Portable (suitcase) solar "install" question

[johnm1]

I've gone back and forth on solar panels on the roof or portable. Well, due to a tight budget, portable is the only way I'm going to get solar for now and it makes sense for me to try it out 1st as we camp in shade a lot.

I'm looking at the 100-160w "suitcase" styles that are out there and the size/brand don't matter for my question ... unless someone has a real concern about a particular brand or company. Some, like Zamp, are not in the running due to cost.

Most of the kits come with a charge controller (which except Zamp is not water proof) and it's mounted to the back of the panel(s). I want to move it to inside the rv nearer the batteries.

- Using alligator clips to the batteries would be a pain in the backside for my setup. What kind of disconnect plug/connector should I use when I set up and take down the panels?

- I have the "Zamp Solar ready" outlet on the outside of the rv. Can I use that? Is it big enough wire for 100-160 watts of solar?

- Do I need to worry about arcing while connecting/disconnecting?

- Should I install a power cut-off on the wire right near the panels? Which one and I assume it should be water-proof?

- No system that I've seen has any fusing/circuit protection. I assume I should? And where does it go ... between the panels and CC or between the CC and the batteries?

Thanks,
John

[BFL13]

PWM controllers don't care about power as such. So some power loss between panel and controller doesn't matter to how many amps you are charging with. There is no Vmp or Imp with PWM. With PWM you can get away with long wires from controller to panel, but not from controller to battery.

Power matters with MPPT with their buck converters as how they do the amps to battery so now line loss between controller and panel matters- to keep input power up--but if your voltage there is 24 vs 12 you can use thinner wire of course. If it is MPPT and 12-12 you need fatter wire there too.

Both types of controller are affected by line loss between controller and battery.

BTW, WFCO does four hours max at its 14.4 (if you can get it to do 14.4 at all)

[2oldman]

johnm1 wrote:
The panels might be 50 - 100 ft from the batteries.

That's where the inefficiency (loss) is.

[red31]

so johnny is using 60ah a day and replacing 30, when he goona get to absorption camping? late absorption?

So there is no need to use 0.5A in any voltage drop calculator. Time is limited.

12g landscape wire would be ok for 50', if I use 5A in a voltage drop calculator
http://www.genuinedealz.com/voltage-drop-calculator
it yields .8v drop.
10g, 5A, 50' yields .5v drop.

It becomes a eco 101 lesson, how much does wire cost/availability
Would 3A be a better number to use?
12g, 3A, 50' 0.5v
10g, 3A, 50' 0.3v

[mike-s]

When it comes out of bulk doesn't make much difference. It's when it changes from absorption to float when charging really slows to a trickle (pun intended).

If the controller simply switches to float as soon as the absorption voltage is hit (like the infamous WFCO converters), then all bets are off - it's not charging right to begin with, and you've got bigger issues than which end of the wire to connect the controller to.

Quality controllers tend to use time and/or current to end the absorption stage (they also tend to support remote voltage and temperature sensing). Most cheap controllers don't document how they work, but I found one which did (LMS 2420). It says "When offline voltage of battery is close to constant regulated voltage, the battery is fully charged." So, it's stopping to measure the short term resting voltage vs. the desired voltage. So, the change from absorp to float would be unaffected by voltage drop.

50 feet of 2 conductor 12 gauge copper has a resistance of about 0.16 ohms. By the time you get to the late absorption stage (say, <0.5 A), the voltage drop will be <0.1 V. 100 ft of 10 ga will do similar. Mice nuts. The fixed setpoints on most cheap controllers have a greater difference than that vs. what the battery really wants. I've seen them come with fixed voltages from 14.2 to 14.7, and that's making the unwarranted assumption that they even measure that accurately.

[johnm1]

I don't have any real world experience on this subject but most everything that I have read (on this forum and solar companies websites & info) say to either use larger wire or shorter distance from CC to batteries. The 2nd option is preferred over the 1st.

Now, this brings up an interesting question. The panels might be 50 - 100 ft from the batteries. The cable connecting from the CC to the batteries is only 10 ft. What size wire should I use to make the extension cable? Would it change if the CC is moved near the batteries or just make it 10 gauge and be done with it?

[Tom_M1]

I helped a fellow camper clean up his solar install. The charge controller was installed at least 30ft from the batteries. Because of the voltage drop in the wire the controller was coming out of bulk way too soon. I shortened up the wire path and used much larger wire. He is now a happy camper.

[red31]

bologna, there is no need for a panel to operate between Vmp and Voc. With Vmp lowered by heat and low light, voltage drop can have the panel operate at lower current as the current drops radically at voltages over Vmp. PWM

If there is enough time then current taper can make up for voltage drop between the CC and batt but many a controller is limited to 2hrs which is not long enough if the charge rate is high enough and the sun goes down. In any event power is wasted due to voltage drop. This wasted power could have been used to charge the battery FULLER.

[BFL13]

Here is what Specialty Concepts has to say about that. Note they specify the voltage drop controller to battery be no more than 1/4 volt but that you can have 1/2 volt controller to panel.

