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 > Sizing a battery bank. Ah VS wh?

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2oldman

Nevada

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Posted: 01/01/22 12:08pm Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

Is you inverter up to the task of running the frying pan, toaster and coffee pot at the same time ?
My inverter might be, but my battery and the wiring wouldn't.

pianotuna

Regina, SK, Canada

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Posted: 01/01/22 12:11pm Link  |  Quote  |  Print  |  Notify Moderator

Use one or the other. I prefer watt-hours.

If planning on using an inverter for everything (which is not recommended), forget about 12 volt and jump to 48 volts. Why? Because the inverter may be a lot more efficient at 48 volts compared to 12 volts. Cabling between the battery bank will be far cheaper.

If you are stationary, and have a beer budget, use six volt golf cart batteries. Lead acid batteries do want to be fully charged as often as humanly possible. They needs must be equalized at least every 30 days, and once a week would be a better time frame.

To find the solar wattage needed go to a site that lists the solar insulation hours for your location. If that is too much trouble--then divide the watt-hours used in a day by 5 (example 2200 / 5 = 440 watts of panels).

For full time off grid the battery bank size ought to reflect at least 3 days of no sun.

If you are mobile and do not plan on cold weather use, go to 24 volt lifepo4 batteries with 2 in series. Or better yet, "roll your own". It will be needful to have a proper battery management system. Li are great, but they are UNFORGIVING. They can be seriously damaged or destroyed by just one seeming small error on your part (the human factor).

A back up generator will be needful. It needs to be large enough to meet the daily requirements AND recharge the battery bank.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

pianotuna

Regina, SK, Canada

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Posted: 01/01/22 12:15pm Link  |  Quote  |  Print  |  Notify Moderator

theoldwizard1 wrote:

Is you inverter up to the task of running the frying pan, toaster and coffee pot at the same time ?


That would be a slam dunk for my system. Frying pan = 1200 watts max, toaster 800 watts, coffee pot 400 watts. Heck, I could add the fridge, too!

Sarahps33

Winchester, VA

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Posted: 01/01/22 04:22pm Link  |  Quote  |  Print  |  Notify Moderator

The camper I have was already ran with 120ac electric, nothing 12v to plug into except ciggertte lighter.

I've heard about the inverter powerless, I thought most of them were 80-90 % efficient,  so I'd lose that 10-20%.

Not sure what you mean by the 10:1 ratio. From what I've learned so far I've seen that different inverters draw different amount of amps depending on the wattage inverted.

Generators I've seen locally are pretty cheap, like $275 for 1500w. I'm thinking when its cloudy it may be worth having.

OldWizard said "when you want Amp-hours at 12V (instead of 120V) you need to multiply be 10, so about 31,000 Ah !"  I'm confused on why I would need to multiple that if I'm using an inverter and everything I'd being turned into AC?

Thanks Piano, I didnt think about the leap the inverter would have to take from 12 as opposed to 48v. I would have liked to run a 12v system but I dont have but a month left before my lease is up. So maybe something for the future.

Also you mentioned "divide the watt-hours used in a day by 5 (example 2200 / 5 = 440 watts of panels)." Is the '5' in that formula the hours of sunlight a day? 2510/4.5 = 113
That seems like such a little amount. I thought it would be more about the solar's charging rates. Like "25amps per hour" or 25ah x 4.5hrs of sunlight = 100 amps charged in 'one day.' I havnt quite gotten to that research yet...

To clarify no electric frying pans and no toasters lol. Just a propane stove top. We will be mobile and hope not to encounter weather any less than 40 degrees (at night.)

202ah sounds kinda like a lot to me considering what we plan on running, if anyone feels like reading a list, feel free if not I totally understand lol.

Laptop x2
Mp3player charger x2
E-cig charger x2
Phone charger x2
Flashlight charger
Coleman lantern charger
Mini dehumidifier 22.50w
Small fan
Overhead lights
Coffee maker 700w (10mins daily)
4.5 cubic foot fridge (not 12v)
Printer (100-200v/.6a)
Heating pad
And a couple other odds and ends
With that I ended up with 2510wh / 202ah

That's without the coleman mach 3 AC on top.

Sarahps33

Winchester, VA

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Posted: 01/01/22 04:22pm Link  |  Quote  |  Print  |  Notify Moderator

Oh, just realized I forgot to add the diesel block heater to that :/

wanderingaimlessly

Buggs Island lake

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Posted: 01/01/22 05:04pm Link  |  Quote  |  Print  |  Notify Moderator

If you are on a budget, in a hurry, and are really planning on being mobile. Start with a pair of GC2 6volt batteries, four would be better. If you don't want to get the residential panel, get at least 2, 100 watt panels, a 40 amp mppt controller, and if you foresee yourself wanting to run a rooftop AC, add a generator, inverter units are more expensive, but much quieter.
GC2 batteries Sams club $90 each
mppt controller Renogy/amazon $140
solar panels typically $1 per watt Amazon or others if you dont want the residential panel
3500 inverter generator predator/harbor freight $899

The oversized mppt will allow for adding panels up to 400 watts without having to replace the controller.
along with these items add for a cut out switch for the panels, wire, connectors etc.

