VERY LONG - My 12V Electrical Modifications and Solar Power System Installation

[Fire Instructor]

I "de-winterized" my system today (for the first time), and had a fault on my solar controller that took me a while to figure out. I take my batteries out, and store them in the house basement in the winter. I didn't realize that the controller temp sensor had to be connected to the battery before any power was connected, or the controller display acts irradically. So after re-reading the manual, I disconnected everything, made sure that the panel disconnect was in the off position, connected the temp sensor, and then the power, and the controller STILL showed the fault....

So I disconnected the power AGAIN, and RE-READ the manual, and couldn't find any that I was doing wrong. I took a big breath, had another cup of coffee, and figured I'd try again. I happened to look at the display on the controller with the battery disconnected, and it STILL read "fault", so now I'm REALLY confused.... How can the controller read "fault" with no power??? On a whim, I reached over and turned on the 120v inverter... it came on.... confusion turning to frustration, I flipped on the ceiling fan, and it came on. So is the trailer haunted? Did my wife or someone else plug the TT into the garage while I wasn't looking?????

That's when the "DUH! I sure am STUPID!" thought came into my mind. The TT was still connected to the tow vehicle, and was drawing 12v supply from THERE! Unplug the TT, make sure that the battery is completely disconnected, reconnect everything in the PROPER order, turned the disconnect for the panels back on, and VUALA! Everything functions properly....

I'm now charging my batteries again, with nothing plugged in!

And the BEST news of the week is that as a "second home", (I claim the loan interest on the TT on my taxes as such), my accountant took ALL of the receipts from my solar installation, so that they could be factored into my taxes as a "renewable energy" home improvement!!!!

 

[Rod Johnson]

Fire, do you run your fridge on electricity, or strictly propane?

 

[Fire Instructor]

When in the driveway, between trips, I plug the TT into the garage, so that that all outlets have 120v and the fridge doesn't burn propane. I keep the 12v inverter breaker on the inverter panel off, so it just acts as a distribution point for 120v, and all 12v comes from the batteries, being recharged by the solar. The solar easily handles all of my lighting use and the parasite loads, between trips.

While traveling or camping, the fridge runs on propane, unless I happen to be at a CG with electric available.

 

[Rod Johnson]

And, did you fuse the leads from your solar panels to your charge controller?

You mentioned a disconnect for your solar array. Where and how did you install that? I was thinking about using the same battery disconnect that Forest River uses and installing that next to my charge controller?

Or, would a heavy duty switch like this (I have one that switches most of my outlets from shore power to generator power)
Switches | Wall Switches | Bryant 3025I Industrial Grade Toggle, Double Pole, Double Throw, 30A, 120/277V AC | B211353 - GlobalIndustrial.com

Sorry for the all the questions, just trying to make sure I get all the parts ordered.

 

[Fire Instructor]

And, did you fuse the leads from your solar panels to your charge controller?

No. I saw nothing in my research that recommended or required it.

You mentioned a disconnect for your solar array. Where and how did you install that?

If you look at the photos, linked in the original post, you can see the disconnect inside a hanging closet, directly below the roof mounted junction box and the controller. TI used a marine-grade disconnect, like
this one: Amazon.com: Perko 9601DP Marine Battery Disconnect Switch: Automotive

Or, would a heavy duty switch like this (I have one that switches most of my outlets from shore power to generator power)
Switches | Wall Switches | Bryant 3025I Industrial Grade Toggle, Double Pole, Double Throw, 30A, 120/277V AC | B211353 - GlobalIndustrial.com

That Bryant switch is an AC switch. You need a DC switch. The marine switch seemed to me to be the best use/best value.

[/QUOTE]Sorry for the all the questions, just trying to make sure I get all the parts ordered.[/QUOTE]

Thank you for the interest, and I hope that I helped you!

 

[Bennington Camper]

If you disconnect the source circuit conductors (those from your PV) under load, you will pull a DC arc in your switch. Very few switches are rated for this 'load break' arc. Each operation will burn off contact metal, and at some point probably weld the contacts.

The switch will be fine if there is no load on the array - the charge controller in this case provides the load. Would be OK after dark, if the module(s) were covered, if the charge controller was not charging, or turned off (if this is an option).

Fusing in the source (or output strings if combined) is necessary if a short in the DC wiring could cause more than the individual module fuse rating (printed on the back of the module, and usually on module cut sheets). This is usually if more than 2 modules are wired in parallel (or 2 strings of modules if using a MPPT charge controller).

