Basic DC setup for a few lights

[kim_jong_un]

Greetings Comrades

Just doing a super basic setup to have a few lights and ventilation fans running in my shed. It is going to be a DC only setup (no inverter). This is my first dabbling in the realm of solar and I am having trouble coming up with a clear answer on where to put fuses and safety switches.

Setup is as follows:
2x 12V 200w rigid PV in parallel (overkill but I got a second panel for free) [Isc 11.90A, Imp 10.87A] - I have no intention of adding any extra panels so I do not need to future proof for this
30A MPPT 12V controller
12V 15AH Lead Acid battery (the weak link in my setup but I am really not anticipating much usage - but believe if I needed more I would just replace the battery with a single larger unit rather than having multiple batteries),

At this stage devices are going to be USB powered via the MPPT USB ports rather than wired in on the DC out circuit

Solar panels to the MPPT are about 100cm. MPPT to battery is about 50cm.

So my questions are:
1. Wiring - some online calculators are suggesting 10 gauge, but some other online graphics are suggesting 10 gauge is for 15A max (whereas I was thinking I probably need 25-30A capable wiring) - what gauge wiring would be appropriate from:
1a. PV to MPPT
1b. MPPT to battery.
2. Fusing/Safety switches
2a. where should I put fuses and safety switches (PV to MPPT, MPPT to battery)
2b. what rating fuses/safety switches are appropriate?
3. Should I not waste my time wiring in the second PV panel? The battery has a max charge current of 3A. I am planning on having the ventilation fans running continuously throughout the day because the shed isnt insulated and can feel like a steam room even with an ambient temp of around 25deg C. Can the solar power feed the devices directly during the day or does the power to the devices have to come from the battery?
> In other words if I am using more than 3A during the day when the PV is in the sun am I going to be draining the battery (assuming we have simplified the scenario to assume no losses/inefficiencies)

Sorry for the n00b questions - I have tried doing a bit of reading up but the vast majority of info that I have come across when trying to google it is is for people running inverters and wanting to power fridges, tvs and microwaves. My plan is literally two exhaust fans running during daylight hours and a small standalone fan and some LED light strips for when I am in the shed.

many thanks in advance

 

[eppich8479]

You could use 18ga really in my opinion, depending on how many you gang together. Gauge is about amps. If your lights are 1A i think its fine. If you see yourself at 5A then maybe 16ga. If you are really worried about just use standard 14ga romex

I honestly think you will need something like a car battery because lead batteries are not meant to go below 50%, especially in freezing weather. Plus fans have a high draw.

I would pit the second panel in because you will never get 100% and current is drawn, you wont over load it in parallel.

The power is all mixed. Think of it like a dam between 2 bodies of water. Basically the load will drop the voltage, so the water will flow from the highest point to the lowest point. The high point could be the battery or the solar. And if you think about 3 bodies of water im sure you could visualize how that works. The mppt should have a diode or full bridge rectifier so voltage wont go back to the mppt i think.

I would suggest using LED tape lights for your situation. They are 12v so you can just cut the transformer off and wire them to the battery, and that is about 18ga wire. They have a remote and often RGB if you want.

 

[wdwtx2.0]

Just doing a super basic setup to have a few lights and ventilation fans running in my shed.

Hahahaha.
That's how it starts.
It is an insidious addiction.

 

[kim_jong_un]

You could use 18ga really in my opinion, depending on how many you gang together. Gauge is about amps. If your lights are 1A i think its fine. If you see yourself at 5A then maybe 16ga. If you are really worried about just use standard 14ga romex

I honestly think you will need something like a car battery because lead batteries are not meant to go below 50%, especially in freezing weather. Plus fans have a high draw.

I would pit the second panel in because you will never get 100% and current is drawn, you wont over load it in parallel.

The power is all mixed. Think of it like a dam between 2 bodies of water. Basically the load will drop the voltage, so the water will flow from the highest point to the lowest point. The high point could be the battery or the solar. And if you think about 3 bodies of water im sure you could visualize how that works. The mppt should have a diode or full bridge rectifier so voltage wont go back to the mppt i think.

I would suggest using LED tape lights for your situation. They are 12v so you can just cut the transformer off and wire them to the battery, and that is about 18ga wire. They have a remote and often RGB if you want.

Did you have any recommendations for fuses/safety switches?

 

[eppich8479]

Did you have any recommendations for fuses/safety switches?

You can put a finger on + and - of a 12v batter and you will be fine. Fuses will protect the wires i guess. Or you could just not screw up and dead short something with power on. If you want fuses car fuses from autozone or what have you should work great. I have an ecoworthy pv combiner, but i have 9 400w panels.

The $0.68 120v light switches from home depot will work just fine for 12v too.

 

[kim_jong_un]

You can put a finger on + and - of a 12v batter and you will be fine. Fuses will protect the wires i guess. Or you could just not screw up and dead short something with power on. If you want fuses car fuses from autozone or what have you should work great. I have an ecoworthy pv combiner, but i have 9 400w panels.

The $0.68 120v light switches from home depot will work just fine for 12v too.

im not so worried about electrocution, its more just the risk of the wires catching on fire. So you think with a super basic setup like this im good to run it without a fuse?

 

[Rednecktek]

At this stage devices are going to be USB powered via the MPPT USB ports rather than wired in on the DC out circuit

Red Flag!! I've only ever seen one true MPPT controller with a USB port. A dead giveaway of a PWM controller pretending to be MPPT is a USB port.

