# How to determine the needed solar panel

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#### poxkix

##### Member level 5
I have a deep cycle golf cart battery -> 6v 235A

How do I compute/determine the solar panel needed to charge this battery? thanks.

#### goldsmith

Hey guy!
6*235=1410VA you will need solar cell with 6 volts and 300Amperes.
You can use some solar cell in 6 volts in parallel as well as

#### poxkix

##### Member level 5
@goldsmith
how did you come-up with 6 volts and 300Amperes? How does it relate to the 1410VA?

#### goldsmith

Again Hi
my mean is : if your current being 300 Amperes , your battery will charge soon, but its life will decrease. you need lower than this type but time of charging will increase! and about 1410 VA: in some of countries , price of solar cell will calculate with its power.
Best wishes
Goldsmith

#### poxkix

##### Member level 5
@goldsmith
What you mean is 6v 300A will charge the battery in more or less 4hrs?
okay what is the importance of 1410VA?

#### kak111

Solar cells required depends on the power consumption,
the battery is only a energy buffer for times when the solar cells do not produce energy

Simple example

If the consumption is 2kwh / day and the sun gives energy 10 hours / day.
Charge should be dimensioned so that the battery is fully charged after this 10 hour period

Needed energy from solar cells is normal consumption + charge needed for battery calculated so that
battery can take full charge during these solar hours.

2kWh = 2000 VAh >> 2000VAh / 6V = 333 Ah per day. >> average current is 333Ah / 24h = 14A for normalized consumption

"Dark hours" 14 h * 14 A = 196 Ah this is used from battery at night
"Sun hours" 10h * 14 A = 140 Ah this is used at day time

So charging battery needs those 333 Ah in 10 h = 33.3 A current from solar cells in 10 h period / day

Of cause consumption varies during day / night , but with this example you can evaluate and calculate
the needed current magnitude for charging.

KAK

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#### Raza

HI poxkix,

I have a deep cycle golf cart battery -> 6v 235A

How do I compute/determine the solar panel needed to charge this battery? thanks.
You did not mention what will be your discharge cycle of the battery. You are asking only for charging energy from Solar Cells. If this then kak111 gave you the best calculation guide.

#### poxkix

##### Member level 5
Sorry. I forgot some details.
Actually the battery will be used as a source for 4 docks, each dock will be used to charge mobile phones. My problem is, the only info I got regarding the phones is that they are 3.4v. Can I determine the power consumption by just this information?
So the total discharge is the total of each dock multiplied by 4 an hour. Am I correct?

#### Raza

Hi poxkix,
For such a big battery this load is nothing. A modern mobile phone of this age consumes only 100mA to 300mA in nominal situation for charging the battery. The voltage (in general) of a mobile phone battery is 3.7 volts.
I also repair the Mobile Phone chargers and to experience the chargers are 5~6 VOLTS DC with 500~800mA output current. Now if you take all the four docks connected same time their max consumption may be 4x0.8A=3.2A. Even if you keep them 24 hours connected the max energy consumed will be (in AH) 3.2Ax24=76.8AH which is just nothing for such a (300AH) battery.
To my opinion you need just 100 watts Solar Panel for your battery.
Any further query welcomed.

#### poxkix

##### Member level 5
@Raza
How does the 235A contribute in the calculations? Or what does it mean?
uhhm, 3.7v is equivalent to how many A?
With a 100w panel, how many hours will it take to charge the battery?

#### kak111

Simple words..... and picture ........

1. Imagine that battery is a tank for energy.
- energy tank is full when there is 235 Ah ( Ampere hour )

2. All the time energy is used 3.2 A (Ampere) (flows out from tank)
- so in 24 hours it flows out 3.2 A * 24 h = 76.8 Ah

3. When sun is shining solar cells gets energy ,
solar energy transforms to electric energy in solar cells.
Charger convert voltage suitable for battery ( 6V battery needs 7V for charging)
During time when sun gives energy , the tank for energy should be filled full.
ie. tank (battery) needs 76.8Ah during solar hours.

