Voltage Drop and Other Solar Musings/Solar Lunchbox

ScottG

I'm still pondering options for increasing the efficiency of my solar suitcase while retaining ease of use. If I extend the leads from the suitcase-mounted controller, voltage drop between the controller and the battery can reduce (or even negate) the charging capacity of the panels. I could relocate the controller (and might end up doing so) but I kinda' like the self contained nature of the suitcase.

However, it occurred to me that the charging voltage of my controller can be manually adjusted. Using a voltage drop calculator like this one (thanks, jkjenn): https://www.wholesalesolar.com/solar-information/voltage-drop I could increase the output to compensate for the voltage drop when using the suitcase with a long or smaller gauge extension.

Does this seem reasonable? Any reason it wouldn't work?

jcfaber1

I would mount the controller next to the batteries and increase the the thickness of the wire (lower guage)  to reduce the voltage drop.

ScottG

Understood--and that's probably what I will ultimately end up doing. However, I have 30' of weatherproof 12g super-flexible cable that would allow me try out the extension cord approach with minimum investment of time or money. I'm a tinkerer, but also a thinkerer...  :-)

Sharon_is_SAM

Go for it Scott and let us know.  Maybe check with Renogy?

Nomad

Remind me, how much of a drop are you trying to negate?

ScottG

The voltage drop depends on several factors, but for for my proposed project (30' of 12g at 6A) the calculator shows a drop of ~0.7V. That's pushing 5%--not a huge amount, but enough to bring bulk phase closer to float voltage, and float voltage closer to battery voltage.

Since 0.7V is within the user-defined parameters of the charge controller, it seems an easy way to experiment with my existing set-up before diving into another mod. I'm no solar guru however, so there may be some additional aspect I'm overlooking.

As SAM suggested, I did sent an inquiry to Renogy. I'll post back when I get their response.

Ratkity

I know you want to increase the efficiency of the controller and panels, but most of the time, your prime theft of your panel efficiency is heat plus the amount/strength of direct sun (including time of year). Panels work optimum at 77F and the most time you'll get out of sun is 4.5-5.5 hours (give or take). The hotter outside it is, the less efficient your panel is... panels can go down down to nearly 0.1% efficiency (depends on panel type, what it's made of, air flow around the panel and position/angel towards the sun).

It was just a few thoughts. For a big bank of expensive batteries and lots of panels, voltage drop over distance is a big deal. Many here have found that 25' extension of 10g wire (some say 10') hasn't done much for how well their panels work (the suitcase ones).

jcfaber1

For the voltage drop calculation, I am using an app on my phone from Southwire.  The implication is a lot more than meets the eye with the charging potential.  I have shown the math in another thread on this forum.  If you can't find it let me know.

wizard1880

Also keep in mind that voltage drop only occurs when the panel is putting full current into the battery.  If you're almost charged up and only 1 amp is going in, the increased voltage might boil out your battery faster.

I'd look into a thicker wire or moving the charge controller closer to the batteries, instead of increasing the charging voltage.

Sharon_is_SAM

This is why when I purchased the Renogy suitcase, I ordered the suitcase and a separate controller.  My plan is to mount the controller in the tub.  Can you easily separate the controller, Scott, or do you need to bypass it and get a new one?

ScottG

Here's the response I got from Renogy...

We would not recommend using the charging voltage output modification to compensate for voltage drop, this option is mainly used to match a batteries necessary charging voltage. Potential problems can arise if your system has had the charging voltages modified and you start producing at maximum output, your charge controller will send a higher voltage to your battery and this will result in damage to your battery.

While short on technical details, this does seem consistent with comments here (and with my vague suspicions)--variables such as light intensity, amperage, and battery condition also affect charging parameters, so mucking around with the controller's output voltage may have detrimental effects. The idea was more a wild hair over morning coffee than anything based on a solid understanding of electrical physics!

SAM, the suitcase has the same controller as what could have been bought separately. It's only taped to a hinged mount on the panel, so it could be easily separated and relocated. (Renogy says doing so will void the warranty, but that's not major concern for such an economical system.) I'll probably revert to my original plan (as discussed in another thread) of mounting the controller somewhere inside the cabin. Details TBD... 

Thanks for the input!  

jcfaber1

The voltage drop occurs due to resistance on the line.  Here is a calculator.

http://www.southwire.com/support/voltage-drop-calculator.htm

John

ericnliz

ScottG, "I could relocate the controller (and might end up doing so) but I kinda' like the self contained nature of the suitcase." I have thought the same as you, about moving the controller, but your statement reflects my thoughts on moving it as well. I've looked in to it, and spoke with a technician at Renogy who didn't really see that moving it would be a big advantage at all (and the warranty issue came up as well). From speaking with him, and considering a few of the comments here as well, I personally don't think, even if you purchase the longer extender cords, that it will have an advantage to offset moving the controller. Do you have the MC4 connectors for your extended cables, and do you have an in-line fuse for them as well. At any rate, what ever you decide to do, please keep us curious one's posted as to the outcome. Thanks!

