Need help reviewing design for my RV conversion solar

[MambaJack]

This is a work in progress, and I am sure parts of it aren't right, but wanted to get some feedback
Specifically I am not sure where to put things like shunts/meters, switches.

Thanks for your help.

[MambaJack]

I was looking at using some renogy 40 amp charge controllers, but I called and talked to them today and they said that they don't support multiple charge controllers on the same bank, interesting

[Sunking]

I do not have time right now, will be back later to explain. In the meantime STOP, you have an abortion on your hands and it is not pretty. Throw your drawing away, it is useless and dangerous.

[MambaJack]

Awesome SunKing! Thanks for taking the time to respond, I am very much looking forward to learning and getting this worked out.

[Sunking]

OK a little more time on my hands. Don't let my rhetoric run you off. You will not like everything I have to say, but if you hang in there I will save you a lot of money, will work, and most important safe and sane.

First throw you drawing away. it is useless and dangerous.
Second discard your whole concept, there are much better less expensive ways to do what you want,

Took me a minute or two to figure out what you are trying to do. So it appears you want a 1200 watt panel system? Not sure you really need that much honestly, in fact I doubt it because you have left out one major piece of equipment that is required, an Electronic Battery Isolator for your house batteries which allows your engine alternator to charge the house batteries when the engine is running. Your RV alternator can generate more usable energy in a hours than the panels can generate in a day. Batteries get low, cloudy day, run the engine or a generator to save your butt. The real benefit is you would not need 1200 watts which creates some other issues you have. I suggest 1000 watts or less and recommend 600 watts. That will allow you to run 12 volts (eliminates the 24/12 volt converter), only use one 50 to 80 amp charge controller (50 amp at 600 watts or 80 amps for 1000 watts), half the installation hardware, and a lot less and smaller less expensive wire. That will save you at least $1500 to $2000 and you stil get everything you want. Smart Money.

Next Item up is Inverter and you are not going to like this initially. Forget using a 3000 Watt Inverter. You are playing with fire, have no use for it, and waste power. It is a Fire and Money pit you can afford to do without. At 24 volts a 3000 Watt Inverter requires 150 amps. That requires a huge 1/0 AWG copper wire and you have no means to terminate that size wire correctly. Not to mention it is highly unlikely the Inverter can even handle a 1/0 Terminal Connector. It is like Alcohol, Tobacco, and Ganja. You can buy them, but does not imply they are good for you or that you should use them . All you get is spending a lot of money on something you will never need, and increases fire danger exponentially. Please reconsider and use a 12 volt Inverter no greater than 1000 watts. Not only will it save you quite a bit of money, it will meet your needs and allow you to sleep at night knowing it is exponentially safer. Having said that if panel wattage exceeds 1000 watts, then you can use a 24 volt 1000 watt Inverter . Use the saving to buy a 24 to 12 volt converter. 1200 watts at 24 volts only requires a 50 amp Controler. You do not need or want 2 controllers as that is just throwing money away.

OK let's jump to wiring schematic. Look below and you will see exactly what I am talking about. A 600 Watt RV system. One with 12 volt distribution and Inverter like you want, and one without DC distribution only using an Inverter. Take note and look at the batteries and the fuses on the battery Term Post. That is how to properly protect the battery wiring. The batteries are the source of power, not the panels. Solar panels are current sources. You can short them out all day long, and nothing happens except there is no power. Batteries are voltage sources and can deliver thousands of amps in a short circuit. Short a battery out without proper protection, and you might not have any days left to live. What the fire does not burn up, boiling hot sulfuric acid will. Put the right size fuses in the right location and all that goes away and you are protected.

Last is batteries my friend, and again you may not like this. Do not parallel batteries unless absolutely necessary. It will work initially but significantly shorten battery life. In an RV is a bit of a toss-up to be honest because RV's are not normally used everyday, so there is time between usage for the batteries to equalize in parallel. More to the point though is batteries have minimum and maximum charge/discharge rate based on the AH capacity we call "C". Minimum charge current = C/12 and max charge rate roughly C/6 on golf cart batteries where C = battery capacity in Amp Hours, and the number is hours. Example say a 225 AH battery needs a minimum of 225 AH / 12 H = 18.75 amps and p to a maximum of 225 / 6 H = 37.5 amps. If operating on a 12 volt battery corresponds to a panel wattage minimum of 250 watts up 500 watts. You can get away with 600 watts on a pair of 225 AH golf cart batteries. At 1000 watt panel into a 12 volt battery would require a minimum 480 AH up to 960 AH. C/10 is the perfect charge rate. With 600 watt panels on a 12 volt battery a 500 AH, and at 1000 watts is 800 AH. They make 6-volt batteries as small as 200 AH up to 900 AH So if you need 500 AH batteries, buy 500 AH battery vs buying 2 x 250 AH in parallel. Again Smart Money and will maximize cycle life. You get the bes tof every thing at a lower cost entry point.

