Need help setting up solar electric system on our converted bus/motor home

BB.

1. You are very welcome Bill... We all try our best here.

4. I know I keep harping on this... 3,000 Watts is the rate of energy usage (like miles per hour). And Watt*Hours is the amount of energy used (like miles = 20 mph * 2 hours= 40 miles driven).

So, 3,000 Watts would be if all the appliances are turned on at once (at least the appliances and lights you plan on turning on at once). That is quite a bit of power... Typically, for a "cabin/small home" system, i would be suggesting around 1,200 to 1,500 Watt AC inverter (fridge, some lights, small microwave OR Washer OR such)... If you had other loads (well pump, induction cook top, etc.) where you needed more power--So be it. Just plan on a large enough battery bank to keep the 3 kWatt inverter fully supplied with current and voltage (for FLA battery bank a rough rule of thumb, around 100 AH per 500 Watt inverter @ 24 volt bank, or 100 AH per 250 Watt inverter @ 12 volt battery bank).

3,000 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff = 336 Amps @ 12 volt battery bank for 3,000 Watt AC load

And then there are Watt*Hours used per day (as an example). Suggest a minimum of 3,300 WH per day as a minimum for a 'near normal' electric life...

3,300 Watt*Hour * 2 days storage * 1/0.50 max planned discharge * 1/0.85 AC inverter eff * 1/12 volt battery bank = 1,294 AH @ 12 volts

Assuming 2 days of "no sun", and 50% planned discharge on a 12 volt battery bank...

1,294 AH @ 12 volts is a good sized battery bank... And would suggest a 24 volt battery bank (keep wire size smaller, fewer charge controllers, etc.)....

A refrigerator running 1.5 kWH per day (typical full size standard Energy Star Fridge)... Say runs at 125 Watts at 50% duty cycle 24 hours per day (typically >600 Watts peak starting load, and defrost heaters):

• 125 Watts * 0.50 duty cycle * 24 hours per day = 1,500 WH per day (less in winter typically)

Typically it is the appliances that run 12 or 24 hours per day that "burn Watt*Hours" (fridge, computer, TV, etc.). For example, a 1,200 Watt microwave:

• 1,200 Watts * 1/3rd hour per day (20 minutes) = 400 WH per day

Vs around 1,500 WH for a refrigerator....

That you want/need to use a 3,000 Watt AC inverter--That is based on your choices of what to power and your energy needs.

We have been through this earlier in the thread--But larger inverters do typically "waste more energy" (tare losses, or just being turned on) and need a larger AH battery bank (and wiring) to properly function.... With solar power--There are always trade-offs to be made.

5. Getting experience with your existing battery bank is always a good place to start before $ending money on more batteries.

6. "Ground" is a common definition of "zero volts"... The dirt is "zero volts", the frame of the bus is "zero volts", etc... Basically anything that is expected to be touched by humans (and animals, and such).

Since the bus is on rubber tires;.. You could run 120 VAC hot to the frame of the trailer and Neutral to your earth ground rod... Where people could get shocked is walking from wet ground/grass and grabbing the metal door handle for the bus--And get electrocuted. Similarly if you have metal pipes from well to the sink in the bus. A person could get shocked by touching plumbing and sheet metal in the bus...

Looking "inside the bus" for a moment... All metal should be at "ground potential" (zero volts). If somebody grabs a water faucet and a blender with a metal case next to the sink at the same time. we what those to be "at ground potential"--So no current flows through the person touching two different metal objects.

In NEC Code, cold and hot water pipes are tied together with a copper jumper. Also a copper jumper to the gas pipe (I don't know about propane--This is for natural gas with black iron pipes). To the green wire ground bus in the main AC panel, and typically to the Negative Battery Bus, and to the frame of the vehicle... All those are now at zero volts to each other, and there should be no shock hazards.

Also, by tying all of these major metal parts are now grounded and even if there was a short from (120 VAC Hot) to something (electric mixer dropped into sink), no other major piece of sheet metal will become "Hot" and an electrocution hazard. And if 120 VAC Hot (or 12 VDC +) touches that grounded metal object, then the short circuit will draw enough current to trip a fuse or circuit breaker.

For example, in an RV... Metal Sink and plastic pipes to a faucet mounted through a wooden counter... A mixer could fall into the sink and "energize" the metal of the sink... And shock a person trying to pull the mixer out of the water/sink. And that is why we use GFI outlets near sinks/water/wet areas. With a GFI, it measures that current that is leaving the Hot/Neutral wiring and going into the sink/person (shock). It only takes 10-25 mAmps (0.010-0/25 amps) to trip a typical US GFI breaker/outlet.

For an "independent" on board RV power system... Grounding to "earth" does not do anything. We do clip a car to a ground rod when parking it overnight (we do however clip a ground wire to an airplane when fueling to prevent a spark between grounded fuel nozzle and the metal fuel tank) as aircraft and fueling can generate large static electric charges.