If system get energy from sun 10 h / day, charger must give flow into tank X A.
X = 76.8Ah / 10h = 7.68A

If system get energy from sun 7 h / day, charger must give flow into tank X A.
X = 76.8Ah / 7h = 10.97A

Charger must take care that tank is not filled over.
ie. cut off charging when battery voltage is 7.2V.

4. Because tank capacity is 235Ah , the full battery has energy for 3 days used with this load.
This is used for reserve , cloudy days etc..

5. These are theoretical values for charger and load.
If we guess effiency is 0.75. then...

needed solar system power for 7h sun / day is (11A * 7V ) / 0.75 = 103 VA ( This is power for solar system )

I would like to take 150...200W system.

Hope this helps you forward.

KAK

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#### poxkix

##### Member level 5
@kak111
Now i'm beginning to understand how it works.
I still have follow-up questions, how/where did you get the 3.2A?
Because at some batteries I checked it only supplied the information 3.7v. Nothing else. How will I determine that battery's amperes or watts?
And other batteries have a complete info like 3.7v 950mAh 3.6Wh.

#### kak111

In picture i take an example , there is 4 pieces identical loads , every one is taken 800mA current out from battery , ie. 4 * 800mA = 3.2A.

If every phone needs 450mA current ,when it is on , then this value is 4*450mA=1.8A and needed Ah/day is 24h*1.8A = 43.2 Ah.

Value you checked on battery is capacity of battery.
This value is not needed in these calculations, we need only know value of current taken from 235Ah battery.

KAK

#### poxkix

##### Member level 5
Yosh! Now I understand.
I can now compute the needed solar panel, one thing confuses me though.
We assumed here that all the loads are identical, what if the loads differ? For example, the 1st phone needs 950mAh, the other is 700mAh. How do I act on this problem?
Here, when we charge a phone we need a charger, right? For example. The needed source of a charger is 110v. Now, my battery bank only supplies 6v 235Ah. How will this be done? I've heard of a step down power converter (like 110v to 24v) but is there such thing as step up (6v to 110v)?

#### john007007

##### Newbie level 2
hi friend !
today, the scientists have done many type of experience related with solar back up energy. and it is successful.
there many types of batteris whch are charged with solar energy.
thank u

Event Management Company

#### kak111

when we charge a phone we need a charger
For charging phone you need voltage regulator from battery voltage to phone voltage.
( Battery voltage is 7.2V...5.5V )

Inverter 6Vdc / 110Vac is not good solution.
First to 110Vac and then back to 5Vdc ( depend on phone)
Efficiency can be 0.6...0.7
and you will lose all this energy for nothing in converters.

For example.............
You need something like these circuits from battery to phone...........

USB Powered Mobile Phone Battery Charger Circuit Diagram

http://www.discovercircuits.com/DJ-Circuits/images/5vsolarcharger/5V SOLAR CHARGER 1.pdf

KAK

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#### poxkix

##### Member level 5
Oh my! I didn't notice that. It is the total battery load. Thank you for the heads up.
So you mean to say, instead of using the standard charger, I'll make my own circuit?

#### kak111

If you somehow can leave out the 110Vac converter,
you save perhaps 1/3 or 1/4 of the energy taken from battery.

Here is booklet for Nokia 2-mm DC Charging Interface Specification
Look page 17

When a charger is connected to the mobile device, the device's system will start the chargerrecognition
procedure by checking the charger voltage with 1 – 2 mA current. Identification is based
on measured average voltage and waveform: 4.65 V – 5.20 V is identified as a special charger and 5.5
V – 9.3 V is identified as a standard charger.

http://www.herjulf.se/solar/charge-..._Charging_Interface_Specification_v1_2_en.pdf

KAK

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#### poxkix

##### Member level 5
oh.. A lot of things are to be considered. I thought my project would be this easy.
Okay. I'll be using the first link you gave me, with some modifications on the circuit I think I can make it happen.

Sorry for this sir, but I still have lots of questions.
I done a search, I found that some phone batteries differ in mAh. Why is that? What is its purpose?

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