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Old 02-03-2018, 03:26 PM   #21
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Originally Posted by AKCamper View Post
Here is a quote from “Bob”,
“From the controller to the batteries the wire size is critical. The bigger the better. If you cannot design for less than a 1% drop due to the length of run, it is possible with better controllers (Morningstar Tristar & Prostar, plus a few others) to use remote voltage sensing and the controller will boost the voltage going out, so that the correct voltage reaches the batteries."
Yep, that's what I said.

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Originally Posted by AKCamper View Post
...
“Do not be tempted to use this as a way of installing smaller wires. Voltage drop in the run between the controller and the batteries equals wattage loss in charging. Fewer watts come out of the end of the wire than go in when the voltage drops. This means that using smaller wires here will cost you watts charging every day forever. This is a foolish place to save a few dollars.”
Bob has missed that it would be "wattage loss" on the other side of the controller, as well, for the same reason.
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Old 02-03-2018, 04:27 PM   #22
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While voltage drop on both sides of the trailer follow the same rules, there is an advantage of using short & larger wire for the controller to battery side. As Brian noted, Wattage (power) loss is dependent on the wire size & current (W=I squared times R). The reason for using larger wire on the controller/battery side is the controller can only approximate battery voltage. Surface charge, etc produce inaccuracies. Instead, it determines its output based on the algorithms built into it, then goes into the various charging stages, often determined by time rather than voltage.

Low resistance loss is important because the differences between the various stages of charging (bulk, absorption, and float) are, in some cases, just a few tenths of a volt. For example, If the loss between the controller & battery is more than a few tenths of a volt, the battery may "see" Float voltages rather than the Absorption voltage the controller is producing. This results in much longer charging times, and may result in the battery never reaching full charge.

On the input side, you may lose the same amount of voltage due to resistance, but since the panel is usually capable of producing higher voltages than the controller output needs, the loss is not as important. In the case of a PWM controller, it just increases the on time to make up for the lost input voltage, resulting in the same voltage going to the output & battery.
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Old 02-03-2018, 06:50 PM   #23
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Originally Posted by Vermilye View Post
While voltage drop on both sides of the trailer follow the same rules, there is an advantage of using short & larger wire for the controller to battery side. As Brian noted, Wattage (power) loss is dependent on the wire size & current (W=I squared times R). The reason for using larger wire on the controller/battery side is the controller can only approximate battery voltage. Surface charge, etc produce inaccuracies. Instead, it determines its output based on the algorithms built into it, then goes into the various charging stages, often determined by time rather than voltage.

Low resistance loss is important because the differences between the various stages of charging (bulk, absorption, and float) are, in some cases, just a few tenths of a volt. For example, If the loss between the controller & battery is more than a few tenths of a volt, the battery may "see" Float voltages rather than the Absorption voltage the controller is producing. This results in much longer charging times, and may result in the battery never reaching full charge.

On the input side, you may lose the same amount of voltage due to resistance, but since the panel is usually capable of producing higher voltages than the controller output needs, the loss is not as important. In the case of a PWM controller, it just increases the on time to make up for the lost input voltage, resulting in the same voltage going to the output & battery.
That’s what I thought I said. Anyway, it doesn’t matter on our system because I use 40ft. Of 6 gauge silicone polar flex duplex wire on our portable panel and 18 in. Of the same between the controller and the battery. It all works, i’m Just a more is better type of guy. Right now I only have a portable panel, but I plan on mounting two 100watt panels on the roof of my truck canopy. That way we can park in the shade and put the truck in the sun.
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Old 02-03-2018, 09:36 PM   #24
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...

Low resistance loss is important ...
Truer words have never been spoken.
And there are two ways of cutting the resistance in half.

One is to go up approximately 2 standard gauge sizes between the controller and the battery. For example, going up from 10 Ga to 6 Ga will cut the resistance in half (and therefore the voltage drop in half by definition).
Or... Cut the length of wire in half. If the distance from the controller to the battery is 10 feet, moving the controller to 5 feet will cut the resistance (voltage drop) exactly in half.

