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crazyvwvanman Sun Aug 17, 2014 4:47 pm

So, how much does the cable length and gauge matter? I wanted to find out, so I could decide how much cable to buy and what gauge for a portable panel so I could park the van in the shade and place a panel in the sun. The results showed that longer and thinner cabling lost some of the system capacity but not all that much. Keep in mind that a smaller panel would lose less and a larger panel would lose more.

80 watt rated poly panel, 4.7 amp spec, Ebay $120
low price charge controller, Ebay $25
volts/amps/shunt meter, Ebay $15
approx 75ah flooded lead acid car battery, used

Full sun, high noon, panel aimed at sun.
I hooked a volt and amp meter to the battery cables.
I also had a low beam headlight attached to the battery posts to force the need for charging to remain constant.

1. VERY short cable, direct from panel to controller 13.9v @ 4.7amps
2. 25 foot extension #12 gauge panel to controller 13.8v @ 4.6amps
3. 40 foot extension #16 gauge panel to controller 13.6v @ 4.4amps

Then BOTH extensions to make extra long 65' total
25' #12 plus 40' #16 inline from panel to controller 13.6v @ 4.0amps

This meter is not a high precision device so the numbers have to be considered all slightly rough.





I cut the ends from a cheap extension cord to use for adapters wired to the panel and to the controller. That let me add standard long extension cords in the middle for my tests and enabled me to quickly switch back and forth during testing. I would not use that method for any actual installation since there is the danger that someone could mistakenly plug something in to 110v without realizing what was going on.

I have some other panels and charge controllers so I will add to this thread when I get a chance to test some other configurations. I am most curious to compare different charge controllers so if the sun is available in the next couple of days I hope to give it a go.

Mark

DAV!D Sun Aug 17, 2014 5:12 pm

The distance and wire from the panel to the charge controller isn't as big a issue as the wire from the charge controller to the batteries. For the small sizes of our solar arrays on a van, you likely won't lose much from the panel to the controller unless you use very small cables. It's from the charge controller to the batteries that matter the most.

j_dirge Sun Aug 17, 2014 5:59 pm

DAV!D wrote: The distance and wire from the panel to the charge controller isn't as big a issue as the wire from the charge controller to the batteries. For the small sizes of our solar arrays on a van, you likely won't lose much from the panel to the controller unless you use very small cables. It's from the charge controller to the batteries that matter the most.
I think the point here is to illustrate that you can use cord extensions to place a panel further away to get better sun, if needed.. and not lose a bunch in wire resistance.

If you are running small arrays it is even MORE important to get sun on the panels (and charge to the controller).. so a mobile panel, perhaps on a long cord makes sense.

A decent cable and short run from controller to your battery bank is the easy part.


Thanks for positing this test set-up and results!

goffoz Sun Aug 17, 2014 7:26 pm

Interesting :-k
My charge controller is on my panel, So any extension puts the controller further from the battery :?
Maybe the controller should be in the van ?

jmranger Sun Aug 17, 2014 8:17 pm

Thanks for taking the time to experiment and sharing your results Mark.

I'm puzzled by the drop in charging voltage. Do you understand why it is dropping? Battery internal resistance? Battery or panel temperature?

Also, do you know what technology your charge controller is based on? On/off, PWM, MPPT?

Jean-Marc

Howesight Sun Aug 17, 2014 10:04 pm

goffoz wrote: Interesting :-k
My charge controller is on my panel, So any extension puts the controller further from the battery :?
Maybe the controller should be in the van ?

Yup. The better charge controllers can vary voltage to what your battery needs. Even then, however, the charge controller does not "know" how much voltage your battery is getting because the resistance of the wire to the battery is assumed to be near zero. If you lose, say, 0.4 volts due to wire length, if your controller is on the panel and you use a long cable, then your battery will only receive, say, 13.8 volts instead of 14.2. Assuming your battery needs 14.2 volts and your charge controller puts our 14.2 volts, only 13.8 will get to the battery. Your battery will not get a full charge.

