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New Solar Install


Bill&Cindy

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I am ready to begin installing solar on my 2013 KZ stoneridge 36RK. I have a couple of specific questions and would also appreciate any suggestions. I have calculated electrical usage for the way we RV. We typically spend 2 to 3 nights in a boondock situation and then several nights in a compground. Rarely are stays longer than a week. Our inverter usage (1000 psw) will primarily be TV/Dish, recharging electronics, morning hair dryer and brief microwave. The last two and morning coffee while running the generator. All lighting is LED. Water heater and refer are gas. I have a Yamaha 2400i that can be used to supplement/charge when needed. Charger is 75amp 3 stage WFCO that came with the 5er.

My plan is to install two Renogy 150 watt panels with the following specs.

Vmp 17.9 volts

Imp 8.38A

Voc 22.5v

Isc 9.05A

These will be mounted flat on the roof. Leads from the panel are 10AWG and will run <10 ft to a combiner box. From there #6 wire will be run down to the charge controller, a length of 13 ft.. I want to use the Bogart/Trimetrics SC-2030 controller and TM-2030 monitor. From there. it will be less than 3 feet to the batteries, so I will use #4 wire (the largest recommend recommended for the SC-2030). At this time I have two Trojan 245 amp 6 volt batteries. A couple of questions

1. Fuses: Where, what size and brand

2. Will this wiring allow me to add a third panel and MPPT 45 amp later

3. I have room for a second set of batteries. Are they needed now?

Any other comments/suggestions?

 

Thanks for the help

Bill

 

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For the wiring I have been using the voltage drop calculator available on this site. http://www.oynot.com/solar-info.html. (Remember to double length of wiring runs). Without running the numbers I am guessing you are in good shape. Your wiring is going to be sufficient with more panels and an MPPT but you would need to wire the panels in series to get a higher voltage to the controller.(If You are thinking that way, higher voltage panels and an MPPT would be the way to go right now) A nyway, I am just a beginner struggling through these issues myself. I am sure the experts will be by. If you have not looked at Jack Mayer's web site, do yourself a huge favor. http://www.jackdanmayer.com/. I think the general rule on sizing batteries and wattage is to get approx a 1:1 ratio of battery Ah and solar wattage. I would say you are good on that.Jack's site has info on fusing.

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Also, on the batteries, as I said I do not think the size of your proposed solar bank is significantly out of line with your battery bank, so the real factor in whether you want to add more batteries is whether you need more reserve to support your boondocking . Just remember, later on, that to add two more batteries to your exisiting bank will be hard on the new ones. If two is okay for you right now, I would hold off and replace with all new batteries when needed. dave

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I think your plan will work out for the needs you listed. You'll probably need the generator now and then but so do we,

 

I bought a circuit breaker panel made by Midnite Solar from Amazon instead of using fuses (from the solar array to the controller). I do like Midnite Solar. You can also buy DC circuit breakers. Size the breaker(s) according to the maximum current (remember that solar panels can put out a lot more current in very cold, very bright weather... and in winter in the desert it can be very cold in the morning but still very sunny. Amazon has a lot of solar stuff which makes it a lot easier now than just a couple of years ago. I did not buy enough of the MC4 connectors due to stupid mistakes on my part. There is a learning curve and while my learning curve is usually quite fast.... unfortunately my forgetting curve is even quicker.

 

Here is a link (on Amazon) to one of the Midnite Solar combiner/circuit breaker boxes: http://www.amazon.com/Midnite-Solar-Photovoltaic-Combiner-3-Position/dp/B004XFYV8U/ref=sr_1_19?ie=UTF8&qid=1423418374&sr=8-19&keywords=solar+circuit+breaker that also shows DC breakers (with pricing).

 

I have a combiner box on the rooftop but since my panels are all in series that is not, strictly speaking, necessary.

 

I also used a plus (red) and a minus (black) busbar from Amazon for connections from the solar charge controller, the inverter, and the shore power charger/converter to combine these circuits to the battery bank: http://www.amazon.com/OutBack-Terminal-Bus-Bar--TBB-Red/dp/B00A6XPSLW/ref=sr_1_10?ie=UTF8&qid=1423418783&sr=8-10&keywords=dc+busbar

 

The busbar makes it a lot easier to work with the wiring.

 

Size your breakers/fuses/wiring yourself. Remember that current can flow backwards in the event of a short circuit.

 

Don't expect miracles with 300-watts of 12vdc (nominal) panels. If you install oversize wiring you will have a good basis for expansion later if you need it. I am beginning to think that with fixed panels it takes a kilowatt to get what we expect to get from a solar array. Especially on a cloudy day. But it all helps. :)

 

WDR

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HERE is the article on solar controller disconnect. You might find that interesting if you have not seen it. I'm not sure if that is linked from the website or not....

