Bendable Solar Panels and Compressor Refrigerators

[billharr]

In order to accurately measure the drop in voltage due to wire size, you need to have a load connected that is drawing current. If you simply measure the voltage at the solar panel and then at the end of the attached wire with no current being drawn, you will only get the same reading. The voltage reading going to the battery after the controller is the voltage determined by the controller to be the needed charge voltage.
To determine the voltage drop due to the wiring, measure at the panel, then at the entry point into the controller, as the panel is feeding current into the controller. The difference should be the loss due to wire size. Harv

Harv could you read the Ohms between the two sizes for the length you are using. Say 15 ft of 10g and 15 ft of 12g. and then calculate the difference for the % of loss?

 

[RC Pilot Jim]

Wow thanks Harv I. Did not know that.
How much load to get a good reading?

 

[MarkBC]

Wow thanks Harv I. Did not know that.
How much load to get a good reading?

In this case "load" is just the current flow from the solar panel to the battery (or to the charge controller).
It's current flow that "cares" about wire size, so you need to use whatever current flow you expect to normally experience to determine if the wire is big enough. It's "big enough" when the voltage drop through the wire run is minimized.

I have my two panels on my camper connected in series so that the current stayed within the limits of the OEM wiring -- higher voltage but not higher current. (Then my MPPT charge controller does its magic to convert that "extra" voltage back to more current at the voltage that the battery needs.)

 

[billharr]

Resistance calculator.

15 ft 12g = .024 ohms
15 ft 10g = .015 ohms

I know enough to know what I don't know (or am not sure of) .009 ohms less resistance. But how does it affect the loss of current??

EDIT: another calculator

 

[MarkBC]

Resistance calculator.

15 ft 12g = .024 ohms
15 ft 10g = .015 ohms

I know enough to know what I don't know (or am not sure of) .009 ohms less resistance. But how does it affect the loss of current??

If I know what I think I know: You don't lose current by high resistance (e.g., too skinny or too long a wire), you lose voltage.

 

[billharr]

Found it, clear now


Wire resistance calculations
The n gauge wire resistance R in ohms per kilofeet (Ω/kft) is equal to 0.3048×1000000000 times the wire's resistivity ρ in ohm-meters (Ω·m) divided by 25.42 times the cross sectional area An in square inches (in2):
Rn (Ω/kft) = 0.3048 × 109 × ρ(Ω·m) / (25.42 × An (in2))
The n gauge wire resistance R in ohms per kilometer (Ω/km) is equal to 1000000000 times the wire's resistivity ρ in ohm-meters (Ω·m) divided by the cross sectional area An in square millimeters (mm2):
Rn (Ω/km) = 109 × ρ(Ω·m) / An (mm2)

 

[photohc]

Resistance calculator.

15 ft 12g = .024 ohms
15 ft 10g = .015 ohms

I know enough to know what I don't know (or am not sure of) .009 ohms less resistance. But how does it affect the loss of current??

EDIT: another calculator

It doesn't necessarily affect the current. The amount of current entering the panel side will come out on the controller side. Ultimately, what matters is the total wattage that ends up at the controller. Thats volts x current. If voltage is lost, then the net wattage (power) that is entering the controller is less than what started at the panel end. Harv

 

[RC Pilot Jim]

Mark,Bill, and Harv,
All of the above is the reason I have to "play" with the system as I don't always know or understand what I think I am talking about.

 

[billharr]

I did a quick overnight to Burney CA to see my cousin I have not seen in years. He lives in Idaho and was on a fishing trip. Stayed at the PGEs Cassel campground, but I digress. First trip with the 100w panel on the roof. I started the Waeco the day before without plugging in to 110v to charge, just solar. Spent the night, used lights, heater, water pump and fridge. I only have the digital volt gauge and had 12.4 in the morning with the heater and fridge running, still dark. Spent the day, drove home and parked the camper left the fridge running. About 10 the next morning I emptied out the fridge and had 13 volts before I shut it off. Not sure if a true test but I am happy. Now if I sell that old Maherajah on ebay for enough I will get a Trimetric.



