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 > Amp draw vs battery bank & solar array = totally confused!

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valhalla360

No paticular place.

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Posted: 12/23/21 07:14pm Link  |  Quote  |  Print  |  Notify Moderator

Make sure to distinguish between amps & amp-hours (also watts & watt-hours).

Amps used per day is a nonsense term. So when you say you came up with 347 amps per day it makes no sense (I have a pretty good idea of what you mean but it confuses the discussion)

Amps and watts are an instantaneous measurement. Your truck engine may take 600amps @ 12v to turn over but since it only takes a few seconds to start, it uses almost no amp-hours.

On the other hand your TV may only draw 4amps @ 12v but if it's on for 10hours, it will burn thru 40 amp-hours.

Second, issue is your laptop has two separate things going on.
- Your average laptop will draw somewhere around 60-70watts when running.
- The battery charger may or may not charge at the same time or the same rate as it's feeding the battery...ie: if you shut down the computer and the battery isn't full, the charger will keep charging.
- Then you have parasitic losses. If the battery is full, don't leave it plugged in as keeping the brick powered can eat up 5-15watts. Not a big issue when plugged into shore power but when operating on the RV's battery bank, it adds to the amp-hour consumption.
- In the end, I would find the wattage draw of the computer and add 20%, then multiply by the assumed hours per day to get an estimate of the watt-hours per day. Divide by 12 to get an idea of the amp-hours.


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wanderingaimlessly

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Posted: 12/24/21 07:25am Link  |  Quote  |  Print  |  Notify Moderator

Another consideration is how you will be using/consuming the power. The fridge with freezer, are you saying you want a large residential type unit for a cabin? Or is a 10-14 cuft Gas/elec rv type unit sufficient?
Big difference in electrical consumption between the two.
Also trying to scale the solar to worst case scenario is forcing you to an extreme sized unit in both panels and batteries.
Attacking the issue from multiple fronts is usually the best.
A more modest solar and battery package that meets most of your needs on a "most of the time" basis, with a portable generator to supplement charging during bad weather, or high use periods as a backup is very common.
Also off grid folks often tend to eliminate things like electric coffeemakers, and use stovetop methods to save electricity.
Please give a little more info on what you are actually trying to do. Is this to be a full time proposition? In a fixed or mobile setup, and at least a region, so amount of sun available can be figured into the calculations.

SJ-Chris

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Posted: 12/24/21 03:16pm Link  |  Quote  |  Print  |  Notify Moderator

wanderingaimlessly wrote:


A more modest solar and battery package that meets most of your needs on a "most of the time" basis, with a portable generator to supplement charging during bad weather, or high use periods as a backup is very common.

^^^This

My opinion: The BEST way to see how much power each of your items will ACTUALLY drain from your batteries is to purchase a Battery Monitor. They have real fancy ones available. But I have used the $45 Aili (from Amazon...or try google) battery monitors and have been VERY happy with them. Pretty easy to set up and once you do it will take ALL guesswork out of your equations.

I'm not sure if you are planning on living in your RV full time and having the ability to run 100% off batteries for multiple (even cloudy) days is something that is critical for you or not. If you're just someone who uses their RV for occasional trips for a few days or a couple weeks, and you have a generator as a backup charging, or perhaps you drive (which charges your batteries) a bit every couple of days to a new destination.

Most casual (not-fulltimers) RV users can probably get by with 200-400AH of cheap lead acid batteries and 300-500w of solar power (assuming you are boondocking).

It would help to know HOW you plan on using your RV. How long will your trips be? Will you be boondocking for extended periods of time? I'm sure you are aware that every time you plug in at a campsite for a day, or drive for 4-5hrs, your batteries will generally get a good charging.

Before you overdue it on adding way too much batteries, and/or very expensive Lithium batteries, and/or a huge solar system....Start small and go on a trip and see how your battery needs work out.

Happy Camping!
Chris


San Jose, CA
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Posted: 12/24/21 04:02pm Link  |  Quote  |  Print  |  Notify Moderator

Good input and lots of questions on the OPs usage. 7 hours on a laptop might suggest it's work related or games or ???


