I know that this subject has been discussed before, but I’ve never found exact clarification. I currently have two factory install solar panels on my 2006 midbath, and I Would like to sometimes use a portable solar panel to get out from under trees etc. I’m looking at the renergy portable panels.
My question is, can I simply connect the clips directly to my positive and negative on the two house batteries, Or would I need to connect it somewhere before it gets to my Blue Sky charge controller?
Anyone actually do this and is it really simple or does it require some specific skill or knowledge?
Scroll down to the Q/A section (assuming you are looking at solar "suitcases"). "Renogy systems are designed to make direct battery connections."
Renogy Folding Solar Suitcases (https://www.renogy.com/solar-panels/folding-solar-suitcases/)
Charles
Scroll down to the Q/A section (assuming you are looking at solar "suitcases"). "Renogy systems are designed to make direct battery connections."
Renogy Folding Solar Suitcases (https://www.renogy.com/solar-panels/folding-solar-suitcases/)
Charles
Thanks and I looked at this. I am thinking perhaps I didn't ask the question correctly. I guess that I am really asking if I can have two different but parallel charge systems directly connected to the batteries?
I guess that I am really asking if I can have two different but parallel charge systems directly connected to the batteries?
Yes, you can connect two different arrays and charge controllers to the same battery bank. The Array 1 and Array 2 voltages could be different. And you can connect more than two arrays and charge controllers - all in parallel.
Note - This only applies if the added solar array has it's own controller.Also, you already have three different charging systems tied to the house battery bank in addition to the house solar system; when the engine is running, when you run the generator, or when you are connected to 120V and the converter is on.
Charles
Yes, you can connect two different arrays and charge controllers to the same battery bank. The Array 1 and Array 2 voltages could be different. And you can connect more than two arrays and charge controllers - all in parallel. Note - This only applies if the added solar array has it's own controller.
Also, you already have three different charging systems tied to the house battery bank in addition to the house solar system when the engine is running, or when you run the generator, or you are connected to 120V and the converter is on.
Charles
Very good explanation. I can’t think of any downside. Sounds like something I can use my stimulus check for. Now I need to pick out the perfect one that includes controller and get long enough cables, all at the best price. The Renegery site looked pretty good and I can get through Amazon I believe. Thanks
Greetings,
I have been using the exact setup that you are proposing for the last 6 months and it has worked perfectly. I have the Renogy 200 watt Eclipse Solar Suitcase. As long as you use the included solar controller and set it to your type of batteries you should be fine. Just as an aside, I also use the panels to charge my Goal Zero(GZ) YETI 1000 on occasion and this also works fine as long as you disconnect the Renogy charge controller and just direct connect the panels to the generator. The GZ already has a controller to manage the input. I am pretty sure you will really appreciate the additional flexibility your setup provides for power generation.
Matt
Me again :D
I forgot to mention that you might consider purchasing (2) 25' power cables. 25' seems like plenty but I have found that 30-40% of the time that additional 25' has allowed a more optimum panel position for me and often reduces the amount of adjusting required over the course of a day. I just like having as much flexibility as possible(or maybe I am just lazy:) and these cables do not require much storage space.
Matt
Now I’m thinking that I can’t believe I haven’t done this before. Thanks to you guys.
Me again :D
I forgot to mention that you might consider purchasing (2) 25' power cables. 25' seems like plenty but I have found that 30-40% of the time that additional 25' has allowed a more optimum panel position for me and often reduces the amount of adjusting required over the course of a day. I just like having as much flexibility as possible(or maybe I am just lazy:) and these cables do not require much storage space.
Matt
Does the extension cable go between panels and controller, or between controller and battery? Are they 10 gauge?
Yes, the cables connect from the the solar controller to the battery. I purchased 10 gauge cables. If you end up buying a Renogy 200 watt portable suitcase the solar controller comes connected to the back of one of the panels right in the suitcase. It is water and weatherproof. I do believe it is easy to remove if you prefer to surface mount it permanently somewhere on your coach.
Matt
Most excellent and thank you. Perfect
A thread on and about my experience on this very issue .....
cheap but very doable
Homemade Portable Solar Panel Built (https://www.lazydazeowners.com/index.php?topic=33245.0)
glen
One way to get your 25 or 50 ft distance is to buy 2 25ft outdoor extension cords (up to 10 ga. are readily available for reasonable prices) and cut off the male end of one of them, leaving a couple feet of cord on it. Attach the cut end of the long piece to your controller, and attach the short piece to whatever you will be using to connect to your battery (maybe large alligator clips if connecting directly to your battery). When all you need is 25 ft. just plug the two together, but when you need 50 ft. just put the other 25 ft. cord between them.
