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18650 battery charged with solar panel
#11
^^^ I did read carefully, but you haven't given enough info to answer that, e.g. the power used by the hotspot.
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#12
(08-24-2020, 07:28 PM)Hrvatin Wrote: Would lets say 10000mah be able to make this small hotspot work 24 hours during the summer?

Update : i just seen one battery is 3000mah,i really have no idea about capacity and usage, but since one battery is 3000mah i assume it takes lot more for 24 hour duration of hot spot work

Depends on the power requirements of the hotspot. Each router is different in how much power it uses. When there is no load, it'll be one value (for example maybe 100mA), and when it's at full load like streaming for instance it'll be a lot higher (for example, it could be as much as 1.5A or more).
You need to see what the power supply of the hotspot delivers. That'll give you a ball park figure to work towards. Some are 5V, some are 8V, some are 12V. I've even seen some at 15V (been a long time, tho).

Let's say it uses 5V @ 2A as the wall powersupply states on it. So that'd be 10W. Using the formula (Wh)/(V) =(Ah), then 10W / 5V = 2Ah; or 2000mAh. This is the power needed for 1 hour. If you want the hotspot to run 12hours, then you'd need 24Ah (24,000mAh) of capacity.
Notice I used the upper limits of the powersupply to determine the required capacity. This is so that you 1) are covered under max load 2) covered for when 100% stored capacity is not available; like during overcast, or someone sitting on the seat too long.

So if 1 cell = 2000mAh (2Ah), then you'd need 24 / 2 = 12 cells connected in parallel. Then to get the voltage of 24V (as mentioned earlier), you'd need 7 in series. 7 * 12 = 84 cells total.
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#13
(08-24-2020, 08:33 PM)Korishan Wrote: Let's say it uses 5V @ 2A as the wall powersupply states on it. So that'd be 10W. Using the formula (Wh)/(V) =(Ah), then 10W / 5V = 2Ah; or 2000mAh. This is the power needed for 1 hour. If you want the hotspot to run 12hours, then you'd need 24Ah (24,000mAh) of capacity.

That's not correct. Instead: 10W * 12h = 120Wh, and 120Wh/3.7V = 32.4Ah

But the 10W = 5V * 2A rating on the power supply is going to be more than it actually uses at full load. Also the 3.7V is only an estimate of the "average" voltage under (that) load - not to be confused with "nominal" (label) voltage of the cell.
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#14
(08-24-2020, 09:10 PM)gauss163 Wrote:
(08-24-2020, 08:33 PM)Korishan Wrote: Let's say it uses 5V @ 2A as the wall powersupply states on it. So that'd be 10W. Using the formula (Wh)/(V) =(Ah), then 10W / 5V = 2Ah; or 2000mAh. This is the power needed for 1 hour. If you want the hotspot to run 12hours, then you'd need 24Ah (24,000mAh) of capacity.

That's not correct. Instead: 10W * 12h = 120Wh, and 120Wh/3.7V = 32.4Ah

That would be correct. I didn't finish the calculation. But you left out an important note.

3.7V is the nominal voltage of the cells in parallel.

@gauss163: when giving help to newbies, please provide full details and not vague details. After all, we're looking out for the safety and proper way to work with these cells. Thank you.
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#15
^^^ No, 3.7V in my calculation is an "average" voltage estimate (not "nominal" = label) - see my edit (written before your post appeared here).  Generally the two needn't coincide.

Your error has nothing to do with "finishing". Rather it is due to a confusion between 5V vs. 3.7V - a common oversight (e.g. when determining the cell capacity of powerbanks using rated capacity at 5V USB). You can't "finish" a conceptually erroneous calculation.

Such capacity calculation estimates have nothing to do with "safety" (unless you are unsafe if your hotspot runs out of juice!).

If you think something is "vague" then you are more than welcome to ask for elaboration. But I can't read your mind so I have no idea what that might be.
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#16
(08-24-2020, 09:33 PM)gauss163 Wrote: see my edit (written before your post appeared here). Generally they needn't coincide.

You were editing while I was posting. Kinda hard to respond to a comment that didn't show up until after I posted Wink
Also, you edited the post at least 4 times

(08-24-2020, 09:33 PM)gauss163 Wrote: Your error has nothing to do with "finishing". Rather it is due to a confusion between 5V and 3.7V - a common oversight (e.g. when determining the cell capacity of powerbanks using rated capacity at 5V USB).