In your case with an RV that is not moving--Typically a ground to RV Frame (or your common RV Grounding) is usually there for lightning control... Directing lightning energy strike from RV to earth (instead of arching over the rubber tires).

There are other reasons for grounding--Such as connecting to a home AC utility power. We are used to cars and trucks using the chassis for the negative terminal instead of a separate run of copper wire. Works OK, but there are reasons we (for example) run a ground strap across metal hinges on aircraft... We don't want electrical current flowing through the bearings and ruining them (or even spot welding them in position) if there is stray current.

The reason we "ground" the negative battery bank terminals is a little arbitrary (as far as I know). Older cars, many older British cars. ran perfectly fine with a positive grounded battery. There were some issues (a new USA car radio with negative grounded frame vs positive grounded car--Needed a -12 to +12 VDC converter, changing or instating a new generator needed to be "flashed" for the correct charging polarity, etc.).

There are other issues with grounding for metal structures in dirt (and telephone systems, natural gas piping, etc.)... That can call for a cathodic protection system... To prevent small DC voltages from rapidly corroding metal pipes/structures. Similar to using zinc sacrificial anodes on metal ships, dam gates, etc.

https://en.wikipedia.org/wiki/Cathodic_protection

Grounding is actually one of the more complex subjects here on the forum... I may not have answered your question(s)--So please feel free to ask again.

-Bill

TellGRBill

A couple more "ground" questions:

1. Is the frame on a solar panel usually "ground" and connected to the black DC wire ?

2. Can the black DC wire coming from the solar panel be connected to the "ground" and ultimately to a "ground" rod ?

3. Because I want to be able to easily disconnect and store the solar array in a different location when not in use. When I wire the solar array 100' to the controller, I want to have a female electrical outlet on the solar panel mount and a male electrical outlet mounted on the bus connected to the controller.  The 10awg cable from the array outlet to the controller outlet would have male connectors on one end and a female connector on the other. The 100' 10awg wire will have a bare wire for "ground" and a white wire for DC neutral/"ground". Can both the bare and the white wire be connected to the "ground" rod ?  Should a ground fault connection be mounted on a solar panel mount if the solar panel frame and mount are easily accessible by someone walking by the solar array ?

Not TMI but TMQ ?

BB.

1. In general, NO, do not connect the black (negative) or red (positive) lead to the solar panel frame...

If you live in an area with lightning (or possible shorting from power line crosses, etc.), you do not want to bring lightning into your home. You want the frames and trailer frame connected with a short/straight run to "earth" (ground rod, ground plate, etc.). 

And you would run three wires from "home" (battery shed) to the trailer.. +/- and a safety ground wire... In a permanent installation, I would be suggesting at least a 6 AWG ground cable (minimum size that will generally survive a lightning strike from readings I have made). Using a 6 AWG bare copper cable buried in the earth also better dissipates lightning energy to the dirt.

There are other issues... For some MPPT Controllers (such as Schneider some MPPT models--As I recall), they are 4 port devices: +/- in from panels and +/- out to battery/loads. If you "bypass" current from negative, to gnd cable, to battery (around the MPPT controller), the controller will not function correctly (some MPPT controllers measure  panel current in the negative lead).

Other controllers (such as many/most/all? Outback controllers), they do not measure current in the negative panel lead and you can bus them together (multiple arrays, multiple charge controller), grounding, etc. and they will work fine.

Anyway--The basic desire is to avoid bringing lighting energy into the building (i.e., ground rod/plate near trailer, ground rod/plate near home/bus). And normally, the DC power system will be grounding in one place (i.e., the negative battery bus) and ground that to the home/bus/ground rod (and AC green wire ground connection to the same rod).

This is so that if there is a short circuit somewhere in the system, you want that short to return current back to the source (such as DC battery bank or AC inverter's output) and trip the "local circuit breaker".

If you have lightning possibilities, then using surge protector(s) is also recommended. The Midnite Brand are very nice. One installed at the entrance to the power shed/bus. And a second set at the solar array (better). Of course, nothing will survive a direct lightning strike--But this helps:

https://www.solar-electric.com/search/?q=surge+suppressor

2. Usually looking for "single point grounding". That would normally be the battery bank negative battery bus/common point to the local earth ground rod/plate/cold water pipe (depending on your code). Again, mostly for lightning strike protection... "Dirt" will not conduit much current at 12-120 Volts into a 25 Ohm earth ground (max acceptable ground to dirt resistance per code).

You can do other connection points (such as the solar panel DC negative bus for most(?) Outback MPPT controllers--But is not typical (again, read the manuals--They are where you start with proper grounding (some manuals are very thin or have non-existent grounding instructions--Which is a pain). If no information, default to the rule of thumb of single point grounding (battery negative bus to ground rod, plus other grounds such as AC green wire ground and bonding to AC neutral--For PSW/TSW type inverters--MSW type inverters would never have a ground bonded neutral connection because...).

