Looking for confirmation for a small D/C setup I want to do.

[Janachovsky]

So it's just small D/C fan that runs 24/7/365 on a composting toilet. The fan is 12v 2.5w so it uses 60 watt hours every day. In Colorado near 1 hr west of Pueblo and supposed to get 4.5 hours of sun minimum. 2 day battery backup 50%discharge. Looking for advice on the setup I think I need.

Bank capacity
46 amp hours needed, ,
So 2- 6v Trojan t105re 225ah or something else? What configuration?

Need 17 watt panel so a 20 w panel?

2amp mppt CHG controller w low volt disconnect?

What size wiring?

Also this is an unheated cabin when were not there.

Thanks in advance, so much misinformation and info in general about solar, it's all pretty overwhelming to me to decide what's best.

[jflorey2]

So it's just small D/C fan that runs 24/7/365 on a composting toilet. The fan is 12v 2.5w so it uses 60 watt hours every day. In Colorado near 1 hr west of Pueblo and supposed to get 4.5 hours of sun minimum. 2 day battery backup 50%discharge. Looking for advice on the setup I think I need.

Bank capacity
46 amp hours needed, ,
So 2- 6v Trojan t105re 225ah or something else? What configuration?

Need 17 watt panel so a 20 w panel?
2amp mppt CHG controller w low volt disconnect?
What size wiring?
Also this is an unheated cabin when were not there.
Thanks in advance, so much misinformation and info in general about solar, it's all pretty overwhelming to me to decide what's best.

A few notes -

Generally you don't want to go lower than about a C/13 charge rate, so that means you'd need a ~200W panel to support that battery. Consider going smaller on batteries there. On the other hand the T105 is available everywhere; if you have any additional loads you might run off the system you might consider that 200W panel with an MPPT controller.

So you basically have two choices -

Larger system with grid tie (HV) panel, MPPT controller and two T105's
Smaller system with 12V panel, PWM controller and small (~25ah) battery.

AGM batteries survive freezing better than flooded batteries do - but if you are always at full charge the odds of freezing go down significantly.

Wiring will depend on panel size. Size wiring to handle max amperage; size protection to protect the wires.

[Sunking]

I have no clue where Jefff is coming up with his numbers. He must be a drinker or self medicated using ganja.

Fist step is determine your battery size for 5 day capacity with 50% usable or roughly 3 days.

Battery = 2.5 watts x 24 hours x 5 days / 12 volts = 12 volts @ 25 AH. How Jeff came up with 225 AH I do not know.

For this small of a system all you need to do is provide a C/10 charge current of 2.5 amps using a PWM controller. Find a 12 Volt Battery Solar Panel with a Imp of 2.5 to 3 amps. That should be a panel of roughly 40 to 60 watts. Look for the smallest controller you can find of around 5 amps. It just needs to be equal to or slightly greater than the panel Imp current. A 20 watt panel you thought of does not have enough current to support the battery. A 20 watt panel Imp is roughly 20 watts / 18 volts = 1.1 amps. No need to worry about Sun Hours in this application in your location.

As for wire, 14 AWG is as small as the Code allows and is overkill. 14 AWG is good for 15 amps up to 10 feet. At most you will be running 3 amps at worse case. The Important thing is to use 4- 5 Amp fuses connected directly to the battery Term Post. One pair facing the Controller, and one pair facing the fan to protect the wiring from the battery.

The drawing below is not exactly what you need, but to demonstrate where to place the fuses on the battery for a Floating System (first drawing). Ignore the rest

[Janachovsky]

Awesome thanks SunKing! All your info is very helpful! And Florey too.

Sounds like a good project to get my feet wet on.

SunKing do you have an opinion on battery type/brand for this application? Or my choices are limited to only 1or 2? Thanks again!

[Sunking]

Awesome thanks SunKing! All your info is very helpful! And Florey too.

Sounds like a good project to get my feet wet on.

SunKing do you have an opinion on battery type/brand for this application? Or my choices are limited to only 1or 2? Thanks again!

At this small of a scale there are dozens of candidates. Depends on how much you want to spend. If it were me I would look at Powersonic AGM PG series which is a long life AGM battery. Something like this one. They are a little pricey but good enough for the military aircraft.

If you want something cheap, go to Batteries Plus or look online for what they call a Universal Battery AGM or UB AGM. It is a generic name. Example UB122260T.

[Janachovsky]

Awesome thank you very much, I'll explore all battery options.

[Sunking]

Awesome thank you very much, I'll explore all battery options.

You are welcome. 12 volts @ 25 AH are a dime a dozen.Just make sure whatever panel you buy is a Battery Panel with a Imp of roughly C/10 of the battery you use. Battery panels Vmp is 18 volts, so a 2.5 amp panel is 18 volts x 2.5 amps = 45 watts.

At this low of a power does not make economic sense to use a MPPT controller which only requires a 30 watt panel to make 2.5 amps..

[Laspher]

I am currently looking at this setup for my low power need project: this battery with this solar kit. Fairly cheap for a 12v system from what I've been able to find.