My RV system

[medic5678]

Hey guys, got a 400 watt Renogy solar kit with MPPT controller. I am in the process of finding a charger/inverter so I can run my generator as needed to charger the batteries. The question I have is what is the best bang for the buck in AGM 12 volt batteries?

[Sunking]

Careful what you ask for. Example a pair of Trojan T-105's (2-6volt 225 AH batteries for 12 volts @ 225 AH) will cost you roughly $300 and last you 4 years with TLC. A Concorde PVX 2120L 6-volt 200 AH making 12 volts @ 200 AH will cost you $600 and last 2 to 3 years. In the end you will pay 400% more for AGM.

Can you justify 400% higher cost?

Sure you can buy a 12 volt 200 AH AGM for less than $600. You can also buy 12 volt 225 AH FLA for less than $300. When you compare Apple to Apple quality, it is still 400% difference. So be careful what you ask for and can justify what you ask for.

The two best AGM batteries out there are Concord PVX series and Odyssey. The two best FLA are Trojan and Rolls. FWIW both Trojan and Rolls make AGM, but cha-ching twice the initial cost and half the service life.

[medic5678]

Careful what you ask for. Example a pair of Trojan T-105's (2-6volt 225 AH batteries for 12 volts @ 225 AH) will cost you roughly $300 and last you 4 years with TLC. A Concorde PVX 2120L 6-volt 200 AH making 12 volts @ 200 AH will cost you $600 and last 2 to 3 years. In the end you will pay 400% more for AGM.

Can you justify 400% higher cost?

Sure you can buy a 12 volt 200 AH AGM for less than $600. You can also buy 12 volt 225 AH FLA for less than $300. When you compare Apple to Apple quality, it is still 400% difference. So be careful what you ask for and can justify what you ask for.

The two best AGM batteries out there are Concord PVX series and Odyssey. The two best FLA are Trojan and Rolls. FWIW both Trojan and Rolls make AGM, but cha-ching twice the initial cost and half the service life.

okay, I'm not sure what you're telling me to do. Obviously you have more knowledge here in your little finger than I will grasp in the next 10 years.

The RV system is 12 volt. Let me ask it this way: what would you do ? I've read that the thing to do is use golf cart batteries. The batteries, are, by the way, in an area where I can't protect the people in the RV from any gasses or fumes. That's one of the reasons I was thinking AGM. I do suppose I could engineer a way to seal the batteries if this were an issue.

[Sunking]

What I am trying to tell you is both Flooded Lead Acid and AGM will work. But if you use AGM, you are paying a huge premium price for it and you need to know that to make a sound informed decision. FLA is the default choice because they have longer service life and the best value for your battery money. AGM has their place, but you need a good reason IMHO to justify the expense.Some of those reasons are:

• In a tightly confined space without ventilation.
• In extremely cold climates where temps drop below -40 F
• In mobile applications where the battery can become inverted like aircraft or spills cannot be tolerated.
• Where high charge and discharge currents are encountered.

OK an RV can meet some of those conditions, but also can be negated.

Example in a tight space without ventilation can easily be corrected. Hydrogen is lighter than air. All it takes is a escape route that goes up to vent outside.

Another example RVer's like to use huge Inverters that use currents higher than most FLA batteries can handle for their size. RVer's at least smart ones also use Electronic Battery Isolators to charge their batteries while driving using the alternator, or run engines while operation a large load like a Microwave or coffee pot. AGM's work better. However if you use a Hybrid FLA battery like a Golf Cart Battery like a Trojan T-105 gets around the problem.

So I am not going to tell you what to do. I am just going to give the info you need to make a informed purchase decision.

For FLA look at Trojan T-105's, Rolls, or US Battery 6-volt batteries. Both are Hybrid Golf Cart batteries with US Battery being a little less expensive, but both are good with Trojan and Rolls having a slight edge. For AGM Concord and Odyssey are very good. Keep in mind there are less expensive FLA and AGM's, but you get what you pay for.

Good luck and happy shopping.

[medic5678]

I'm trying to figure out exactly how much battery capacity I need. Let's say I want to average 360 watts for 8 hours at 120 volts. That would be 3 amps at 120 volts, and 30 amps at 12 volts. For 8 hours that would amount to 240 amps at 12 volts. How deeply can I discharge at Trojan 105? How many will I need? (Please look over these calcs and let me know if this is unrealistic)

[SunEagle]

If you need 2880 watt hours a "day"(360watts x 8 hours = 2880 watt hours) which calculates to 240Ah (2880wh / 12v = 240Ah) you should never discharge a battery system more than 25% a day so your battery would need to be 960Ah at 12volt.