Ratkity

When Renogy had a recall on their flexible panels, I opted to get a suitcase as a replacement because of all the positive reviews here on the Zamps and other suitcase panels - it doesn't have a controller because I already had a controller installed in the T@B bin and monitor inside the T@B. Now, I don't have a bin anymore! I've been playing with the idea of getting the controller that Renogy puts on their suitcases, but it's not waterproof (I can't leave panels out when I'm at home and it rains overnight). The new Retro has a built-in Zamp plug, btw.

As a weekend camper and an east-coast dweller, I'd mostly use the solar suitcase as I've used solar before, just as a battery maintainer and for infrequent boondocking weekends. In most of the parks I camp, there isn't a cord long enough to get the panels out of the shade to full sun (which is usually shining brightly in the middle of a river). 

Should I get the Renogy controller and put a waterproof case around it somehow? (have drills and caulking, will travel) and plug into the Zamp connection (with adaptor)?.... Should I put a waterproof box beside the battery and run the Zamp connector into the box, have the controller/monitor there plus a cut-off breaker for the battery that I need and then run the wires to the panels? I'd have to run cable from the Zamp connector to the front where the battery box is..not a big deal - probably 6-8ft to make it around the corner to the center of the tongue. I'm not as creative as some folks here!! Help a poor flamingo and bunny burn-out here!!

ScottG

Thanks, John. I assume I should be doing these calculations with the maximum rated amperage of the system (6A in my case). Am I correct in that regard?

ScottG

Eric and Ratkity, I haven't constructed any cables yet, but here is what I will probably do:

1) Attach MC4 connectors to the existing short pigtails on the suitcase panels.
2) Construct an extension cable out 12-2 or 10-2 SJOOW cable. (SJOOW is super flexible cable used to create industrial power cords in rough environments). One one end of the cable I'll put MC4 connectors to attach to the panel. On the other end I'll put an SAE connector to attach to the Zamp port. (Same thing I did with my current set up.)
3) Relocate the controller to some sort of protective cover in the tub, or to the inside of the cabin.
4) Remove the the Zamp wires from the battery and run them into the relocated controller.
5) Run new wires from the controller back to the battery, with an in-line fuse on the positive leg.

Ratkity, your comment about not being able to find sun except in the middle of the river is precisely my concern, since I typically camp in wooded sites. That's why I was thinking of cheap easy prototypes to see if an extension cord would be worth the fuss for my purposes. I may just start with Eric's simpler approach and run a suitable extension from the panel-mounted controller to the Zamp port.

It's all just mental calisthenics to pass the time while the snow (sloooowly) melts!

Ratkity

Is the SJOOW the same as landscaping cable? Is it better or the same and which is the least expensive?

ericnliz

ScottG, I prefer to think of it as a soothing meditation. The only problem I've run into is that Liz (God love her!) keeps moving my notes, or using them to jot down her own, and not putting 'em back. ( not too sure why she insists on using mine as I've given her new note pads on several occasions ) Still lookin' for the one I had on dual 6 Volt Interstate batteries that our service guy gave to me as a recommendation. I think she does it to keep me on my toes so I won't get bored until I get the trailer moved and up and running from winter! Now, where did she put my pen!

ScottG

Ratkity said:

Is the SJOOW the same as landscaping cable? Is it better or the same and which is the least expensive?

Not the same. Landscape cable looks like it might be a little cheaper. It's suitable for direct burial but may not be as flexible. I've never used it, so I'm not sure.

Another option may be something called "marine cable"--I think Verna used this for her extension.

SJOOW (left) vs landscape cable (right):


Marine cable:

Nomad

I used landscape cable - matches the look, feel, and flexibility of the Zamp cable and is dirt cheap.

Ratkity

Thanks! Still musing on controllers (especially since Zamp sells theirs individually and are waterproof) and cabling..... then still wondering where to put the battery cutoff/breaker switch when all I have is the battery box.

Verna

Yes, @ScottG, I have a 20' 10 gauge marine cable (it looks just like your photo) that have used for my Zamp extension. It works very well with no noticeable loss of power. It is very flexible, easy to roll up. It is expensive.....but, I did buy it originally for my ARB (which didn't work well--I need to revisit that sometime). 

Ratkity

Oh, Scott, I forgot to tell you. There's an inline MC4 fuse that is purchased separately. It goes on the positive side.

jcfaber1

Scott G lets say you have the Renogy 100W solar suitcase The operating voltage is 17.6 and the operating amps are 5.68.  Lets say you want a 30 ft. cable and want a voltage loss of less than 3%.  Southwire app says you need 10AWG for a 2.03% loss over 30 ft.  40ft will give you 2.71% loss or .53 volts.  Remember the only charging will be done when the voltage going to the battery is >13.2v.  So with a 40 ft. 10 AWG cable you will be getting 17.07 volts to your batteries.  The resulting charging voltage will be 3.87. (17.07-13.2).  So if you used 12 AWG cable you will loose 4.48% or .88V.  The resulting voltage to the batteries 16.72 or charging voltage is 3.52 V.  3.87-3.52= .35 loss due to the resistance in the cable.  .35/3.52 or about 10%.  Make sense?  If you are looking for a new PWM controller then I suggest Morningstar or get the Bogart Engineering one along with their meter. 


