Did I buy the wrong inverter?

[djdalfaro]

Flooded batteries vs Sealed AGM

Both have to be treated as venting fumes and hydrogen. Flooded does this at every recharge, AGM does it at end of life.
I would suggest flooded under the chassis, with a easily removable cover in the floor of the bus so you can service the batteries every 2 weeks (check water levels.
Or pay the expenses for AGM. You could put batteries inside in a plastic tote, or well painted plywood box.
i would consider 6v golf cart batteries, not too tall, cheap to locate and buy. 4 of them would give you 12V @ 400ah, or 24v @ 200ah

Sorry I somehow missed this post earlier while I was replying to others. I didn't realize AGM vent at EOL. Is this something that I would be able to anticipate via battery monitoring? I have heard 6V golf cart batteries mentioned many times, but on here I read a sticky I think that basically said, buy lower voltage batteries in the AH rating you are seeking, and string them in series. I don't truly understand why though.

[Mike90250]

Sorry I somehow missed this post earlier while I was replying to others. I didn't realize AGM vent at EOL. Is this something that I would be able to anticipate via battery monitoring? I have heard 6V golf cart batteries mentioned many times, but on here I read a sticky I think that basically said, buy lower voltage batteries in the AH rating you are seeking, and string them in series. I don't truly understand why though.

Predicting battery failure - go by the battery warranty. 36 months in your car, month 38 it's dead.

Parallel batteries do not share the work evenly. So that is why it's recommended to use low voltage, high amp batteries in series. And it's fewer cells to check !

[PNW_Steve]

A couple of comments:

They do make chargers that will charge your 24 volt house batteries from a 12 volt source. Victron is one manufacturer.

Sureflo makes a 24 volt RV water pump.

For LED lights, I am tinkering with pairs of 12 volt lights in series to run on 24volts.

[jflorey2]

Forgive my ignorance, I'm still confused about the advantages/disadvantages of series or parallel wiring in a small system such as mine.
The longest run between a panel and the CC in my case would be 20ft. I originally had been lead to believe the benefit of parallel panel wiring was because it would help to eliminate loses due to partial panel shading.

That is an advantage. Normally copper is expensive enough that you want to save wiring cost by going to thinner gauge wire, which is an argument for series connection. However, if you can afford the copper and the fuses, then there's nothing wrong with parallel connection (provided the voltage is high enough to charge the battery, which in your case almost certainly is.)

SunEagle implied (if I understood correctly) that if I went MPPT it didn't matter.

MPPT allows you to do either one.

You are saying (I think) that as long as my runs aren't too long, I should go 4P in an attempt to keep the difference between the panel voltage and the system voltage low, except that if I do, I will have the added expense of fuses and/or breakers for each string.

Correct. If you can afford the fuses and the copper, you can go parallel.

I asked in my previous reply to SunEagle if it would be sufficient to put an 80A breaker on the inverter input, to prevent it from overdrawing on the system. Do you have any recommendations for/against this?

The problem isn't that you will 'overdraw' the system; if you do, the voltage will sag and you'll shut down pretty quickly anyway. The main problem for your system is that larger inverters have larger tare losses, so you will always be wasting a few watts. If you are diligent about turning the inverter off when you don't need it that's not as much of a problem.

[djdalfaro]

Predicting battery failure - go by the battery warranty. 36 months in your car, month 38 it's dead.

Parallel batteries do not share the work evenly. So that is why it's recommended to use low voltage, high amp batteries in series. And it's fewer cells to check !

Are AGM batteries safe to have in a vented box inside the bus. My understanding is that FLA are not. Is this correct? Is there any advantage going with 6 2v batteries over 2 6v batteries if the Ah are identical?

[Sunking]

Gotcha, so in your expert opinion the partial shading that I would undoubtably see in RV usage should not be severe enough to warrant the extra expense/hazard of running the PV in parallel.

OK first lets clear up Hazard. Solar panels are current sources, not a voltage source like a battery with almost unlimited current. You can short a panel out all day long and nothing bad happens. It cannot deliver 1 ma more current than the Isc specification of around 9 amps. That is why if you limit parallel strings to 2, no fuses are required. Add the 3rd parallel string and you are now needing fuses and combiners. So for HAZARD, not so much, it is expense and efficiency.

As for shading, err shade should not be an issue. Don't park where you have shade when using the system. If you are concerned with shade then put thought into how you orient the panels so at least two will have direct sun. For long term parking and assuming your batteries are fully charged up, so is no real problem as it takes very little power to keep them charged up.

It's not too late. If 24V is the answer, I can do 24V. I can sell the 12V inverter.