3. "Portable" power systems--Always issues with connections and grounding....

I don't remember your lightning possibilities... But a plan would be:

Power shed/bus, single point grounding of battery bus to bus frame (and typically to local ground rod). Bring out +/- cable(s) from power shed to trailer. At trailer, plug +/- controller to +/- trailer array (watch polarity). Run 6 AWG cable from panel frames to trailer frame to earth ground (fixed ground rod, or bury a copper ground plate a bit below the surface). Ground plates may be easier to move vs an 8-10 foot ground rod driven into the soil.

https://www.nvent.com/en-us/erico/products/copper-ground-plate-0 (example copper ground plates)

https://www.hunker.com/12445983/how-to-install-an-electric-ground-plate (bury a 1' x 1' plate 30 inches deep in this example)

Running a 6 AWG from trailer to RV/power shed is a good thing--But may be more $$$ than you want to spend (idea is the "6 AWG will give a good electrical ground/return everywhere--Say you bring a 120 VAC from power shed and mount on the trailer for an area light... The 6 AWG trailer to shed ground prevents the trailer from becoming energized in a short circuit from 120 Hot to trailer frame. An acceptable (and required anyway) a GFI protected 120 VAC breaker/outlet from power shed will trip if there is a Hot to Ground short--So a 6 AWG is not  needed to reduce electrocution risks.

And if there is a lightning risk, Surge Suppressors at power shed, at least (for DC solar array power and even AC power to other exterior 120 VAC power usage...

120 VAC GFI is cheap and functions well to reduce the chances of electrocution (down to the ~15 mAmp range).

For DC power, there is really no equivalent DC GFI. There are several ways of doing DC GFI:

https://www.morningstarcorp.com/products/ground-fault-protection-device/ (300 mAmp range--Not cheap)

And there are remote shutdowns and ganged breakers (one 1 amp breaker ganged with 60+ amp +/- breakers). I don't really believe these will do what you ask (prevent trailer from becoming "DC hot" with 100's of volts from solar array).

A 6 AWG from trailer/panel frames back to single point ground in the power shed should do what you want.... Back to +/-/6 AWG ground cable between trailer and power shed/bus.

Grounding is a complex subject and (many times) has to be designed for the application and local requirements. Portable systems are a pain and do represent some grounding/safety issues that fixed systems do not.

Being careful with wiring, bundle ties, conduit, connections, making sure a tilting array does not "cut" wiring when hinging, etc. are all critical.

For things that need to be inspected--You can do something like a separate ground X feet away and measure from trailer to separate ground once a month--And if you measure AC or DC voltage >~24 volts--That would be an issue.

I think I said here before, I actually got a shock >60 VAC when touching the connections between two "earth ground rods 100 feet apart in a saltwater aquarium with multiple HP 240+ VAC sea water pumps. Surprised the heck out of me (facility no longer exists).

You might be looking at "over kill" in your system... But accidents do happen. There are so many ways "weird events" can happen--It is difficult to say what to avoid (other than following code and good practices). Anyway, some examples:

https://www.ecmweb.com/safety/shock-electrocution/article/20896466/electrical-accidents-lessons-learned

Murphy's Law is based on this. “Anything that can go wrong will go wrong,”. It also states that if there are two or more ways to do anything and one of them potentially result in disaster, someone will do it.

And a corollary... Anything that can go wrong will go wrong at the worst possible moment.

TMI?

-Bill

TellGRBill

1. Thank you for the additional "grounding" details.  I will re-read several times to absorb the information and remember, and apply it.

2. I'm not clear about all the Parallel and Series connection possibilities for solar panel arrays.  I am wondering, once I get the second trailer solar panels installed in series on the trailer, how best to connect it to the first trailer or the controller.

BB.

What solar charge controller(s), and what is the Voc/Vmp/Imp and number of solar panels that will be connected to the trailers(s)? And the panels at the bus (if using the same charge controller)?

For longer distances, running the array(s) at higher voltages is usually the rule to keep the copper cables a reasonably (smaller) size and keep voltage drop/loss of power down.

Usually, you want to do these paper calculations first before buying/building the array.

Details matter here.

-Bill

TellGRBill

1. You have impressed on me the importance of, and sensitivity of calculations with solar systems.  Soon be using two boat trailer mount bases for two arrays of  (4)175 watt 12 volt panels, They will be connected to a 60amp controller. (controller data sheet attached)  I have planned to connect the panels in series on both trailers to make the voltage higher and the amperage lower.  I'm aware that the controller has limitations, and the 100' lead wire (10awg ) has limitations for effectiveness. Now, I'm wondering how best to connect the two arrays/trailers to the controller. If I decide to add more trailers with solar panel arrays, 3 & 4 how should they be connected?

2. Thanks to your advice, yesterday I crawled under the bus and added the anti copper to Aluminum corrosion prevention "grease" to the triple cable connections , Thanks for the warning notice!  Here in Michigan, it's pretty cold and I had to warm the connectors and the grease to get it to flow better.

