Portable solar panel and wire length to trailer

[AKCamper]

Originally Posted by alanmalk

Plenty of options. All depend on your pocket book, space for heavy wire, where and when you camp, how much power you pull from batteries, and so much more. The best approach is to try out something simple and go camping and see how it works.

--
Alan

Alan,
So true. Half the fun is the journey.

[Jim Bennett]

I agree with your assessment, Alan. It was something you said, more the way you put it, last winter that made the light bulb in my head glow bright, and finally wrapped my head around some simple solar theory.

I have always maintained that everything in life we deal with is actually simple, it is just a matter of learning all these simple things, and putting a whole bunch of them together, in order to understand stuff.

[Tin]

Originally Posted by Jim Bennett

Using 10 AWG for 30' from a 100W panel, with a max output of 5.6A, results in only a 1.9% voltage drop. And this is for optimal solar gain, which one could definitely more closely achieved with a portable unit, just as long as you keep moving it, which in practice nobody does.

Results here;
Voltage Drop Calculator

I wired my system in at 36V to the controller, using pairs of panels in series. I did the same with my 80W portable which is actually two 40W panels that fold up. This gives me a max of 2.2A with a voltage drop of 0.36%. If I had of left it at 18V, I would have had a max of 4.4A, with a voltage drop of 1.44%. Makes a good difference. Once through the controller coming out at say 14V, this results in an ideal max of 5.66A of charging power. This is why power transmission is always done with high voltage, there is way less line loss this way.

Nice Jim, looks like you are set for quartz.

[Jim Bennett]

Originally Posted by Tin

Nice Jim, looks like you are set for quartz.

Let's hope so, though still more things to do.

[Tin]

Originally Posted by AKCamper

Tin,
We use a Renogy 100 watt folding panel which puts out more in the realm of 5.75 amps. Unfortunately Renogy’s voltage drop calculator doesn’t allow for fractions. Renogy does spec out the panel at 6.17 amps shorted out. I guess it depends on your panel. Jim is correct though in the fact that controller to battery voltage drop is the most critical. Like I said before, it all works and it just depends on how efficient you want your system to be. I used 6 gauge wire since I plan on mounting two 100 watt tilting panels on my truck canopy and can park my truck in the sun while our trailer is in the shade. You also are correct in the fact that some controllers will not accept large wire. My EP Solar 20 amp controller said it would only accept 8 gauge wire but it accepted 6 gauge wire.

Hi AKCamper,
Wow two tilted 100 watt panel sounds great and would definitely justify 6 ga. wire. should be a really nice setup.

[Tin]

Originally Posted by Jim Bennett

Let's hope so, though still more things to do.

Tell me about it, I am still trying to wrap up our trailer port.

[Tin]

Originally Posted by alanmalk

Regardless of the gauge of wire - and I will repeat - it doesn't matter if you are using beefy 6 gauge or skinny 14 gauge - the voltage drop will exactly double if you double the length. It is linear so it is easy to calculate using one of the many online calculators.

But doubling a tiny drop still results in a tiny drop. This will be true for beefy 6 gauge. Now, double the rather significant voltage drop of skinny 14 gauge and you have a significant loss of power in your wire.

Solution? To offset the voltage loss when you double the length, you go "down" approximately 4 "gauge counts". Or, for example, you want to double the length your current piece of 14 gauge and not increase the loss, you would go to 10 gauge.

But is this practical or cost effective? These factors are harder to compute. You could compromise by keeping your current piece of 14 gauge and when camped in trees then add a piece of 10 gauge (using some connectors) as needed to reach the batteries.

Or as others below have pointed out, moving the controller off the panel and close to the batteries will also give significant results. Why? The controller only (usually) needs a couple of volts above battery voltage to work. So, batteries full at 14 volts, the controller needs 16 volts. If your panel is 18 volts you can afford to loose 2 volts in the wires. And this works in your favor if the batteries are low at 12 volts.

My personal solution: I used about 40 feet of silicone 8 gauge speaker wire (super flexible as others have mentioned). But for the last 4 feet or so into the trailer and to the controller, I used 12 gauge. Yes, a bit of skinny wire but we're only talking 5 to 8 amps so a trivial drop.

Plenty of options. All depend on your pocket book, space for heavy wire, where and when you camp, how much power you pull from batteries, and so much more. The best approach is to try out something simple and go camping and see how it works.

--
Alan

Hi Alan,
All your points are well taken, I like your ending statement "The best approach is to try out something simple and go camping and see how it works." sound advise!

[parfsten]

Thanks Alan. Very helpful in my quest to get a better understanding of this. I like your advice to use what you've got and see how it goes. I am camping as I type. Winter sun is low in the sky and where I am I get ~.4 amps from the roof panel. When I add the solar panel (100W lensun) it bumps up to 3.5. I'm not sure what to expect from the portable panel I have and I know it depends on time of year, position and angle of the sun. At any rate... more amps are coming in with the panel...

