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Old 09-19-2016, 08:27 AM   #1
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Measuring Solar Panel Charging Rate

When we left on our most recent trip without hookups, our single 12v battery was at 14.2v. After we set up, we ran the Max Fan for about 7 hours which brought the battery down to 12.2v. After a full day of unobstructed sunshine the next day, and no electrical draw on the battery, the 95w panel brought the battery to only 12.6v. I have nothing to base my expectations on; is there any way to measure the panel's charging rate and any performance standards to compare it against? (And, for what it's worth, the battery charge level topped-out at 13.4v over the next 48 hours with little to no draw, e.g., one overhead light on for less than 30 minutes.)
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Old 09-19-2016, 08:38 AM   #2
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That's about the same as I see on a camping trip in September in the PNW (low sun angle). And that's why I bought an additional 90-watt portable unit to supplement the fixed-roof panel. I haven't been out camping since I bought this so cannot report yet on its efficacy.

You can check your charge rate buy clicking through the "menu" on the Go Power panel inside your trailer.
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Old 09-19-2016, 09:08 AM   #3
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I suspect the 14.2v you saw was actually the charger voltage as opposed to the batterys charge level. To get a good battery reading, the battery has to sit for a while after charging. If hooked up to AC unplug from AC and let it sit for a day, or as close to that as practical. If only on solar, take your reading in the am before the sun starts it's charging. Either way It should be about 12.7vdc.

To get an accurate voltage reading during a trip, you have to have any load OFF. Did you have the fan OFF when you noticed the 12.2vdc? any draw on the battery/s while reading the voltage will give a reading that is lower then it really is.
12.2vdc is about 60%.
12.6-12.7vdc is 100% charged.

Here's a chart
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Old 09-19-2016, 09:09 AM   #4
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Quote:
Originally Posted by KarenH View Post
That's about the same as I see on a camping trip in September in the PNW (low sun angle). And that's why I bought an additional 90-watt portable unit to supplement the fixed-roof panel. I haven't been out camping since I bought this so cannot report yet on its efficacy.

You can check your charge rate buy clicking through the "menu" on the Go Power panel inside your trailer.

A year or so ago I posted some actual measurements I made comparing sun angles (simulated by tilting the solar panels) and posted here: http://www.escapeforum.org/forums/f3...ls-4775-3.html

The bottom line was that any tilt away from overhead was detrimental. Its just the laws of physics (or perhaps the laws of Winter) - lower sun = less charging. A second portable panel of the same wattage can double or triple what the fixed panel on the roof can produce late in the season.

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Old 09-19-2016, 09:25 AM   #5
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Originally Posted by KarenH View Post
That's about the same as I see on a camping trip in September in the PNW (low sun angle). And that's why I bought an additional 90-watt portable unit to supplement the fixed-roof panel. I haven't been out camping since I bought this so cannot report yet on its efficacy.

You can check your charge rate buy clicking through the "menu" on the Go Power panel inside your trailer.
Thanks, Karen. I did switch the GoPower buttons "A" & "B" and "B" gave me a percentage, but I thought that was the current state of charge of the battery. Are you saying that the percentage shown is how efficiently the panel is operating? Thanks again!
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Old 09-19-2016, 09:31 AM   #6
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Originally Posted by padlin View Post
I suspect the 14.2v you saw was actually the charger voltage as opposed to the batterys charge level. To get a good battery reading, the battery has to sit for a while after charging. If hooked up to AC unplug from AC and let it sit for a day, or as close to that as practical. If only on solar, take your reading in the am before the sun starts it's charging. Either way It should be about 12.7vdc.

To get an accurate voltage reading during a trip, you have to have any load OFF. Did you have the fan OFF when you noticed the 12.2vdc? any draw on the battery/s while reading the voltage will give a reading that is lower then it really is.
12.2vdc is about 60%.
12.6-12.7vdc is 100% charged.

Here's a chart
Great information, Bob; thanks! So, to make sure I understand, the "drop" to 12.6v is the "real" charge level of the battery? I could (conceivably) operate 12v power down until the charge read 12.0v before needing to shut everything down and recharge back to 12.6v. Is this correct?
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Old 09-19-2016, 09:35 AM   #7
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Originally Posted by alanmalk View Post
A year or so ago I posted some actual measurements I made comparing sun angles (simulated by tilting the solar panels) and posted here: http://www.escapeforum.org/forums/f3...ls-4775-3.html

The bottom line was that any tilt away from overhead was detrimental. Its just the laws of physics (or perhaps the laws of Winter) - lower sun = less charging. A second portable panel of the same wattage can double or triple what the fixed panel on the roof can produce late in the season.