The voltage from the panel to the controller can be anywhere between 15 and 19 volts. The charge controller controls voltage output to the battery to avoid overcharging and overheating your battery. The charge controller, if adjustable, will come pre-set at around 14.2 volts output. Cheaper non-adjustable controllers are pre-set and non-adjustable. However, very few batteries will get a full charge with less than 14.2 volts.

So, Mark's experiment shows a few things. First, cable length really does affects output significantly. This is only understandable, however, in light of what lead-acid batteries actually need to charge fully. Without a full charge, they deteriorate (mostly from sulfation) pretty quickly.

Those tenths of volts actually mean a lot in a solar charging system. If your panel is in the van, then it can deal better with the 0.4 volt drop on a long cable because it will still provide 14.2 volts to the battery provided that the panel is putting out 14.2 volts or more.

Also, the adjustable charge controllers typically have a temperature sensor. The back of the panel is quite hot and the controller mounted there ends up reducing output to "protect" your battery from being damaged from overcharging.

Howesight Sun Aug 17, 2014 10:40 pm

jmranger wrote: Thanks for taking the time to experiment and sharing your results Mark.

I'm puzzled by the drop in charging voltage. Do you understand why it is dropping? Battery internal resistance? Battery or panel temperature?

Also, do you know what technology your charge controller is based on? On/off, PWM, MPPT?

Jean-Marc

The voltage is dropping due to the cable length. In Mark's first, short cable, experiment, he gets 65.33 watts at the battery. That's about 87% of the theoretical panel output.

In the long cable scenario, he gets 54.4 watts. That is 72% of theoretical panel output. It's also 17% less than the "scenario #1" short wire. In the world of battery charging, that is a lot. Put another way, with the worst case scenario of Mark's longest/thinnest wires, you would need a panel with 105 watts to generate 75 watts at the battery.

Conclusion: Go long with cabling to get your portable panel in the sun, but use a large gauge of cable.

morymob Mon Aug 18, 2014 4:56 am

I'm going to use 10guage & I have 50ft of wire to get out into sun 4 most conditions, I guessa voltage check at both ends would be needed, controller inside .

crazyvwvanman Mon Aug 18, 2014 5:19 am

This thread was only meant to help quantify how different cable lengths and wire gauges from the panel change the output of the charge controller. I did these reported tests just a few hours before I posted the results here.

For my application as well as most vans the portable solar panel is going to get used only intermittently and for me that means I don't need to be very concerned with trying to attain near perfection. My concern is with general practicality. I have a DC fridge installed in my Westy and I want to be able to deploy a portable solar panel in situations where I will be staying put longer than my battery storage alone will allow. I already have a solar panel mounted on the Westy roof but that arrangement often has severe limitations when camped with the top popped. I have had it up there for 4 years and there is no doubt at all about those limitations with respect to my needs so I am going to add a portable panel. I wanted to see how long of a cable was practical and how much loss would be involved. I also wanted to see if I would be ok with just one very long cable or if multiple cables would be justified so I could run a shorter cable when that was all that was needed and thus reduce the losses unless the extra length was needed at a particular campsite. Also big coils of long heavy cable are not something I want to haul around for just occasional use so I wanted to determine what cabling gauge was actually needed. Based on my tests so far I likely won't be buying any #10 for my portable panel setups. Looks like #12 at most is all I need. More tests are needed though.

The charge controller I used is these particular tests is supposedly an MPPT design. I say supposedly because at just $25 I have some doubts. I have a couple other PWM controllers that I tested side by side with this MPPT unit and the MPPT unit does appear to go through some additional output level steps each time a solar panel is connected. Also keep in mind that I mentioned having a headlight powered on by the battery during these cable length tests. The headlight was drawing power from the battery about equal to what the solar was supplying.

In performing the tests I tried to keep everything consistent so I could better judge what was due to just the cabling differences. I kept the panel covered by cardboard while making setup changes. Then I uncovered the panel and let things stabilize for a couple minutes before taking readings. I also switched back and forth to do multiple tests of each combination.

EDIT: I have some other controllers to try and other sizes of panel as well. I will test a smaller and a larger panel to compare the cabling needs. It looks like today will be sunny so it may happen soon.