So here is the drawing. Take note here wire and fuse sizes will change if you do not use the component listed. They may be smaller or larger. Also note the Battery Isolator which you left out. Top drawing is Inverter only, bottom drawing Inverter and 12 volt dc distribution.

[MambaJack]

SunKing, Thanks so much for taking the time.

Still trying to absorb everything that is here.
I think I was trying to overbuild as a measure of caution to make sure i could power everything I wanted and for as long as I wanted, and it gradually got a little out of hand.

There are so many variables that I am running through in my head still
i estimated my daily consumption at 2.5 kWh,

Panels

• Am i right in thinking that 600w of solar for 5 hours produces 3 kWh which accomplish replacing that?
• Since the panels are flat on the top of the bus, should i account for a specific percentage of loss?
• Is there disadvantage to using larger panels? I was thinking less mounting, and the dimensions of the 300W panels I was looking at fit nicely in a 2x2 rectangle on my roof
  • Would be about the same size / cost for rack to fit 3 panels as 4

Inverter

• Wasn't sure how to size this, but what you are saying makes sense
  • Chose 3000W because it wasn't much more cost than those a little smaller than it.
  • Had anticipated getting a combination Inverter / Charger because it seemed less complex
  • In order to get a higher charge rate for batteries, the wattage on the inverter seemed to increase.
    • is it better to buy a separate charger/inverter/transfer switch?

Batteries

• Already purchased 8 gc batteries 6v 235AH, I think i can take some back if i need to if i do so within the week, not sure if i get cores back.
  • The reason I got this size is was because they fit nicely into my storage compartment below the bus, couldn't handle much taller.
• One of my goals was to be able to be disconnected from shore or generator for a 3 day weekend.
  • The bus would stay parked for that time, and I currently don't have a generator.
  • I worry that reducing the size of the bank to just 2 batteries wouldn't accomplish this, would 4 6v230 be a happy medium?

Thanks,
dave

[MambaJack]

On the battery bank, I had also read quite a bit about the importance of them matching and you couldn't just add later, which is one main reason I went overkill to start with

[Sunking]

SunKing, Thanks so much for taking the time.

Still trying to absorb everything that is here.
I think I was trying to overbuild as a measure of caution to make sure i could power everything I wanted and for as long as I wanted, and it gradually got a little out of hand.

I understand that, happens to everyone. Now if this were a fixed system like a house, overkill is fine and required to minimize gen run time. In an RV, you are not using it everyday, so specs change and are relaxed. Example in fixed application with daily use you would want 5 full days of capacity in your battery to extend cycle life and cover your butt for a couple of rainy days. In an RV you only need 3-day capacity, not to mention save a lot dead weight drinking up your RV gasoline

Am i right in thinking that 600w of solar for 5 hours produces 3 kWh which accomplish replacing that?

Yes theoretically you panels can generate 3 Kw. But there a few catches. Although you may generate 3 Kwh at the panels, it is not available because you have not accounted for system efficiency of 66%. S in practice you would have 2 Kwh usable. To account for all the losses take your daily Kwh and multiply by 1.5. 3 Kwh x 1.5 = 4.5 Kwh. Now you can factor out the watts required. 3000 wh x 1.5 divided by 5 hours = 900 watts.

Since the panels are flat on the top of the bus, should i account for a specific percentage of loss?

Absolutely if you want to play that fools game and spend a wad of cash you do not need to spend. Example go back to my last comments where you asked about 3 Kwh and 5 sun hours requiring 600 watts of panels. That will only work in ideal condition where the panels are at optimum tilt angle and looking due solar south with no shade issues, and cool temps. That is difficult to do on a fixed system, impossible on an RV

Is there disadvantage to using larger panels?

There can be, but the advantage of larger panels is a good chance of lower $/watt cost. Otherwise it does not make a lot of difference. Only other thing I can think of is geometry and form factor making it fit in the available space.

is it better to buy a separate charger/inverter/transfer switch?

Not IMO. I would advise anyone in a RV to buy a combo unit containing Inverter, AC Charger, and ATS. Only thing to look out for is the Charge Current. Make sure it is not too high or low for your batteries.

