RV Install, wiring advice/help

System

I just registered and this is my first post. I have read over a lot of the posts similar to mine but I want to make sure I have all the information I need before I start hooking things up.

The plan: Install (1) Kyocera 125 watt on the roof of my 30 foot travel trailer. Wired to a BlueSky SB2512iX and IPN Pro remote to a bank of (4) 75Ah batteries wired in parallel.

I am installing the battery bank in center of my front compartment running the width of my trailer just behind the tongue but still inside the trailer. I will install the solar panel directly above on the roof where I will drill a hole to feed the MC4 cables down the wall into the compartment. The plan is to run an addition pair of MC4 cables to add another panel later on in parallel directly at the controller not on the roof. The wiring is being routed this way because if I go in through the fridge roof vent the wiring will be longer and very difficult to route to this location, plus I am not sure if the gauge of the MC4 wire is big enough for that length.
The charge controller will be inches from the battery bank so I did not plan on using a battery temp wire.

Questions

1. Is the MC4 cable wire sold here the right gauge at 15 feet for one panel?

2. I had planned on running an additional pair of MC4 cables back to the controller, if I do it this way will it eliminate the need for larger gauge wire since I am running parallel?

3. The controller I have BlueSky SB2512iX, will it handle (3) of the Kyocera 135watt panels above if I decide to run (3) pairs of MC4 cables to the roof back to the controller in parallel?

4. What size wire do I need to run from the controller to the battery bank (12-18” max)

5. What size cable to I need to run between each battery in parallel? They will be butted next to each other.

6. What size cable do I need to run from my battery bank to my 1500watt TrippLite inverter (12-36”) max

I already have in my possession all of this equipment.

Any other advice or suggestions are welcome.

Thank you

Luke

BB.

Re: RV Install, wiring advice/help

luked wrote: »

The plan: Install (1) Kyocera 125 watt [note that this is a 135 watt panel] on the roof of my 30 foot travel trailer. Wired to a BlueSky SB2512iX and IPN Pro remote to a bank of (4) 75Ah batteries wired in parallel.

Lots of questions--I will take a stab them.

• 135 watt panel * 0.77 system derating * 1/14.5 volts charging = 7.2 amps charging
• 7.2 amps / (4*75AH batteries) = 0.024 or 2.4 % rate of charge

Normally, we would recommend that a battery bank be charged with 5% (to 13%) maximum rate of charge (for flooded cell batteries).

Ideally, you should have at least one more panel if this is intended for long term camping/RV'ing use. If just weekends and you will use Utility power and/or backup genset for charging--you can use the solar panels to just extend your power some.

Questions

1. Is the MC4 cable wire sold here the right gauge at 15 feet for one panel?

From our host's store, they say:

All MC cables are made with #10 AWG stranded UL/NEC approved RHW-2/RHH (USE-2) sunlight resistant wire.

So there are two questions...

1. 10 AWG wire is good for 30 amps or more (per NEC). So Isc of 8.37 amps is well under 10 AWG wire--so that is fine.
2. Is there too much resistance for this wire run

For #2 we use a voltage drop calculator, the one-way wire length, 7.63 amps and find the voltage drop for, say 30 ft wire 10 AWG run is:

• 0.6 volts for 10 AWG, 30 ft @ 7.73 amps

That is actually a bit high of voltage drop (3.5% or so)... Ideally, most people would aim for less than 2% voltage drop. However, if my 30' run was too long of guess for the wire run--then you are perfectly OK with a 15' run.

Second, you have choosen a BlueSky MPPT controller... Have you already purchased it yet? If not, you may want to think about another brand/model.

The BlueSky has a maximum PV input voltage of 35 volts--For your setup, ideally with two Kyocera 135 watt solar panels, you should be connecting them in series for a Vmp of ~35 volts (Voc will be higher).

This gives you several advantages... Lower current flow through the copper wiring for the PV array (lower voltage drop) and if you camp in very hot areas--your battery charging voltage from the array will be better (Vmp drops with high temperatures, and can limit the maximum charging voltage / charging current to the battery bank).