John

jcfaber1

I suggest 10AWG landscaping cable from HomeDepot or other store if you do not want to break the bank.  I have 50 ft 8AWG marine cable that I spent $90 for so have fun.

Ratkity

So I have:
1. The suitcase panel with MC4 pigtails (check)
2. Already have 2xMC4 25' extension cables with a fuse in the positive lead (check)
3. Have MC4 with bare ends to have connected to whatever controller and then connect to extension cables to suitcase panel (check)
4. Have Negative terminal battery shunt

Can't access Zamp port wiring like on T@B - goes to a waterproof junction box with single leads out of box. If I used Zamp port:

Need Zamp extension cable to go from outside camper port to controller by battery - Zamp cables do not need to be run permanently - store in waterproof box with Renogy or Zamp controller? Battery cut off/breaker switch can go in there too.


Need controller:

If I get Zamp controller, I only need 15A, Has auto equalization which I'm not sure I want, it's waterproof, but no temperature sensor included (bought separately) and no battery voltage sensor (that I could find).

Renogy controller is 30A - not waterproof. Has temp sensor. Has equalization capability (but not auto). Comes with temperature sensor and battery voltage sensor.

Use Trimetrix controller and monitor (2 separate units) that I already have (not waterproof) and mount both inside waterproof box and forget Zamp port altogether. Trimax monitor has voltage sensor with monitor and temperature sensor. Eliminates Zamp extension cables.

jcfaber1

Use the Trimetrix setup and forget the Zamp.  Equalization is only pertinent if you are using flooded wet cell batteries.  I am unsure of the guage of the Zamp extension cables but the wires could be joined with the MC4 connectors.  Don't forget to get the tool for quickly disconnecting the MC4 connectors.  I use MC4 to go from the PV to the cable.  On the other end of the cable I use a trolling motor plug in (Male end).  The female end is through the t@b.  From inside the T@B I go to the charge controller.  This makes setup and teardown really fast.  I use the renogy MC4 disconnect tool for the PV end.

ScottG

Ratkity, it's hard to make specific suggestions without knowing the configuration of your new toy hauler, but here's a few thoughts:

Ratkity said:

...
then still wondering where to put the battery cutoff/breaker switch when all I have is the battery box.

Can you put it somewhere inside the camper. I have mine under the T@B's driver's side bench. It's in the positive wire that connects the battery to the converter.

Ratkity said:

...
Can't access Zamp port wiring like on T@B - goes to a waterproof junction box with single leads out of box. If I used Zamp port:

Need Zamp extension cable to go from outside camper port to controller by battery - Zamp cables do not need to be run permanently - store in waterproof box with Renogy or Zamp controller? Battery cut off/breaker switch can go in there too.
...

Somebody had to get stuff into that junction box at some point, but if you really can't find a way to open it, you could just cut the leads coming out of it and splice in new leads going to your controller. (Be certain to disconnect the original leads from the battery first--if you're not sure why, ask PXL!) The other side of the cut cable could possibly be used to connect the controller to the battery (or you could just run new wires for that).

I wouldn't want to futz with multiple cables every time I deployed my panels. If your connections were suitably weatherproof, you could leave it all in place and just plug the suitcase into the Zamp port when you need it. That's what I hope to achieve with my mod once I get it done.

Ratkity

This is the breaker/cutoff. It is both fuse (breaker) and cutoff. 

Bussmann CB185-30 Surface-Mount Circuit Breakers, 30 Amps

It's waterproof, but I'm not sure how it could be. Those rubber covers don't go all the way over the connections. It's made to flush mount however. I'll have to see if there is room where the converter is located. I should show a picture of the location, but it's pouring rain outside and I'm too lazy to go out and get wet! lol. Inside is still best, I think. I will remember the burning bunnies and flaming flamingos, no matter where I put it!!!! Thanks for the reminder

PS... I tend to be more like eric... except I don't have a Liz to steal my complex and illegible notes for a project that could be done much more simply than I wrote up.

ScottG

Is there a particular reason you're going with the combo unit? I would guess you already have 30A fuses at the battery and/or the converter (as is the case with the T@B). A basic switch like the Blue Sea Systems might be easier and more elegant, particularly in a visible location.

Ratkity

That is the exact reason I am going with the combo unit. No (40) amp fuses at the battery or converter!!! Just reverse polarity ones. Wha? Not sure why. It took me forever to disconnect all fuses and realize the battery was still connected (metering! I didn't lick the connections).