Newbie in need of set up info - looking for great article or whitepaper

[Nicolia]

Hello all,

I'm another noob looking to get into solar for my Skoolie project. I have not purchased anything yet and won't until I get a really solid understanding of exactly what I need first.

Here is what I will be using in the Skoolie when just using solar:
- 210w air conditioner (24V with internal inverter for 12V usage) --- approx 6-7 hours/day = 122.5 Ah
- 6 13W LED lights --- approx 4 hours/day = 26 Ah
- small fridge (24 hours/day) 36.7W or 322 kWh/year = 73.4 Ah
- water heating element for RinseKit (9CDA) --- approx 1 hours/day = 9Ah
- inverter or solar equipment (this is what I don't understand yet - no idea what I actually need outside the batteries) = ?
- laptop and phone will be powered by an existing camping solar panel case

From this the calculators say I'm using somewhere around 230 Ah per day from my battery bank. (is this first assumption correct?)

I plan on purchasing 6 of these batteries (https://www.batteriesplus.com/produc...le/12/sli31mdc) for a total of 630Ah bank with a usable amount of 315Ah per day.

My question is what additional equipment do I need to monitor/maintain the batteries and system? Invertor, fuses, etc...and I'm happy to read any articles of books that anyone would recommend to explain this system. (someone mentioned Solar for Dummies - good option?)

My other question is if I'm usually only in one off-grid spot for two days, is it cheaper/easier to up the battery bank and refill from a second alternator while driving, or it is best to install solar panels? I will also most likely have the ability to plug in at a camp every third or so day.

Thanks for any and all insights!

[Mike90250]

Whoa.. 230ah daily at 12V , that's about 3KW That's going to need a lot of solar PV on the roof, or an additional HD alternator for while you are driving. See http://www.balmar.net/ for alternators.

[Nicolia]

I'm definitely not trying to replenish all 230Ah per day via solar -- I wouldn't even have enough room for that many panels on my skoolie.

That's why I'm asking would it be better to up the batteries to an 840Ah bank and get that second alternator -- perhaps forego the panels altogether?

[Mike90250]

You won't like this, but I'll say it anyway.
4, golf cart batteries. 6V , 200ah, $95 at a big box store

2, 300w PV panels, best fit for your roof (only if you want to figure a way to mount them, or use a pair of sandwich boards and park them in the sunlight.) Don't forget them when you drive off
1, MPPT solar charge controller

1 small inverter generator (harbor freight - https://www.consumerreports.org/inve...ter-generator/ ) & a 40A battery charger. This will save you a lot of fuel from idling your prime mover engine to charge batteries.

Yes, you are burning gasoline, but less than running the bus engine just to charge. Power the air con during the day and top off the batteries, and be quiet at night

[Nicolia]

I don't really have one path decided over another and am open to any alternate recommendations.

1. I can't find any golf cart batteries that are 6V 200Ah for $95.
2. To get close to 315Ah usable daily, wouldn't I need at least 6 of those 6V batteries wired in a series/parallel configuration? the cost would be about the same as six 12V 105Ah batteries...is there a benefit going with 6V series/parallel over the 12V batteries? (Four 6V 200Ah batteries would only provide me 200Ah usable daily...and my need is higher than that.)
3. Now to the MPPT solar charge controller and 40A battery charger -- what are the duties of each of these devices? i.e. what do they do specifically? Do I need a MPPT solar charge controller if I don't have solar panels and just go with a HD alternator and a bigger battery bank?
4. If the inverter generator you listed from HF is rated at 1600 watts does that mean it would run the 210w AC unit for 7 hours on one gallon of gas?

Sorry for the beginner questions...trying to do a lot of research and every post I learn something...thank you.

[Mike90250]

Is there no Costco, or Sams Club anywhere near you ? 4 golf cart batteries would give you 12V @ 400ah. $100 is tops for those batteries even at a auto parts store. And while you are running the little generator to run the battery charger, you can run your AC. Once the batteries are 80% full, you let the solar & the MPPT charger take over for the next 3 or 4 hours to top off the batteries.