You may want to look at the Morning Star 15 amp MPPT or (even 45 amp MPPT if you plan on adding more panels in the future) charge controllers.

Or look at the Rogue 30 amp MPPT charge controller.

Note: All three of these charge controller have differing Varray-Voc maximum input voltage--Depending on how many panels you plan on installing and which controller you pick--will affect your wiring choices.

2. I had planned on running an additional pair of MC4 cables back to the controller, if I do it this way will it eliminate the need for larger gauge wire since I am running parallel?

See above--depends on length of wire run and if you will be running more than one panel in parallel. Also, if you can run a different MPPT charge controller, you can (and should) run your two solar panels in series.

3. The controller I have BlueSky SB2512iX, will it handle (3) of the Kyocera 135watt panels above if I decide to run (3) pairs of MC4 cables to the roof back to the controller in parallel?

The maximum "optimum" wattage I would recommend for a 25 amp 12 volt charge controller would, roughly, be:

• 25 amps * 14.5 volts charging batt * 1/0.77 system derating = 471 watts
• 3x 135 watts = 405 watts

So, yes, no problem with 3x 135 watt Kyocera panels in parallel on this controller.

4. What size wire do I need to run from the controller to the battery bank (12-18” max)

Depends on the maximum amount of solar panels you will be running... But for 25 amps, using NEC 1.25 safety factor:

• 25 amps * 1.25 = 31.25 amp rate fuse/wiring minimum

So, you are looking at the next standard fuse/breaker size of 30-40 amps and 10-8 awg wire.

You also want a low voltage drop between the controller and the battery bank--but your wire run is so short that is not an issue here.

5. What size cable to I need to run between each battery in parallel? They will be butted next to each other.

Really depends on the charging current/maximum load... With four batteries in parallel, I would assume that the interconnect cable must be rated to carry at least 1/2 of the expected maximum current (x 1.25 safety factor). The batteries should share 1/4 of the current, but frequently that does not happen (why I picked 1/2 rather than 1/4 for cable sizing).

6. What size cable do I need to run from my battery bank to my 1500watt TrippLite inverter (12-36”) max

Generally, the inverter manuals should discuss their wiring requirements... But working from back of the envelope calculations... 1,500 watt inverter running 12 volt battery bank, assume 80% efficient, and 10.5 cutout voltage for inverter (dead battery voltage) with NEC 1.25 derating for fuses / wiring:

• 1,500 watts * 1/10.5 volts * 1/0.80 eff * 1.25 = 223 amps rated circuit

There is a fuse rated at 250 Amps or 250 Amp Circuit Breaker so that would be the wire rating too.

If your maximum draw will be less than 1,500 watts, then you could size the wiring/fusing for less.

I already have in my possession all of this equipment.

Any other advice or suggestions are welcome.

If you eventually get a another charge controller--look for those with remote battery temperature sensors (the small MorningStar 15 amp MPPT controller really needs one).

In general, RV and small cabin use should plan on using as little DC/AC power as possible. Refrigerators should be propane powered. Use florescent or LED lighting, efficient appliances (like laptop computers and such). People do use microwave ovens--but as you can see, that is a tremendous load on a 12 volt battery bank...

For a 4x75AH battery bank, the maximum continuous power you should draw from them is around C/2.5 or:

• 4x75 amps / 2.5 = 120 amps

For an inverter load that would be:

• 120 amps * 10.5 volts (low battery) * 0.80 inverter eff = 1,008 watts max 120 VAC load for this bank

If you can get your loads down to 300 watts or so maximum--The MorningStar 300 watt True Sine Wave 12 volt inverter (600 watt surge) would be ideal for your setup.

Anyway, my 2 cents worth--and the above are just suggestions and rules of thumb I like to look at when designing a system. There are good reasons to not follow rules of thumb--but we need to discuss those in a bit more detail.

I hope I was helpful.