Rich - Birch Bay, WA
One more idea, if you don't mind spending a little more and you want 10 ga., buy 2 30 AMP RV extension cords ($40 each on Amazon) (www.amazon.com/Conntek-14363-Extension-Black-25-Feet/dp/B00F17Q8BM/ref=sr_1_26?crid=1IGLNIBEIMZKP&dchild=1&keywords=10+gauge+extension&qid=1615238921&refinements=p_n_feature_keywords_two_browse-bin%3A7065062011%2Cp_36%3A1253529011&rnid=1243644011&s=lamps-light&sprefix=10+guage+%2Caps%2C271&sr=1-26) and do as I described in previous post. Advantage there is if you don't need it for the solar panels it is available if and when you need an extension for normal RV AC.
Rich
"buy 2 30 AMP RV extension cords..."
If I understand what you're saying, that would mean using 30A RV plugs and sockets for your solar panel connections. In order to avoid exposed live terminals, you'd want to mount a 30 A Marinco or SmartPlug power inlet on the coach--similar to the existing shore-power inlet--and connect that to the solar controller's input side.
Maybe I'm being over-cautious here, but that seems potentially hazardous. Of course, you as the original owner would never make the mistake of plugging your shore power cord into the solar power inlet (would you?)... but what about the next owner? Doing that would result in a catastrophic failure of the solar controller, and possibly a fire, given that it's expecting 18 VDC on those inputs, and all of a sudden it's seeing 120 VAC.
It just doesn't seem like a good idea to use 120V 30A hardware for a low-voltage DC circuit.
Or something like this
Amazon.com: 10 Gauge 10AWG One Pair 30 Feet Red + 30 Feet Black Solar Panel... (https://www.amazon.com/Gauge-10AWG-Extension-Female-Connectors/dp/B08HYWHB9Y/ref=sr_1_8?crid=Z2G0QCSOJTNV&dchild=1&keywords=solar+panel+wire+extension&qid=1615249522&sprefix=solar+panel+wire%2Caps%2C250&sr=8-8)
Comes in all sorts of lengths.
glen
It just doesn't seem like a good idea to use 120V 30A hardware for a low-voltage DC circuit.
I'm in 100% agreement with Andy, mixing high voltage plugs with low voltage applications is a recipe for disaster.
There are plenty of low voltage plugs to choose from that will not cause potential issues.
Running extra-long extension cords for solar panels can lead to significant voltage drop and less effective charging unless the wire size is upgraded accordingly. Volage drop makes a big difference in charging circuits.
Larry
There’s something we haven’t talked about with regard to portable panels, and it’s a big potential “gotcha.” A controller that's mounted on the panel (as in the case of many "suitcase" systems) is convenient, but it puts out a voltage suitable for charging your batteries--much lower than the voltage straight out of a solar panel. That means voltage drop—already a concern with long connecting cables—is even worse. I’ll go into detail in my next message, but let me summarize.
Suppose you have a 200 W solar suitcase with built-in controller, connected to your batteries with a 35' 10-gauge extension cord. Your voltage drop is going to be 6.2%. That means instead of getting the 14 V they need, your batteries will be getting only 13.1 V. They won't ever charge properly at that voltage!
Bottom line: if possible, avoid suitcase solar panels that have built-in controllers. (Many of these are cheap, inefficient PWM controllers, which is another strike against them.) And if you must buy one of these, make your connecting cable as short and as heavy gauge as possible. If you buy one of these controller-equipped suitcase systems and put it at the end of a twenty- or thirty-foot cable, don't be surprised if your batteries never get a full charge.
Important: the following assumes you have an MPPT (not PWM) charging controller that can handle more than 18 V, and that the controller is in your coach--not on the panels. See my last post for the reasons.
"There are plenty of low voltage plugs to choose from that will not cause potential issues."
I use MC4 connectors, but trolling motor connectors are another possibility. I carry a 10' and a 25' extension cable (Ancor 10/2) for my portable solar panels. I use the 10' cable when I can, the 25' cable when necessary, and both together once in a blue moon.
With long cables, voltage drop is a serious concern. Assuming #10 cables, the voltage drop (http://www.nooutage.com/vdrop.htm) for 200 watts of 18V panels wired in parallel would be as follows:
10' - 1.4%
25' - 3.4%
35' - 4.8%
As you can see, with a 35' extension cord you lose almost a volt, and with an 18V setup that's serious.