BB.

Your controller MPPT input is rated for 145 VDC at -25C... More or less, that means your maximum array Vmp voltage is around 100-110 VDC (depending on how cold it gets, what the Voc of the panel is, etc.)...

Some basic rule of thumbs calculations... Assuming your battery bus voltage is still 12 VDC and a 60 Amp rated charge controller, the typical max-nominal array would be:

• 60 amps * 14.5 volts charging * 1/0.77 panel+controller derating = 1,130 Watts (usually you can go higher, just more clipping of output current in cold/clear weather around solar noon).
• 1,130 Watts / 175 Watt panels = 6.5 panels would max-nominal over paneling
• 175 volt panels / 18 volts (guess) Vmp = 9.72 amps Imp (again, guess)
• 100 VDC Vmp-array max voltage in sub freezing weather = 5.5 panels in series = 5 panels max (guessing)
• With 4 panels per trailer, trying to work in 5 panels on 4 panel trailers
• Left with 4 panels per trailer, wired in series.
• 18 volts Vmp * 4 series = 72 volt Vmp-array @ 9.72 amps per string
• "max-nominal over paneling" of 6.5 panels... You are left with the choice of 4 panels or 8 panels per 60 amp controller
• If panels are cheap and controllers are expensive, then 4s x 2p would work--And you would get clipped to 6.5 panels worth of power on cool/clear days when batteries are less than 80% SoC (as batteries go above ~80% SoC, they accept less charging current)
• If controllers are "cheap" and panels are expensive, then having 4sx1p per controller would be fine (parallel controllers to battery bus).
• 4*175Watt * 1/0.14.5 volts * 0.77 panel+controller deratings = 37 ~ 40 Amp MPPT controller per trailer is all that is needed

Now voltage drop calculations.. Say 10 AWG, 100 Feet, 9.72 amps:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=72&phase=dc&noofconductor=1&distance=100&distanceunit=feet&amperes=9.72&x=57&y=20&ctype=nec

Result

Voltage drop: 2.31
Voltage drop percentage: 3.21%
Voltage at the end: 69.69

You will lose ~3.21% of your energy from the array using 10 AWG cable... Not bad

• 175 Watt panels * 4 series * 0.77 panel+controller = 539 Watts max (cool clear day) per trailer array
  
• 175 Watt panels * 4 series * 0.77 panel+controller * 0.0321 losses = 17 Watt loss per "trailer"

Without exact panel ratings (Voc/Vmp/Imp/Ioc), battery bus voltage, minimum temperatures in winter, etc.. The above are guesses--But the numbers are "close enough" to understand the limitations/requirements of your setup (i.e., 4s x 1p or 2p calculations/setup per 4 panel trailer won't change with exact Voc/Temps).

You could add a 5th panel per trailer if you wanted per trailer (5s*1p)... Lower losses on 10 AWG cable, better use of your 60 amp @ 12 volt battery bus MPPT charge controller... This is one of the examples I was talking about doing paper calculations before purchase and building.

-Bill

TellGRBill

1. " With 4 panels per trailer, trying to work in 5 panels on 4 panel trailers "

The trailers are pretty much limited to four panels

2. "You are left with the choice of 4 panels or 8 panels per 60 amp controller"

"4*175Watt * 1/0.14.5 volts * 0.77 panel+controller deratings = 37 ~ 40 Amp MPPT controller per trailer is all that is needed"

a.  If I understand (slightly) your explanation, then I can wire both 4 panel trailers to the controller, but I will lose some power, and under some conditions more power.

b. Can I wire the two, four panel trailers with a total of 8 panels to the 60 amp controller that I have?  If I can, how would you recommend they be wired to the controller on the one 100' 10awg wire ? or do I need to wire each trailer separately to the controller? I would rather wire both trailer arrays together on the one 100' 10awg cable.

BB.

a. Yes, that is correct... In most cases, the most your 2x trailer array can produce (we are usually talking a few or few 10's of hours per year of "clipping" around 37 amps per array, or 74 amps for two arrays in parallel with a 60 amp controller--Which will clip to 60 amps on the cool/clear days around solar noon with a battery bank at less than (typically) 80% SoC... As the battery bank aproaches 90%+ state of charge, the batteries themselves will reduce there current draw...

But there are your loads too... Say running an irrigation pump and/or clothes washer, cooking, etc... Also draws from the solar array (if sun is up)--Sharing solar output from charge controller with loads and charging of battery bank.

At this point--I would suggest just running a single 60 Amp controller to your 2x 4 panel battery banks (4s x 2p wired solar array). And see what happens.

There are so many variables (location, weather, dust & moisture in air, dust on panels, time of day, battery bank state of charge, temperatures, other electrical loads, etc.) that I (or you) really cannot predict the actual harvest from the battery bank. We can make estimates--Such as you might lose 10 amps of harvest (at 10 amps * 14.5 volts charging = 145 Watts) of harvest/energy usage in the middle of the day...

