# How to calculate the battery usage ??

Discussion in 'Renewable Energy' started by AskerOfGeeks, Oct 11, 2013.

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MY PLAN IS TO USE A SOLAR PANEL TO CHARGE A MOBILE PHONE.

THIS IS MY SETUP
12V 10W SOLAR PANEL -> HEAVY DUTY Solar Panel Charge Control/Controller 12V/24V 10A 10 AMP -> SMF UPS BATTERY 12V 7.0AH -> 12VDC TO 5.7VDC CONVERTER -> USB female port -> DATA CABLE -> MOBILE PHONE ( 3.7v 1200mah)

I WOULD LIKE TO KNOW
1. if i am using this 12V 7AH to recharge 3.7V 1.2AH battery, how many times i wud be able to recharge this 1.2ah battery ?? (is it 7ah / 1.2ah = 5.8 times ??)
2. 12VDC TO 5.7VDC CONVERTER = MC34063A based. So tell me how much loss (if there is me a newbie in electronics ) does this makes wen it is charging this 1.2ah battery at 350ma at 5v

pls ask me for more details if u guys think something is missing i dont know, did i missed anything to mention

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2. ### MikeMlWell-Known MemberMost Helpful Member

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Since the 10W solar panel delivers only 0.8A in full sun, the charge controller is overkill, and may be inefficient, say only 50%. To fully charge the 7Ah battery, it is going to take >(7/0.5)/0.8 = 17.5 h of bright sun.

The efficiency of the MC34063 down-converter is likely ~75%. The efficiency of the charging process inside the cell phone is likely to be ~80%, too. To get 1.2Ah into the cell phone, you will likely need (1.2/0.8)/0.75 = 2Ah out of the battery, so only about three full recharges...

Doesn't a device that expects charging via USB want only 5.0V?

If it was me, I would have used a 6V SLA.

Last edited: Oct 11, 2013
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so considering ur advises i redesigned my setup
the new setup is as follows but pls fill in some values tat i am not able to calculate

1. 6V 5W SOLAR PANEL x 4 in parallel = 6V 20W (is MAX OUTPUT 20W/6V = 3A ??)
2. 6V 5A or above rated Float Charge Controller with discharge protection ( pls giv a link for the circut diagram with best efficiency if u know one )
3. SLA BATTERY 6V 4AH X 2 in parallel = 6V 8AH (?)Ac* (?)Ad**
4. 6VDC TO 5VDC CONVERTER 500ma supported (i took it out of a 12V car FM transmitter. will it support 500ma ??)
5. USB female port
6. DATA CABLE
7. MOBILE PHONE ( 3.7v 1200mah)

one more doubt if u pls
is there a way to calculate the
*charging current Ac
of an sla battery if we know only the volt and ah ?? ( most of those batteries dosent come with all those details )

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5. ### MikeMlWell-Known MemberMost Helpful Member

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Read up on the following topics:

Discharging

Calculating Runtime

Charging from a USB port

A solar panel suitable for charging a 6V SLA battery should have an open-circuit voltage of ~12V.

A charge regulator to terminate charging of the 6V SLA battery could be a simple shunt regulator.

I wouldn't use a switcher between the SLA and cell phone. A LDO linear IC regulator chip could drop the 6. 3V from the battery to the required 5V at the input of the cell phone. The power wastage here is not very significant.

How long does it take for the cell phone to charge from USB(5V)?

6. ### audioguruWell-Known MemberMost Helpful Member

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DO NOT EVER charge a 3.7V Lithium battery from 5V because it might blow up and might catch on fire.
The cell phone has a Lithium battery charger circuit inside that has a 5V input and its output properly charges the 3.7V Lithium battery then turns off when it detects a full charge.

7. ### MikeMlWell-Known MemberMost Helpful Member

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AFAIK, the OP was planning to just supply 5V to the cell ph0ne and let the internal charger take care of it.

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8. ### audioguruWell-Known MemberMost Helpful Member

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I mentioned it because he talked about his "MOBILE PHONE ( 3.7v 1200mah)" which sounds like the spec's for his battery.

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tanks for ur tip audioguru
but my plan is exactly wat mike said
"AFAIK, the OP was planning to just supply 5V to the cell ph0ne and let the internal charger take care of it."