That's why I connect my portable panels in series. They are 20 V panels, so instead of 18 V, I'm putting 40 V through the connecting cable. Thus my numbers for 200 watts of panels would look like this:
10' - 0.6%
25' - 1.5%
35' - 2.1%
That cuts my voltage drop to less than half, compared to running panels in parallel at 18 V. To achieve such small voltage drops at 18 V, you'd have to go from #10 to #6 cable. That's a lot more expensive, heavier and bulkier. (And you can't fit MC4s onto it.)
In short, if you can put your portable panels in series, you'll cut your voltage drop in half. Given the long extension cords we've been talking about, that's a huge benefit.
Important: the following assumes you have an MPPT (not PWM) charging controller that can handle more than 18 V, and that the controller is in your coach--not on the panels. See my last post for the reasons.
"There are plenty of low voltage plugs to choose from that will not cause potential issues."
I use MC4 connectors, but trolling motor connectors are another possibility. I carry a 10' and a 25' extension cable (Ancor 10/2) for my portable solar panels. I use the 10' cable when I can, the 25' cable when necessary, and both together once in a blue moon.
With long cables, voltage drop is a serious concern. Assuming #10 cables, the voltage drop (http://www.nooutage.com/vdrop.htm) for 200 watts of 18V panels wired in parallel would be as follows:
10' - 1.4%
25' - 3.4%
35' - 4.8%
As you can see, with a 35' extension cord you lose almost a volt, and with an 18V setup that's serious.
That's why I connect my portable panels in series. They are 20 V panels, so instead of 18 V, I'm putting 40 V through the connecting cable. Thus my numbers for 200 watts of panels would look like this:
10' - 0.6%
25' - 1.5%
35' - 2.1%
That cuts my voltage drop to less than half, compared to running panels in parallel at 18 V. To achieve such small voltage drops at 18 V, you'd have to go from #10 to #6 cable. That's a lot more expensive, heavier and bulkier. (And you can't fit MC4s onto it.)
In short, if you can put your portable panels in series, you'll cut your voltage drop in half. Given the long extension cords we've been talking about, that's a huge benefit.
Here's a good explanation of the difference between MPPT vs PWM solar controllers: https://www.solar4rvs.com.au/buying/buyer-guides/choosing-the-right-solar-charge-controller-regulat/
Chris
This may up being a long post, so be warned, but maybe it will shed a little more light on solar systems, both on top and portable. First let me say that I'm a pretty practical guy, so things like cost, weight and space are all important to me. So, with that in mind, going back to one or two of my previous posts on this subject, I suggested ways to use other useful cables to extend the distance between portable solar panels and the rig. I should have put in a disclaimer that if you didn't feel comfortable with the difference between 12 volt DC and 120 volt AC systems you should not try it at home.
With that out of the way, I'd like to respond to Andy's posts. 1st, the second post. I agree, with all he had to say, and if portable systems of 200 watts or more with no roof mounted solar is all you have, I would say his method is should be your method of choice. I was one of the first on this forum to recommend putting panels in series, and actually ran tests on my panels, series vs parallel and reported my results back in 2005 or so. Most said I was nuts because of shade. Oh well, time and ideas change, but I still say, that for most folks who want to add to their factory mounted panels you can at least double their capacity without changing wiring by putting them in series. One important thing to think about, if you use Andy's method for portable panels, in my opinion, you MUST mount that MPPT controller as close as possible to the battery bank.
Now Andy's 1st post. The way a PWM controller works is to turn the voltage from the panels on and off for varying pieces of time. As a result, the battery will always see the voltage the panel is putting out, minus the loss in the cable. Therefor what he said about a battery never seeing enough voltage to fully charge it may be true if it were a MPPT controller mounted on the panels but not a PWM. It might take a little longer, but it would take a really long cable to reduce 18 or so volts from the panels to less than 15 volts to not fully charge most batteries. Both types of controllers rely on sensing the battery voltage, and the difference in voltage between sensing and charging can make them both crazy with long distance which is why an MPPT controller should always be close to the battery....better for a PWM controller too, but not as important.