 

Why switch controllers later? Or am I confused. Go to the MPPT now, and be done with it, if that is your longer term intentions.

 

Take a look at the KID if you have not seen it, for a charge controller. In combination with the Whiz Bang Jr. it makes for a nice package and the total price is not as bad as you might first expect. But it is 30 amps total -although you can network two. Still more than a Morningstar, though.

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DIN breakers are passthru breakers, so it would work as shown. However, you are correct - it is best wired with the array line entering the bottom - which is the conventional way to do it. That is the conventional power flow for this application. I corrected the drawing - good catch.....it was sure easier to draw the original way. :)

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Thanks for all the input so far. I picked up a couple of things I missed, like breakers on both sides of the controller and a 250 fuse between the inverter and the battery bank. Thanks jack for the list of resources on your site. I have saved money by going to several sites.

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DIN breakers are passthru breakers, so it would work as shown. However, you are correct - it is best wired with the array line entering the bottom - which is the conventional way to do it. That is the conventional power flow for this application. I corrected the drawing - good catch.....it was sure easier to draw the original way. :)

 

I only remember because of MidNite Solar's ETL Testing (check the 5th paragraph).

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Bill & Cindy, without running all the calculations I will still offer a few comments:

 

1) Based on my experience in our 29 Ft Class C with two people onboard and DC loads consisting primarily of (the biggest load) my forced air LP furnace (of course its load depends on temperature), water pump, vent fans and LED lighting, in my opinion only two batteries (your 245 amp hours of stored energy) is a bit on the marginal side. Im running four batteries with a total of 460 amp hours which is working fine where my previous two batteries was close if the furnace had to run a lot at night. I just don't like to let my batteries dip much below 12.3 even though that's on the conservative side lol

 

2) The wire size depends on current and distance of course, but if you wire your panels in series and operate at a higher voltage (say 24 series instead of 12 volts in parallel) current is reduced.

 

3) Thanks to advice offered here, I went ahead and installed a "smart" 4 Stage (Bulk, Absorption, Float, Equalize) MPPT Solar Charge Controller AND AM PLEASED AND WELL SATISFIED versus my previous cheapie PWM unit

 

4) My Solar Charge Controller manufacturer advised me if I operated at 24 or even 48 volts (instead of only 12 as I was originally configured) the MPPT function would operate better which my rewire (put the two panels in series versus parallel) proved to be true.

 

5) While it depends on the hours and quality of sunlight and the angle and your actual loads, for my use four batteries (460 Amp Hours) is where I am more comfortable and while 200 watts of rooftop solar is getting me by currently, before I head west next summer for extended dry camping Im adding another 200 to 240 watts for a total of 400 to 440.

 

In closing Id suggest two more batteries for you and a quality "smart" 4 stage MPPT Controller and your 300 watts of solar can suffice (subject to sun and loads)

 

Best wishes, John T Too long retired electrical engineer and rusty as an old nail especially regarding electronics, so no warranty

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  • 1 month later...

As Spring approaches and I'm moving from the Theoretical to the Practical, I'm running into a few questions.

 

First (there will undoubtedly be more): Combiner Box -- I had envisioned installing a waterproof box flat on the roof of our trailer. However, any of the combiner boxes with circuit breakers (as I believe Jack has suggested, like the Midnight Solar MNPV 6) require verticle to a 3/12 roof pitch. How/where do you recommend mounting the combiner box? Am I missing something?

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Keep posting the questions as I will be installing in the last two weeks of April. I was thinking of just getting some type of plastic junction box at one of the big boxes, doing the connections and making it water proof. I am thinking the roof also. In fact I know mine will be the roof since I will either be using the fifth wheels pre-wiring or if I drop new wires they are going to be at least 6 gauge and I want to limit the length of the 10 gauge wires coming off the panels. I will be watching for other replies. I thought Jack made a couple of different suggestions including more of a home made option. I will need to look at that again.

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You can't put many of the breaker boxes on the roof. They have to be vertical. You can make your own in various forms, but for breakers you can mount DIN rails in a waterproof box and put in the appropriate breakers. OR, if you are doing a high voltage system you can bring the individual wires down into the RV to a breaker box inside.....high voltage usually allows that - but you need to run the numbers on the wire lengths.

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Another "practical" question -- What do you use or recommend for Breakers between the various devices and the battery bank?

 

The Tristar TS-MPPT-60 is a 60 Amp controller - at a +25%, that would call for a 12 vdc 75 Amp breaker

 

Am looking at a 3000w inverter, with 6000w surg capability. If my math is right, that would be 250A at 12 vdc, not counting the surge nor the +25%.