One method costs a lot of $$$, the other saves $$$. If you have the option, pick the best one for you.

Now obviously if you move the controller closer to the battery then you have moved it further from the panel and have to add back the wire. But this side of the system is not as critical - within reason. The controller still needs to see its design minimum input voltage (varies with brand and style). But a loss to voltage drop of around one volt, say from 18 at the panel down to 17 at the controller input, may be tolerable.

Is the power wasted? Not in a real sense because the controller's job is to reduce the input voltage down from 18 (or 17) to the battery charge voltage of around 14.5. That too is voltage drop. 3.5 volts (or 2.5) is dropped by the controller intentionally. Voltage drop is voltage drop. Of course the controller is changing this drop amount as needed for the correct stage of charge. The problem as many others have mentioned below is that the controller will be fooled by voltage drop on the battery side.

Note that the controller we're talking about is the standard (cheaper) pulse-width design as supplied by Escape. Using the alternate (expensive) MPPT design changes everything.

Something to think about...

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Old 02-04-2018, 11:26 PM   #25
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We have talked about loss of watts. If watts equals amps times volts, then voltage drop from too small of wire equals a loss of watt output as well. Considering a 100 watt panel with say a max output of 19 volts and lets say only 5 amps if you have a 40 foot run of 16 gauge wire a voltage drop calculator shows 16.98 volt output or a 2.02 voltdrop or 84.9 watts of output with a 15.1 watt loss. If you run the same sinarrio using 6 gauge wire the output would be 18.8 volts or a .2 volt drop. This results in a 94 watt output or a 6 watt loss. Hopefully I did my calculations correctly. I think this is what Bob Shearer “Handymen Bob” meant.
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Old 02-04-2018, 11:41 PM   #26
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I'm no electrician or solar expert, but I have a related (I think) observation. A major brand name solar powered battery minder I purchased came with long, small wires from the solar panel to the controller, then short, big wires from the controller to the battery. I assume that their engineers knew what they were doing when they designed it that way - keeping the controller close to the battery and with heavier gauge wires carrying the charge over that shorter distance. Again, just an observation....
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Old 02-05-2018, 03:07 AM   #27
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... the controller's job is to reduce the input voltage down from 18 (or 17) to the battery charge voltage of around 14.5
The panel voltage is only that high under one specific load. When actually delivering maximum current, the panel voltage drops.

During early stages of charging, the PWM controller is a just a switch turned "on" (pulse width 100%). Check the voltage on the input terminals and the output terminals of the controller, and you'll only see the semiconductor junction drop (which is as low as the controller designer can afford to make it), with the panel voltage tracking up as the battery charges.

Once the PWM controller starts reducing pulse width, there is more power available than the battery can accept (or more than the controller is programmed to provide), so power loss in the wiring becomes irrelevant.

Yes, an MPPT controller changes this completely, but in that case the controller is not just throttling off voltage, it is trading voltage for current.
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Old 02-05-2018, 03:11 AM   #28
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A major brand name solar powered battery minder I purchased came with long, small wires from the solar panel to the controller, then short, big wires from the controller to the battery. I assume that their engineers knew what they were doing when they designed it that way - keeping the controller close to the battery and with heavier gauge wires carrying the charge over that shorter distance. Again, just an observation....
As a "battery minder" it is presumably designed for very low power. The small-gauge wires to the panel as chosen for minimum cost, and are adequate because current is low (a "trickle" charge). The large-gauge wires to the battery are to minimize voltage drop just so the controller can more accurately see the battery voltage; they are not needed for energy efficiency.
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Old 02-05-2018, 01:20 PM   #29
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The panel voltage is only that high under one specific load. When actually delivering maximum current, the panel voltage drops.
Both statements are true and worth taking a closer look at.