So, lets go back to the original post. As I recall, our poster had 200 watts of solar on the roof and wanted info on adding portable solar when he was parked under the shade. In his situation, again remembering my practical nature, I would recommend a 100 or 200 watt suitcase with a waterproof PWM controller mounted on the panels. ( If it were me, I would order 2 100 watt panels , a waterproof PWM controller and build it myself...again, I'm practical and cheap). Talk about being cheap, if a person was willing to monitor the battery voltage, one might not need a controller at all. Just connect the panels (wouldn't recommend this for more than about 100 watts) thru a diode (to prevent discharging the battery) and monitor the battery voltage. As I recall, Trojan recommends 14.8 V as a daily charge and then disconnect it. Not a recommendation for most, but then again, something to think about.
Rich
Rich - Birch Bay, WA
Thanks to all who have contributed to this portable solar panel thread. This is what our members do best - provide valuable Lazy Daze and general RV technical information to those of us who are technology/mechanically challenged, which includes me.🙂
Chris
One more thing that should be mentioned when talking about adding portable solar is fusing. It may be well understood, but it is extremely important to remember to fuse anything new that you attach to a battery as close to the battery as possible. For portable solar, it should be sized by considering both the safe current handling capacity of the cable used (probably 30 A for 10 ga. cable) or the maximum current expected from the panel(s) (probably 15 A for 200 Watts of solar panel) whichever is less. Hopefully that will always be the maximum solar panel current. In my opinion, fusing between panels and controller is rarely if ever necessary, but if it makes you feel better, put one in there too.
Thank you Rich for your succinct and straightforward explanation of how a PWN and MPPT controller would interact in the described portable set up. My experience over the last year with a 200 watt Renogy solar suitcase matches your description perfectly, i.e., the charge time increases somewhat when I add a second 25' power cable extension but can still achieve a full charge. Thanks again to you and everyone else who has contributed to this thread. Once again, I feel like I am more knowledgeable after reading everyone's thoughtful contributions.
Matt
"what [Andy] said about a battery never seeing enough voltage to fully charge it may be true if it were a MPPT controller mounted on the panels but not a PWM. It might take a little longer, but it would take a really long cable to reduce 18 or so volts from the panels to less than 15 volts to not fully charge most batteries."
That's a good point. Using my example (200 W of 18 V panels connected in parallel, with a 35' cable), with a PWM controller mounted on one panel you'd see 0.86 V drop in the cable, so you'd still have more than 17 V hitting the batteries. This setup would fully charge your batteries, contrary to what I said.
If you wired those same two panels in series and used an MPPT controller mounted close to the batteries, you'd get significantly faster and more efficient charging... and I hate to throw away potential solar power. But a solar suitcase with a built-in PWM controller is a convenient, off-the-shelf solution, no denying that. If your needs are modest, that could be your best bet.
Based on all the info, assuming I understand correctly, I am ordering the “Renogy 200 Watt Monocrystalline Foldable Solar Suitcase, 200W Panel-20A Controller” from Amazon (it has PWM controller) and the 10 gauge 30’ extension cables.
This summer we will be at Matterhorn campground above Telluride, site 20. On google earth it is bordered by trees, but I am thinking the extra solar will be a positive boost. As a side note, the Jeep I tow is getting heavier with everything I buy.
If you're talking about the Renogy 200 Watt suitcase for $336 on Amazon, I don't think you will be disappointed. (www.amazon.com/Renogy-200-Watt-Monocrystalline-Controller/dp/B07RFQVB9M/ref=sr_1_3?crid=1UFAGLD43W73F&dchild=1&keywords=200%2Bwatt%2Bsolar%2Bsuitcase&qid=1615505472&sprefix=200%2Bwatt%2Bsolar%2Bsui%2Cautomotive%2C253&sr=8-3&th=1)
It has the waterproof 20A Voyager Charge Controller, and a fused cable, but only 8 ft. long. Not sure what you are thinking about for the extra 30 ft. of cable, but you have lots of options for it. You could probably put one together yourself for less, but it wouldn't have the nice case and stand.
Rich
If you're talking about the Renogy 200 Watt suitcase for $336 on Amazon, I don't think you will be disappointed. (www.amazon.com/Renogy-200-Watt-Monocrystalline-Controller/dp/B07RFQVB9M/ref=sr_1_3?crid=1UFAGLD43W73F&dchild=1&keywords=200%2Bwatt%2Bsolar%2Bsuitcase&qid=1615505472&sprefix=200%2Bwatt%2Bsolar%2Bsui%2Cautomotive%2C253&sr=8-3&th=1)
It has the waterproof 20A Voyager Charge Controller, and a fused cable, but only 8 ft. long. Not sure what you are thinking about for the extra 30 ft. of cable, but you have lots of options for it. You could probably put one together yourself for less, but it wouldn't have the nice case and stand.