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mike i didnt just left you. i will be back wen i finish reading those links that u provided me ok

11. ### NorthGuyWell-Known Member

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Why do you want to use an interim battery? It is possible to charge your phone directly from the solar panel using simple controller.

Lead-Acid batteries are difficult to deal with - you cannot fully discharge it, and you need to make sure it is fully recharged at least once a week. To meet these requirements, you may need a two-stage controller.

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ya u r right bro

i first planned to charge mob using the panel directly but then i thought of one obstacle in it. i might be charging the mob while traveling and if i do it, it wud be a discontinuous process as the road will be having shaded area and bright sunny area. during this time the phone's charger will be going through charging and charger disconnected mode vigorously and i thought this wud damage its controller also it wud be disturbing for me to see those notifications on the screen as i wud be watching movies or browsing net in it

but using an sla in between can help me stabilize this ( i think ) tats why i included an sla

but if u think a direct charging is better then pls help me
my needs
1. need to charge a 3.7v 1200mah to its full charge as fast as possible ( charging at its max rated charging current, i think its not more than 500ma at 5v(its charger had these ratings ))
2. i can stop by somewhere to charge directly using panel (so sla is not an issue anymore (also i can avoid sla's weight )

i just want you or some one to help me calculate the voltage and watt of the solar panel that can provide a continuous supply not less than 5v (even during dim light conditions) and 500ma of current. plssss helppp

MY PRESENT SETUP
1. ? V ? W SOLAR PANEL
2. 12 - 6 VDC TO 5VDC CONVERTER 500ma supported (i took it out of a 12V car FM transmitter. will it support 500ma ??)
3. USB female port
4. DATA CABLE
5. MOBILE PHONE ( 3.7v 1200mah)

13. ### audioguruWell-Known MemberMost Helpful Member

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When a solar panel is not pointing directly at the sun then its voltage and current are low.
That is why a solar panel moves so that it is always facing the sun.

When a solar panel is shaded then its voltage and current are very low.
That is why a solar panel is never shaded. Also that is why a windmill generator is usually seen beside a solar panel so a battery can be charged even when it is cloudy.

Please (pls?) type in English with proper spelling bro (broken?) so that we wud (wood?) understand wat (watt?) u r (you are?) toking about.

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14. ### Al ManzoliMember

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I totally agree !

Please take a few extra minutes and write legibly.

I am an old curmudgeon , but I would rather not call in the grammar police or the spelling police .

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15. ### NorthGuyWell-Known Member

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You phone already has a charger in it, so all you need to do is provide 5V from the panel. Solar panels act mostly as a current source. A capacitor followed by a voltage converter/regulator should be able to do it.

Of course if you shade the panel, it will not produce anything (may be few percent of nominal). Will also jump up and down as clouds pass by. I don't think it would damage the charger because it must be designed so that you can plug/unplug it at any time. I do it few times a day with my phone, and it's fine. If you're afraid of voltage sugging, you may need some sort of brown-out protection.

If you're driving, it is much easier to charge the phone from your car.

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you are not helping

please replay to this if u can

my needs
1. need to charge a 3.7v 1200mah to its full charge as fast as possible ( charging at its max rated charging current, i think its not more than 500ma at 5v(its charger had these ratings ))
2. i can stop by somewhere to charge directly using panel (so sla is not an issue anymore (also i can avoid sla's weight )

i just want you or some one to help me calculate the voltage and watt of the solar panel that can provide a continuous supply not less than 5v (even during dim light conditions) and 500ma of current. plssss helppp

MY PRESENT SETUP
1. ? V ? W SOLAR PANEL
2. 12 - 6 VDC TO 5VDC CONVERTER 500ma supported (i took it out of a 12V car FM transmitter. will it support 500ma ??)
3. USB female port
4. DATA CABLE
5. MOBILE PHONE ( 3.7v 1200mah)

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i know

MY PRESENT SETUP
1. ? V ? W SOLAR PANEL
2. 12 - 6 VDC TO 5VDC CONVERTER 500ma supported (i took it out of a 12V car FM transmitter. will it support 500ma ??)
3. USB female port
4. DATA CABLE
5. MOBILE PHONE ( 3.7v 1200mah)

from the above setup, component (2) is used to regulate the voltage to 5v

i am now planning to charge directly from panel ( i did mention it earlier and i want u to give me the values of voltage and watt of the panel that i need for my setup help me please )
"1. ? V ? W SOLAR PANEL"
replace "?" with values

what's sugging and brown out protection ??

no i dont travel much in my personal vehicles

19. ### audioguruWell-Known MemberMost Helpful Member

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I think you need a massive solar panel. It will be expensive and difficult to carry. In direct sunlight its voltage and current will be much too high so you will need a voltage and current regulator.
When it is cloudy and if it is huge enough then it will charge your phone slowly.
In the shade it will do nothing.