Rated voltage is at a rated current provided by the manufacturer. From the Renogy site, using their 100 watt folding panel that seems to be very popular now: 17.6 volts at 5.68 amps at maximum power. And an open circuit voltage of 21.6 volts. This means that at any load (current going to the battery) of 5.68 amps, the panel can provide from 17.6 volts minimum, up to a max of 21.6 volts (at near zero amps). Bottom line: At maximum rated amps you are getting 17.6 volts. Above maximum current (which is quite likely with a pair of 6 volt trailer batteries that are even just a little discharged) then the panel voltage drops, quite likely to close to the present battery voltage. This is the scenario where thin wires really do waste power.

To elaborate further on "maximum current". The absolute maximum current a Renogy 100 watt panel will produce is 6.1 amps into a short circuit. The interesting thing about this scenario is that 6.1 amps times zero volts = 0 watts. No power being produced by a panel in full sunlight into a "no resistance" load. Odd concept...

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Old 02-05-2018, 05:51 PM   #30
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The ratings for panels cause a lot of confusion, and leave most people not understanding the conditions under which the panel operates.

The panel produces no power in the open circuit condition (voltage VOC, 21.6 V in Alan's example) because it can't deliver any current at that voltage. This is like a cyclist pushing on the pedals on a steep hill, just holding position and unable to move: lots of push, but no movement, so there's no power.

The panel produces no power in the short circuit condition (current ISC, 6.1 amps in Alan's example) because it can't push that current with any voltage. This is like a cyclist madly spinning the pedals on a downhill, not able to spin them fast enough to keep up with the coasting bike: lots of motion, but no force, so there's no power.

The nominal power rating is based on ideal sun exposure and just the right load, allowing the panel to run at the optimal balance of the maximum power state (voltage VMP and current IMP, 17.6 V and 5.68 A in Alan's example). This is like the cyclist having found the right gear and speed, working hard and putting out maximum power... with less pedal force the stuck condition, and less speed than the free spinning.
Unless you have a Maximum Power Point Tracking (MPPT) controller, you don't get to choose which state your panel is running in. The panel voltage doesn't just drop at very high current - until the controller starts "throttling", the panel is tied (physically) to the battery. It doesn't matter if the sun is blazing and your panel could produce 100 watts if it were putting out 17.6 volts when the battery is at 14 volts - it will be forced to run at 14 volts (plus whatever voltage the wire resistance and controller transistors force), and will put out less than 100 watts. It is like the cyclist with a one-speed bike and forced to match a certain speed, even if it doesn't suit the cyclist's pace.

With the panel stuck at the battery voltage, and with a PWM controller doing nothing but passing power through (and losing some), the wires from panel to controller and from controller to battery are equally important to loss of power to resistance. With voltage at the battery terminals of (for instance) 14 volts, the current in ideal sun will be more than the IMP (5.68 A) but less than the ISC (6.1 A)... and not high enough to produce 100 watts (so much less current than 100W/14V=7.1 A, and even less power than 14V*6.1A=85 W).

An MPPT controller is like a multi-speed bike, allowing the cyclist to choose a different combination of speed and force to reach optimum output.
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Old 02-05-2018, 06:13 PM   #31
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Brian, I was once told that a solar panel's wattage rating (for example, a 100W panel) represents how many total watts it can generate under ideal conditions over an average "manufacturer determined" period of daylight such as a 12 hour day - from sun up to sun down. So for example, under ideal conditions, a panel rated at 100W would be expected to produce 8.33W per hour over a 12-hour long day (100/12=8.33). Is that a correct interpretation of panel wattage ratings?
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Old 02-05-2018, 09:18 PM   #32
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Brian, I was once told that a solar panel's wattage rating (for example, a 100W panel) represents how many total watts it can generate under ideal conditions over an average "manufacturer determined" period of daylight such as a 12 hour day - from sun up to sun down. So for example, under ideal conditions, a panel rated at 100W would be expected to produce 8.33W per hour over a 12-hour long day (100/12=8.33). Is that a correct interpretation of panel wattage ratings?
This is a mix of correct and incorrect statements.