Mark


Howesight wrote: jmranger wrote: Thanks for taking the time to experiment and sharing your results Mark.

I'm puzzled by the drop in charging voltage. Do you understand why it is dropping? Battery internal resistance? Battery or panel temperature?

Also, do you know what technology your charge controller is based on? On/off, PWM, MPPT?

Jean-Marc

The voltage is dropping due to the cable length. In Mark's first, short cable, experiment, he gets 65.33 watts at the battery. That's about 87% of the theoretical panel output.

In the long cable scenario, he gets 54.4 watts. That is 72% of theoretical panel output. It's also 17% less than the "scenario #1" short wire. In the world of battery charging, that is a lot. Put another way, with the worst case scenario of Mark's longest/thinnest wires, you would need a panel with 105 watts to generate 75 watts at the battery.

Conclusion: Go long with cabling to get your portable panel in the sun, but use a large gauge of cable.

teej Mon Aug 18, 2014 5:47 am

Interesting tests, thanks for sharing.

They mostly confirm what I have been seeing with our set up. We have a couple portable panels, 60w and 130w. Usually we just bring the 60w and move it for optimal solar positioning. Our extension cable is about 45' made from 14-2 landscape wire and SAE style 2-pin connectors. This setup has not much trouble maintaining our 88Ah aux battery that powers a fridge, lights, sometimes some stereo. The length of cable allows us to put the panel where the sun is in the often shaded PNW campsites.

A made a second shorter cable out of 12-2 which gets used with the 130w panel. When the longer cable needs replacing I will use 12-2.

We use a 20a SunSaver PWM controller mounted next to the battery, with 10ga run from controller to battery.

After a trip the battery gets fully charged with the big panel before storage.

TequilaSunSet Mon Aug 18, 2014 6:03 am

Going slightly OT... would a 100w set up be a solid choice, to recharge 2 batteries?

j_dirge Mon Aug 18, 2014 6:58 am

TequilaSunSet wrote: Going slightly OT... would a 100w set up be a solid choice, to recharge 2 batteries?
That depends on how far you drain them in a typical cycle.

But, yes.. I have had good success charging a starter and house battery off of 80-100 watt panels that sees a couple hrs of direct sun.

The longer your stay at camp between running your engine or generator, the more solar you'll want.

For me, this is an ongoing "chore" of sorts while we are road tripping.. I watch the monitor, pay attention to use, pay attention to sun/cloud cover. But I enjoy it...


One nice thing about solar is that if you don't have enough, just add a panel.
Everything is pretty much plug and play, once you have the basics.

4x4BNB Mon Aug 18, 2014 7:30 am

I now carry two lengths of cable...a 50 and a 25 foot. Both are a 10g. My mppt controller is right next to my batteries but...now I must check the gauge from these controller to the batteries....
Great post!! Thanks for sharing the information....

Howesight Mon Aug 18, 2014 11:25 am

crazyvwvanman wrote: This thread was only meant to help quantify how different cable lengths and wire gauges from the panel change the output of the charge controller. I did these reported tests just a few hours before I posted the results here.

For my application as well as most vans the portable solar panel is going to get used only intermittently and for me that means I don't need to be very concerned with trying to attain near perfection. My concern is with general practicality. I have a DC fridge installed in my Westy and I want to be able to deploy a portable solar panel in situations where I will be staying put longer than my battery storage alone will allow. I already have a solar panel mounted on the Westy roof but that arrangement often has severe limitations when camped with the top popped. I have had it up there for 4 years and there is no doubt at all about those limitations with respect to my needs so I am going to add a portable panel. I wanted to see how long of a cable was practical and how much loss would be involved. I also wanted to see if I would be ok with just one very long cable or if multiple cables would be justified so I could run a shorter cable when that was all that was needed and thus reduce the losses unless the extra length was needed at a particular campsite. Also big coils of long heavy cable are not something I want to haul around for just occasional use so I wanted to determine what cabling gauge was actually needed. Based on my tests so far I likely won't be buying any #10 for my portable panel setups. Looks like #12 at most is all I need. More tests are needed though.

