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Old 03-20-2019, 08:30 PM   #1
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Work from RV off grid (batteries and inverter discussion)

We will take possession of our Winnebago Minnie soon, the wife is fortunate to be able to work remotely while I have to use up my vacation hours. Our Winnie will come with two 12 volt batteries (not sure of brand or amp hours, most likely cheaper batteries as they're supplied by dealer). I'd like to set her up with enough power to comfortably work while on vacation.

I anticipate our power needs will be running/charging a laptop throughout the day and charging several mobile devices. Perhaps a couple of led lights and radio in the background. I don't foresee any other appliances having to run. I am planning to buy a Champion 3100W generator that will be used everyday (hopefully only once a day for couple hours at most) to recharge batteries and if we need to run any higher powered appliances.

My question is will two 12V's serve our needs? What type/wattage of inverter is best suited for our needs? Will we most definitely need a pure sine inverter? Is it best to run our inverter straight into the workspace and plug electronics directly into it?

I'm very new to all of this, any help is most appreciated!
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Old 03-20-2019, 09:27 PM   #2
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Quote:
Originally Posted by crazymason View Post
I'm very new to all of this, any help is most appreciated!
We were all new at this once.

Get a power meter and measure how much electricity you are using with appliances on propane.

https://www.amazon.com/Poniie-PN2000.../dp/B0777H8MS8

With our first MH used a 700 watt generator from Harbor Freight. Also had a 700 watt inverter from Lowe's. That is all you need for the loads you described.

With 4 golf cart batteries, we only have to charge for about an hour.

With 2 batteries, you may have charge more often and for a longer time.
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Old 03-21-2019, 04:42 AM   #3
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Work from RV off grid (batteries and inverter discussion)

Call your salesperson and ask for the battery details especially the amp hours. Also ask if there is a generator and inverter already. Most people limit battery use to about 50% of rated capacity on a regular basis to increase battery life. But there are some other opinions too.

Are you getting a new one? Winnebago web site says that new ones have one Group 24 deep cycle house battery is standard. These are about 70 amp hour. Web site also says that a 4000 Watt generator is standard. A 1000 Watt inverter is listed as an option. I hope you do have two of these batteries as only one sounds on the small side.

Most laptops run fine on a modified sine wave inverter. Iíd say just buy a small inexpensive 100-200 Watt one and give it a try if the Winnie doesnít already have one. Or get 12 Volt adapters for the laptop and small electronics.

Before spending a bunch of money upgrading things try a few days of camping in your driveway or a nearby campground and see how it goes. Then decide if you need any changes.

Iím able to work from my RV fine with my laptop and all the RV energy uses including a non-propane refrigerator with 220 amp hours of battery and daily charging. This is without running any AC or microwave. I have to turn on the built in generator to run these.

Have fun with your RV.
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Old 03-21-2019, 06:48 AM   #4
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Solar would be a big help to you, unless you're in shaded camp sites. It takes a long time to get batteries to full charge, you don't want to be running a generator for 8 hours just to get the batteries that last 10%.

If you don't regularly get the batteries fully charged, it shortens the life of them.

We'll run the generator in the morning to bulk charge, then shut it down and the solar tops off the batteries during the day.
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Old 03-21-2019, 09:22 AM   #5
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I did this for a little while, but I used a 200W portable solar panel set for the battery that ran my laptop and cellphone/internet access. It was plenty of power to charge the 110amp/hr battery and run these things all morning.

You won't know how much battery recharging time from the gennie you'll need until you know how much energy you'll actually be using.

One thing is certain in my opinion, you almost can't have enough energy storage. If the two batteries you will get with your rig aren't enough, then double your capacity. I was given two 12v marine batteries when I bought my trailer, and I sold them and replaced them with two 6v GC2 golf cart batteries because they are true deep cycle batteries. The true deep cycle batteries have thicker plates and can withstand a deeper draw down without as much damage, but I try not to draw them down more than 50% before recharging.