So a Trojan T105 is a 6volt 225Ah battery and your system would need to be composed of 8 of them wired 4 sets of 2 in parallel to get 900Ah. But that is not a good way to build a battery system.

It would be better if you used 6 x 2volt 1110Ah Trojan L16RE-2V wired in series. to get your 12volt system.

[Sunking]

Sorry very unrealistic. Forget Amps for right now as it means nothing . Think Watt Hours.

Watt Hours = Watts x Hours

360 watts x 8 Hours = 2880 Watt Hours. That is a hell of a lot of power from a solar system. Impossible for an RV system.In order to generate 2880 watt hours of usable energy from solar requires the panels to generate 1.5 times that much or 4320 watt hours or 4.32 Kwh.

You cannot mount solar panels on an RV at the Optimum orientation (due solar south) at the optimum Tilt Angle. Nor is it realistic to park your RV where it has direct Sun Light from dawn to dusk. If you could you can get up to 5 Sun Hours in the right locations. Even if it that were possible it would require a panel wattage of 4320 wh / 5 Sun Hours = 864 watts of panels. Highly unlikely you could get that many panels up.

Bu tlets say you could put up 900 watts of panels. That will be on top of the RV pointing straight up. That cuts Sun Hours way down to around 3 if you parked in the Sun. Well with 900 wattts of panels x 3 Sun Hours x .66 efficiency only gives you 1780 watt hours. Way short of what you want. Absolutely no problem for a generator or RV alternator running a couple of hours.

OK back to batteries. If you want them to last for any length of time, you only discharge them 20 to 30% a day, and never discharge them more than 50%. So if you want 2880 watt hours per day, you need a battery with a capacity of 8640 to 14,400 watt hours or 8.6 to 14.4 Kwh. So how many amp hours is that. Well you need to know the battery operating voltage. So you want 12 volts. AH = Watt Hours / Battery Voltage. That means 8640 / 12 volts = 720 AH, or 14400 / 12 volts = 1200 AH. At this power level is not a 12 volt system, it is a 24 or 48 volt system. Makes no difference really because a battery weighs 60 pounds for every Kwh and cost $200 for every Kwh. You are talking about 500 to 900 pound battery costing you $1700 to $3000 every 2 or 3 years. Want AGM cheese with that burger?. Double the cost.

So be careful what you ask for. I was not kidding.

[medic5678]

What you're telling me in a nutshell is that I'm being unrealistic. I will need to cut my battery use to half of that, and try to schlep by on 4 Trojan 105's. As they say, every watt matters. It's looking like I'll be running the champion 1200 watt generator if I need the AC. I am sure your solution with the 2 volt batteries is the best, but it's way pricey. To even think of this shows my ignorance here. Thanks for the education .

[medic5678]

I do have a generator and an inverter/charger. The solar panels are there to provide what they can, but I would expect the bulk of my energy needs with cooling, will come from the generator. I'd just like to run the generator as little as possible. At times of the year when you don't need AC, it *might* be possible to schlep by on solar.

One other question: i bought this inverter/charger... https://www.amazon.com/Power-PICOGLF...verter+charger

Is it harmful to the batteries if I use an item that requires a lot of energy (for example, I cook with a 700 watt microwave for 20 minutes)? As long as I stayed under the 25% in 25 hours, would there be any harm done?

[medic5678]

A few more newbie questions: Do you need to cycle the batteries to make them last? Let's say you top off the charge and park your RV for a month. Is that harmful? Let's say you run items that take a lot of electricity for short periods on the batteries. Is this hard on the batteries? I'm going for the Trojan 105's.

[Mike90250]

At least it's not the 3,000 watt product. But it is Aims, which many RE vendors stopped carrying, because of failures
Wow it has 2 different chargers ? or a typo.

No 12V inverter is going to run a air conditioner for very long. Going to have to run that off the generator.

• 2000 Watt continuous pure sine power
• 6000 watt peak power for 20s
• Built in 70A smart battery charger with 7 selectable battery type settings
• Auto gen start feature
• Marine and industrial grade
• Built in 40A smart battery charger with 7 selectable battery type settings

[Sunking]

Do you need to cycle the batteries to make them last?