Rich
This is exactly the one I just ordered. Makes me feel better that you just suggested this one. I need to go camping and stop spending money
You will be happy with the Renogy product and appreciate the additional flexibility it brings to power generation. One other item to mention direct from my own personal school of hard knocks; be sure secure the panel stand to the ground in some way to prevent them from falling over in the event of a stiff breeze coming from just the right direction :)
Matt
"be sure secure the panel stand to the ground in some way to prevent them from falling over in the event of a stiff breeze"
Amen! The wind can flip a panel over on its face. If that happens on rocky ground, it could crack the glass. It hasn't happened to me yet (the breakage), but I've had a few close calls.
Thank you all for this enlightening conversation! I had this same question about suitcase solar use. I also had some of the same circuitous thoughts that always landed me back at, “better safe than sorry,” so I never hooked the clamps to the battery! I have a small suitcase with a built in PMW, and 10G cable that I put MC4 clips on for an extension. I can now take a deep breath and proceed with a semblance of confidence when I gator clip this set up to the battery. BTW, I have a ‘92 with the original solar panels, inverter/converter and meter... the system still works, thus my hesitance to mess with it.
Tina, I'm glad this conversation gave you what you needed to go ahead and hook it up. Just don't forget what I said about fusing that cable near the battery. A 10 amp fuse on the positive side should do the job nicely.
Rich
As a follow-up to my original post I ordered and received the 200 KW Renegy portable suitcase system. Darned if it wasn’t too heavy. I ended up returning it and got the 100 KW version. At least this one I can actually lift and carry around. It’s unbelievable how much strength I’ve lost over the years.
Jackery has just announced its new product (https://www.jackery.com/products/jackery-solar-generator-2000-jackery-2000-4-x-solarsaga-200w). At 2060 watt hours and 800 watts of solar panels . . . well, that's pretty breathtaking!
Virtual hugs,
Judie
Jackery has just announced its new product (https://www.jackery.com/products/jackery-solar-generator-2000-jackery-2000-4-x-solarsaga-200w). At 2060 watt hours and 800 watts of solar panels . . . well, that's pretty breathtaking!
At a breathtaking price! :o
Jack, while everyone's needs are different, maybe 100 watts is enough to supplement your roof system. My case is probably very different from most, but here's my story. First, I have no roof system on my small trailer. Second, my power needs are less than most. We use this trailer to go to music (Bluegrass) festivals almost exclusively and during the summer with long days in the Pacific Northwest. We spend very little time in the trailer, as our time is spent making or listening to music. While we are boondocking, our power is mostly used for keeping the refrigerator going, lights to get ready for bed, etc. Even here in the NW, where the sun is pretty far south, 100 watts is usually all we need to keep our 2 golf cart batteries charged. Sometimes we need a little more, especially if the morning is cold and we run the furnace to warm it up. My solution is a 100 watt solar suitcase with a 20 AMP controller. In addition, I carry a separate 100 watt panel. I have put connectors on the panels such that I can run either the suitcase by itself or put the second panel in parallel with the suitcase to give me 200 watts. Finding room for this stuff can be a challenge, but we have the bed of the truck available. I usually just set the extra panel on something to give it an angle to the sun when I need it. A 100 watt panel is pretty cheap these days, and if your controller is capable of handling a second 100 watts, and if you have the room, it might be something you want to think about.
Rich
"We use this trailer to go to music (Bluegrass) festivals almost exclusively and during the summer with long days in the Pacific Northwest."
----
I do miss the bluegrass festivals! :(
Jack, while everyone's needs are different, maybe 100 watts is enough to supplement your roof system. My case is probably very different from most, but here's my story. First, I have no roof system on my small trailer. Second, my power needs are less than most. We use this trailer to go to music (Bluegrass) festivals almost exclusively and during the summer with long days in the Pacific Northwest. We spend very little time in the trailer, as our time is spent making or listening to music. While we are boondocking, our power is mostly used for keeping the refrigerator going, lights to get ready for bed, etc. Even her in the NW, where the sun is pretty far south, 100 watts is usually all we need to keep our 2 golf cart batteries charged. Sometimes we need a little more, especially if the morning is cold and we run the furnace to warm it up. My solution is a 100 watt solar suitcase with a 20 AMP controller. In addition, I carry a separate 100 watt panel. I have put connectors on the panels such that I can run either the suitcase by itself or put the second panel in parallel with the suitcase to give me 200 watts. Finding room for this stuff can be a challenge, but we have the bed of the truck available. I usually just set the extra panel on something to give it an angle to the sun when I need it. A 100 watt panel is pretty cheap these days, and if your controller is capable of handling a second 100 watts, and if you have the room, it might be something you want to think about.