[alanmalk]

Originally Posted by parfsten

...
When I add the solar panel (100W lensun) it bumps up to 3.5. I'm not sure what to expect from the portable panel I have and I know it depends on time of year, position and angle of the sun. At any rate... more amps are coming in with the panel...

Very useful observations.

Personally I have observed essentially the same. In winter (late fall, early spring), a small panel pointed in the right direction produces a lot more power than the big panel mounted on the roof.

However, in the low sun, cloudy, short days of winter there is much less power to be had, and the average camper is going to have to cut back on the microwave, toaster oven, 600 watt stereo, etc. Unless you are willing to drag along 3 or 4 panels, in which case you may not need to alter your camping style. Some folks on this forum can generate enough power to supply not only themselves, but their neighbors too. You will find me camping next to them with my jumper cables ready should I need a boost!

--
Alan

[parfsten]

Originally Posted by alanmalk

Very useful observations.

Personally I have observed essentially the same. In winter (late fall, early spring), a small panel pointed in the right direction produces a lot more power than the big panel mounted on the roof.

However, in the low sun, cloudy, short days of winter there is much less power to be had, and the average camper is going to have to cut back on the microwave, toaster oven, 600 watt stereo, etc. Unless you are willing to drag along 3 or 4 panels, in which case you may not need to alter your camping style. Some folks on this forum can generate enough power to supply not only themselves, but their neighbors too. You will find me camping next to them with my jumper cables ready should I need a boost!

--
Alan

My previous camping experience (aliner) was 99% dry camping - my camping style has not changed much so no high energy needs so far (no microwave, toast oven, high watt stereo.... etc). It is a delight to have the power I have now for lights and 12 volt things. Love it!

A question on the wire gauge - did I read it correctly that you can mix wire gauges? IE 14 guage with a string of 10 gauge? Just curious about this - the 14 gauge seems to be working out fine for juicing up the batteries so far.

[alanmalk]

Originally Posted by parfsten

...
A question on the wire gauge - did I read it correctly that you can mix wire gauges? IE 14 guage with a string of 10 gauge? Just curious about this - the 14 gauge seems to be working out fine for juicing up the batteries so far.

The real answer is "maybe". You can mix gauges as long as the smaller wire is rated to carry the highest amps that might be needed.

To clarify, any given wire has a rating called ampacity. It can get complicated if you factor in temperature, number of nearby wires, etc. But in general a 14 gauge wire can handle 20 amps. And my solar panel can't produce more than 9 or 10 amps in the worst (best) case, so nothing to worry about regarding overheating of the wire.

Different from ampacity is voltage drop. The smaller wire will have more voltage drop than the bigger so for an application where every volt is critical - like solar charging of batteries - it is important to minimize voltage drop by using the largest gauge practical. And to keep the length of the wire to a minimum since doubling the length will double the voltage drop (regardless of wire size).

But - to answer your question directly - I followed a 40 foot length of 10 ga wire with 3 feet of 14 gauge. Since I was adding less than 10 percent of small wire to the total length the extra voltage drop due to the small wire was minimal. Not even worth calculating in my opinion.

Why did I terminate my 10 gauge with 14 gauge? At the point where my solar cable entered the trailer it was only 3 feet from the controller. And I needed to leave the ETI solar panel wire in the controller terminal plus add the wire from the portable panel. There just wasn't enough room at the terminal for a pair of 10 ga wires so a bit of smaller wire worked just fine to solve that problem. It could have been 10 inches or what ever was convienient.

Hope that helped rather than confusing everyone.
--
Alan

[HappyCampers]

One thing that confuses me is the use of a charge controller for a portable solar panel and how it may interact with the charge controller for the roof mounted solar panel. If two separate charge controllers are connected to the batteries, how do they manage to work together? Similarly, if the roof mounted collector is charging when the tow vehicle is connected and supplying power, how does that all manage to work together?

[alanmalk]

Originally Posted by HappyCampers

One thing that confuses me is the use of a charge controller for a portable solar panel and how it may interact with the charge controller for the roof mounted solar panel. If two separate charge controllers are connected to the batteries, how do they manage to work together? Similarly, if the roof mounted collector is charging when the tow vehicle is connected and supplying power, how does that all manage to work together?

To simplify this - and it really does need simplification - the source with the highest voltage reaching the batteries will do the most charging.

A little more detail: Imagine the batteries are rather low. A pair of 6 volt batteries can easily suck up (absorbe) 30 amps or more. Your two panels together can provide perhaps half that total or less ( real world - less for sure ). Since the most controllers are set to recognize a certain voltage as full (typically 14.4) each controllers will think the batteries are low and provide a maximum charge.