As to your other questions, I don't know, but others will. You've come to the right place with these questions. In the meantime, you can learn more by reading part one and two of the following article:
The 12volt Side of Life (Part 1)
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Old 03-21-2019, 11:16 AM   #6
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Originally Posted by crazymason View Post
My question is will two 12V's serve our needs? What type/wattage of inverter is best suited for our needs? Will we most definitely need a pure sine inverter? Is it best to run our inverter straight into the workspace and plug electronics directly into it?
The following are OPINIONS based on TWO Group 24 Marine batteries because you have not supplied very many facts.
  • At a minimum, you want a 1000W pure sine wave inverter. You may want to go larger depending on what other appliance you might want to run. 2000W is not out of the question, but it will cost a lot more.
  • If you don't plan on permanently wiring in an inverter (or what I REALLY would recommend is an inverter/charger/automatic transfer switch), the simplest way to use it is to plug your shore power cord into the inverter.
  • With TWO Group 24 batteries, you will be "on the edge" of getting a full 8 hour work day with only running your generator/charger ONCE per day. You would be much better off with TWO 6V golf cart batteries. They can store a lot more power.
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Old 03-22-2019, 10:48 AM   #7
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most your things will & should run off 12 volts, why waste power inverting?
Maybe laptop needs 120 volts, for that a small 300 watt inverter.
After you have tried that for a while, decide how to improve.
A small 100 or 200 watt portable solar panel setup can keep your batteries charged.
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Old 03-23-2019, 01:10 PM   #8
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Batteries come in lots of different types and sizes. They are typically flooded cell deep draw or AGM deep draw. Many TT owners are now installing lithium batteries at much high initial expense.

For regular daily charge/discharge cycling many RVíers recommend a larger battery bank using Trojan gulf cart batteries. Maybe 240 amp hours.

I recommend a larger battery bank using AGM batteries. Maybe 200 amp hours.

200 amp hour lithium would work wonders and charge fastest of all. $2000 for a pair of 100 amp hour batteries.

The two flooded cell batteries you are planning on will be enough, but they will need to be replaced soon due to heavy use (maybe 2 years). You could use them up and replace with a larger longer lasting battery bank, or get the dealer to substitute a larger pair to start with.

Strategy charge fast to minimize generator run time.

1) Marine deep draw AGM batteries can usually be charged 5 times faster than deep draw flooded cell batteries.

2) Even a small generator can run a large battery charger.
A 40 amp 12v charger = 480 watts. The charger would work with a 30 pound Honda i1000 1000 watt generator. (The generator cannot run most heating devices like hair dryers.)
80 amp 12v = 960 watts needs Honda i2000 2000 watt generator. (More charger than is needed for a 140 amp hour battery bank, but the generator will run some electric coffee pots.)
A 2500 watt generator is more than needed for battery charging, but will run one air conditioner or one microwave.

3) Lead acid batteries cannot be properly charged in one hour. You must periodically bring them to full 100% charge. That takes 16 hours more or less. Many RVíers run the generator 4 hours a day. Even so the batteries still need the 16 hour full charge periodically. Flooded cell batteries are more sensitive to under charging than AGMís. But they both need a periodic full charge.

4) You can put a substantial charge into the batteries fast if they are at a low percent of charge.
140 amp hour battery bank
Start with the battery static voltage = 12.0 v (50% of charge capacity)
Charge with 40 amp charger for one hour = 35 amp hours.
End with battery static voltage = 12.4 v (80%) more or less.
Charging the remaining 20% takes 7 to 10 hours (must be done periodically)
It takes about the same amount of time to put the last 20% into a large battery bank as it does a small battery bank. Within reason a large charger or a small one does not change that time. It is the lead acid chemistry that limits.

See the Battery University website article Charging Lead Acid Batteries https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Inverter
1) A 1000 watt 115 volt inverter can be used to charge a laptop or other small powered device. When used to full capacity the inverter draws about 84 amps from 12 volt batteries. That is a hefty load for a 140 amp hour battery bank. It is a hefty load for a 200 amp hour battery bank. Your 140 amp hour bank will be below 50% is one hour. It will take three or four hours to recharge and the battery and the bank will not be fully charged. It still takes many hours to finish.

2) A laptop brick may take 100 watts from a 115 volt inverter. Three hours of charging your laptop could draw about 30 amp hours from your batteries. You can recharge in about 1 hour. Running the laptop using 12 volts instead of 115 from an inverter will save about 5%. In both cases it still takes many hours to finish charging the battery bank.