I worry that reducing the size of the bank to just 2 batteries wouldn't accomplish this, would 4 6v230 be a happy medium?

Use them for now, fix it later when they need to be replaced. Listen up here is what I would tell any RV'er. RV design process is not the same as a fixed stationary. The very first step is determine your daily Kwh. So lets say 2 Kwh per day. In an RV size your battery for 3 day reserve or 6 Kwh. Determine battery voltage which is typically 12 volts in n RV. To find the AH = Watt Hours / Battery Voltage. So a 6000 watts / 12 volts = 500 AH. That knocks off the battery drill. The rest is super easy. Forget all the formulas to calculate panel wattage, it is not going to work. Instead we design the system to provide a perfect C/10 charge rate, and a 500 AH / 10 H = 50 Amps. That takes care of the Controller selection. For the panels you just find what wattage required to deliver 50 amps charge current. Panel Wattage = Amps x [Battery Voltage. 50 amps x 12 volts = 600 watts. Your done, have a safe trip.

If your batteries get low, run genny or drive a while if you have an Isolator to charge the batteries from the alternator.

[MambaJack]

Thanks, I think I am starting to get part of this

So it looks like if I take my daily usage, add in some extra to deal with the 66% efficiency, multiply for 2 days of no charging, account for only bringing the bank down to 50%, the battery bank I have would be sized about right?

But, this gets me into a situation where I have too many batteries in parallel to charge correctly at 12v,
Am I better to go ahead and move to a 24v or 48v bank if i am good with not connecting to my alternator?
Step down converters to run some of my 12v stuff don't seem very expensive, probably negated by the larger wire cost for 12v.
The inverter chargers I have looked at also cost very similarly between the different voltages.
Would there be any issue with me just running a 48v system?

Thanks,
dave



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[Sunking]

So it looks like if I take my daily usage, add in some extra to deal with the 66% efficiency, multiply for 2 days of no charging, account for only bringing the bank down to 50%, the battery bank I have would be sized about right?

No Sir, efficiency is not used to calculate the battery size. That is for panel wattage on a fixed system. For an RV no efficiency is considered. For an RV panel wattage is calculated on a C/10 or higher charge rate.

Battery AH Capacity = Daily Wh x 3 days / Battery Voltage.

But, this gets me into a situation where I have too many batteries in parallel to charge correctly at 12v,
Am I better to go ahead and move to a 24v or 48v bank if i am good with not connecting to my alternator?
Step down converters to run some of my 12v stuff don't seem very expensive, probably negated by the larger wire cost for 12v.
The inverter chargers I have looked at also cost very similarly between the different voltages.
Would there be any issue with me just running a 48v system?

To start you are not in 48 volt battery territory yet. Try to find a small 20-amp MPPT controller for 48 volt battery. Do not think you can find any, smallest I know of is 30 amps a Midnite Kid which will do 12, 24, and 48 volt battery. You are in between 12 and 24 volt application with your panel wattage. With panel wattage of 600 watts into a 48 volt battery would only require 12 amp controller. You would have to pay up for a 30 amp controller to find one compatible with 48 volt battery.

You are in an RV. If you elect to go up to 24 volts you are sacrificing a lot of options available to you made for RV life. I am not big in the RV world but one example I can think of is buying a combo Inverter/Charger/ATS made for RV applications. Then there are those 12 volt gizmos made for the RV market.

My suggestion is use 12 volt for now. Parallel batteries in an RV are not that big of deal especially if you are only using it 3 to 5 days a month. Time between usage is more than adequate for the batteries to equalize. When those need replaced, deal with it then.

The only down side of 12 volts is a larger more expensive MPPT Controller is required and you need to put some thought into selection. If you have 600 watts of panels, smallest controller you would want is 45 amps like a Morningstar TS-45-MPPT. Catch is at 12 volts, max power is 600 watts with no room to grow unless you went to 24 volts with a 1200 input limit. You might consider a 60 or 80 amp controller for future growth. At 60 amps max power is 800 watts, and 1000 watts @ 80 amps.

About the largest controller you can buy is 80 amps as a point of reference. A 80 amp controller has the following power input limitations

1000 watts @ 12 Volt
2000 watts @ 24 volts
4000 watts @ 48 volts

[MambaJack]

Thanks. I see what you mean about the efficiency being on the panels not on the bank.


on the controller. I like the idea of being able to expand if needed. The 80 amp controller I was looking at was outback brand for like 450. I guess that's where I wondered if I shouldn't just go 48v. Little cost difference in inverter charger. Controller would support it. Is there a disadvantage to the 48v bank outside of having to step down for some rv lights and a water pump?

also I appreciate your help. Do you have a paypal account I can send a few bucks to to hook you up with a 6 pack?