The charge controller I used is these particular tests is supposedly an MPPT design. I say supposedly because at just $25 I have some doubts. I have a couple other PWM controllers that I tested side by side with this MPPT unit and the MPPT unit does appear to go through some additional output level steps each time a solar panel is connected. Also keep in mind that I mentioned having a headlight powered on by the battery during these cable length tests. The headlight was drawing power from the battery about equal to what the solar was supplying.

In performing the tests I tried to keep everything consistent so I could better judge what was due to just the cabling differences. I kept the panel covered by cardboard while making setup changes. Then I uncovered the panel and let things stabilize for a couple minutes before taking readings. I also switched back and forth to do multiple tests of each combination.

EDIT: I have some other controllers to try and other sizes of panel as well. I will test a smaller and a larger panel to compare the cabling needs. It looks like today will be sunny so it may happen soon.

Mark



Hey Mark:

I just wanted you and everyone else reading this thread to understand that I did not in any way intend to slag you or your findings. You are the electrical guru on the Samba and I have learned a lot from your many threads.

The real-world example you gave is very helpful to many people who would zone out poring over a voltage-drop/wire gauge/wire length chart.

My comments were meant only to re-iterate my oft-repeated comments on solar set ups: Start with the charging recommendations from your battery manufacturer and work backwards from there to ensure your charge controller puts out the volts and amps for the length of time your battery needs them. That means checking the charge controller output at the battery, adjusting your controller parameters setup to ensure you are at the target voltage (for me, it is 14.8 volts - - Trojan flooded) and to ensure your controller is getting sufficient current and volts to achieve its output. At a certain point, long cables of small gauge will prevent your controller from getting sufficient volts and amps.

It is important to remember that any solar setup will, if there is no draw on the battery, eventually re-charge your battery. The key is, do you want it recharged today or not. The panel size and the allowed losses due to cable length and gauge only affect how long it takes to mostly re-charge your battery. (I say mostly, because a battery like mine will not get to 100% charge without bulk and absorption phases first occurring at 14.8 volts.) The system must replace, in the available daylight hours, all the power that was removed when the solar system was not charging. The combination of panel size and wiring losses needs to be calculated to be sufficient to replace that power. So, there is nothing wrong with some line losses if you upsize the panel to compensate.

For me, I found a folding panel (100W Renogy) that would fit in my luggage rack and I therefore had to use big wire to avoid line losses that would yield insufficient total power for my power budget. I had no wiggle room to go to a bigger panel. Bonus: My cable still fits inside the folded panel!

shadetreetim Mon Aug 18, 2014 3:03 pm

Thanks for taking the time to do an actual test on this subject Mark. Always fun to see real test results illustrating the effects of what may seem to be simple choices. It would be interesting to have seen a comparison of the #12 and #14 cords at comparable lengths.

I used #10 on my fixed panel install, although perhaps that was influenced by the fact I already had some UV protected 10/2 cable on hand. :lol:

4x4BNB Mon Aug 18, 2014 6:31 pm

Here's an interesting site....http://handybobsolar.wordpress.com

jmranger Mon Aug 18, 2014 6:57 pm

Howesight wrote: jmranger wrote: I'm puzzled by the drop in charging voltage. Do you understand why it is dropping? Battery internal resistance? Battery or panel temperature?
The voltage is dropping due to the cable length.
While this would be true in a "normal" DC system, where the power source is regulated and have a (relatively) infinite energy supply, I believe this is a significant oversimplification in the context of a solar panel, which is closer to a current source than a voltage source. A good reference on the theory of solar cells/panels is PVEducation. I don't pretend I understand it all.

In a very simple PV system (only a panel and a load), increasing the (ohm) value of the load increases the voltage output of the panel, but lowers the current output, and usually the power output too. But without specific load characteristics, I'm unable to predict how the voltage will split between the original and the extra load, and therefore whether the original load voltage will increase or decrease.

crazyvwvanman wrote: The charge controller I used is these particular tests is supposedly an MPPT design.
Thanks.