Glenn
Technical Specialist
Real Goods Solar
NABCEP Certified PV Installer
NYSERDA Eligible installer
Adjunct instructor Hudson Valley Community College

 

[Bennington Camper]

Inverter to battery wire sizing is done using the full rated power of the inverter (2000W) divided by its lowest rated DC voltage (let's say 10.5VDC), multiplied by the inverter's efficiency at that power (probably not its most effecient point of operation, let's say 85%).

(2000W / 10.5VDC) * 0.85 = 162A

Because you never want to push your conductors to their limits (and the NEC says so), you must upsize this so there is a 20% safety factor.

162A * 1.25 = 138A

Then this number would be modified by other conditions of use, such as if it were in a conduit, exposed to high temperatures, etc.

Using the tables in the NEC for the type of wire to be used, you would pick a size larger than this number. By the way, 138A would be the value you would use for fuse sizing and DC battery disconnect as well.

Also note that no voltage drop consideration was done on this calculation.
If the wires are to be used outdoors, be sure to select an insulation suitable for that application.

2 AWG UF copper conductor would be suitable for this with an ampacity of 140A.

Glenn

Yes. I've drilled a total of five holes in the floor in that area. The first pair was to bring the new #4 cables from the battery to the inside compartment junction box. I also drilled a hole and ran the factory positive and ground (originally connected to the battery) into the same box PLUS a twisted pair control wires for the controller, PLUS the battery temp monitoring wires for the controller. (Six small wires

 

[Bennington Camper]

Not likely this is an MPPT controller. Specs are for a 12VDC input - MPPT uses higher than the battery voltage...
Glenn

 

[Bennington Camper]

The below listed switch seems to only be rated for AC.
Do not use AC only switches on DC circuits - DC arcing will weld the contacts - AC crosses zero volts 60 times a second and is easier to quench, thus more cheaply made.

-Glenn

And, did you fuse the leads from your solar panels to your charge controller?

You mentioned a disconnect for your solar array. Where and how did you install that? I was thinking about using the same battery disconnect that Forest River uses and installing that next to my charge controller?

Or, would a heavy duty switch like this (I have one that switches most of my outlets from shore power to generator power)
Switches | Wall Switches | Bryant 3025I Industrial Grade Toggle, Double Pole, Double Throw, 30A, 120/277V AC | B211353 - GlobalIndustrial.com

Sorry for the all the questions, just trying to make sure I get all the parts ordered.

 

[Herk7769]

Inverter to battery wire sizing is done using the full rated power of the inverter (2000W) divided by its lowest rated DC voltage (let's say 10.5VDC), multiplied by the inverter's efficiency at that power (probably not its most efficient point of operation, let's say 85%).

(2000W / 10.5VDC) * 0.85 = 162A

Because you never want to push your conductors to their limits (and the NEC says so), you must upsize this so there is a 20% safety factor.

162A * 1.25 = 138A

I understand that the "equalizing" of AC/DC wattage requires the power factor be used. I get your calculation logic (2000W / 10.5 VDC) * 0.85 = 162A However I am not following your 20% safety factor math. 162A * 1.25 = 138A (think an error was made here)

As I understand what you are trying to say though, adding a 20% safety factor means either "upgrading the wires to handle a load 20% greater than the maximum rated load; yet fusing for 100%" (Wire size based on 195 amps and fuse based on 162A - which I get) OR (Wires size based on 162A and fused for 130A (20% less than full load).

If you were to use 1.0 as a power factor, 2000/10.5 = 190 amps and fuse (15-20% less or 162-175A) accordingly it pretty much wipes out the power conversion factor and the safety margin math. Makes things easy for me.

In fact to make it even easier, if you use 12 VDC and a 1.0 power factor, the amp load is 2000/12*1 which equals 166 amps. Right about where you want your circuits fused.

 

[Bennington Camper]

My mistake - too many open windows on the computer at once...

Power factor is a term used in AC power for a completely different purpose - be careful not to mix terms (completely different topic).

Inverter efficiency at the available DC voltage is the factor to be used in the calculation (in this example 85%, but can be found for the inverter you are using from its specifications).

The safety factor should have been calculated:
162A * 1.25 = 203A
with overcurrent protection using the 162A and wire sizing using the 203A value.

The problem is in the 'what if' scenerios. This is why we use Inverter rated max output power (2000W) and minimum rated DC voltage the manufacturer says this can be produced at (10.5VDC). The manufacturer further has a graph that shows the inverter effeciency across its operating range of DC voltage (85%).