"result in a voltage loss that will cause the batteries to be under-charged and/or
result in excessive heat at the connection. A poor connection to the battery will
also distort the battery voltage reading and cause the charging to stop too soon.
To check the connections, a voltage multi-meter is required and the ASC must be
charging with maximum expected charge current (very sunny conditions).
Battery Connection: - First, note the voltage at the battery terminals. Select the
positive and negative terminals that are used for the ASC connection. Then,
immediately check the voltage at the ASC terminals for “BATT (+)” and “BATT (-
)”. The difference in voltage should not be more than ¼ volt*.
Array Connection: - Next, note the voltage at the panel wires. Select the
positive and negative wires that are used for the ASC connection. Then
immediately check the voltage at the ASC terminals for “ARRAY (+)” and
“ARRAY (-)”. The difference should also be no more than ½ volt*."

See para 14

http://specialtyconcepts.com/SPECIALTY_CONCEPTS_PDF_FILES/ASC_INSTRUC_MANUAL.PDF

[mike-s]

BFL13 wrote:
The main reason to still keep the controller close to the battery is so the voltage drop between battery and controller does not mess up the controller set points.

The high set point will never be reached with voltage drop, because the controller will "see" the battery voltage as being higher than it really is, so that can leave the battery undercharged.

BS. When in bulk charge, all available current is provided - it makes exactly zero difference to charging where the voltage drop occurs. Voltage drop after the controller will cause the controller to go into constant voltage (i.e. absorp) mode slightly sooner than it otherwise would, but current and consequently voltage drop begin to taper off soon after that, anyway. Either way, whether current or time based, by the time the absorption stage is done there should be minimal current, and therefore minimal voltage drop. Same when in float - minimal current, minimal drop. Moving the controller closer to the battery does not affect the final results in any meaningful way.

It will definitely NOT cause a battery to be undercharged.

[BFL13]

mike-s wrote:

johnm1 wrote:
If I need to move the CC for efficiency and since it's not waterproof, should I replace it with something better?

Moving the CC won't change the efficiency one bit. Whether the voltage drop occurs in the wiring before or after the controller makes no difference.

The only reason to move a PWM CC closer to the battery is if it supports temperature compensation and that will keep it from being at a significantly different temperature than the battery.

Not the only reason.

The main reason to still keep the controller close to the battery is so the voltage drop between battery and controller does not mess up the controller set points.

The high set point will never be reached with voltage drop, because the controller will "see" the battery voltage as being higher than it really is, so that can leave the battery undercharged.

[mike-s]

johnm1 wrote:
If I need to move the CC for efficiency and since it's not waterproof, should I replace it with something better?

Moving the CC won't change the efficiency one bit. Whether the voltage drop occurs in the wiring before or after the controller makes no difference.

The only reason to move a PWM CC closer to the battery is if it supports temperature compensation and that will keep it from being at a significantly different temperature than the battery.

[johnm1]

Info overload is a real possibility 🙂

I think I've settled on the HQST 100w suitcase.

If I need to move the CC for efficiency and since it's not waterproof, should I replace it with something better?

With this setup, would a cheap mppt be worth it? Or would I be better off getting the Grape solar CC?

[JiminDenver]

Each 80w panel is rated for 4.89a Isc.

[JiminDenver]

A friend that camps with me on and off ordered the Solarblvd portable after having his grp 24 get down to 11.2v when running the generator for a hour daily. first we used my trailer as shore power and allowed his 45a dumb converter run all day. Then we did it again until the battery was up to 13.6v, then switched to a Meanwell 30a powersource to take it up to 14.4v for 3 hours, and then equalized it at 15v for the rest of the day. The next morning he saw 12.6v resting.

We both ordered the 160w portable and we set his up, mine is still in the box for demonstration use next year. I also ordered a new Eco-worthy 20 MPPT to be able to show the differences between it and the PWM controller that comes with the portable. The first thing I'll say is my friend has not ran his generator since getting his. The second thing is the POS controller is glued to the back of the panel and can't be moved near the battery. Setting it is a pain and it resets when he unhooks it. The third thing is there is no cords for between the portable and the battery.

My friend is thrilled as he can use the limited amount of power he does and the portable keeps up even with the cheap controller on the panels and the extension cord he is using to connect it. He asked about upgrading and I told him he could buy a inexpensive PWM controller and mount it nearer to the battery. He could buy a third panel which would do more for him than going MPPT with the two panels he has. Even the cheap controller would handle the third panel. As it is he is wondering if he even needs to upgrade the solar or battery at this point. He has a built in generator for the microwave, A/C and boosting the battery early when it's cloudy for too long allowing the solar to take over afterwards.

In his case it is perfect but with the low prices I have seen on 12v panels I wonder if making your own with a few hinges and a set of legs may not be better considering the cheap controller and the fact that it can't be taken off to be put by the battery as well as the lack of cables/fuse. Aside from demonstration purposes at a talk I agreed to give next year mine will be used to keep the trucks battery as well as a small battery I use for a portable water pump up when I sit long term. It is not worth adding it into the house systems even if it does bring my total up to 1345w.

I will try to remember to check the Isc of his tomorrow, the rating does seem low.

[2oldman]

I think the OP may be getting into information overload.