Being a cheap guy myself--I would just wire up the two trailers (4s x 2p array) to a single 60 amp MPPT controller--And just keep an eye on its output... I

If you see 60 amps "clipped" output for many hours per day and you need a 145 Watts of more power in middle of day (say 2 hours * 145 Watts lost harvest = 290 WH lost--Purely a made up example)... But as you can see, getting clipped by 10 amps for a couple hours per day is not something to worry about... Over paneling still gives you a lot of "extra trailer harvest" (175 Watts * 2 sets * 4 panels per trailer * 0.77 "typical best case array harvest" = 1,078 Watts best case average for your portable array vs MPPT controller output of 60 amps * 14.5 volts charging = 870 Watts MPPT clipped/max output).

b. The design of 10 AWG cable was "per trailer"... If you want to make only one wire run, then, for example, 6 AWG, 2*9.72A=19.44a total, at 72 volt array:

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=4&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=72&phase=dc&noofconductor=1&distance=100&distanceunit=feet&amperes=19.44&x=27&y=20&ctype=nec

Result

Voltage drop: 1.91
Voltage drop percentage: 2.65%
Voltage at the end: 70.09

There is nothing "magic" about 1% to 3% wiring losses... Just a good place to start. If you want to use a single pair 10 AWG run, you will have ~6.4% losses... If you run 2x pair of 10 AWG, then 3.2% wire loss... Vs 1x pair of 6 AWG for 2.7% loss...

These are all the trade-offs you can try (voltage drop calculator, etc.).... 

Note that you cannot connect 2x MPPT controllers to a single array... If you were to go with 2x MPPT controllers, each one would need its own wire run from Trailer A to MPPT A, and Trailer B to MPPT B....

So 2x pair or 10 AWG cable (one set per trailer A and and a second set of wires to trailer B ) gives you the choice to wire up 1x MPPT controller now and 2x MPPT controllers in the future as you already have the 2x pairs of cables... 

VS just 1x pair of 6 AWG (example) now to 1x MPPT controller... You could not add a 2nd MPPT controller unless you run a second pair of cables to Trailer B.

Just lots of juggling going on here....

-Bill

TellGRBill

1. Should both trailer arrays be wired in series or parallel into this one 60 amp controller?

2. Do you have a suggestion of how to wire two cables into the one controller, other that connect both positive wires together and attach them into the positive controller port and both negative wires together and attach then to the negative controller port?

BB.

1. Each trailer should have its set of 4 panels wired in series... You get 4*18v= Vmp-array (or approximately 4*21Voc=84 volts Voc--array. Voltage open circuit array @ ~75F).

For two strings in parallel, you would simply connect Trailer A+ to Trailer B+ and Trailer A- to Trailer B- for a ~72 Vmp-array @ 19.44 Imp-array...

You can combine in parallel the two arrays at the trailers, and send (for example) down a pair of 6 AWG cables 100' to the MPPT controller Vpanel input...

Or you can run Trailer A +/- from trailers to the Bus MPPT box, and Trailer B +/- cables (both 10 AWG @ 100 feet) and connect them together A+ to B+ and A- to B- and run those +/- cables into the MPPT Vpanel input.

You can put breakers/fuses/switches on the cables--But they are not needed. (if you had three or more strings in parallel, then you would need a "series protection fuse or breaker per string" to protect the array against short circuits). Breakers and/or switches can be handy for debugging and maintenance of the MPPT controller and wiring/array.

2. Do you have a suggestion of how to wire two cables into the one controller, other that connect both positive wires together and attach them into the positive controller port and both negative wires together and attach then to the negative controller port?

Basically, that is how you do it... There are lots of hardware you can use. From "Y" cables for solar panels to Bus Bars:

https://www.solar-electric.com/solarland-slcbl-46-mc4-parallel-connectors.html
https://www.solar-electric.com/search/?q=bus+bars

To Wire nuts, crimp connections, etc...

Exactly how/where/cable sizes/etc. are your choice...

Just a quick hint... If you need to wire up to your solar panels, you can buy a XX Foot long male/female MC4 cable (or whatever the connections are on your panels) and cut it in 1/2. Then you have the male/female mates and jumper cables with raw ends to terminate as needed (connector, box, etc.).

Just make sure you have the polarity correct (use Red/Black wires, use red and black tape wrap on last 6 inches of wire in boxes, etc.). Many devices claim to be polarity protected--But you don't want to test that. Also, solar panels themselves, can be fried if connected "backwards" to other panels or a battery bank... Panels will look like a dead short to a backwards connected power source.

Just make sure the connections are weather proof. Inside a box with drip loops (bring the cables into the bottom of the box, not the sides or top, so water does not follow wiring into the box and corrode the connections.

-Bill

TellGRBill

Thank you.

You have been very patient with me.

I've been thinking again ... maybe dangerous LOL

I already have purchased the 100' of 10awg wire.

