Solar Charger and Panels - Page 6 - Fiberglass RV


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Old 09-07-2007, 12:00 PM   #71
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..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...
Thanks for the reminder of these cutoff levels, Peter; I think those are roughly the same limits as my controller, and simple automatic battery chargers.

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...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.
But it is the panel voltage under the operating condition of being attached to the battery. The panel's voltage depends on the current passing through the panel, due to internal resistance, just as a battery's output voltage drops while it is delivering high current, and comes up to a higher level instantly when the current stops. So my "30W" panel puts out close to 20V in full sun when open-circuited, but when I connect it to a battery to be charged it delivers a couple of amps at a lower voltage determined by the battery's state of charge and internal resistance; the intervening controller sees that voltage is less than 14.2V, and stays on. Eventually, the battery's internal voltage comes up with charging, the resulting voltage at the terminals rises as the panel puts out more voltage and less current, and the controller shuts off at 14.2V.


Anyway, in a real panel-and-load combination, I would expect the operating voltage to be easily less than the controller's cutoff or controlling level, and so it seems that wire resistance both limits charge rate and dissipates energy.
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Old 09-07-2007, 12:28 PM   #72
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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.
A meter on the high-current setting should have extremely low resistance. An ideal ammeter has no resistance at all, but realistically it needs enough to produce an accurately measurable voltage internally... I just checked two of my (cheap digital) meters against each other; I measured the resistance with one (set to various ohms ranges) across the terminals of the other (set to various amps ranges). Meter resistance (of the meter set to a current range) in each case varied from about 2 ohms (on the highest low-range current setting of 200mA) to about 1000 ohms (on the lowest current setting of 200 microamps), and was too low to read (less than or about equal to 0.1 ohms) on the 10A setting (and using the 10A terminals).

To sustain 17.5 V across the ammeter at a current of 3 A, the meter would need to have about 6 ohms of resistance in 10A mode - I certainly hope it doesn't have that much, which would cause major interference with the operation of the circuit being measured.

I'm not questioning Peter's observed current - that's interesting information. It's just that the characteristics of the meter ensure that this is nearly a short-circuit current, and does not occur in combination with the open-circuit voltage.
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Old 09-07-2007, 12:41 PM   #73
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Ok, Brian - Peter, great info but you guys lost me about 4 threads up.

In laymans terms if I can find the 15% off coupon and go get the Harbor Freight Panels for $169(pretty screaming deal) will they work well with my Group 27 deep cycle wally special battery right out of the box or will I need something else in addition to what is included?
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Old 09-07-2007, 02:13 PM   #74
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Ok, Brian - Peter, great info but you guys lost me about 4 threads up.

In laymans terms if I can find the 15% off coupon and go get the Harbor Freight Panels for $169(pretty screaming deal) will they work well with my Group 27 deep cycle wally special battery right out of the box or will I need something else in addition to what is included?
The Harbor Freight system will charge your batteries just fine, though you'll need to make some adjustments to what lights and appliances you run when you boondock. (Things like using LED lights instead of the 12v incandescent bulbs most RVer use.) Gina's article on going solar has lots of good advice & ideas. The only think I'm not sure about is the charge controller that comes with the panels; the reviews I've read suggest you should buy a different charge controller.

Brian and I are being nerds; he's giving me something to think about and some more experiments with electricity to perform. With a little luck my valued mentor will teach me something.

--P
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Old 09-08-2007, 07:48 AM   #75
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In laymans terms ... will they work well with my Group 27 deep cycle wally special battery right out of the box or will I need something else in addition to what is included?
Greg,

It should work OK right out of the box, start back at the beginning of this thread to see what others have done.

I don't know how your system is wired, but you might want to check the diagram in this thread and see where a fuse is placed on the +ve line between your battery and the rest of your wiring in the trailer.
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Old 09-08-2007, 08:01 AM   #76
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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 you friends and get you 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.
Considering this thread started off discussing the Harbour Freight Panels, the manual is online which gives the specs below.


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Old 09-08-2007, 12:57 PM   #77
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Excellent find, Roy!
Such a radical idea... reading the manual

I downloaded the whole manual (over 8 minutes of dial-up ). Although Roy has already extracted the only real technical content for the panels, this setup does have an interesting controller/meter/adapter box, and I think this is a good opportunity for anyone considering buying the setup to have a look to see if it's what they want.

