Small 12V Design Review

[avekevin]

Hello Forum!

I've been lurking on this site and a few others for awhile.

I'm putting together a small solar system that will power a wireless network repeater to extend network connectivity throughout my property.

The device being powered uses a 24v Power over Ethernet (PoE) connection with a max draw of ~11 watts.

I've documented my current design in the attached diagram. The full parts lists can be found at the following link:

https://www.amazon.com/gp/registry/wishlist/3P34O1KCM031G/ref=nav_wishlist_lists_3

Does this design seem right? Any advice or changes that you think I should make?

The controller has a dedicated 12v out, but my research seems to indicate that it's best to come off of the battery directly. Does that make sense?

Does it make sense to create a small output post off the battery of is this not needed?

Thanks for your advice!

[Guest]

In my opinion two 12 V car batteries or golf cart batteries in series that you can maintain for acid levels would do better . If you feed in directly then no losses through a DC-DC unit . If you could get a higher solar panel voltage , say one panel with 30V output it could be put directly across the batteries or fed to a 24V controller. Why start at 12 V if you need 24?

[Logan5]

If your device consumes 19 watts, this set up should only operate less than 10hrs after solar insolation and unless you include an in line LVD you will destroy your batteries in a very short period of time. If you use a step up converter to create 24v from 12v it gets even worse. Your 35AH battery is apx. 210 to 220WH @ 50% with out more solar panels you will not be able to operate equipment and charge your batteries at the same time. Resulting in an accumulative deficit and battery damage. You will want to monitor SOC and go out to the site with a generator periodically to equalize your bank.

[Wy_White_Wolf]

11 watts * 24 hours / 12volts = 22 amp hours daily. You battery and panel are too small to provide that. You need at least a 110 AH battery at 12 V or 55AH at 24 volt. Panel should be in the 150 watt range for a MPPT controller or 200 watts with a PWM controller.

Going with a 24 volt system would converting to a higher voltage and the efficiency losses in doing that.

WWW

[Mike90250]

What sort of bad things happen when the power at the site fails? As planned, it's going to fail frequently.

[Sunking]

Simple 5th grade math answers all your questions.

Your device uses 11 watts x 24 hours = 264 Watt Hours.

Minimum requirement is:

Minimum Panel Wattage = 120 watts with MPPT Controller, or 180 watts with PWM Controller.
Minimum Battery Size = 12 volts @ 110 AH
Controller Required = 10 amps

Nothing you have on your list meets those requirements. Bare in mind those are minimums and does not mean it will work. If you try to run with your battery, it will be dead day 2 and useless.

[David 68]

Hello forum,
i am new to the RV - Solar world and have several questions that i have not found any answers to.
i will try to ask correctly as possible w some background. i have been searching "Google" for over a month for any clarification w NO luck.
i have a RV with 30 amp service..., a wife that has to have AC when sleeping due to medical needs, i would like to "Relax" by rivers, streams, mountains... not at RV parks.
in review of electrical systems with converters / inverters and 120 AC needs my impression is the higher the battery (stored voltage) the better.
can i utilize a 48 V battery bank with solar charging and generator when needed. i am fine w Lithium batteries...soft start for AC unit. or whatever is needed.
is this a efficient design?
sorry for the run-on...

[Mike90250]

From what I understand, the Mini-Split air cond/heat pump units are the way to go. They slowly ramp up, and are pretty efficient, I don't know if they can be adapted to an RV though.

[skyking]

The Mini split is really the only way to go IMO. They do not have the massive locked rotor amperage of a typical RV air conditioner, which is more than 50 amps. Planning a system that can take a hit like that is costly and you have not even started cooling with it.
I have an RV design I have been working on for years that will utilize a 9000 BTU Mini split similar to this unit.

https://www.amazon.com/Pioneer-Air-Conditioner-Inverter-Ductless/dp/B01DVW6BG0/ref=sr_1_2?ie=UTF8&qid=1481486804&sr=8-2&keywords=9000+btu+mini+split+heat+pump

Mike has already mentioned the ramp up of an inverter based system. The variable speed is also a big advantage, but the other big benefit with a min split happens when you plug in somewhere.
If you did your homework and purchased a heat pump unit, now you have heat as well. Propane is the way to go when you need significant heating, but the heat pump will handle moderate heating needs efficiently and quietly.