitate charging.

Roy
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Old 09-05-2007, 01:40 AM   #63
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Is there any difference when one is not under full sun? Not being too knowlegeable in this area, I would think that in less than perfect conditions, one would want to minimize voltage drop to keep the voltage heading into the controller up to 14.5 to facilitate charging.

Roy
You're confusing the number of volts the panel puts out with the amount of power the panel produces. That's not surprising: the relationship between volts, amps, and watts are kind of complex and non-intuitive.

The voltage from a solar panel and the amount of power it puts out are two different things. Once a solar panel starts getting enough light to produce power it'll generally register close to or the same voltage whether it's in the shade or under full sun. What changes as the sun gets brighter is the number of amps the panel produces at that voltage; the actual power output of the panel, measured in watts, is equal to volts the panel produces times the number of amps produced. So Volts * Amps = Watts.

Using the panel on my trailer's roof as an example, my panel pumps out 17 volts whether it's in full sun or in the shade. Under full sun it pumps out 3 amps for a total of 51 watts of power (17 volts * 3 amps = 51 watts); when it's sitting under the shade tree in my front yard it'll still put out 17 volts, but might well only manage 1 amp for a total output of 17 watts of power.

The sad news is, because pumping 3 amps at 17 volts into my 12 volt battery isn't good for it, my charge controller "down regulates" the voltage it sends the battery to a maximum of 14.5 volts. Doing the math, that means my battery only sees 44.5 of the 51 watts of power my panel pumps out under full sun.

--Peter
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Old 09-06-2007, 08:31 PM   #64
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Why does this matter? Since most charge controllers limit the charging voltage sent to the battery to 14.5 volts or less, any volts over 14.5v are lost anyway, so buying heavier, more expensive wire won't improve your solar system performance.
Peter, you're assuming that the panel can sustain enough output voltage to get 14.5V to the controller. If not, then the loss in the cabling does matter; in 8 of the 12 example calculations, the loss would matter.

Quote:
...The sad news is, because pumping 3 amps at 17 volts into my 12 volt battery isn't good for it, my charge controller "down regulates" the voltage it sends the battery to a maximum of 14.5 volts. Doing the math, that means my battery only sees 44.5 of the 51 watts of power my panel pumps out under full sun.
This sounds like a PWM (pulse-width modulated) controller. It is the most common type of advanced controller, but not the only one. The panel is not likely producing 51 W, since it is not putting out 3A at 17V... it's pulsing at that rate, with zero current in the off times between the pulses. It's only putting out 44.5 W, plus some lost in the controller. If the 17V and 3A are average readings, then it's really pulsing at more than 3A, and the difference between 44.5W and 51W is all controller loss.

My simple controller is just on-off: it's a switch which allows the panel output to connect directly to the battery, or just turns it off. The switching off occurs at something like the 14.5 V level, and it comes back on when the battery drops to some lower level. Again in this case, if the panel can't maintain more than the switch-off voltage, less cable resistance will mean more charging current. Since it doesn't frantically switch on and off, I know the 30W panel is not maintaining anything like 17V of output while connected to the battery... it's not even maintaining 14.5V after a couple feet of wire.

The best controllers are MPPT - Maximum Power Point Tracking. They work as voltage converters, shifting the voltage up or down (and thus the current down or up) to maximize the panel output. An MPPT controller in Peter's 17V/3A situation would convert the panel output voltage down to meet the battery needs, and thus pump more than 3A into the battery, getting the full 51W from the panel... if the panel can really produce that much. I've only read about these... it would cost more than my little 30W panel is worth.
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Old 09-06-2007, 08:41 PM   #65
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Just got my Harbor Freight mailer today ("Postmaster: please deliver between 9-4-07 & 9-6-07")
Hurry! Sale ends September 24, 2007

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45 watt Solar Panel Kit, LOT # 90599
$199.99 regular price: $249.99
plus, there is a coupon to take an additional 15% off on the front page
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Old 09-06-2007, 10:44 PM   #66
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You're confusing the number of volts the panel puts out with the amount of power the panel produces. That's not surprising: the relationship between volts, amps, and watts are kind of complex and non-intuitive.

The voltage from a solar panel and the amount of power it puts out are two different things. Once a solar panel starts getting enough light to produce power it'll generally register close to or the same voltage whether it's in the shade or under full sun. What changes as the sun gets brighter is the number of amps the panel produces at that voltage; the actual power output of the panel, measured in watts, is equal to volts the panel produces times the number of amps produced. So Volts * Amps = Watts.
Thanks for the explanation Peter, I know have a better understanding how the solar panels work.
Although I consider Volts * Amps = Watts to be a simple mathmatical relationship.

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Frederick L. Simson Posted Sep 5 2007, 09:41 PM
plus, there is a coupon to take an additional 15% off on the front page
Thanks Frederick!