The Harbor Freight specs include:
  • Peak Voltage - 23.57 OCV (Open Circuit Volts)
  • Panel - 15 watts per panel, 14.5 volts output (working)
  • Nominal Voltage - 14.5 volts battery output
In other words, placed in full sun with no load (open circuit, zero current) you should measure 23.57 volts from the panel, but the 15 watts is produced at 14.5 volts, and just over one amp, which is the condition normally encountered near the end of charging a battery.

My guess is that Peter is seeing a lower open-circuit voltage on his panel because he's not sitting in an equatorial desert at high noon on a perfectly clear day...
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Old 09-09-2007, 08:18 AM   #78
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Excellent find, Roy!
Such a radical idea... reading the manual
Thanks Brian,

I got one better for you, and it is a real big download (1.2 M. Charlie C posted yesterday about the Coleman solar panel deal at Costco. That includes the Phocos charge regulator (manual onlline here), they just announced a new remote LCD display that works with this controller which displays panel current, load current and battery voltage.

I've got some questions that I'll be asking you and Peter about this which really should be in topic on its own in another area since this discussion has strayed Frederick's original topic.

And from what I see on the bottom of page 4 of the HF maual, Peter's readings might also be affected by the fact that PV panels can experience a 20% degradation within the 1st six months.
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Old 09-09-2007, 11:43 AM   #79
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...I've got some questions that I'll be asking you and Peter about this which really should be in topic on its own in another area since this discussion has strayed Frederick's original topic...
A separate thread sounds like a good idea. The Moderators could even move many of the recent posts in this thread to a new one, for that reason... maybe called something like "Solar Panel Performance and Wiring".
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Old 09-09-2007, 11:55 AM   #80
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...the Phocos charge regulator... just announced a new remote LCD display that works with this controller which displays panel current, load current and battery voltage.
That dislay looks like a nicely packaged unit. The termination block can mount on a DIN rail, which will be familiar to many industrial electronics users. The controller can be mounted to a DIN rail, as well.

Hey, Per, you've got enough stuff in your trailer (and change it enough) that serious equipment management options might be of interest. Ready for DIN rail mounting?

The meter shows panel current and "load" current separately, because the associated controllers are intended to have the loads (your trailer's lights, fans, pumps, etc) connected through the controller, not directly to the battery.

It is not, however, a serious battery monitor: it doesn't keep track of charge into and out of the battery, so it can't act as a battery "fuel gauge".
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Old 09-09-2007, 12:04 PM   #81
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...And from what I see on the bottom of page 4 of the HF maual, Peter's readings might also be affected by the fact that PV panels can experience a 20% degradation within the 1st six months.
I noticed that, too...
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Originally posted by HF Model 90599 Manual
[b]Note: It is normal to see up to 20% degradation in amorphous silicon solar panels within the first 6 months life of the product before the amorphous coating stabilizes.
My panel is a single-crystal silicon type, not amporphous silicon, and I don't know if there is a corresponding effect - the manual didn't say anything about it. I don't know what design Peter's Siemens panel uses.
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Old 09-10-2007, 10:22 AM   #82
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I noticed that, too...
My panel is a single-crystal silicon type, not amporphous silicon, and I don't know if there is a corresponding effect - the manual didn't say anything about it. I don't know what design Peter's Siemens panel uses.
Mine is a poly-crystalline panel. The mono- and poly- crystalline panels are supposed to see a gradual, 5% drop in efficiency over a ten year span with full exposure to the sun.

It's gonna be a hot day today, record-breaking, even. I'm hoping I can pull my trailer out and measure some volts and amps under the mid-day sun, then I'll report back.

There's some dumb saying that Kipling recites: "Mad Dogs and Englishmen . . ." But I'm sure that's just superstition. Has nothing to do with the fact I was born in England . . .

--P
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Old 09-10-2007, 05:11 PM   #83
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Harbor Freight has a bunch of these up on their Ebay store and no one is bidding on them. The starting bid is $189.00 so you would only save $10 on it.

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Old 09-11-2007, 01:16 AM   #84
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Well I broke down & ordered the 3, 45 watt solar panels from Harbor Freight.
Hope I made the right decision. Still have to get the battery. Should that be a 12v deep cycle?? Thanks, Colleen
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