3) A 2000 watt inverter is too big for a 140 amp hour battery bank. It would try to draw about 170 amps from the batteries at full load and probably cause damage to the batteries.

Lithium Batteries
Short and sweet:
Charge a 200 amp hour lithium battery bank using 80 amp battery charger in 2.5 hours. It does not need a periodic full charge. The batteries may last longer than your new travel trailer. Run a 2000 watt inverter with no problem. For better authority check my numbers with the lithium battery supplier. Specs change every year.
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Old 03-23-2019, 01:23 PM   #9
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Sine wave inverters

Spend the extra for a sine wave inverter if you are going to buy one. Many people use modified sine wave inverters, but others have reported damaged electronics including furnace, refrigerator, and water heater controls.

Do you feel lucky?
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Old 03-24-2019, 04:11 AM   #10
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1) Marine deep draw AGM batteries can usually be charged 5 times faster than deep draw flooded cell batteries.
I have never heard this until today (But I did find the reference on Battery University) !

I have NOT been able to find any corroborating evidence. On the contrary, The data sheet for the Trojan T1275-AGM states the maximum charging rate is 20% of the 20 hour capacity.

Click image for larger version

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That would be about 26A.

Quote:
Originally Posted by Persistent View Post
Start with the battery static voltage = 12.0 v (50% of charge capacity)
Again, I have never hear that it is "good practice" to take any type of lead acid battery down to 50% SOC. Also, from the same Trojan spec sheet

Click image for larger version

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12.0V would be close to 25% SOC. Repeatedly drawing any lead acid battery that low would shorten its life span.
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Old 03-24-2019, 04:23 AM   #11
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Originally Posted by Persistent View Post
Lithium Batteries
Short and sweet:
Charge a 200 amp hour lithium battery bank using 80 amp battery charger in 2.5 hours. It does not need a periodic full charge. The batteries may last longer than your new travel trailer. Run a 2000 watt inverter with no problem.
Most of us simply can NOT afford Lithium Batteries ! If you are "full time" and reliable power is a necessity without shore power or a generator, they are probably worth their cost. The number of discharge/cycle is huge compared to lead acid and taking them down to near 0% SOC does not hurt them. Add in the fast recharge rate and they are the battery of choice for boondocking full timers !
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Old 03-25-2019, 09:54 AM   #12
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Originally Posted by theoldwizard View Post
I have never heard this until today (But I did find the reference on Battery University) !

I have NOT been able to find any corroborating evidence. On the contrary, The data sheet for the Trojan T1275-AGM states the maximum charging rate is 20% of the 20 hour capacity.

Attachment 239242

That would be about 26A.


Again, I have never hear that it is "good practice" to take any type of lead acid battery down to 50% SOC. Also, from the same Trojan spec sheet

Attachment 239243

12.0V would be close to 25% SOC. Repeatedly drawing any lead acid battery that low would shorten its life span.
Every battery design is different. Battery University has proven to be a reliable, data supported source. BU is documenting typical designs and is of course a little behind the new technology just being released.

A battery manufacturer that extensively tests and publishes results is an excellent manufacturer. Use the data from the manufacture of your battery. Keep in mind Trojan builds many different designs for many different purposes. Be sure to use the data for the battery you are using. I have seen many posts indicating RV's have different types of Trojan batteries.

I round values and approximate to make the calculation simple for my old stuttering brain. However, the following chart from one manufacture indicates 12.06 is 50%. Different battery designs could have slightly different voltage profiles, but not 25 % for lead acid.
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Old 03-25-2019, 09:58 AM   #13
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Sorry, I can't seem to copy the table from Word for Windows.
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Old 03-25-2019, 11:15 AM   #14
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Wow, so much great info in here, thanks! Looks like the most obvious limitations will be my 12v batteries. I might discuss with the dealership and see if we can upgrade immediately to 2 6volts instead of trying to sell and upgrade the 12 volts down the road.

I don't feel lucky so I will save up for the pure sine inverter. This will all be a work in progress, baby steps as finances allow...
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