How about my connecting the two trailer mounted solar arrays in series and run the one 10awg wire at 144 volts and 9.72 amps to the controller

18 volts vmp * 4 series * 2 arrays = 144 volt Vmp-array @ 9.72 amps ?

This will give me some flexibility to use the trailer mounted solar panels for either the converted bus, the farm house, or separated for very limited use in both the farm house and bus when needed.

If this design works as envisioned, I think we may have a way to expand the solar system for both the bus and the farm house, with the flexibility to shift the panel trailers where needed, being careful to watch the capacity of the batteries

TellGRBill

From: support US (support@renogy.com)
Date: 12/15/22 02:01

Subject: Re: Capacity of our 60amp Renogy controller
Hi William

Thank you for contacting Renogy. This is Mike, It's a great pleasure to be at your service.

Thank you very much for choosing our product, it is dangerous if you connect eight 175 watt solar panels (SKU: RNG-175D-US) in series and then connect them to our 60 amp ROVER charge controller. Because eight 175 watt solar panels in series The total voltage of the solar panels is about 172.8 volts (21.6*8=172.8V) which is beyond the range of our 60 amp charge controller (It can only withstand a maximum input voltage of 140 volts). You need to divide the eight solar panels into two groups and connect each group in series, then connect the two groups of solar panels in parallel and then connect them to your charging controller. The total power of eight 175 watt solar panels is 1400 watts, if you need to use a 24 volt, 36 volt or 48 volt battery bank. If you use a 12 volt battery pack then the total power of the eight solar panels cannot be used effectively.

If you are using 16 175 watt solar panels then you need to divide them into four groups, connect each group in series then connect the four groups of solar panels in parallel and finally connect them to your 60 amp charge controller. This time you have to use a 48 volt battery pack to get the maximum solar output.

Dear Renogy advisor, Mike,

 

We will have three groups of batteries: 1, (3) group 31 12v 100AH    2. (5) group 31 12v 100AH    3. (2) group 27 12v 135AH

How can I connect these three groups of batteries to work effectively with eight panels of two groups and connected in series, then connected the two groups of solar panels in parallel and then connect them to our charging controller.

 How can I connect these three groups of batteries to work effectively with sixteen 175 watt solar panels divided into four groups, each group connected in series then connect the four groups of solar panels in parallel and finally connecting them to our 60 amp charge controller. 

The solar panels will be connected to the controller with at least one 10agw 100' cable.

I will still want to draw 12volts from a battery bank for some 12volt articles in the stationary motor home.

Bill

TellGRBill

---

From: support US (support@renogy.com)
Date: 12/16/22 05:04

Subject: Re: Capacity of our 60amp Renogy controller

Hi William

Good day! Thank you very much for your reply.

1:We do not recommend that you mix different types of batteries as this is detrimental to battery life and safety.

2:If you need to use a 100ft solar panel extension cable to connect 16pcs 175W solar panels to your 60A ROVER charge controller, you need to use thicker cables.

3:If you are using 16 solar panels of 175 watts then you can't use 12 volt system voltage, you need to use 48 volt system voltage for solar system. We don't have proper equipment right now that would allow you to run 2800 watts of solar input and still use 12 volts of system voltage.

If you have any further questions, please feel free to let us know. We are always here to help you.

Best regards
Mike

If I use all the same type battery, how can I connect my three banks of batteries to make it a 48 volt system?

Or maybe two banks of three 100AH in one bank and five batteries in the other.

If the solar panel arrays are spread out, I will be using more than one10awg cable to connect them in parallel. OK?

Bill

TellGRBill

TO: support US (support@renogy.com)
Date: 12/17/22 11:20

Subject: Re: Capacity of our 60amp Renogy controller

Mike

My last question was: if I get eight Batteries together, how do I WIRE THEM TO PRODUCE 48 VOLTS ? TWO GROUPS OF FOUR EACH IN SERIES AND THEN TOGETHER IN PARALLEL TO THE CONTROLLER ?

Will this accomplish what we need?  The sixteen panels:  four panels grouped in series getting 48 volts, 10 amps, linked to another array of four panels grouped in series getting 48volts 10 amps, the two groups of  arrays linked in parallel getting 48volts and 20amps. DOING THIS TWICE, linking both 2x(2X4) 8 panel arrays getting 48 volts and 40amps to the controller ?  

I would like to wire both halves of this arrangement: (2X4 panel arrays) x2 up to the controller with a 10awg cable. Hereby using two 100' 10awg cables.

Note:  each four panel array will be mounted on a small trailer  

Bill

TellGRBill

An update for anyone who stumbles across this conversation, and is interested enough and patient enough to get this far.

1. After getting discouraged recognizing that I have a lot of work and financial spending to generate enough to provide for a 2400-3000 watt load, I asked about how to make better use my 60amp controller/charger, and adjusted my expectations back to my original perspective.  The advisor B.B. helped me better adjust my perspective for solar panel output expectation and controller/charger capability.

