Newbie questions

[georgia088]

Hello and thanks in advance for any help and with patience for my stupidity. I wanted to learn the basics of solar power/ dc/ac inverting, and I have a dock that I wanted some power at. So, I decided to purchase the Harbor Freight 100w Solar kit (yes I know this is a cheap set and maybe even worthless). However, I didn't want to break the bank, and I just want to tinker with it.

So, this is what I have the Harbor freight panels, charge controller, and a HF 750/1500 peak inverter. I have a 101ah deep cell battery from Wal-Mart to store the energy. I am attempting to power some small wireless devices to keep internet at the dock full time (ubiquiti nanostation, wireless switch, 2 ip cameras). This leads me to my first question. I look on the back of these devices to see how many amps they draw.

If the back says .5a @ 24 volts does this mean that it will draw 1 amp @ 12v per hour that it is connected (totaling 24amps in a day)? They don't all give this information, but on the power adapter it will say the input/output power. Which do I look at? I would assume you look at the output power. I think I understand how to convert from amps to watts and vice versa, but when I do I don't understand if this is how much the device is drawing per hour because some say "at max"?

Another question I have, I understand that you should never draw a battery below 50%. So, for my 101ah battery this would be about 50ah. I assume as the amps are drawn the voltage will drop. I had a problem with the inverter buzzing and the controller giving a low voltage warning with these small devices. Even though, for the life of me I can't figure out how they are drawing too much from my battery.

Is my system just undersized to run these 4 wireless devices (all reading about .5a) around the clock? If so, what would I need to add? a battery? more panels? a bigger inverter?

I guess I should add, I am figuring I am receiving at least 4-5 hours of good sun/day. They are mounted to the roof of the dock facing southwest. I am located 45 miles southwest of Atlanta in Georgia.

I know that is a lot of questions, but any help would be greatly appreciated!



Thanks!

[SunEagle]

Quick rule of thumb for FLA type batteries is that you need the charging amps to be 1/10th the Ah rating of the battery. So about 10.1amps which I seriously doubt that HF 100 watt system can provide so you are short on panel wattage.

I am curious about those loads. Do they require 24 volts or 12 volts to run. Since your battery is only 12V then your loads better work on that voltage or they could be draining your battery faster they you calculated.

If they can run on 12volt then you are looking at 4 x 0.5amps or 2A x 12V = 24watts x 24 hours = 576 watt hours a day. You really need a 200Ah system to safely run that load daily to keep the discharge to 25% of the system. A 50% discharge will kill a battery quickly.

Also with a 200Ah battery you would need about 400watts of panels.

[georgia088]

I guess I didn't explain everything very well. The wireless device I am talking about has a POE (power over ethernet) adapter. So the input is 120v and it changes the voltage to the 24v @.5 amps atleast thats what I assume.... I have them running through my inverter to be powered.

I have 4 of these devices running (actually two and two ip cameras that I am assuming use about the same power) ..... so following your math would I need 4 times what you are calculating to run these (1600 watts of panels and 800ah of batteries)?
I think I answered my own question. I see where you multiplied .5amps x 4 to get 2a. So, that should mean I will need 200ah battery and 400 watts of panels to supply this.

So, on the back label of a power supply do you look at the output power to figure how much it is using? My 101ah battery will supply 1212 watt hours is this correct?

Thanks so much for your help!

[SunEagle]

I guess I didn't explain everything very well. The wireless device I am talking about has a POE (power over ethernet) adapter. So the input is 120v and it changes the voltage to the 24v @.5 amps atleast thats what I assume.... I have them running through my inverter to be powered.

I have 4 of these devices running (actually two and two ip cameras that I am assuming use about the same power) ..... so following your math would I need 4 times what you are calculating to run these (1600 watts of panels and 800ah of batteries)?
I think I answered my own question. I see where you multiplied .5amps x 4 to get 2a. So, that should mean I will need 200ah battery and 400 watts of panels to supply this.

So, on the back label of a power supply do you look at the output power to figure how much it is using? My 101ah battery will supply 1212 watt hours is this correct?

Thanks so much for your help!

A 101Ah 12volt battery can provide 1212 watt hours but that is 100% discharge and you won't be able to get that out of it more than once. Even a 50% discharge of 606 watt hours will shorten the life of the battery.