Post a link to it and we'll verify, but at this point assume you are being lied to all the way to the bank. You're going to want a real 40a MPPT SCC, and fortunately there are many options out there that will turn solar DC into battery DC, so don't get browbeat into buying something blue.

Also, the USB ports on cheap controllers is a 2.5w port so expect it to take all day to actually charge anything. You'll be better off to get the 12v USB PD sockets on Amazon and a paddle bit to mount them.

Wire guage is based on amps, so size accordingly. As a rule of thumb:
10awg - 30a
12awg - 20a
14awg - 15a
16awg - 10a

With 400w of panels you'll want 8awg from panels to controller to battery. Use the same 8awg from the battery to a fuse block. From there you should be able to get a bulk spool of 16awg DC wire and run it out from the fuse block to all the things if 3a is really the heaviest load you've got. That way you only need 2 sizes of wire.

Plan now to get a bigger battery. Lead doesn't like to go below 50% so that battery of yours is only good for 7ah, or 2 rechargable flashlights worth. LFP is getting to be cheaper than lead nowadays if you don't feel the need to pronounce what's on the label. As a comparison, a WallyWorld DC29 120ah battery in town is $169, and good for 60ah of usable power. A Djingelburie 100ah LFP is about $120 and good for 100ah. Better value right there.

PV -> SCC -> 40A Fuse -> Battery.
Battery -> Fuse Block
Fuse Block -> 5a Fuse -> Switch ->Fan
Fuse Block -> 3a Fuse -> Switch -> Lights
Fuse Block -> 10a Fuse -> High Power USB Charging

 

[mikefitz]

12V 15AH Lead Acid battery

Recomended charge current will be a few amps. Possibility of overcharging, set charge voltage low at 13.8 volts.

USB powered via the MPPT USB ports

Any controller with USB ports is not MPPT , its almost certain to be a PWM controller. One panel will put 10 ampe maximum into the battery and system.

Wiring

10 awg, panels, controller battery. 15 amp fuse at battery with one panel, 30 amp fuse with two panels
Stuff connected to the USB ports, awg 14, series fuse at 5 amps
Fuses installed as close the power source, the battery, as possible.
Edit, typing as Red posted.

 

[kim_jong_un]

Hi Rednecktek and Mikefitz
Thanks for the detailed replies.

Re the controller: I have a cheapo PWM controller already
> https://www.aliexpress.com/item/100....order_list.order_list_main.53.1e221802pIa2tO

It said it only supports lead acid batteries so i thought I would get an MPPT that supports other battery types so I have the option later on to change it. Based on what you are both saying re the usb I would assume I have just got another PWM

https://www.aliexpress.com/item/1005005621385813.html?spm=a2g0o.order_list.order_list_main.5.1e221802pIa2tO

@Rednecktek
For the usb power supply would something like this work?

https://www.amazon.com.au/Outlet-Charger-Socket-Recessed-Caravan/dp/B0D4V98NZ7

Thank you also both for the detailed info on wiring/fuses!

Any recommendations for a budget MPPT controller or if it is even worth going with an MPPT controller for what I am doing? Or should I just get a better PWM?

 

[mikefitz]

re the usb I would assume I have just got another PWM

Definitely PWM, most likely will have the same internals as your other PWM. They will say supports many battery types but they all just put out a voltage set to a maximum target value, PWM modulated. Putting current into the battery charges all battery types .
Don't expect a three stage charging profile.

should I just get a better PWM?

The unit you have will be enough for your modest system as a introduction to solar. Slightly better PWM controllers exist but not worth the effort of installing.

usb power supply would something like this work?

There are many 12v to USB converters, the output current maybe lower than specified.

 

[kim_jong_un]

PV -> SCC -> 40A Fuse -> Battery.
Battery -> Fuse Block
Fuse Block -> 5a Fuse -> Switch ->Fan
Fuse Block -> 3a Fuse -> Switch -> Lights
Fuse Block -> 10a Fuse -> High Power USB Charging

With adding a fuse block - I run this directly off the battery? Or should I wire it to the power output from the controller?

 

[Rednecktek]

Fuse block should go directly to the battery.

 

[kim_jong_un]

Fuse block should go directly to the battery.

Would you ever run anything directly on the power output on the controller? (where they have marked loads in the picture)

 

[mikefitz]

Would you ever run anything directly on the power output on the controller?

You can connect loads to the load output. Typical for your PWM controller is the be able to turn lighting on after sunset. The 'on' period may be programmable. The other usually available feature is to turn off the load output if the battery volts get too low.
The downside of powering of the load outputs is that the current is limited , normally to the rated current of the controller.
Where you power direct of the battery the current limit is that of the battery , so high current loads connect directly.

 

[Rednecktek]

The other usually available feature is to turn off the load output if the battery volts get too low.

I find this is a handy function for tending ATV/Mower/Motorcycle/Generator batteries over the year at my cabin. It keeps the batteries topped up and when snow season hits (evidently Nov - April so far) and the standby draw gets to dragging the system down, it cuts the tending off until the sun comes back out and gets the main batteries back up. Once the main batts are charged up, the tending turns back on.

The other useful purpose to the LOAD ports is some low power LED lighting on a motion sensor. I have that set up in my utility room so when I get to camp and open the door, the lights come on and I can see all my switches and buttons to get my system turned on.