When the batteries are full - 14.4 - the controllers see that as well and taper down the voltage and current to the float level (typically 13.8).

There is a grey area - "almost full" - where only one controller is working hard and the other is loafing. But since the batteries are "almost full", this hardly matters.

The above also applies to the alternator on the tow. (Complicated by the voltage drop caused by the long run of cheap automotive wire. Using my Toyota as an example - so much voltage drop that the alternator hardly contributes anything.)

The bottom line: No need to be worried unless you absolutely must have perfection. In that case run both panels to the largest controller and mount it near the batteries.

--
Alan

[Patandlinda]

Originally Posted by alanmalk

To simplify this - and it really does need simplification - the source with the highest voltage reaching the batteries will do the most charging.

A little more detail: Imagine the batteries are rather low. A pair of 6 volt batteries can easily suck up (absorbe) 30 amps or more. Your two panels together can provide perhaps half that total or less ( real world - less for sure ). Since the most controllers are set to recognize a certain voltage as full (typically 14.4) each controllers will think the batteries are low and provide a maximum charge.

When the batteries are full - 14.4 - the controllers see that as well and taper down the voltage and current to the float level (typically 13.8).

There is a grey area - "almost full" - where only one controller is working hard and the other is loafing. But since the batteries are "almost full", this hardly matters.

The above also applies to the alternator on the tow. (Complicated by the voltage drop caused by the long run of cheap automotive wire. Using my Toyota as an example - so much voltage drop that the alternator hardly contributes anything.)

The bottom line: No need to be worried unless you absolutely must have perfection. In that case run both panels to the largest controller and mount it near the batteries.

--
Alan

Allan when you say controller needs to be near batteries , how far away from batteries canntge controller be ? Pat

[AKCamper]

Originally Posted by Patandlinda

Allan when you say controller needs to be near batteries , how far away from batteries canntge controller be ? Pat

Has anybody read the blog “The RV Battery Charging Puzzle” Bob states it a little more emphatically than Alan. As close as possible with the largest wire possible. I kind of aim for perfection, although I rarely hit it.

[padlin]

Originally Posted by alanmalk

The real answer is "maybe". You can mix gauges as long as the smaller wire is rated to carry the highest amps that might be needed.

To clarify, any given wire has a rating called ampacity. It can get complicated if you factor in temperature, number of nearby wires, etc. But in general a 14 gauge wire can handle 20 amps. And my solar panel can't produce more than 9 or 10 amps in the worst (best) case, so nothing to worry about regarding overheating of the wire.

Different from ampacity is voltage drop. The smaller wire will have more voltage drop than the bigger so for an application where every volt is critical - like solar charging of batteries - it is important to minimize voltage drop by using the largest gauge practical. And to keep the length of the wire to a minimum since doubling the length will double the voltage drop (regardless of wire size).

But - to answer your question directly - I followed a 40 foot length of 10 ga wire with 3 feet of 14 gauge. Since I was adding less than 10 percent of small wire to the total length the extra voltage drop due to the small wire was minimal. Not even worth calculating in my opinion.

Why did I terminate my 10 gauge with 14 gauge? At the point where my solar cable entered the trailer it was only 3 feet from the controller. And I needed to leave the ETI solar panel wire in the controller terminal plus add the wire from the portable panel. There just wasn't enough room at the terminal for a pair of 10 ga wires so a bit of smaller wire worked just fine to solve that problem. It could have been 10 inches or what ever was convienient.

Hope that helped rather than confusing everyone.
--
Alan

Excellent explanation Alan.

[fudge_brownie]

Alan

Very good description of transitioning wire. Another situation that may create a need to transition is when you are wiring directly into a solar controller. Many will not take a 10 gauge, mine said it would take 8 gauge but I had to pluck some strands of wire out of the 8 gauge to make it fit. An easier method might have been to make the transition to a lighter gauge wire.

[rotateclockwise]

When joining two feeds (portable and roof mount), is it best to use an MC4 Y connector with a single output to the existing controller or is there an alternative to joining and stepping down the feeds?

[padlin]

Originally Posted by rotateclockwise

When joining two feeds (portable and roof mount), is it best to use an MC4 Y connector with a single output to the existing controller or is there an alternative to joining and stepping down the feeds?

I find the mc4 connectors a PIA to put together and take apart, even with the tool. If I redo it I'll go to something simpler to connect the portable.

[AKCamper]

Originally Posted by rotateclockwise

When joining two feeds (portable and roof mount), is it best to use an MC4 Y connector with a single output to the existing controller or is there an alternative to joining and stepping down the feeds?

A simple collector box could be made or purchased and installed next to the controller since all the wires may not have MC4 connectors.