[Sunking]

on the controller. I like the idea of being able to expand if needed. The 80 amp controller I was looking at was outback brand for like 450. I guess that's where I wondered if I shouldn't just go 48v. Little cost difference in inverter charger. Controller would support it. Is there a disadvantage to the 48v bank outside of having to step down for some rv lights and a water pump?

Yeah there is one thing you have to give up you will kick yourself for later when you need it. The vehicle alternator is the major power source and your backup. In fact it is so good if you drove every day or two with a few hours between stops, you would not need solar, or at least cut back on power to just supplement. If it were me, I would not give that up, its too important. Like I said 1 hour engine run time will generate as much or more than the panels can in a day. Of course the work around is a generator with a 48 volt charger and those can get pricey in the size you need.

The advantage of 48 volts is high panel and Inverters wattage over 1500 watts. 48 volt systems are best utilized for high power stationary fixed location like a home or cabin. If this system you want in an RV were instead be placed in a cabin, no question 24 volts would be the way to go. But houses do not come with vehicle alternators we can tap the power too. IMO normally panel wattage are determine battery voltage, The boundaries are points where economics cross-over.

12 volts up to 500 watts
24 volts up to 500 to 1500 watts
48 volts 1500 watts and higher

RV's are special applications with unique power requirements. The importance of 12 volt compatible equipment requires different practices to take advantage, and a major power source is top priority on limited RE sources.

So it sounds like you are taking your time, asking good questions, and weighing options to come to a decision. I am just here to give you options and why. 600 Watt range is on the medium high end from what I have seen. Seen larger, more smaller, but they all have one thing in common, 12 volts. There are some 24 volt systems, but not many and ones I know of are converted diesel buses with 24 volt engine system. Rest is on you. You will make the decision right for you knowing some facts pro and con.

also I appreciate your help. Do you have a paypal account I can send a few bucks to to hook you up with a 6 pack?

Oh gosh I am flattered, thank you, but no thank you. Glad I could help is all I need.

[PNW_Steve]

Sunking,

you mentioned that RV usage is a different animal than a stationary installation and tollerates some deviation from design guidelines that you would apply in a stationary installation.

Would this hold true in a "full time" scenario? A number of us bus folk spend months or years on the road .

[Mike90250]

It all varys, do you drive daily or only every other week - how much will the vehicle alternator contribute to your power budget ? will you park in blasting sun, or in shade ? is there stuff on the roof that will obstruct panels, or is roof clean ?

[Sunking]

Would this hold true in a "full time" scenario? A number of us bus folk spend months or years on the road

No nothing really changes much. You have the exact same challenges of weight and space limitation. Panels cannot be optimally oriented with the panels pointing straight up on a scorching hot roof with shade issues. So forget about using calculations modeled for fixed stations, the application requirements have changed. Sun hours mean nothing in an RV because it is not fixed in stationary position.

Where I relax a bit, and perhaps that is what you meant, batteries in Parallel. With the infrequent part-time use the batteries have time to equalize between uses. So that would be the only difference in my design philosophy. Otherwise series all the way.

RV and Buses are just straight forward 2-step process.

1. Determine battery capacity required for 3-day reserve, vs 5 days for stationary. You really do not need any more battery than 3-days on an RV because because at a minimum should have 2 power sources. If you are smart long term roadies 4 power sources. Sources are Alternator as your primary source, Generator/Charger, Shore Power, and supplemental Solar which can be eliminated if you drive every day or two. If that is not enough to think about, the slam dunk is all that dead extra weight of batteries with that much more toxic crap on board.

2. Once you got the batteries figured out the rest is a piece of cake. You need a controller and panel wattage sufficient enough to charge at C/10 to C/8. So if your battery is say 12 volts @ 400 AH you know instantly you need at least 40 charger controller. Panel wattage required is stupid simple 40 amps x 12.5 volts = 500 watts and you are done.

In a nutshell as Mike pointed out there are so may variables at play, if you took all inefficiencies and sacrifices using an RV into account and then factor them in to determine panel wattage, you would need a trailer to haul panels. . You just throw normal design processes out the door, size the batteries for 3 days, and size panels for C/10 if you can. That is why you should have Alternator and Generator so you do not have to worry about that crap.

Batteries get low, burn Dino. Besides, gasoline and LPG are solar power, just concentrated.