First offgrid RV setup, dazed and confused

[dave1122]

First off I apologize if these questions have been answered but I have read quite a few posts and cant seem to make heads or tails of it. I have done a fair bit of electrical work before, I finished my entire basement myself.

Essentially I am looking to do a small offgrid setup for my RV travel trailer, I am pretty set on two Grape 250W panels, everything I have read about them just glows awesome. But I have read reviews that say they are quite high powered panels and as such require a 24V charger and inverter.

So here in lies my first question, do I need 24V or can I get away with 12V for a setup of 2 250W panels?
Second question is can I get away with just a digital charge controller or do I need a MPPT, if so what would be a suggested MPPT (brand, amp, etc), keep in mind the for this system I will never add any additional panels as I wouldnt have room for them on the trailer.
Third question, what would be an appropriate inverter for this system
and final question, obviously depending on if this is a 24 or 12v setup what sort of battery configuration would I need for something like 1500w ?

Thanks in advance, and feel free to ask me for further details.

[Sunking]

Dave the panels are fine, they will just need a 40 amp MPPT controller for 12 volt or 20 amp for 24 volt battery. Wire the panels in series and use whatever battery voltage you like. There is one catch.

If you run 12 volt battery, and that is the right voltage for an RV so you can use the RV alternator to do most of the battery charging, requires a 40 amp MPPT charger. At 24 volts only requires a 20 amp mppt charger with 500 watts of panel power.

Do not use a cheap PWM controller. It will turn 500 watts into 150 watts.

[dave1122]

Hi Sunking, thank you for the quick reply, I would prefer to run 12v as it matches the trailer voltage. When you say the RV can do most of the charging on the batteries Im assuming youre talking about when its plugged into grid voltage right?

Im looking to get the highest efficiencies between all components so a cheap charge controller is not what Im looking for, I would be look at something more like a TS-MPPT-45 (little pricey) or one of the Tracer 40A/45A series, do you feel that either of these would be sufficient?

What would your recommendation be for an inverter to match this system (watt and efficiency wise)

[inetdog]

Hi Sunking, thank you for the quick reply, I would prefer to run 12v as it matches the trailer voltage. When you say the RV can do most of the charging on the batteries Im assuming youre talking about when its plugged into grid voltage right?

Im looking to get the highest efficiencies between all components so a cheap charge controller is not what Im looking for, I would be look at something more like a TS-MPPT-45 (little pricey) or one of the Tracer 40A/45A series, do you feel that either of these would be sufficient?

What would your recommendation be for an inverter to match this system (watt and efficiency wise)

It is more likely that he was referring to the engine alternator charging both the starting batteries and the house batteries when you are moving from one place to another or just running the engine to charge batteries.
It may justify putting in a heavier duty alternator.
If you have a grid hookup available, you can certainly use that to charge the batteries, but at the same time you would not be using the batteries and inverter, so neither grid nor solar charging come into play.

[paulcheung]

Hi Sunking, thank you for the quick reply, I would prefer to run 12v as it matches the trailer voltage. When you say the RV can do most of the charging on the batteries Im assuming youre talking about when its plugged into grid voltage right?

Im looking to get the highest efficiencies between all components so a cheap charge controller is not what Im looking for, I would be look at something more like a TS-MPPT-45 (little pricey) or one of the Tracer 40A/45A series, do you feel that either of these would be sufficient?

What would your recommendation be for an inverter to match this system (watt and efficiency wise)

I would go with the Morning Star TS-MPPT-45, the Tracer 40A don't have the option to adjust the absorb charge voltage, the pre set voltage is too low for solar application. The inverter I would go with a Xantrex Pro-watt 1000, it is a pure shine wave 900watts continues power. the only problem is the GFCI plug go bad sometime, need to be replace.

The batteries I would go with 2 Trojan L16RE-B or Rolls S-550.

[Amy@altE]

Outback, Xantrex (Schneider), and Magnum all make nice mobile inverters that are designed to be hooked up to shore power when needed.

If you are going to be powering electronics, you should pay the extra money for a pure sine wave rather than modified.

You need to do a loads list to determine the size battery bank you need. How many watts will your loads draw, and for how many hours. Then how many days do you need to run them off the battery with no sun recharging them.

[Sunking]

When you say the RV can do most of the charging on the batteries Im assuming youre talking about when its plugged into grid voltage right?

No I mean your RV Alternator. It can generate more energy in an hour than your panels can generate over a few days. It requires a $50 Battery Isolator.

[jimindenver]

That's one heck of an alternator Sunking. My two 245w panels were good for around 400Ah after a few good days tracking. Even flat at least 100 Ah each on a summers day.

In any event welcome to the forum Dave. You have taken the step of finding out what fits on your roof and that's is dipping your toe in to what you will eventually wade into. Every choice you make from here on be it the controller, batteries, wire, inverter will all be interlinked and have to play well together.

With the controller I agree with at least 40 amp. You could go 30 amp and clip the excess mid day but what a waste when the step up isn't that much. I just had a thread here about the choices for my three 250w panels and the Morningstar TS-MPPT-60 was the winner for lack of fan which the newer models had. The TS-MPPT-45 would be a bit of overkill but I don't know of many mainstream 40 amp MPPT controllers.

The inverter depends on what you want to run. We use a large inverter that is turned on and off for large loads like the microwave, a tiny 150w stays on all the time for the TV/satellite. I can't tell you what to buy but I can tell you I went cheap the first time, it lasted one season.

Battery selection is where I am now. So many choices and so much money. You need to look at how much room you have, your budget and what you want to run with them. The more info you have, the more the choices thin out. Add to that rules of thumb like no more that three in parallel or 2 6v wont like your microwave... like I said, you have just dipped your toe in the water.

So the first things are what do you want out of your system, how much room and what kind of budget. It's taken me years to get to where I am but I am slow and cheap. That doesn't mean I didn't take the solar, we used it on the ground and left the generator home.

[nova]

I did 600 W with a Kid Controller, went off grid 3 months elec fridge all worked fine off 4 6V T-105

2000 watt inverter, just can't run AC

[mschulz]

I did 600 W with a Kid Controller, went off grid 3 months elec fridge all worked fine off 4 6V T-105

2000 watt inverter, just can't run AC

Did you wire those batteries up to produce 24 volt?

[nova]

no reason to, 12V

[mschulz]

So you ran 50 amps through a 30 amp charge controller and no issues?

[nova]

The Kid controller can handle any overage without an issue.

Remember U don't get full power all day long.

oversize helps early and late in the day along with overcast.

I spent a lot of time with one of their engineers on the phone it is a dream to setup and has a great display.

The batteries rarely dropped under 12V by morning.

[Sunking]

The batteries rarely dropped under 12V by morning.

If they even touch 12.2 volts is too low. Under 12 is dead.

[Sunking]

oversize helps early and late in the day along with overcast.

It also waste a lot of power, like 40% of your power is forever lost.