How can we get a coupon if we are not on the mailing list?
Are copies available in store or on line?
Seems worth the trip to cross the border ... might even get to check out the Niagara meet at the same time!

Unless of course someone here is crossing the border into Canada ... (hint hint)
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Old 09-06-2007, 10:58 PM   #67
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How can we get a coupon if we are not on the mailing list?
Are copies available in store or on line?
I have seen copies of the ad available in the store, and at one time there were coupons available online, but not at the Harbor Freight site.
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Old 09-07-2007, 12:37 AM   #68
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Harbor Freight 45 Watt Solar Panel Kit
http://www.harborfreight.com/cpi/ctaf/disp...temnumber=90599
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Old 09-07-2007, 02:36 AM   #69
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Peter, you're assuming that the panel can sustain enough output voltage to get 14.5V to the controller. If not, then the loss in the cabling does matter; in 8 of the 12 example calculations, the loss would matter.
My solar panel may differ from other panels, but my understanding is that the amps any solar panel produces will drop off more rapidly than the voltage does when the sun goes down. Curious about that, I tested my panel when it arrived. (This was to both confirm my "new" used panel was in working condition and operating as advertised, as well as to satisfy my curiosity about the functioning of a solar panel.) I measure my panel's output by hooking both leads from the panel to the 10 Amp leads on my multitester and reading the value -- in other words, I shorted the panel out to measure the amps it produces. In full summer sun my panel pumps out 2.99 amps at 17.5 volts (so my panel's output is actually 52.3 watts, right in the middle of the 50-55 watts range Seimens advertises.); under my shade tree it pumps just under an amp, and still registers just over 17 volts. When I flip the panel over at a 30 degree angle over my cement driveway it registers just over 7 volts and virtually no amps at all. This performance mirrors what I have read about solar panel current production (amps) falling off much more rapidly than its voltage. (If you test your panel by this method make sure you connect your multimeter leads to the 10 amp plugs and set the multimeter to the 10 amp test setting BEFORE you touch the probes to the panel leads, otherwise you'll blow your multimeter's internal fuse and it won't measure amps anymore until you replace the fuse. Trust me on this.)

Quote:
This sounds like a PWM (pulse-width modulated) controller. It is the most common type of advanced controller, but not the only one.
You've pegged it. Mine is a Sunsei 10 amp (PWM) controller that lets on-off-on-off pulses of electricity through so the voltage value on the wires going to the battery average out to a maximum of 14.5 volts when charging at its highest rate.

Quote:
My simple controller is just on-off: it's a switch which allows the panel output to connect directly to the battery, or just turns it off. The switching off occurs at something like the 14.5 V level, and it comes back on when the battery drops to some lower level. Again in this case, if the panel can't maintain more than the switch-off voltage, less cable resistance will mean more charging current. Since it doesn't frantically switch on and off, I know the 30W panel is not maintaining anything like 17V of output while connected to the battery... it's not even maintaining 14.5V after a couple feet of wire.
The simple on/off charge controllers I looked at when I was building my system turned on at 13.0 volts and off at 14.2 volts, but remember that that voltage level doesn't represent the voltage of the panel, it represents the voltage of the panel + battery system, which will be lower. As for voltage loss due to wiring, that's easy to calculate if you know the resistance of the wire using Ohms Law, volts = amps * resistance. I used the resistance values and calculator on this web page to come up with my figures.

--Peter
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Old 09-07-2007, 11:58 AM   #70
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...I measure my panel's output by hooking both leads from the panel to the 10 Amp leads on my multitester and reading the value -- in other words, I shorted the panel out to measure the amps it produces. In full summer sun my panel pumps out 2.99 amps at 17.5 volts (so my panel's output is actually 52.3 watts, right in the middle of the 50-55 watts range Seimens advertises.); under my shade tree it pumps just under an amp, and still registers just over 17 volts.
Peter, maybe I'm just misreading your description, but it sounds like you're combining the open-circuit voltage (nothing but the voltmeter connected to the panel output; no current flow) with the short-circuit current (ammeter across the panel output with no other resistance). If you hook up both ammeter and voltmeter at the same time (call your friends and get your spare meter back...), I think you'll see that while delivering 2.99 amps, it is delivering much less than 17.5 volts. The two separate readings can't be multiplied to get power, because they're not happening at the same time, or under the same conditions.

For the mechanically inclined, you can think of open-circuit voltage like peak engine torque, and short-circuit current like redline speed: you can't multiply the two together to get engine power available. The peak torque (voltage) is only available at a lower speed (current), and at the maximum speed (current) much less torque (voltage) is available.

I agree that open-circuit panel voltage does not vary strongly with sun intensity, but the ability to deliver current does.
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