Hold the Bus Gus. Thi sis an RV application and you stated one goal is to use 12 volt gizmos. That is fine. My recommendation to you is salvage what you can from the Inverter you bought to cut losses. Just by wiring 2S2P saved you a couple hundred of dollars to take the sting out. Not only is it much too large, it is also a MSW model which can cause issues with sensitive electronics and motor type circuits like fans, pumps, and refrigerators. By a good quality 12 volt up to 1000 Watt True Sine Wave Inverter, made for an RV. Which means it has a Built-In Charger and ATS for Shore Power/Generator input. If not that at least a good TSW model. Either way limit power to 1000 watts, and keep your plan to run 12 volt gizmos.

Below is a wiring diagram to get an idea of what you are doing. Pay attention to the bottom drawing as it fits what you are doing using both Inverter and 12 volt DC power.

[Sunking]

Are AGM batteries safe to have in a vented box inside the bus. My understanding is that FLA are not. Is this correct?

Both are safe if vented to outside air. Think a little outside the box. Ideally your batteries want to be exposed to the same temps you do. They do best at 70 to 80 degrees. So you can have a battery box on the inside keeping temps more suitable, you just put it on an outside wall, with a vent of some sort to outside air. Access can be internal or external via Access Panel or cabinet door. Just do not expose either to the elements. .

Is there any advantage going with 6 2v batteries over 2 6v batteries if the Ah are identical?

Again this is an expense/efficiency thing and the rule to apply is again high voltage rules. 6 x 2-volt cells require 5 times more wire and connectors, thus 5 times the resistance (power loss) and cost. What voltage the batteries are is more of a function of weight and size limitations. Example a 400 AH 12 volt battery would weigh around 260 to 300 pounds, where as a 6 volt 400 AH battery half that weight and size. So apply the golden rule of highest possible voltage vs how much weight per unit and size you can fit in. There are some restrictions manufactures limit you too.You are in 6-volt territory unless you want more than say 500 AH which you coul duse 4-volt batteries. 2-volts is silly.

Example a 12 volt batteries are available from a few AH up to about 200 AH.
6 volts range from around 200 to 900 AH
4 volts from 600 to 1500 AH
2 volts from 1000 up to 10,000 AH for Nuke submarines and telephone offices.

[littleharbor]

This advice comes from Sunking's vast experience and rock solid common sense. Not only will following this advice save you money by building it right and safe the first time, consider the value of this "free" advice. He has a knack for relating some fairly complex descriptions into easily understandable terms.

Not taking anything away from all other regular contributors, they all add valuable info here. I just have to say I really admire his ability to convey this info in a straightforward, no BS kind of way..

[djdalfaro]

Sunking WOW! Thank you for the treasure trove of information. You've given me a ton of digestable directions on how a proper system should be run. Now that I have these design issues figured out, it will probably be a bit of time before I post again as I'm not ready to build yet.

Thank you to everyone else for helping me with this issue. I know I'll be sure to check here first before I buy any more "deals".

[Sunking]

Sunking WOW! Thank you for the treasure trove of information..

You are welcome.

[PNjunction]

The only thing I'd add is that when you get your batteries, you charge them individually first, before putting them into service and wiring in series / parallel or whatever you have.

AGM's are more than happy to gas out if the cells are in an extremely unbalanced state to begin with, which can be common if you just slap them together from the battery outlet and begin to charge.

Re disasters like hurricanes - think carefully about your loads and days of survival. Mainly because the weather is bad for days well after most events like this happen! You may make it through the first initial phase, but then be let down by mother nature for days afterwards. Of course if you can drive away, different story. But maybe you can't and have to shelter in place. That's where external gennys come in handy.

Not much to add beyond what others have said - just be realistic about bad weather. Here in California, recent fires and their smoke plumes can put a big damper on solar as well, so it isn't just wet weather that's a problem. Be prepared to have panels basically doing nothing, with a "plan b".

[djdalfaro]

PNjunction

Thank you for the quick tip on the batteries. That is most definitely a mistake I would have made.

RE: disasters, my family and I rode out Harvey in our home. We are fortunate enough to have purchased in a 50 yr old neighborhood, on a peninsula, next to huge bayou... All of which may sound like a disaster waiting to happen when you get 50+ inches of rain but there is a ton of drainage which saved our butts. The solar system on the bus will be providing mainly amenities that are not essential for survival. Lights, fans, TV, etc... with the expectation that if we did need to evacuate we would do so hopefully a bit more comfortably than those stuck in tiny cars in gridlock traffic. I will be looking into a generator as well as using a battery isolator to recharge the system.

[djdalfaro]

Both are safe if vented to outside air. ... So you can have a battery box on the inside keeping temps more suitable, you just put it on an outside wall, with a vent of some sort to outside air. ...

How much of a vent is necessary? Is a 1" vent sufficient or do I need something more like a 4" vent? Does the vent need to be above the battery level, or can it be below?

Thank you

[Sunking]

Issue is hydrogen gas while charging which is lighter than air so it goes up.