Solar prototype questions (newbie).

[John Doe]

Hey folks,
I'm a newbie in Solar trying to learn. Best way I learn is by doing things very small and expanding. My goal is to charge DC devices in my house like cell phones, laptops via clean solar power. I will not be using an inverter or grid-tying it. My plan is to buy a battery bank and charge it via two 12V/20Watt panels in series. So I get 24V with very little amps. My house has a satellite dish on the roof and the coax cable comes into the house, the cable is 18 AWG CATV6. This cable is capable of handling the volts and the amps. I will remove the satellite dish and mount the panels on the J-Pole. I have attached the setup to this post. The solar panels will be connected to a Buck Converter that takes in 24V and steps it down to either 19V or 5V (depending on how I adjust it). It will take the extra volts and convert it to additional amps (sort of like an MPPT controller). The battery bank I'm using with either take input 19V or 5V to charge. The battery bank will also either output 19V for laptops and 5V for cellphones/tablets.The battery bank has internal circuitry to shut off power when full charged so I wont be using a controller.

My questions are;
1. Is it ok to use the 18AWG coax cable to carry 24V with ~0.56 Amps in house?
2. am i using the right fuses as shown in the diagram?
3. any other things I'm missing/suggestions ?

Thank you in advance,
John

[Mike90250]

A Buck converter, will pulse itself on & off all day, loosing quite a bit of harvest - Because the sun varys quite a bit in the course of a day. You need a true MPPT circuit to get the most harvest out of your small panels..
Only need a fuse at the battery, 2 small panels usually can't produce enough power to light a fire.

[John Doe]

Thank you so much Mike902550.
I didnt think about the on/off issue. I will replace the buck converter with an MPPT charge controller.

[Sunking]

My goal is to charge DC devices in my house like cell phones, laptops via clean solar power.

Do not fool yourself or believe what you said. We certainly do not believe you. Solar is anything but clean when used to charge batteries. Especially the way you will use it makes you a heavy polluter. Anything you take off grid, the power will cost you 5 to 10 times more than buying it from the POCO and a heavy heavy polluter.

My questions are;
1. Is it ok to use the 18AWG coax cable to carry 24V with ~0.56 Amps in house?

Not that anyone cares but no. Technically the minimum is 14 AWG wire listed for power and lightning. 18 AWG coax is only the center conductor, the shield depends on what it is made of. If it is foil or the cheap crap you buy at a home or electronics store cannot handle any meaningful current and power is out of the question. Coax is made for signals, not power. There are provision for power limited circuits like yours that can use wire smaller than 14 AWG. The catch is at 5 volts voltage drop is critical and you cannot afford any voltage loss. If you can keep the cable short enough like 3 to 5-feet, you can use a 2-conductor cable that is rated for low voltage power limited circuits. Example a USB 3.0 cable is designed and listed for low voltage limited power. Cut the ends off and your in biz.

2. am i using the right fuses as shown in the diagram?

Not needed. The only thing that is capable of generating enough current to heat up wiring is the battery itself which requires a fuse installed directly on the Battery Term Post which is built inside you cell phone, laptop and gizmos

3. any other things I'm missing/suggestions ?

Other than what has already been said it will not work. The Converter you intend to use is designed to use on a stiff VOLTAGE SOURCE OF POWER like a DC power supply. Solar panels need a Regulator made for a unknown soft Current Source. Solar panels are soft current sources, not stiff voltage sources like a battery, generator, or commercial AC Power.

[John Doe]

Thanks for the detailed input Solar King for helping newbies like me.

[Sunking]

Thanks for the detailed input Solar King for helping newbies like me.

You are welcome. Just do not want you to waste all that time and money on something that will not work. It can certainly be done and has been done as you can buy manufactured units today. The question you have to answer; is not can it be done, but rather should it be done. For $20 or less you can buy a USB Charger that will charge a Cell Phone in an hour. For $100 you can do it with solar that takes all day to charge.

Here is the kicker. A solar usb charger might generate as much as 50-cents of electricity if you are lucky before stops working 5 years from now. That is what I call an education.

[John Doe]

My goal is start with 20Watt panels to understand how much I can generate during the day pertaining to my house with some trees and shading. Record the numbers and doing some calculations, Pulling my multimeter, ampmeter and learning, its not just charging phones and tablets. Kinda like I want to learn to swim not just by reading about it but also trying in a small shallow pool before slowing entering the deep end few feet at a time.

[Mike90250]

My goal is start with 20Watt panels to understand how much I can generate during the day pertaining to my house with some trees and shading........

As long as you are aware you should treat shaded solar, as a pool - a hole in the ground you keep throwing money into. Any shade on a panel dramatically reduces the power output of that panel, even the shade of a twig. Panels have Bypass Diodes in them internally, which helps shunt power around the shaded portion, and reduces the voltage of the panel by a third. Some claim to be happy with shade on panels, but I will disagree, it's like they were born with with one eye, and don't grasp the concept of stereo vision. In sun my 5kw of arrays produce 4kw reliably, when shade crosses them, I loose half of that. Shade will increase your ROI / break even, and if you are off-grid, can cause a lot of generator run time to make up for missing production..

[Sunking]

You do not need to charge batteries to measure output. In fact it is a piss poor way because for the most part the panel will not produce full power charging a battery. When the battery is charged there is no power. All you need is a panel and a current meter. Use the meter to short out the panel and measure current through the day. Shade one cell and current falls off a cliff. On a bright crystal clear day in summer, you will see a bell curve. At sunrise very little current. as the day progresses current increases until noon at it peak, then tapers off to Zero by sunset. It is called Isc (current short circuit) test one of two test. The other test is Voc (voltage open circuit) which you can do with a flashlight.

Here is the test procedure.

[John Doe]

This is just a little hobby/tinkering/hacking prototype project, also partly due to that I have never own a panel and controller before. The way my house is I wont be able to get much solar power due to shading. Only a few square feet on the roof where I get sun all day. its kinda like buying a toy ferrari to play with for a bit when you know you cant afford one or the place where you like only allows 40MPH speed limit.

With 2 20W panels, a charge controller like below and battery like below, I'm not going to spend over $120. I dont plan on spending any more.

https://www.amazon.com/gp/product/B01LYW3EAP/ref=ox_sc_act_title_1?smid=AFHAE9RJVUMB&psc=1

https://www.ebay.com/itm/Vinsic-30000mAh-DC-2USB-External-Power-Bank-Portable-Charger-for-Phones-Laptop/182492425467?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

[PNPmacnab]

Your mileage may vary, At home I have two 280W grid tie panels (less than $170 each) only for product testing. At first glance my location doesn't seem that bad, on a hill and clear facing south. I only get one hour of full sun and most of a good day can maybe get 50W operating at the panels power point. You are far too shy on panels to do anything with. Two 20W panels have got to cost you more than that considering the prices you are paying for that other stuff. Get a GT POWER type power meter for your project and please don't spend any more than $10 for it.