Thinking out loud... Would it be possible to do the same experiment without the charge controller and the battery in the circuit? Would it produce meaningful results? I'd do it with enough headlamps in series to stay in their nominal voltage.

crazyvwvanman Tue Aug 19, 2014 7:37 am

If the sun comes out to play today I will try the test you suggested. I have actually been doing lots of testing of different panels, different controllers, different wiring. I have tested 5 different size panels and 5 different controllers, fooling around with them when I get both the time and good sun in the middle of the day.

For most of my testing I measured volts and amps from the panel to the controller as well as volts and amps from the controller to the battery. All 4 meters were wired in so I could see all the readings at the same time. One limitation to my data is that the meters are only 3 digits, with 1 digit to the right of the decimal point. This is not precise enough for me to be satisfied with some aspects of my tests.

I am not very interested in a portable panel setup so large as to 100% fully charge my aux battery each day while I am camped. I don't need it to do that. My goal is to have a panel and long cable with me for those times when I find that I need it with the goal of extending my battery capacity for my 12volt fridge. That is it. I just want to be able to stay put for more than 3 nights and have my fridge still running. That is the same goal I had for my permanently mounted panel on my Westy roof. Our preference is for shady campsites and van orientations that are optimized for US rather than for the solar panel on the roof. That means there have been lots of times when the poptop mounted panel was nearly useless to us. If we were in a hardtop van the orientation issues would be lessened but our enjoyment would be reduced along with the headroom.

I have more controllers and panels coming. I will be doing more testing when I can. I will likely share more of the results.


jmranger wrote: ....
crazyvwvanman wrote: The charge controller I used is these particular tests is supposedly an MPPT design.
Thanks.

Thinking out loud... Would it be possible to do the same experiment without the charge controller and the battery in the circuit? Would it produce meaningful results? I'd do it with enough headlamps in series to stay in their nominal voltage.

j_dirge Tue Aug 19, 2014 8:27 am

crazyvwvanman wrote:

I am not very interested in a portable panel setup so large as to 100% fully charge my aux battery each day while I am camped. I don't need it to do that. My goal is to have a panel and long cable with me for those times when I find that I need it with the goal of extending my battery capacity for my 12volt fridge. That is it. I just want to be able to stay put for more than 3 nights and have my fridge still running.


I think this mirrors the real "needs" of most Westy owners. And if you take the fridge out of the equation you can go a long time on a very small panel.

I found that a 45watt panel, an 85amp/hr battery and a cheap ebay controller was all I needed to keep a 65qt Edgestar fridge\freezer running for 3 days.. The fridge actually ran at 38degs for 2.5 days on a battery with no recover charging (as a baseline) with ambient outside temps of 70-80.

Its good to have baseline numbers to begin to work from. Actual application requires fine tuning.. as you open and close the fridge.. or load room temp items into it, etc.

All said.. 200watts of panel and/or 220 amp/hrs of battery is likely more than most campers really ever need.
But I full understand the desire of many to have the most bitchin set up.
I suffer from gear-itis, too. :wink: But we are running out of room as the kids get bigger.. and things will be prioritized and extra panels, etc will be staying home. One 80-100 watt panel is all we will have next summer.. but it will be portable.. not permanently mounted on top. More flexibility.

Looking forward to more test results.

Kombi Dad Tue Aug 19, 2014 2:42 pm

I too needed to park in the shade and have the panels in the sun. The ones I use are a folding set of 120W charging a 137AH AGM battery. The panels came with about 30 feet of cable of a very thin guage with the regulator mounted on the panels. I ran some experiments as at first I was going to mount the panels on top of the camper. They were about 50% as efficient as when aimed at the sun so they stayed portable. For cable I changed the original cable to a much heavier cable, the type used for connecting vehicles to caravans for charging purposes here in Australia. I also used Anderson plugs either end of the cable to help packing up. The cable is now about 75 feet in length. I am moving regulator from the panels to the battery and will use a MP3129 Powertech regulator. This gives you some idea of how far I can put the panels away from the vehicle.




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