-Bill

BB.

Re: RV Install, wiring advice/help

Oh, I forgot to add a link to a small camper trailer setup thread here that you may also find interesting, a nice thread with video from Keven in Calgary Canada.

-Bill

dmiller

Re: RV Install, wiring advice/help

BB - no one is installing propane refrigeration anymore for high-end remote camping vehicles. The combination of solar and high efficiency 12v compressors make it unnecessary. I even have an installed propane system but use 12v for my two refrigeration units. The propane is just for cooking and emergency heat.

BB.

Re: RV Install, wiring advice/help

DMiller,

Sounds interesting... I would agree if this is a 9+ month a year living situation. Normally--I put in the ~9 month being the break even decision point. I forgot on this last post.

How about the weekend get away folks that only do 20-60 days a year--are they still going with solar/electric fridges?

-Bill

icarus

Re: RV Install, wiring advice/help

dmiller wrote: »

BB - no one is installing propane refrigeration anymore for high-end remote camping vehicles. The combination of solar and high efficiency 12v compressors make it unnecessary. I even have an installed propane system but use 12v for my two refrigeration units. The propane is just for cooking and emergency heat.

That is not entirely true. It may be true for really high end motor homes/trailers, but there are lots of applications that still use LP fridges. In my experience, the more remote someone is likely to be, the further and longer away from shore power, the more likely LP fridges are to be installed.

As for remote cabins/camps, I have always argued that the more a fridge is used, the more it makes sense to use a conventional fridge. For a weekend or part time off grid cabin, LP fridges still win in many cases.

Tony

System2

Re: RV Install, wiring advice/help

BB. wrote: »

Lots of questions--I will take a stab them.

• 135 watt panel * 0.77 system derating * 1/14.5 volts charging = 7.2 amps charging
• 7.2 amps / (4*75AH batteries) = 0.024 or 2.4 % rate of charge

Normally, we would recommend that a battery bank be charged with 5% (to 13%) maximum rate of charge (for flooded cell batteries).

Ideally, you should have at least one more panel if this is intended for long term camping/RV'ing use. If just weekends and you will use Utility power and/or backup genset for charging--you can use the solar panels to just extend your power some.



From our host's store, they say:



So there are two questions...

1. 10 AWG wire is good for 30 amps or more (per NEC). So Isc of 8.37 amps is well under 10 AWG wire--so that is fine.
2. Is there too much resistance for this wire run

For #2 we use a voltage drop calculator, the one-way wire length, 7.63 amps and find the voltage drop for, say 30 ft wire 10 AWG run is:

• 0.6 volts for 10 AWG, 30 ft @ 7.73 amps

That is actually a bit high of voltage drop (3.5% or so)... Ideally, most people would aim for less than 2% voltage drop. However, if my 30' run was too long of guess for the wire run--then you are perfectly OK with a 15' run.

Second, you have choosen a BlueSky MPPT controller... Have you already purchased it yet? If not, you may want to think about another brand/model.

The BlueSky has a maximum PV input voltage of 35 volts--For your setup, ideally with two Kyocera 135 watt solar panels, you should be connecting them in series for a Vmp of ~35 volts (Voc will be higher).

This gives you several advantages... Lower current flow through the copper wiring for the PV array (lower voltage drop) and if you camp in very hot areas--your battery charging voltage from the array will be better (Vmp drops with high temperatures, and can limit the maximum charging voltage / charging current to the battery bank).

You may want to look at the Morning Star 15 amp MPPT or (even 45 amp MPPT if you plan on adding more panels in the future) charge controllers.

Or look at the Rogue 30 amp MPPT charge controller.

Note: All three of these charge controller have differing Varray-Voc maximum input voltage--Depending on how many panels you plan on installing and which controller you pick--will affect your wiring choices.



See above--depends on length of wire run and if you will be running more than one panel in parallel. Also, if you can run a different MPPT charge controller, you can (and should) run your two solar panels in series.