 

I have an existing PD 9260 Converter for when we have shore power, again that is a 60 Amp 12 vdc output.

 

I am "assuming" that a maximum of 60 Amp 12 vdc from the batteries to the 12v DC fuse panel would be reasonable.

 

I was "thinking" about a Midnight Solar box -- but their DIN breakers max out at 63 Amps dc.

 

What do you who have more experience & training suggest?

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I have a 200-amp fusible link between my 12vdc bus in the electrical cabinet and the batteries. The inverter, the charger/converter and the solar charge controller all connect to that bus. That should pop under any load that would be likely to start an electrical fire. The bus makes it easy to connect the wires and for troubleshooting. The cabinet is where the former built-in vacuum cleaner sucker was installed.

 

The circuit breakers between the solar array and the solar charge controller don't need to be as big as the total current handling capability of your MPPT controller; especially if you have used series connections to keep current levels down.

 

Since my 640-watts of solar panels is connected in series I only need to protect 8-amps of current flow. So I have a 15-amp Midnite Solar circuit breaker (only one - on the positive lead right now) between the panels and the solar charge controller.

 

I know that many people don't like series connections because of their greater sensitivity to shadowing but since my panels (and presumably yours) are on the rooftop then shadows are likely only at low sun angles (very early in the morning and very late in the afternoon) when there is not much charging going on anyway. (Most of us try to size our solar installation to fully charge the battery bank by noon-ish on a reasonably good solar day with average loads.)

 

I have been very happy with my Midnite Solar circuit breakers and the panel. The panel is installed at the back of the closed just below (and slightly aft of) where the wiring from the rooftop combiner box enters the refrigerator vent. Easy to flip the breakers off (and Stanley is right about putting breakers in weird places). :)

 

WDR

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Desert Rat

 

"I know that many people don't like series connections because of their greater sensitivity to shadowing but since my panels (and presumably yours) are on the rooftop then shadows are likely only at low sun angles (very early in the morning and very late in the afternoon) when there is not much charging going on anyway"

 

Not to hijack the thread but soon I will be adding 200 or 240 watts of solar to my existing 200 watts configured at 24 volt. I was questioning to add another 24 volts in series or parallel (all panels flat on roof) and have about decided to go series and bring 48 (nominal) volts down to my charge controller (capacity is over 100 volts) to reduce current and voltage drop. Since my existing 200 watts pretty well already handles my loads, with 400 or 440 watts I'm not concerned about achieving the absolute max capacity so shadows aren't a big worry. Series I plan to go unless I learn its a problem????

 

John T

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John T: I have friends with solar arrays running voltages close to 150vdc who are not having issues with shadowing. I have not been able to detect any issues at my installation. I have two panels in parallel wired in series with two different panels. If you have dissimilar panels in an array or when voltage or current issues mandate, the only way to achieve the charging you want is to combine series and parallel configurations. The friend with the high voltage array has two panels in parallel as well; wired that way because on a very cold morning with bright sun (not uncommon in the desert southwest) it would be possible to overload the solar charge controller. He has not reported any shadow issues, either.

 

They probably exist but do not seem to be shutting down the systems.

 

The guy with 150vdc panel voltage reports 3-amps of charging when parked under the lights in a Walmart parking lot, by the way. :P

 

WDR

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There is nothing wrong with series wiring if you do not shadow them. OR if you KNOWINGLY shadow them by design and take that into account. Why would you do that? Because you are maxing out the total collection of the system and don't care if there is a possibility of a shadow on one string early in the morning (as an example). You have to design the WHOLE system and take into account all factors. Look at total system performance, not just one element. That may seem obvious, but I have seen far to many systems that did not do this and thus had some weird anomaly or "heroic attempt" to solve a single issue when the entire system was negatively affected - or it simply did not matter.

 

The other issue that should be considered with very high voltage series panels is controller efficiency. Many of the controller manufacturers publish efficiency curves. Depending on your battery bank current you may find that a very high voltage array is not as efficient in overall solar harvest as one running at a lower voltage. Morningstar and Outback both publish efficiency curves - look in the back of the manual. In general, higher voltage battery banks are affected less. (Less downconversion of voltage from array voltage to charge voltage is more efficient) Most RVers still run 12-volt battery banks. Building an array running at 100+ volts for that bank is not as efficient in most cases as an array running at 38 volts (as a random example). But this is just one design criteria.....and it may be more important to minimize wire loss with existing wires - it just depends on your system. My point is don't focus on ONE element of design, but on the entire system performance.

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