Yes but probable not the way you are thinking. When you first buy a battery, they need cycled several times to form the plates in and maximize capacity.

Let's say you top off the charge and park your RV for a month. Is that harmful?

It could be under the right conditions like hot weather, not so much if it is cold. Here is the deal. Pb batteries start to degrade the day they are activated. The process speeds up anytime the batteries are less than 100% charged up. It accelerates the deeper the battery is discharged. All batteries have a self discharge rate. For Pb batteries is proportional to tempuratue. The hotter it gets, the faster they self discharge. Cold slows it down. At room temps approx 10% per month. So month if stored fully charged at room temps or less is no big deal. .

The best way to store Pb batteries is on a Float Charger in cool temps. This holds them at 100% State of charge and slows down aging to as slow as it can get.

Let's say you run items that take a lot of electricity for short periods on the batteries. Is this hard on the batteries?

No not hard, but Peukert Law comes into play. Peukert Law expresses approximately the change in capacity of rechargeable lead-acid batteries at different rates of discharge. As the rate increases, the battery's available capacity decreases.

When you buy a battery, the capacity is specified at some discharge rate in Hours. Most commonly the 20 Hour discharge rate. So for example if you have a 100 AH battery, the 20 hour discharge rate is 5 amps. Expressed as C/20 where C is the battery Amp Hour Capacity. Lets take Trojan T-105 as an example. It is rated at 225 AH at the 20 hours discharge. That means you can draw 11 amps for 20 hours until completely discharged. But what if you want to discharge at say 45 amps. One would think you should be able to draw 45 amps for 225 AH / 45 Amps = 5 Hours. You would be wrong. At the 5 hour rate is now a 180 AH battery so in reality if you draw 45 amps them 185 AH / 45 Amps = 4.1 hours.

Battery manufactures play games with AH ratings. The good manufacturres will publish AH ratings at various discharge rates and show you what the Peukert Law effect is. Example a Rolls S290 is a 6-volt 220 AH Golf Cart battery equivilent to the Trojan T-105. It is rated 220 AH at the C/20 rate. But look at the specs. That same battery is 293 AH at the 100 hour rate (2.93 amps), and just a 79 AH battery at th e1 hour rate or 79 amps. Many battery manufactures may specify at the 100 Hour rate. So be sure you know what rate they are using. Second tip never buy a battery that does not list AH ratings at various discharge rates. When you look at Industrial batteries they will specify at 4, 6, and 8 hour rates.

[medic5678]

The air conditioner in question is a 5000 btu unit made by frigidaire, takes 410 watts. I was hoping for some limited duty off the battery bank but I will agree it's hopeless.

On the inverter/charger, it's very highly rated by people who bought it on Amazon

[ewarnerusa]

Battery-powered air con is quite difficult, but others have gone over that already. 400 watts of solar is more than enough for a 2-battery bank and adequate for a 4 battery bank. I agree with the AGM discussion, if you don't need AGM due to installation challenges then I recommend 6V golf cart batteries wired in series to make 12V. Costco carries 6V batteries for <$100 each. Your RV is designed to operate on 12V and I think it is unusual for the designed battery location to not accommodate venting. Are you planning on locating them somewhere other than the original design? Your RV most likely already had a converter installed which functions as the battery charger, so there wasn't a need to buy an inverter/charger. Which inverter/charger did you buy?

[medic5678]

I'm building an enclosed trailer with windows into a travel trailer. So no, there's no vented storage for the batteries, no charger, no existing 12V system. Sorry I didnt clarify that earlier, but I didnt think it mattered in the discussion.

[ewarnerusa]

Very cool. Starting from scratch is certainly different than working with what is already there in a typical RV. I would also go with an inverter/charger if starting from scratch and I'm particularly interested in hybrid ones (Magnum brand I think?) that can manage 120V AC from both a generator connection and inverted 12V DC at the same time when needed. So for example, a typical 2000 watt rated generator will often lack the surge capability of starting the compressor on a 13.5 kBtu air conditioner but it can maintain it once it is running just fine. So the hybrid inverter will use the generator power and supplement it with inverted 12V DC to 120V AC to meet that compressor startup surge, then fall back to just generator power once the energy demand goes down.