When you are travelling, the batteries should be charging from the tow vehicle. As well as the solar.
The items I listed are among the cheaper versions while still getting decent quality.
As to an inverter to power other items You likely will want 2000 watt continious with a 4000 watt surge, you can rewire one or two of the existing circuits to run from the inverter instead of shore power. The limitation at that size will be that items such as a microwave, hairdryer, etc, will have to be used , one at a time, but multiple small items can work while a large one is in use.
Hope this helps.

theoldwizard1

SE MI

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Posted: 01/01/22 05:32pm Link  |  Quote  |  Print  |  Notify Moderator

Sarahps33 wrote:


Not sure what you mean by the 10:1 ratio. From what I've learned so far I've seen that different inverters draw different amount of amps depending on the wattage inverted.

12V in, 120v out !

Sarahps33 wrote:

Generators I've seen locally are pretty cheap, like $275 for 1500w. I'm thinking when its cloudy it may be worth having.

TOO SMALL. At least 2000W

Sarahps33 wrote:


Thanks Piano, I didnt think about the leap the inverter would have to take from 12 as opposed to 48v. I would have liked to run a 12v system but I dont have but a month left before my lease is up. So maybe something for the future.

Can't change that down the road.


Sarahps33 wrote:


Laptop x2
Mp3player charger x2
E-cig charger x2
Phone charger x2
Flashlight charger
Coleman lantern charger
Mini dehumidifier 22.50w
Small fan
Overhead lights
Coffee maker 700w (10mins daily)
4.5 cubic foot fridge (not 12v)
Printer (100-200v/.6a)
Heating pad
And a couple other odds and ends
With that I ended up with 2510wh / 202ah

That's without the coleman mach 3 AC on top.

If you leave the A/C out, a good quality 1500W continuous inverter and 200-225Ah of 12V batteries (two 6V golf cart batteries) would easily cover you for a couple of days.

ajriding

st clair

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Posted: 01/01/22 06:51pm Link  |  Quote  |  Print  |  Notify Moderator

Everything off an inverter screams newbie, knows nothing (no offense) and future regrets in short order...

You haven't watched or read nearly enough it sounds like. I have said many times. if youre going to camp. learn to camp. there are a whole world of camper items, and kitchen camper items that are made to work when camping because 120 volt AC current is not always available and will come at a HUGE premium when you have to make it yourself.

On batteries. 6 volt GC batts are talked about a lot bc they are true deep cycle batts. Marine batts are not true deep cycle. there are true deep cycle batteries other than what Autoparts store sells, but you pay more.
General consensus is AGM is a terrible waste of money for an RV.
Two 100 amp hour 6 volt batts run to make 12 volt will equal 100 amp hours.
Two 12 volt 100a/h batts run together to make 12 will equal 200 a/h.

The one watt for each amp hour on a battery sounds about right. You could go two even to be safe as solar panels really are going to to be the cheapest part in the long-term.

Watt hours is a better way to think than amp hours, but amp hours terminology is hard to make go away, learn both.

What are you running or plan to electrically?

Yes, 24 volt can be an advantage under certain circumstances, but will make things more complicated. I have a compressor fridge that runs off either 12 or 24 volts. It is the main electrical draw. I would go 24 volts if I were to do it over again just for the fridge and then make 12 volts for the other RV items off of whatever converter is needed. Unless you have a specific 24 or 48 volt need then stay 12.

KD4UPL

Swoope, VA

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Posted: 01/01/22 07:40pm Link  |  Quote  |  Print  |  Notify Moderator

Low budget and running an entire RV off grid just don't go together. Batteries are quite expensive right now and getting worse. Inverters, generators, and gas are also expensive.
You can figure amp hours or watt hours, which ever is easier. I tend to use watt hours. Either way that's a big heavy expensive battery bank. 2510 WH per day is a lot. You would need at least twice that in battery capacity bare minimum if you want your batteries to survive so that's 5020 AH. With 12 volt batteries that's 418 AH. You could use 4 6v golf cart batteries wired in series/parallel to get that capacity. I would recommend going larger because draining your batteries to 50% every day is still rather hard on them. Further, if you have a couple cloudy days in a row and the solar isn't producing much you either have to run the generator or have a battery bank big enough to last thru the cloudy days. Most people figure on a battery bank big enough for 3 days of no sun. If you do this you will need over 1,200 AH. Now you're getting into a size that really needs to be done with 2v batteries in series. Something like a Rolls battery.
In order to put back roughly 5 kWh a day with solar panels in the winter in VA you will need about 1,500 watts of perfectly oriented panels; that is set to a tilt angle of 45 degrees and pointed due south. Again, this is bare minimum, more solar would be better.
A $275 generator is a piece of junk. It might be fine for someone who only needs it once a year to power their refrigerator during an 8 hour power outage. You'll need to run a generator for at least 4 or 5 hours a day every day to keep up with your demand if it's cloudy or snow is covering your panels. With the price of gas what it is it won't take long for a higher quality more fuel efficient generator to pay for itself.

pianotuna

Regina, SK, Canada

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Posted: 01/01/22 10:20pm Link  |  Quote  |  Print  |  Notify Moderator

Sarahps33,

Are you in the RV now? If so get a kill-a-watt meter and measure the consumption over a six day period.

From that determine the watt-hours of storage needed.

By extension that will allow you to size the solar wattage to fit your needs.

I suggest looking at the predator 3500 inverter generator from Harbor Freight.

I don't mean to be harsh but 2500 watt-hours per day is pretty low.

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