FYI for you fishermen saw some nice trout being caught.

 

[RC Pilot Jim]

Read Bill Harr's test report just preceding this one as mine "turned the page".



After much thought I shortened the panel wires.
Picture 2 shows the wires covered and not touching the roof. The red square on the rectangular block is " + " positive side.
Tested it and it works. Next is overnight when it gets cooler. Current temp 94* 7 miles from the beach - yuck. We need cooler weather!

Second view

 

[DrJ]

Jim
That looks great. That's what I need to do with my mess of wires from 3 panels.
Thanks for posting the pictures.

 

[alano]

I put a couple of 100W Renology flexible panels on my Hawk's roof. Tested the system out at Pismo Beach for 3 days earlier this week. Worked great except I guess I didn't make one of the connections on top so solid as we were solarless upon arrival. Only had our back steps so I ended up standing on the only available portion of the truck bed's wall and hanging on to the Yakima rail to get up and down enough to detach and reattach the cable. Good thing I brought the special connector tools. Fixed the problem but in retrospect I should have borrowed a six-foot ladder from one of the giant RVs in the CG. I noticed several strapped to the back of a motor homes as we walked around later. I'm planning on mounting a hand hold to the rails in case I need to check on things or just wash off the panels in a more remote location.

Another funny thing we noticed is that we had quite a few birds walking on the roof. That hasn't happened before. Wonder if it is a local thing or because the setup looked interesting. Perhaps they were interested in adding solar to their roosts and wanted to see how I did it.

Alan

 

[RC Pilot Jim]

Good install job, Alan . Did you use a " Y " cable to connect the two panels together?
Would you take another picture showing the wiring hookup as the photo is a little hard to see?
Thanks.

 

[RC Pilot Jim]

Bill do you recall your starting voltage?

Monitoring Trimetric battery drops 1% per day no load. This morning drove it to church and was there 4 hours as had meeting afterward. Percent of full 89% when I left and 94% when I returned. Voltage 13.2

 

[billharr]

Jim, I am not sure what I had when I left. Where I have my volt gauge the reading changes if the fridge is running. I will check before the WTW Meadow Lake Rally next weekend and see what I get.

Bill.

 

[PaulT]

About those birds on the roof...

I wonder if they might be checking out the panels for a place to drop clams to break them open. There's a lot of color contrast between the roof & the panels that wasn't there without the panels.

Search for "gulls dropping clams" on your favorite search engine. We've paid for a lot of research in this area. Maybe some of it can lead to protection of these expensive PV panels?

Paul

 

[Hodakaguy]

I've been running 330W worth of flex panels on my Syncro through this summer and they have worked really well! It's so nice being able to camp multiple days without worring about plugging in or driving the vehicle to charge.

We are now looking for a FWC camper for our Tacoma and I'll be using the same panels to set up a system on the camper. I'll fabricate another custom mount to hold the panels but I'll try to keep it lighter on the FWC. The mount has cutout areas under the panels to allow air flow which helps keep the panels cool in the direct sunlight. Can't wait!

Hodakaguy

 

[RC Pilot Jim]

Nice clean setup.
When you do the FWC Hoda.....be mindful of the roof weight.

 

[Hodakaguy]

Nice clean setup.
When you do the FWC Hoda.....be mindful of the roof weight.

Yeah I'm bouncing around ideas on how I want to mount them...haven't finalized the design in my head yet

Hodakaguy

 

[alano]

As requested, here is a shot of my roof wiring with added dirt. I used Y connectors to tie the panel positives and negatives together and then put the appropriate connectors on the cable that FWC provides with the solar mount option. Used a few UV resistant tie wraps and mounts to wrangle the cabling a bit and there it is. If I were a bold warranty-breaking type, I could shorten the whole mess significantly.

As for birds dropping clams on the panels, bring it on. These panels are fairly impact resistant since there is no glass top and If I'm quick enough, I could score some of the seafood. Do you need a fishing license if the birds drop the clams on your property? Would the warden believe my story?

Alan