The maximum "optimum" wattage I would recommend for a 25 amp 12 volt charge controller would, roughly, be:

• 25 amps * 14.5 volts charging batt * 1/0.77 system derating = 471 watts
• 3x 135 watts = 405 watts

So, yes, no problem with 3x 135 watt Kyocera panels in parallel on this controller.



Depends on the maximum amount of solar panels you will be running... But for 25 amps, using NEC 1.25 safety factor:

• 25 amps * 1.25 = 31.25 amp rate fuse/wiring minimum

So, you are looking at the next standard fuse/breaker size of 30-40 amps and 10-8 awg wire.

You also want a low voltage drop between the controller and the battery bank--but your wire run is so short that is not an issue here.



Really depends on the charging current/maximum load... With four batteries in parallel, I would assume that the interconnect cable must be rated to carry at least 1/2 of the expected maximum current (x 1.25 safety factor). The batteries should share 1/4 of the current, but frequently that does not happen (why I picked 1/2 rather than 1/4 for cable sizing).



Generally, the inverter manuals should discuss their wiring requirements... But working from back of the envelope calculations... 1,500 watt inverter running 12 volt battery bank, assume 80% efficient, and 10.5 cutout voltage for inverter (dead battery voltage) with NEC 1.25 derating for fuses / wiring:

• 1,500 watts * 1/10.5 volts * 1/0.80 eff * 1.25 = 223 amps rated circuit

There is a fuse rated at 250 Amps or 250 Amp Circuit Breaker so that would be the wire rating too.

If your maximum draw will be less than 1,500 watts, then you could size the wiring/fusing for less.



If you eventually get a another charge controller--look for those with remote battery temperature sensors (the small MorningStar 15 amp MPPT controller really needs one).

In general, RV and small cabin use should plan on using as little DC/AC power as possible. Refrigerators should be propane powered. Use florescent or LED lighting, efficient appliances (like laptop computers and such). People do use microwave ovens--but as you can see, that is a tremendous load on a 12 volt battery bank...

For a 4x75AH battery bank, the maximum continuous power you should draw from them is around C/2.5 or:

• 4x75 amps / 2.5 = 120 amps

For an inverter load that would be:

• 120 amps * 10.5 volts (low battery) * 0.80 inverter eff = 1,008 watts max 120 VAC load for this bank

If you can get your loads down to 300 watts or so maximum--The MorningStar 300 watt True Sine Wave 12 volt inverter (600 watt surge) would be ideal for your setup.

Anyway, my 2 cents worth--and the above are just suggestions and rules of thumb I like to look at when designing a system. There are good reasons to not follow rules of thumb--but we need to discuss those in a bit more detail.

I hope I was helpful.

-Bill

WOW Bill! I really couldn't have asked for anything more.

I already have all of this equipment. Some was given to me, some was a good deal. I am planning on adding up to (3) 135watt kyoceras to the roof at some point and was planning on running them all in parallel at the controller not on the roof, so that's why I chose the controller I did. Plus it had the option of using a batt temp and external display/remote function.

My basis for this decision was that I do most of my camping in the sierras and if I run the panels in series and any of them get shade it greatly reduces the charging of my battery bank or so I read.

Thanks so much again Bill, I appreciate the detailed response

Luke

bighornram

Re: RV Install, wiring advice/help

dmiller wrote: »

BB - no one is installing propane refrigeration anymore for high-end remote camping vehicles. The combination of solar and high efficiency 12v compressors make it unnecessary. I even have an installed propane system but use 12v for my two refrigeration units. The propane is just for cooking and emergency heat.

Sounds intriguing though Mr. Google seems to point to LP refrigeration for RV's. Does anyone have more info on this?

BB. wrote: »

Oh, I forgot to add a link to a small camper trailer setup thread here that you may also find interesting, a nice thread with video from Keven in Calgary Canada.

-Bill

Bill thanks for that great link. When wiring multiple Kyocera's in series this increases the voltage to the cc, what is the output voltage when you wire like this?