1. The first thing I did upon adjusting my perspective was to buy a 4-5 thousand watt duel fuel generator for the farm house under non-emergency conditions, that has about four thousand watt expected load.

2. Then I decided not to buy two more trailers and eight more solar panels. We will use the two boat trailers already purchased and the eight panels already purchased.

3. We will use two trailers together, for the farm house or the converted bus, or under extreme conditions separate them between the farm house and the converted bus.

4. B.B. helped me realize that the solar panels will seldom provide the maximum wattage output that I was worried about eight 175watt panels providing to overload the 60 amp controller/charger.  They will be wired each trailer series and together wired parallel.  Together they will provide a maximum of 96 volts,1400 watts, and about 30 amps. not considering the loss conducted over 100' + 10awg cable and links and connection loss.  Check the following conversation for those conversation details.

 https://forum.solar-electric.com/discussion/357722/how-can-i-correctly-feed-a-60-amp-renogy-controller-charger-with-eight-12-v-175-watt-solar-panels/p1?new=1

5. The battery assembly is the next issue that we are making progress with.

TellGRBill

I have been looking and searching for a cover/ weather shield for the power cord I am using with inlet and outlet boxes. I finally found them, I think.  Many companies are selling the box, but I haven't found anyone selling the weather shield that screws onto it after the plug in inserted until now.

 https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=This+30+amp+cord+shield+with+locking+ring&_sacat=0&LH_TitleDesc=0&_odkw=This+30+amp+cord+shield&_osacat

 The box has threads around the opening where the plug fits into the box. I would like the cover to screw onto the box when the plug is attached to the box to keep the weather out of the plug and box.

TellGRBill

An update:  I asked for advice from Renogy (the company where I bought my solar panels and other solar equipment ) about the wire I should use to connect the battery bank to the 3000 watt Renogy Inverter.  I was told to use 4/0awg wire.  I searched Facebook Marketplace for someone selling a piece that I could use to connect the batteries together and the bank to the 3000watt inverter.  WOW...I had never seen 4/0awg wire.  I knew it would be heavy but when I got it, I saw that it was more than I needed or could even handle.  Even if I slimmed the ends down for a wire lug it was much too heavy.  I have used 1/0 welding wire by slimming the ends down for the lugs but 4/0 wire can't be handled by me.  Sooo back to Facebook Marketplace and this time to SELL the 4/0 wire to someone wiring an outlet for a heavy duty welder.  I'll go back to 1/0awg welding wire to connect the batteries and the battery bank to the inverter.  The people monitoring this advice web site surely must chuckle if they read my stumbling.  LOL   But I'm learning.  I appreciate all the help and patience I've experienced on this web site!!

Marc Kurth

Back to basics:

3000 watt inverter / 12v input = 250 amps.  4/0 is already borderline. 1/0 is way, way undersized.

Remember that as the battery bank falls below 12v, the current will increase because an inverter is a constant wattage device. Example: 3000 watts / 11 volts = 272 amps.

An undersized cable will result in a high voltage drop between the inverter and the battery. As the voltage falls, the amperage draw will increase.

In motorhomes, I generally see 12v 2,500-3,000 watt inverters wired with 4/0. Larger inverters get multiple cables.

TellGRBill

Thanks for your observation Marc. I have been coming to the same conclusion.  That also applies for the cables connecting the batteries in the battery bank, I think.  I'm wondering how sensitive the wire lugs at the battery connections are to amperage flow, and how heavy they really need to be?  I ask this because I have several copper mechanical lugs made for 1/0 cable that I could use with 4/0 welding cable.   I have been using some welding cable that is labeled 1/0, but after comparing cables, I think it is actually 4/0 copper welding cable since the copper conductor is about 1/2" in diameter.

Marc Kurth

It is important to figure out the voltage drop that you get with the cable selected. There are several online calculators that will let you play the numbers, including using two conductors of smaller wires together for each leg.

A voltage drop of 0.3v or 0.5v is very small in some applications, but it is monstrous in a 12v DC setup.  Picture your battery bank 12.5v but it's only 12.0v at the inverter! Here is one with some parameters already entered. https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=12&necconduit=pvc&necpf=0.85&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=12&phase=dc&noofconductor=1&distance=10&distanceunit=feet&amperes=250&x=71&y=20&ctype=nec

TellGRBill

I went to the calculator but don't understand how the result applies to my situation exactly. I understand that with higher resistance the voltage drops, and that depends on the length of the wire and the gauge (thickness) of the wire.  My demand of the solar system will have a wide range, so I have been trying to prepare the system to have a maximum capacity.  I want to use the maximum capacity components, within reason and budget. Now, after measuring the diameter of what I thought was 1/0 welding cable, I find that I may have connected the battery bank with 25' of (3) parallel 4/0 AWG cables.  Plenty of capacity I think.  I plan to have three groups of batteries feeding two Buss locations, shouldn't that reduce the required size of the cable connecting the batteries?