Such capacity calculation estimates have nothing to do with "safety" (unless you are unsafe if your hotspot runs out of juice!).

If you think something is "vague" then you are more than welcome to ask for elaboration. But I can't read your mind so I have no idea what that might be.

My error was not about confusion. It was an error of not finishing the calculation. There was still more math to be done. Enough said.

The vagueness was not for "me", but for the OP, who needs the correct guidance. Not sarcastic back talk.

Please stay on topic. Enough said on the side chatter and back to the OP's situation
Proceed with caution. Knowledge is Power! Literally! Cool 
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#17
(08-24-2020, 09:10 PM)gauss163 Wrote: 10W * 12h = 120Wh, and 120Wh/3.7V = 32.4Ah

So if the cells were 2000mAh, then you'd need 32400 / 2000 = 16.2 cells in parallel. 16 would be fine, though.
However, if you have actual cells that are 2500mAh, then that'd be 13.5 cells.

If using recycled laptop cells, I doubt you'll get much better than 2000mAh/cell, unless you have new packs.
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#18
(08-24-2020, 07:28 PM)Hrvatin Wrote: I have seen companies offering collored glass with /for panels. I suppose that is strengthen glass that mounts over the panel allowing you to sit on it. And they come in colors.

Would lets say 10000mah be able to make this small hotspot work 24 hours during the summer?

Update : i just seen one battery is 3000mah,i really have no idea about capacity and usage, but since one battery is 3000mah i assume it takes lot more for 24 hour duration of hot spot work


I hate it when all these things spec out xxxxx mAh. That only tells you half the story. You have the amps, but you need to know the voltage to know the actual power used. Like when a powerbank specs out 30000mAh. If I had a powerbank that is 1000V and 150mAh that would be equivalent to a 5V 30000mAh battery.

So let's start with a 3.5W of the hotspot.
3.5W * 24hrs = 84Wh
Therefore you need a battery that can provide at least 84Wh of power

So let's find the amount of batteries you need to power 84Wh
For example, using a single 2400mAh 18650 battery will put out 2.4Ah*3.7V = 8.88Wh
To power the hotspot alone you will need 10 of these batteries 8.8Wh * 10 = 88.8Wh
To be safe you need to have 20% more power than needed so 12 batteries would be good.

So now you have to figure out the solar panels needed to power this hotspot. You need to provide at least 100Wh to charge the batteries.
The amount of solar needed would be dependent on how the solar angle is to the sun and how much sun is being blocked. So I'm trying out a 50W panel and see what we can get out of it.
On a good day we can assume 50W * 4hrs = 200Wh.
But I'm going to factor in ineffeciencies in the solar charge controller that you would need, weather and etc, so let's do a safety factor of 2.
So let's say you have only 2 hours of good sun, ie. from 11am to 1pm (where the sun is almost overhead)
50W * 2hrs = 100Wh.
So I'd say a 50W panel will probably be enough to charge the battery to run the hotspot.

If you plan on charging devices along with it, then you need to plan on how much power you need to charge the devices. That would mean calculating the power of the devices needed. Then go back through the above and factor in how much power is needed.
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#19
In a nutshell: to get Wh = W*h from Ah = A*h we need to multiply by V = (average) voltage (by W = V*A, i.e. Watts = Volts * Amps), i.e. W*h = (V*A)*h = V*(A*h)

But the voltage is often omitted in spec's, e.g. for a 10Ah powerbank, is 10Ah the total cell capacity (at 3.7V), or is it the capacity at 5V USB output? Unscrupulous manufacturers often list the higher cell capacity - misleading users into believing that is the 5V USB capacity. But that is actually much less, e.g. after buck/boost loss (say 85% efficient) we get 0.85 * 37 = 31.4Wh = 6.3Ah(@ 5V USB), not 10Ah.
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#20
Could i connect all that using lets say 30 of these mini panels?

https://www.seeedstudio.com/2W-Solar-Pan...edium=blog

Ok, managed to find some more ifno regarding hot spot. It says next
Power consumption : <3.5w
Charger : AC 100-240V, DC 5V 1A
And it comes with 1500mah battery, claiming it lasts up to 6 hours

Sorry for so many questions that make you no sense, my knowledge about electricity is close to none. If yoi have some internet service questions i will gladly help ?
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