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I recall this thread you started Alan, and searched for it but couldn't find it. GOOD STUFF, thanks. I'm going to read through the entire thread this morning. Kind of makes me think that I should really consider a portable panel rather than the fixed one when I submit my build sheet for the 5.0TA(?). Lots more to learn I suppose. Thanks once again.
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Old 09-19-2016, 09:42 AM   #8
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I recall this thread you started, Alan and searched for it but couldn't find it. GOOD STUFF, thanks. I'm going to read through the entire thread this morning. Kind of makes me think that I should really consider a portable panel rather than the fixed one when I submit my build sheet for the 5.0TA(?). Lots more to learn I suppose. Thanks once again.
You are most welcome.

But if I may offer some advice. Get the fixed panel. You probably won't want to be bothered with a portable panel for 80% of your normal camping. In spring & summer (when the sun is high in the sky) the portable panel just becomes extra baggage. (Don't ask me how I know this. )

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Old 09-19-2016, 09:50 AM   #9
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Quote:
Originally Posted by Zardoz View Post
Thanks, Karen. I did switch the GoPower buttons "A" & "B" and "B" gave me a percentage, but I thought that was the current state of charge of the battery. Are you saying that the percentage shown is how efficiently the panel is operating? Thanks again!
No, not how efficiently the panel is operating but you can toggle through the state of charge, the battery voltage, and the charging current. See here (http://gpelectric.com/files/gpelectr..._GP-PWM-30.pdf), page 13.

And I agree with Alan (and thank him for that forgotten thread!). If I did it again, I would stick with a fixed panel and add the supplemental one only for my late fall and winter camping. Why drag it around when it's not needed?

Edited: Plus the newer panels that ETI installs are 150 watts, I believe, whereas the ones you and I have in the 2013 models are 95 watts.
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Old 09-19-2016, 09:58 AM   #10
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We love our fixed panel for those summer trips with the sun high in the sky, but also carry a portable panel for the times when you have a shady site or late season camping when the sun is at lower angles.
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Old 09-19-2016, 10:24 AM   #11
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Having camped with a portable solar panel, in the spring, with a few trees around, with our Casita..... I remember it being somewhat of a pain to spend much of the day returning to the campsite to move the panel.

Plus it is 90 watts.

The nice thing about our forthcoming 2017 Escape... is that we will have the dual 6v, for much more capacity, plus we are getting TWO fixed roof panels, plus a Zamp Solar Port so we can also plug in our 90 watt portable.

So 320 watts (total) on the roof, plus 90 watt portable. We'll be pretty set for most situations, i think.

I know shade drastically drops solar panel output, but I think our new setup would have done much better than we did in our Casita, overall. With less hassle.
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Old 09-19-2016, 10:27 AM   #12
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Portable panels do have the storage and handling issues to deal with, but they are sure nice when conditions are marginal. You can find a sunny spot to place them and with adjustable kick stands change the vertical angle, and periodically turn them to keep the faces perpendicular to the sun. On optimal days this setup is overkill, and fixed panels should get you by. We leave our portable panels at home when we know there are hookups at the campground. While traveling the panels lay flat on the side bed with a bungee to hold them in place. We had a sunbrella case sewn up that has a foam divider to keep the panels protected. Very little hassle involved. I put 30' long 8 gauge leads on the panels which so far has been long enough to find a sunny patch.
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Old 09-19-2016, 10:33 AM   #13
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Additional considerations I learned on this forum... The fixed solar panel also charges the battery when you're on the road. And it will keep your battery charged when in storage. Both are great benefits!
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Old 09-19-2016, 01:16 PM   #14
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You are most welcome.

But if I may offer some advice. Get the fixed panel. You probably won't want to be bothered with a portable panel for 80% of your normal camping. In spring & summer (when the sun is high in the sky) the portable panel just becomes extra baggage. (Don't ask me how I know this. )

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Old 09-19-2016, 01:27 PM   #15
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The fixed, rooftop panel provided by Escape is always connected to the batteries, even if you turn off the battery disconnect switch (usually - there has been some discussion on this). The only time you can get an accurate voltage measurement using the controller (or any volt meter) is when there is no sun on the panel & no load on the battery.