20. ### NorthGuyWell-Known Member

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I know my phone charges in about an hour (a little bit faster, actually). Assuming it uses 70% of battery capacity, this is 1300 mAh x 0.7/1h = 900 mA. So, you should expect the phone charger to need about 1A. This, of course, depends on the phone. So, 500mA may not be enough. But you can always try this by connecting your 5V regulator to 12V wallwart and measuring the current draw. It'll probably be the highest on severely discharged phone.

On the panel. You need it at least 5V + whatever is the maximum voltage drop on your regulator. 6V might work, but 12V will work better.

If your regulator is a switching one, you need to provide 1A*5V = 5W. With 80% efficiency, it'll give you 6.3W. This is a panel the size of a big book.

If your regulator is liner, you need 1V*12A = 12W. This is quite a big panel.

These numbers are for panel turned directly towars the Sun in ideal conditions.

Most of the time, you probably will need a panel twice as big.

If you want to charge in the cloudy weather, you need a panel about 10 times as big. Just as audioguru said, this is an enormous panel, and probably is not worth the effort. So, I would size the charger for sunny days only.

Your original idea with LA in between would let you slow down the charging, so you would need smaller panel, but then you would need much longer exposure. You would also need to account for losses and inefficiencies in LA.

I don't agree that it is difficult to handle high current from the panel. A capacitor placed accross the panel will take care of it. As the capacitor charges, the voltage will raise and therefore the current from the panel will decrease. When voltage increases to panel's Voc (which is only 20% more than production voltage) , it will be no current at all.

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"1A" how its possible ??!! my phone's charger is only rated for 5v, 350ma max. and it takes around 2hrs or less for a full charge from around 30% charge state ( this may not be not accurate but an approximate ) i am happy with this rate of charging. so i just want a system that supplies "5v and 350ma" i dont think this is too much to ask

so to replace the power plug charge with a solar panel, that solar panel just need to supply 5v and 350ma ( just leave the regular alone for now )
but i even went to a design were the panel was 6v and 20w but that too dint seem to satisfy u guys

"6V 5W SOLAR PANEL x 4 in parallel = 6V 20W (is MAX OUTPUT 20W/6V = 3A ??)"

this panel is capable of supplying 3A. but we need only 350ma. and this 6v panel is capable of supplying 8v to 9v at bright sunlight. now tell me wats wrong with the below setup.

6V 5W SOLAR PANEL x 4 in parallel = 6V 20W (3A) -----------> 5v regulartor ----------->USB female port -----------> DATA CABLE -----------> MOBILE PHONE ( 3.7v 1200mah)

again "i only want less than 350 ma" for my mobile phone. tats wat the original charger of the mobile phone can supply.

i guess step charger wud maintain a constant current through out the charging period frm severely discharged state to the full charge state. and thats wat the mobile phone in built a charger is i think

now u started to answer abt my setup right ??
i mean this following one
MY PRESENT SETUP
1. ? V ? W SOLAR PANEL
2. 12 - 6 VDC TO 5VDC CONVERTER 500ma supported (i took it out of a 12V car FM transmitter. will it support 500ma ??)
3. USB female port
4. DATA CABLE
5. MOBILE PHONE ( 3.7v 1200mah)

ok i will get a panel that will giv out 6v or more even during average sun light ok ( tat is never goes below 6v during average sun light )

1. i dont no wat liner or switching regulator are
2.u sud tell me whether the regulator inside a car's FM transmitter is switching or linear type its a "12VDC TO 5.7VDC CONVERTER = MC34063A based"
3.so panel watt will be either 5w or 12w

oh ok ok

ya i am gonna keep a spare 6v 4.5AH SLA fully charged frm a wallwart with me to use as a backup not gonna charge it using panel as its a time consuming process

are u trying to take avay the regulator and use a capacitor to protect the mobile phone frm high voltage and current frm the panel ?? i didnt get wat u r trying to say here

thanks for spending ur precious time to help me