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Ivylog

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Posted: 12/24/21 05:25pm Link  |  Quote  |  Print  |  Notify Moderator

Welcome to the forums and I’d say you’re worried about some items that I do not worry about… charging electronic as their usage is minor. Even a residential refrigerator is not as much as most think…1.2 to 1.4 Kw/day or 8 amps DC for 10 hours…80AH or one extra battery.
Now the big items like a coffee maker or the micro is real easy, you crank the generator when using them so you are charging them instead of heavily depleting your batteries.
As for solar, you want at least as many watts as you have AH of batteries and double if the batteries are Lithium.


This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
Sold 04 Dynasty to our son after 14 great years.
Upgraded with a 08 HR Navigator 45’...


2oldman

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Posted: 12/25/21 08:03am Link  |  Quote  |  Print  |  Notify Moderator

and now totally gone

Sarahps33

Winchester, VA

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Posted: 12/27/21 05:14am Link  |  Quote  |  Print  |  Notify Moderator

Thank you everyone for the replies and happy holidays!

My husband and I plan on living in the camper full time and travel for at least a year.

We dont plan on being plugged into shore power hardly ever, so I'm looking for something "off grid."

I talked to a friend yesterday who dabbles in electric and he pointed out one huge mistake he thinks I made. I plan on running everything through an inverter. So he said I wouldnt need to multiply the amps by 12v because I'm running everything off AC via the inverter. So, the amps would not increase, does this sound right?

Thanks for pointing out that the chargers and etc list the maximum volts & amps, that's a good point.

I have also recently stumbled upon people using 6v batteries which increases amp hours quite a bit. I've seen for example say they have six 6v batteries, they'll wire pairs in series to create 12v then run them in parallel to up the amp hours. They sell relatively small 6v batts that start at 225ah.

After learning all this, things seem much more possibly without having to use a huge bank and or huge array.

When I finish my new list of appliances/watts/wh etc - I'll share it here to see if it makes sense and for future folks with the same question.

Itinerant1

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Posted: 12/27/21 06:49am Link  |  Quote  |  Print  |  Notify Moderator

Prepare for long generator run times to care for the batteries if longevity might be a concern. Solar will help but won't do much on cloudy/ rainy days or the shoulder seasons.

I fulltime and boondock continously. From my experience living like I'm on hookups using microwave whenever I want, make a couple pots of coffee daily, charge phone/ tablets/ laptops, watch tv/ dvds for hours if we want, have the furnace going and any other appliances in the 5th wheel and inverter on 24/7. With my system (see sig) during spring, summer,late fall we'll average 35% +/- DOD or 175ah daily. Late fall, winter with shorter day light hours for solar DOD goes up to 45% +/- or 225ah daily. Just to give an idea, if you're more of a minimalist or conserve more you can certainly get by on less. [emoticon]

* This post was edited 12/27/21 07:04am by Itinerant1 *


12v 500ah (5,120Wh usable), 20 cells_ 4s5p (GBS LFMP battery system). 8 CTI 160 watt panels (1,280 watts)2s4p,Panels mounted flat. Magnum PT100 SCC, Magnum 3012 hybrid inverter, ME-ARC 50. Installed 4/2016 been on 24/7/365, daily 35-45% DOD 2,000+ cycles.

pianotuna

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Posted: 12/27/21 07:19am Link  |  Quote  |  Print  |  Notify Moderator

Sarahps33 wrote:



We dont plan on being plugged into shore power hardly ever, so I'm looking for something "off grid."

I talked to a friend yesterday who dabbles in electric and he pointed out one huge mistake he thinks I made. I plan on running everything through an inverter.


Running everything off the inverter immediately causes about 12% "waste" from the overhead of the inverter.

Golf cart batteries are not smaller.

I suggest reading the link I sent earlier in the thread. Your understanding of batteries, solar, and electricity are flawed.


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.

Gdetrailer

PA

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Posted: 12/27/21 01:56pm Link  |  Quote  |  Print  |  Notify Moderator

Running everything through an inverter can waste a lot of battery power depending on just how big or small the load is.

For devices like cellphones, tablets, laptops and any other low power device you are better off buying power supplies/chargers which can take the 12V directly from the battery and convert that to 5V (USB items) or 18V-19V for laptops.

Much more efficient than charging cellphones, tablets and laptops from 120V inverter.

For 5V USB charging, you simply use a cig lighter plug in USB charger, like this.

[image]

If you do not have a 12V cig lighter power port in your RV, they can be added fairly easily.

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