Rich
Good info and thanks.
Actually, you had me at Bluegrass. I am addicted to Bluegrass and often search for festivals when we travel. Thanks
Love Bluegrass!
Love Bluegrass!
Do you play at all?
Do you play at all?
A little harmonica and a few chords on the guitar only. Not a musician by any stretch of the imagination.
A little harmonica and a few chords on the guitar only. Not a musician by any stretch of the imagination.
Three chords and you can join the Lazy Daze band.
I just hope most of the festivals are on again this year. Most were canceled last year because of the virus. So far, so good, just keeping my anxious fingers crossed.
At a breathtaking price! :o
At 43 pounds, hardly more than a big bag of dog food. ;)
Actually that is not a bad price for what you get. If you price out systems at the 2060Wh (36V, 57.24Ah) you'll see it's very competitive. Keep in mind you'll get to use 80 to 90% of the power unlike lead acid systems. The station itself is $2000 and change. If I was getting it I'd buy cheaper and imho better solar panels.
glen
"If I was getting it I'd buy cheaper and imho better solar panels."
Agreed. In particular, note this warning from the manufacturer: "The solar panel is not waterproof." Who wants portable solar panels that can't be left outside in wet weather? That's ridiculous.
I like Jackery products in general, but I wouldn't buy non-waterproof solar panels.
Indoor-use-only solar panels. Is it April first already?
Steve
I can guess what their intended market is: weekend tent/car campers who will (it is hoped) dutifully fold up and put away their solar panels every night, or when precipitation threatens. Still, it's a stupid limitation. But I remember seeing an even dumber warning in a similar solar panel's instructions: users are cautioned not to leave the panel outdoors for too long, or "Sun damage will result." !!!
OK, I was still trying to get my head around the 'solar panel is not waterproof' disclaimer! So, there's another solar panel that can suffer 'sun damage' if it's left out in the sun too long!? Buyers of some, if not many, of these types of products must be dreams come true for target marketers and 'influencers'.
As ever, YMMV.
The thing is, a lot of these tent-camper-oriented fold-up or roll-up panel arrays are made mostly of plastic, which houses cheap polycrystalline solar cells. They're not at all like the durable rigid-metal-framed panels most of us are familiar with. They're designed to be thin and lightweight, but they're not very durable if used more than occasionally. If one of these panels is left out for extended periods, I can easily imagine the plastic degrading or even warping.
The same goes for larger flexible panels, although those are at least waterproof. I've seen a few fail after a year or less. You can get better-quality flexible panels that are made for yachts--I have a couple--but even those are not as durable as rigid panels. And you don't really want to lay a flexible panel on the ground. It's likely to get scratched, blown around by the wind because of its light weight, or both.
We recently got the Renolgy 200 watt portable suitcase Solar and have been happy with it.
We wanted it for the same reasons as others - park in the shade, solar in the sun. And a waterproof controller!!
We are pleased with it - we are getting typically 8-9 amps in the afternoon (southern CA coast). We use about 40ah a day so more than enough for us.
One thing I didn’t see mentioned above, while portable solar says to connect directly to the battery (positive and negative) if you use a battery monitor (and shunt) the connection is different. This amsolar video explains this - at about 3 minutes 10 seconds into the video.
https://m.youtube.com/watch?v=KIVeffHqXu4&feature=emb_logo
Our battery bay barely holds the batteries so our victron 712 shunt is inside the Coach (right next to the battery bay, in our power center location).
We added some battery junction posts in a convenient location to reach inside our battery bay so we could easily connect the Renolgy to the positive battery terminal and the shunt load post.
That's a good point--if you're using any shunt-based battery monitoring system (which is pretty much any one worth having), connecting a portable solar panel that has its own solar controller directly to the battery terminals will completely throw off your readings.
That's because the battery monitor can't "see" current that doesn't pass through the shunt, and connecting directly to both battery terminals bypasses the shunt. The result: the monitor will falsely show your batteries slowly losing power, because the input from the portable panel won't register.
Thus, you need to ignore the instructions that came with the portable panel, and connect its negative lead to the same place as all your other negative wires: on the other side of the shunt from the battery. Putting it simply: if there's more than one cable on your battery's negative terminal, you're doing it wrong.
Again, this only applies if you have a shunt-based battery monitor.