BB.

Re: RV Install, wiring advice/help

What information about RV LP refrigerators are you looking for?

Keven used an MPPT type charge controller (a Morningstar SunSaver 15 Amp MPPT Solar Charge Controller) for his setup...

And MPPT controllers takes higher voltage/lower current solar array power and down converts (really like a DC version of an AC transformer) to low voltage/higher amperage for the battery bank... It does it with around 90-95% efficiency. (like anything, there are specific limits for input limits for Voltage and Current for charge PWM and MPPT charge controllers--So you need to know the type and model for proper Array/Battery Bank configuration and installation).

MPPT controllers are quite a bit more expensive than PWM--But they are really nice if you have a large array and/or need to mount the panels a long distance from the charge controller/battery bank... With the higher end controllers, you can use a high Vmp array (upwards of Vmp~100 VDC) instead of ~17 VDC (12 volt battery bank)--The wiring will need to carry about 1/5th the current--so you can use smaller gauge wire and save a bunch of money on copper. Also some advantages for climates that are very hot and/or very cold (solar PV Vmp varies with temperature).

A couple of FAQs:

All About Charge Controllers
Read this page about power tracking controllers

-Bill

bighornram

Re: RV Install, wiring advice/help

BB. wrote: »

What information about RV LP refrigerators are you looking for?

I was interested in reading about these refers as it would be nice not to use LP but I was not very successful at finding many. Dometic didn't have anything listed but LP/110v.

BB. wrote: »

Keven used an MPPT type charge controller (a Morningstar SunSaver 15 Amp MPPT Solar Charge Controller) for his setup...

I'm interested in learning more about techniques/options for installation. If I decide to step up my system I'd like to have done the research ahead of time. It makes sense to me to step up the voltage to lose less power in the wires. Kevin had a pretty short run from the top of his camper but a long run when he unplugged and moved them with the extension. Would it be that advantageous to series the panels when running 2x15'?

Jeff

BB.

Re: RV Install, wiring advice/help

I will let others talk about LP vs DC refrigerator options out there--I would be doing the same as you -- Googling RV sites.

Regarding Series or Parallel... Depending on the MPPT controller, some loose a percent or so of efficiency as the Varray voltage increases... I gather that Varray~2*Vbatt is around optimum for many of the controllers. Many of the controllers include an Efficiency Graph so you can see the issues.

Otherwise, you can do your own calculations... Say you have 2x 135 watts panels with Vmp=17.5 volts and Imp=7.7 amps.

Using any old Voltage Drop Calculator (note some calculators use the real wire length and others use the run length which is 1/2 the real wire length) you can calculate the drop as a percentage of line voltage... Normally, 3% is the maximum drop desired, and many people aim for 2-1 volts for the array wiring drops.

So, lets say you want to run 50' (one way run) of wire on a 17.5 volt run (15.4 amps) and a 35 volt run (7.7 amps):

• 16 awg @ 7.7a => 2.1 volt drop;
• 2.1v/35v = 0.06 = 6% drop
• 12 awg @ 7.7a => 0.8 volt drop;
• 0.8v/35v = 2.2% drop
• 10 awg @ 7.7a => 0.5 volt drop;
• 0.5v/35v = 1.4% drop

Now, the same thing with 15.4 amps and 17.5 volts when running the two panels in series:

• 14 awg @ 15.4a => 2.8 volt drop;
• 2.8v/17.5v = 0.16 = 16% drop
• 10 awg @ 15a => 1.1 volt drop;
• 1.1v/17.5v = 6.2% drop
• 6 awg @ 15a => 0.4 volt drop;
• 0.4v/17.5v = 2.2% drop
• 4 awg @ 15a => 0.3 volt drop;
• 0.3v/17.5v = 1.7% drop

So, roughly (if I got all my numbers correct)--Your two panels in series will have about the same percentage drop on 30' of 10 awg wire as your two panels in parallel on 30' of 4 awg wire... A huge difference.

-Bill