This is all info for YOU to think about, do you want to do it this way or that way ? But do not try to recharge your battery bank from the bus alternator, it's going to shorten it's life - trying to charge a deep cycle battery for 4 hours.

[Nicolia]

Thank you. I understand that you're providing info for me to review and make decisions. I am asking these questions in order to learn what direction to take or what decision to make. In order to do that I'm attempting to understand certain aspects to put apples against apples.

For instance, the four 6V batteries you mention above will not give me the needed 230Ah per day -- they'll only give me 200Ah per day. So I'm trying to detmerine from your suggestion if six 6V 200Ah batteries have a benefit over six 12V 105Ah batteries at the same cost. Does a 6V battery bank have a benefit over a straight 12V bank?

When I made reference to the HD alternator above it was because of traveling every two days -- I did not mean to say that I'd run the diesel engine to refill the bank (I should have made that clear).

If I used the 1600W inverter generator with a 40A battery charger, how many Ah would I be able to put back into the bank? Completely lost on how to make that calculation. Urghhh...trying to learn as quickly as possible.

Again, thanks for all your insights and time.

-Nicolia

[Mike90250]

4 golf cart batteries would give you 12V @ 400ah bank ( 6V, 200ah each battery)

Count the caps you have to check to add water.
using 4, 6V batteries, 3 caps per battery, 12 wells to open and check
Using 6, 12V batteries, 6 caps per battery, 36 wells to check !!
There is a huge time saver there. (original link you had was for a flooded deep cycle battery, 3 wells under each cap plate)


1600w inverter generator @ 120V = 13A going into a 30a 12v charger about 420w consumed

[Nicolia]

On the batteries, I'm attempting to cover a 230Ah daily use. To do that, would I not need Six 6V 200Ah batteries? Or do 6V batteries not have to worry about the 50% rule? This is why I was thinking I'd need six 12V 105Ah batteries -- that would give me a 630Ah bank or 315Ah usable per day. In the above configuration you mention four 6V giving me 400Ah bank...but wouldn't that only give me 200Ah usable? Still I guess it would be half the caps to check.

"1600w inverter generator @ 120V = 13A going into a 30a 12v charger about 420w consumed"

How do I take the above equation and deduce the amp hours I'd put back into the bank?

[Mike90250]

On the batteries, I'm attempting to cover a 230Ah daily use.

It will be close enough. You will be pulling the batteries down 45% daily. You will get a slightly shorter life, but you have 2 fewer batteries to have to mess with. Thehy may even fail within the warranty period !

"1600w inverter generator @ 120V = 13A going into a 30a 12v charger about 420w consumed"

How do I take the above equation and deduce the amp hours I'd put back into the bank?

You have to figure that out yourself, I don't have the answer.

Your loads can be powered by the batteries or by the engine/solar
Load demand met by engine/solar does not deplete the battery, but it does rob capacity from the charger.

Are all your loads 12VDC ? Maybe a 40A charger is what you need, instead of a 30A That would power loads while the batteries are charging.

If you remove 200ah from the batteries, you need to replace with 240ah. At a 30A rate, That's 8 hours of generator time. There are only 5 or 6 usable solar hours in a day, so something is going to have to keep those batteries charged. Or find more efficient gear - the less you use, the less you need to generate.

[Nicolia]

I'm still very confused on the battery discussion. I thought I had it figured out between the 12V and 6V, but the below quote leads me to think I don't.

It will be close enough. You will be pulling the batteries down 45% daily. You will get a slightly shorter life, but you have 2 fewer batteries to have to mess with. They may even fail within the warranty period !

I originally said I was going to use six 12V 105Ah batteries for 630Ah total. You recommended I use 6V batteries instead (I now understand the benefit of less caps to check). Where I'm confused is when you stated that with four 6V 200Ah batteries I'd have two less batteries to worry about...this is where my math is not working out. Would not four 6V 200Ah batteries be the exact same as four 12V 105Ah batteries? I don't understand the quote of "but you have 2 fewer batteries to have to mess with." Again, I'm very new to this whole thing so I may very well be missing something that is super obvious to you.