So selecting copper conductors for use at 86 deg F, and not in conduit, we truly should use 2/0 UF conductors, which are rated for 225A.

Again, no consideration for voltage drop is used yet.


BTW, it is no longer acceptable in residential installations to use welding cable for battery connections to inverters. I am less knowledgeable about RV and SAE regulations.

Glenn

I understand that the "equalizing" of AC/DC wattage requires the power factor be used. I get your calculation logic (2000W / 10.5 VDC) * 0.85 = 162A However I am not following your 20% safety factor math. 162A * 1.25 = 138A (think an error was made here)

As I understand what you are trying to say though, adding a 20% safety factor means either "upgrading the wires to handle a load 20% greater than the maximum rated load; yet fusing for 100%" (Wire size based on 195 amps and fuse based on 162A - which I get) OR (Wires size based on 162A and fused for 130A (20% less than full load).

If you were to use 1.0 as a power factor, 2000/10.5 = 190 amps and fuse (15-20% less or 162-175A) accordingly it pretty much wipes out the power conversion factor and the safety margin math. Makes things easy for me.

In fact to make it even easier, if you use 12 VDC and a 1.0 power factor, the amp load is 2000/12*1 which equals 166 amps. Right about where you want your circuits fused.

 

[Fire Instructor]

COMPLETE SUCCESS!!!!!!!

It's been a while since I added to this thread, mostly because I really hadn't done anything to the system since last reporting, other than use it..... But that has changed!

This Spring, I added two more 6v golf cart batteries, and replaced the existing two, giving me four new batteries, and 260 Amp-hours of power.

Today, I completed 10 days of dry, beach camping. We used the microwave oven, the Kuerig coffee maker, the toaster, the Margarita maker, and charged phones and iPads every day. Additionally, most nights, we ran a 12v Casablanca ceiling fan and a 120v portable fan most evenings, just to make it more comfortable to sleep. Additionally, my son ran a lead cord from the TT to his tent to keep HIS phone and Kindle charged.....

Ten days of this, and I NEVER ONCE started my generator! The 300w of panels kept the batteries full. Even on two days of dreary cloud cover and rain, I got enough recharge that the NEXT day I got off of MPPT and into "float"!!!!

Now if I could just figure out a way for the sun to refill my freshwater tank, and empty my grey and black tanks, I'd be all set!!!!!!

 

[toshu]

As you still on Assateague or did you leave already???

Sounds like the extra battery capacity is the key...more so than the panels!!

 

[Fire Instructor]

As you still on Assateague or did you leave already???

Sounds like the extra battery capacity is the key...more so than the panels!!

I was already back home when I posted that, but the extra batteries made a HUGE difference! It was apparent that with only having two batteries, I was fully recharged relatively early in the day, and switching into "float", often before noon! The extra capacity takes longer every day to restore, but allows for all kinds of use into the evening, all night, and the morning. Someone on the forum, early on in my planning, had suggested shooting for around a 1.50:1 ratio on battery amp-hours to panel watts. Each pair of 6-volts is 230 amp-hours at 112v, so I now have the 460:300, or 1.53:1 ratio. This seems to work well!

Well see how well it works in the lower Fall sun, when I do 5 or 6 days at Dover for the NA$CAR race at the end of September.

 

[toshu]

Can you post a picture of your battery box and make and model of the batteries and box??

Have you checked your tongue and GVW since the most recent install??

 

[Kuba]

Not to hijack the topic or anything, but why are the prices of these solar panels so high??????????????!!!! I purchased two240w24v sharp panels for 299$ each two years ago.

 

[RPAspey-FRF]

A couple of years ago, there was a "price war" of sorts. The Chinese government was apparently subsidizing the cost to manufacture the panels. Thus artificially low prices.

2000 Cherokee 31BH, "flipped axles and raised",LEDs, solar, inverter, etc..aka "boondock ready". '07 Tundra 5.7L DC-LB, modded as well.

 

[Oconomowoc]

Have you thought about the possibility of getting your whole house on solar and getting off the grid? Is this still pie in the sky thinking or getting close?

 

[RPAspey-FRF]

Me, never. It would take a tremendous about of battery bank and solar to maintain our lifestyle at home. But, we've been talking about building a cabin on our farm upstate. There, we could use solar supplemented by a generator.

To live off grid would cost a lot initially, but would be extremely satisfying. In an emergency, we can live in our camper.

 

[RabidRoo]

Hey Fire, great thread. After two years of use is there anything you would change if you were rebuilding from scratch ?


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