Waiting until dark, and turning off the battery disconnect switch will give you a voltage measurement that can be compared to the chart shown in previous posts in this thread for a reasonable indication of the state of charge for the battery.

That said, a far better indication of battery status is measuring with a hydrometer. Another easier, but more expensive method is to purchase and install a battery monitor. One I recommend is the Bogart TriMetric 2030. This keeps track of the total of amp hours removed from the battery and the amount put into it by your solar panels, tow vehicle and converter. When properly configured, it will provide an accurate measurement of the state of charge of the battery.

You can set the GoPower controller to amps, which will show what the panel is producing, however some of that will be running the trailer, and, if anything is left over, filling the battery. It shows that things are working, but, like the voltage & per cent readouts, does not give an accurate measurement for the battery state of charge while the panel is active. For example, I've had the GoPower percentage readout show 100% (while the panel had sun on it) and the more accurate Trimetric meter showing that I was down by 35 amp hours from full charge.
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Old 09-19-2016, 01:31 PM   #16
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Great information, Bob; thanks! So, to make sure I understand, the "drop" to 12.6v is the "real" charge level of the battery? I could (conceivably) operate 12v power down until the charge read 12.0v before needing to shut everything down and recharge back to 12.6v. Is this correct?
Correct, just make sure you turn off any obvious draw and give it a minute to stabilize before checking the state of charge. The chargers put out over 13 volts during the charge, but that isn't the actual state of the battery.

If it were me, I'd use something other then the GoPowers LED panel, I'm under the impression they are not all that accurate. Some use the little meters you plug into a lighter outlet.

Battery chargers, be it solar or the converter/charger, charge relatively quickly to about 80 or 90%%, the last 10% or so goes a lot slower. Late in the year, you may well not have enough sun to fully charge in a day.

I use a Trimetric, but it's kind of a geek thing.
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Old 09-19-2016, 02:16 PM   #17
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I did switch the GoPower buttons "A" & "B" and "B" gave me a percentage, but I thought that was the current state of charge of the battery. Are you saying that the percentage shown is how efficiently the panel is operating?
No, it's a calculation of state of charge based entirely on voltage... but the voltage is affected by the charger's activity. This was recently discussed in Slow Solar Charging and Go Power Display Questions (post #26).

If you really want to know how much charge is in the battery, you need a monitor which actually measures current in and out of the battery, such as the Bogart TriMetric which Jon described.
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Old 09-19-2016, 02:38 PM   #18
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If it were me, I'd use something other then the GoPowers LED panel, I'm under the impression they are not all that accurate. Some use the little meters you plug into a lighter outlet.
Some of those little meters are badly inaccurate, but any voltage measurement which not on the charge controller's end of the wire to the battery has an advantage: the voltage measured by the charge controller is different from the battery voltage due to current flow through the resistance of that wire.

If you want to assess state of charge based only on voltage (which is what most people do), then the best idea is to use a reasonably accurate voltmeter connected to the battery terminals by a wire which is not shared with any other device.
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Old 09-19-2016, 03:15 PM   #19
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Some of those little meters are badly inaccurate, but any voltage measurement which not on the charge controller's end of the wire to the battery has an advantage: the voltage measured by the charge controller is different from the battery voltage due to current flow through the resistance of that wire.

If you want to assess state of charge based only on voltage (which is what most people do), then the best idea is to use a reasonably accurate voltmeter connected to the battery terminals by a wire which is not shared with any other device.
This is why the Trimetric's voltage measurement often differs from that of the controller. The Trimetric runs a pair of voltage measurement wires to the battery that only carry the current necessary to provide the measurement (a few microamps), and will be more accurate than that of the controller.

Again, neither will provide an accurate measurement of the state of charge of the battery unless it is in a resting state - i.e. not being charged or discharged, and after allowing an hour or two for the surface charge to drain.
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Old 09-19-2016, 07:14 PM   #20
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Remarkable. In less than 12 hours all have you have come to my assistance with education, explanation, and other relevant information. Many thanks to every one of you!
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