I am happy to buy the 6V batteries if that is the better way to go vs 12V -- definitely not married to 12V, I only used them in my original post as they were recommended by someone else in a Skoolie forum. (however, they did recommend I come here for much better feedback/insights).

You have to figure that out yourself, I don't have the answer.

I'm trying to understand the math here...this is not something I can simply "figure out" if I don't understand the math. You stated, "1600w inverter generator @ 120V = 13A going into a 30a 12v charger about 420w consumed" -- which I'm sure means something to someone who understands that math behind that statement. To me it's all Greek, but I'm trying. In fact, everything I read seems to be written for people that already understand the above equation you wrote.

I'm trying to put everything into an aspect that I can understand from the discussions that I've already had with some really great folks here...and that is all based on amp hours. What I don't understand is what volts, watts or amps mean to a system when time is not part of the equation...so when you say, "13A going into a 30a 12v charger about 420w consumed" I am left with the following questions:

- is the 13a generated by the generator you listed per hour?
- is the 13a generated in AC? If so, does that mean it is basically producing 130DC amps per hour?
- what is consuming the 420w? Is that the charger? Is that equal to 35.8DC amps or 35.8 amps per hour?
- If it produces 130DC amps per hour and the charger uses 35.8 DC amps per hour -- does that mean I would net roughly 94DC amps per hour?
- assuming a 40a charger uses 40 of those 94DC amps available to replenish the bank, does that mean I would have 54DC amps remaining to power other devices (which is not really anything).

I'm assuming all the above is wrong at some or all levels because I simply have so much more to understand/learn to make educated decisions.

My original idea was to have the system as a 12v AC system for when I have shore power, but I'm fairly sure I can make it a 12VDC system. The AC unit and the water heater are already DC, but the lights, WiFi router and fridge are AC. I can always use my phone for WiFi, so that cancels that out and I'm sure I can find a DC fridge and lights.

[PNW_Steve]

On the batteries, I'm attempting to cover a 230Ah daily use. To do that, would I not need Six 6V 200Ah batteries? Or do 6V batteries not have to worry about the 50% rule? This is why I was thinking I'd need six 12V 105Ah batteries -- that would give me a 630Ah bank or 315Ah usable per day. In the above configuration you mention four 6V giving me 400Ah bank...but wouldn't that only give me 200Ah usable? Still I guess it would be half the caps to check.

"1600w inverter generator @ 120V = 13A going into a 30a 12v charger about 420w consumed"

How do I take the above equation and deduce the amp hours I'd put back into the bank?

Good to see you here Nicolia,

Mike & Company will steer you right. Lots of good knowledge here.

Carry on

[Mike90250]

So, first thing is to use WATT HOURS. If you use amp hr, and start jumping from 12VDC to 120VAC you will get wildly confused and make some mistake and be off by a factor of 10, which will not make your day.

Battery
6v, 200ah = 1200wh
12v, 100ah = 1200wh Same power stored, but formatted differently

4, 70lb batteries hold the same amount of lead and acid, and roughly, same amount of watt hours


When charging batteries with a generator, solar or running off the vehicle, you have 2 things that steal from each other = Loads and Batteries.
When your fridge comes on, it robs your battery of some amount of charging power, so it charges slower. i don't know how your loads will cycle on and off, but Loads while charging the batteries, change the power going into the batteries and they charge slower.

My original idea was to have the system as a 12v AC system for when I have shore power, but I'm fairly sure I can make it a 12VDC system. The AC unit and the water heater are already DC, but the lights, WiFi router and fridge are AC. I can always use my phone for WiFi, so that cancels that out and I'm sure I can find a DC fridge and lights.

Somehow, I thought the fridge was 12VDC and you were not using an inverter. Many routers run on 12vdc and regulate internally, look at the label on your wall wart for your router.

I've not heard of any 12VDC air conditioners, but I'll trust you read it's label correctly.