BB.

"worst case" 3 kWatt inverter DC current input:

• 3,000 watt * 1/0.85 AC inverter eff * 1/10.5 volts battery cutoff = 336 Amps @ 12 volts (worst case)

Note that if you allow for 2x surge power on inverter, you will have 2x surge DC current too.

Using the drop calculator for 11.5 volts @ 336 Amps @ 25 feet @ 3x 4/0 AWG per leg:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=12&necconduit=pvc&necpf=0.99&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=11.5&phase=dc&noofconductor=3&distance=25&distanceunit=feet&amperes=336&x=0&y=0&ctype=nec

Result

Voltage drop: 0.35
Voltage drop percentage: 3.01%
Voltage at the end: 11.15

As I understand your setup--Yes, that is a "workable" system design.

-Bill

TellGRBill

After nearly a years of research, and asking questions and getting advice from advisor BILL , who has been very patient and helpful to me with his T.M.I. advice, WE ARE DISCONNECTED FROM THE POWER LINE, and the system works as we had hoped.

BB.

That is great to read Bill...

As always, this is summer. Need to watch the system closely (loads, harvested energy, battery bank state of charge, etc.) as we get into fall and winter.

Take care,
-Bill

TellGRBill

I have been researching and asking how I can put a low voltage disconnect on the 120v output of my 3000watt inverter.

I was given what I think was good advice for achieving a low voltage disconnect on the 12volt system, but I want to just disconnect the 120 volt output of the inverter, so I disconnect the high energy  users of our electrical system while allowing that we can still use the 12 volt low energy users while the battery bank recovers.

I think I found the solution to what I have been looking for: a Solar low voltage disconnect DC to DC then DC to AC relay connected to the inverter output. Check out the drawing.

Using a low voltage disconnect device and a solid state relay DC to AC.

TellGRBill

Good afternoon,

I have installed a meter reading the output of my inverter and have two readings that I don't understand.

energy watts and power watts.

What is the difference?

Here are some readings on my meter presently

Volts 116

Amps 63

Energy watts  143

power watts 61.0

This reading was when our refrigerator was in running mode.

When the refrigerator was in startup mode the energy watts reading was over 3000 watts energy watts and our volts reading for the battery bank dropped 2 tenths of a volt.

SteveK

Power Watts is what, in watts, is being used right now. Energy Watts is what, in watts, has been used over time.

Of course, this makes no sense as you claim your Energy Watts spiked momentarily when your fridge kicked on..... it should be the opposite.

TellGRBill

B.B. Please check the Solar Expert reply, and clarify it for me.

BB.

Can you tell us which meter you are using? AC or DC? etc....

In general (for a first approximation)...

Power is a Rate of energy usage: Watts = Joules per Second (helpful?)
Energy is the "total" energy usage: Watts*TIme = Watts * Seconds = Watt*Seconds

Now--For our homes and nuclear power plants, we use Watt*Time where time is measured in hours. Watt*Seconds (the actual "SI" unit) is a pretty small number....

I.E;, 3.3 kWH per day system (a smallish off grid system):

• 3.3 kWH * 1,000 W per kW = 3,300 WH
• 3,300 WH * 3,600 seconds per Hour = 11,880,000 Watt*Seconds (if you are in High School Physics class)

Obviously, we (home scale systems) use Watt*Hours and kWatt*Hours as our energy measurements (reasonably sized "numbers" to write out).

Now that I have probably confused you more than helped.... We really need to know what type of meter(s) you are using to measure these numbers.

Again, a general explanation:

• Watts = Power => rate of energy usage => sort of like miles per hour... 60 Miles per hour
• Watts*Hours = Energy used => sort of like miles driven say 2 hours => 60 miles per hour * 2 hours = 120 miles driven

Say you have a typical refrigerator... Uses 120 Watts (rate) for about 30 minutes (1/2 hour) in an hour. The math:

• 120 Watt fridge motor * 0.50 duty cycle * 24 hour = 1,440 Watt*Hours per day = 1.44 kWH per day

Your numbers:

Here are some readings on my meter presently:

Volts 116

Amps 63

Energy watts  143

power watts 61.0

The above does not make a lot of sense....

Is Volts 116 VAC or 11.6 VDC or what?

Using your Volts and Amps:

116 VAC * 63 Amps = 7,308 Watts = 7.308 kWatts (that is something like 5 portable electric space heaters running at the same time)

Watts is POWER. A rate (like miles per hour, gallons per minute, etc.)

Watt*Hours is ENERGY. An amount of energy used (like driving 120 miles, pumping 200 gallons, etc.).

Energy Watts does not make sense (units). Energy = Watt*Hours

Power Watts does make sense. Power and Watts are rates (like miles per hour, amount of energy used per hour, etc.).

100 Watts * 2 hours = 200 Watt*Hours used
Rate * Time = Energy Used

-Bill