Yes, the manufacturer rates their panels under ideal conditions - impossibly ideal conditions in the real world. (But that's OK if everyone understands those conditions). They are: a cool panel, sun directly (90*) overhead, maximum theoretical sunlight, and maybe more that I am not remembering.

For example, the panel we are using as an example produces a maximum power at 17.6 V and 5.68 A under the above conditions, into a pure resistive load (another theoretical situation). That combination of voltage and amperage is 99.8 watts. So they call it a 100 watt panel - the absolute max it can produce on the surface of the earth.

How much power you put into your battery depends on many factors outside of the manufacturer's control. I personally have never heard of an industry standard 12 hour sunlight equivalent. The real world conditions are far more important than a possible theoretical number. Battery type and condition, wire length and diameter, controller type and efficiency, shade and cloud cover, time of year, etc, etc, all contribute to the total power you put into your battery. Unfortunately in the real world winter you may get one-tenth of the total power you could produce in the summer. And that could be one-tenth of the power you really need to keep the lights and furnace running. Makes winter camping a real challenge...

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Old 02-06-2018, 12:16 AM   #33
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Yes, the manufacturer rates their panels under ideal conditions - impossibly ideal conditions in the real world. (But that's OK if everyone understands those conditions). They are: a cool panel, sun directly (90*) overhead, maximum theoretical sunlight, and maybe more that I am not remembering.

For example, the panel we are using as an example produces a maximum power at 17.6 V and 5.68 A under the above conditions, into a pure resistive load (another theoretical situation). That combination of voltage and amperage is 99.8 watts. So they call it a 100 watt panel - the absolute max it can produce on the surface of the earth.
That's my understanding, too. The rated power is an ideal peak output, not an average over some period. Observations by RV owners are consistent with that - no one ever sees the peak output, but the best conditions experienced can get close enough that the rating is plausible for ideal conditions.

In a real day, the ends of the day have very poor light intensity compared to noon (when it could approach the ideal, on the equator, at mid-day). One rule of thumb is to assume that averaged over the year, and in clear weather, a whole day might get the output of six hours of ideal output. So, a "100 watt" panel could produce 600 watt-hours (50 amp-hours at 12 volts, much less given actual voltage required to charge a battery) over a clear day. Good luck getting that.
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Old 02-06-2018, 12:22 AM   #34
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I'm definitely thinking I'd like to add another 160W panel to my Escape. I'd really like to be able to tilt the panels up as much as 45 degrees to improve their angle in low winter sun.
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Old 02-06-2018, 10:34 AM   #35
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I'm definitely thinking I'd like to add another 160W panel to my Escape. I'd really like to be able to tilt the panels up as much as 45 degrees to improve their angle in low winter sun.
If you come to the February Quartzsite rally, I have a 2017 21 with two Escape installed panels that I modified to tilt.
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Old 02-06-2018, 03:36 PM   #36
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How do people store their portable solar panels so they don't get damaged? Did you make a case or anything?
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Old 02-06-2018, 03:59 PM   #37
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My Renogy came with a nice rigid case.
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Old 02-06-2018, 04:03 PM   #38
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How do people store their portable solar panels so they don't get damaged? Did you make a case or anything?
My Renogy came with a semi-rigid case as well. I also cut some 1/8 inch plywood the size of the glass on my panels and placed them over the glass when I put it in the case for extra measure. If you laid the Renogy case flat on the ground it could break the glass if you like dropped a hammer on it. I store mine in the truck canopy sitting on the fenderwell inside the canopy with a strap keeping it standing up.
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Old 02-06-2018, 04:08 PM   #39
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I bought an Eco-Worthy folding solar panel. And while it does fold up nicely the solar cells are exposed. I'll have to devise a cover for it.
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Old 02-06-2018, 04:17 PM   #40
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I plastered packing tape over all the corners and edges of the cardboard boxes that mine came it. Some day, I'll do something better, I guess.
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