Using your information, each unit will use 0.5amps at 24volts then that comes to about 12 watts each (24v x 0.5A = 12W). 4 of them will use 48 watts and over a period of 24 hours that comes to 1152 watt hours or more total.

So you need at least a 300Ah battery or bigger to make sure you don't discharge it more then 30%. A 50% discharge is ok for once or twice but doing it daily will kill off the battery system quickly.

If you have a "kill a watt" meter you can actually measure what you would use over a period of a couple of days which might be less then 1152 watt hours per day. Knowing that will help you size your battery system better.

[georgia088]

Ok, I think I am understanding it much better. So, I went back and checked and this is what the actual readings are on the power supplies output (I was just giving you a guestimate, and I was wrong, sorry) Do you mind checking me and see if I am understanding.

ubiquiti (24v @ .5 A) = 12 watts
wireless switch/router (12v @ .5A) 6 watts
IP camera 1 (1000ma @ 5v) 5 watts
IP camera 2 (1200ma @ 5v) 6 Watts
Access Point (24v @ .5 ) 12 Watts (I am going to eliminate this unit because it is not necessary.

So, if I eliminate the AP and total up the other devices, I get 29 Watts. Multiplied by 24 hours gives me 696 Watts in a day. If you still need 70% of your battery when the 696 watts are used, I would need 2320 watt hours of battery or 193 AH. This would require about 19.3 amps coming in from solar panels. Does this sound correct?

Also, I have read not to mix old batteries with new, but is the downside of this it will damage the new battery?

Thanks again for all of your help!

[Sinjin]

I applaud you trying to do the math, but, um.. the output of a wall wart (I.e., a small AC powered electronic device with its own DC power supply) rarely matches the AC input because they are (typically) horrendously innefficient.

My $.02, follow SunEagle

[SunEagle]

Ok, I think I am understanding it much better. So, I went back and checked and this is what the actual readings are on the power supplies output (I was just giving you a guestimate, and I was wrong, sorry) Do you mind checking me and see if I am understanding.

ubiquiti (24v @ .5 A) = 12 watts
wireless switch/router (12v @ .5A) 6 watts
IP camera 1 (1000ma @ 5v) 5 watts
IP camera 2 (1200ma @ 5v) 6 Watts
Access Point (24v @ .5 ) 12 Watts (I am going to eliminate this unit because it is not necessary.

So, if I eliminate the AP and total up the other devices, I get 29 Watts. Multiplied by 24 hours gives me 696 Watts in a day. If you still need 70% of your battery when the 696 watts are used, I would need 2320 watt hours of battery or 193 AH. This would require about 19.3 amps coming in from solar panels. Does this sound correct?

Also, I have read not to mix old batteries with new, but is the downside of this it will damage the new battery?

Thanks again for all of your help!

Based on your math a 200Ah battery should work as long as you have about 20amps of charging.

The problem is sometimes math is only good on paper and not in real life. So you can try a system around 200Ah but it should all be new because you are correct it is not good to mix old with new batteries because the new one will drop down to the condition of the old relatively quick.

[drfart]

Hey i have a similar question and can't figure out how to post a new thread. I am working on wire sizing for my system. I have 2 100 watt solar panels wired parallel. I have a 45 amp morningstar tristar pwm CC. I have 2 12v 100amp AGM batteries. I have yet to purchase an inverter. The run from panel to CC is about 12 feet and I have sized at 8AWG. From CC to battery i have 10AWG cables for a 4 foot run. wiring the batteries in parallel i have 1/0 cable for a 2 foot run or less. The same wire is to be used for the future wiring of likely a 800w pure sine wave inverter which will also be about a 2 to 4 foot run. Do these wire sizes sound correct?
The next question is regarding fusing. going from my 2 100watt solar panels to a 45 amp controller, is there a need for a fuse being that the CCs rating is for so much larger an array? What are the parameters for sizing fuses from CC to batteries and then batteries to inverter? All basic utilities are to be wired into a 12vDC marine switchboard that comes pre breakered, should a fuse go between the batteries and that switchboard?
thanks
Dr.Fart

[Sinjin]

Do these wire sizes sound correct?

I found this image, posted by Sunking in another thread, sums it up pretty well.

DBC50361-232D-4130-BE83-4C74B4E00A44.jpeg

The next question is regarding fusing. [...] should a fuse go between the batteries and that switchboard?

I

[drfart]

when i open that it says invalid file specified