### Author Topic: Battery bank and solarrrrrrr  (Read 1425 times)

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##### Battery bank and solarrrrrrr
« on: September 26, 2018, 01:53:10 pm »
Hello,
I have 4000mah 3.7V battery and 4000mah means that it draws 4A for the whole time in one hour (https://www.ifihomes.com/blog/how-much-time-it-takes-to-charge-a-solar-power-bank/).

Is this means that it's output current is 4A? What is the meaning of draw here? Is this mean that 4A is the maximum current it holds?

How much voltage and wattage of solar cell need to charge this battery?

Thanks

#### grifftech

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##### Re: Battery bank and solarrrrrrr
« Reply #1 on: September 26, 2018, 02:07:03 pm »
you need a charge/protection board for lithium batteries, solar panel voltage should be 5 volts wattage is not as important, more watts = faster charge

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#### m98

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##### Re: Battery bank and solarrrrrrr
« Reply #2 on: September 26, 2018, 02:26:30 pm »
Ahoy!
4000 mAh means that you could draw a current of 4 A for one hour from that cell. 1 Ah is just another unit for charrrge and equals 3600 Coulomb.
Discharge and charge current capability is something different. For a Li-ion cell you should rather pick something like half the nominal charge per hour, in this case 2 A. For discharge you can usually go up to twice nominal capacity per hour, 8 A.
For plundering the sun using you could use a simple linearrr charger module and a 5 V 10 W solarrrr cell.

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##### Re: Battery bank and solarrrrrrr
« Reply #3 on: September 26, 2018, 03:39:32 pm »
Ahoy!
4000 mAh means that you could draw a current of 4 A for one hour from that cell. 1 Ah is just another unit for charrrge and equals 3600 Coulomb.
Discharge and charge current capability is something different. For a Li-ion cell you should rather pick something like half the nominal charge per hour, in this case 2 A. For discharge you can usually go up to twice nominal capacity per hour, 8 A.
For plundering the sun using you could use a simple linearrr charger module and a 5 V 10 W solarrrr cell.

I am using a battery which have already builtin protection circuit. And I am using 4 these kind of battery which attached in parallel way to get 3.7V and 16000mah capacity. Do I need more protection circuit?

#### sleemanj

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##### Re: Battery bank and solarrrrrrr
« Reply #4 on: September 27, 2018, 02:58:51 am »

Is this means that it's output current is 4A? Is this mean that 4A is the maximum current it holds?

No.

Just because a cell is 4Ah does not mean you can draw 4A (for an hour), the cell might only be able to supply 1A continuously, just it can do that for 4 hours.

Similarly, it goes in the other direction too, very high current Lithium Ion Cells for example might be able to discharge at 50A or 100A or more, but not for very long.

Furthermore the more current you draw (instantaneous current) the less capacity (current over time) you can extract, that is to say "4Ah" might be true only at a current draw of 500mA (for 8 hours), and if you draw 4A maybe you would only be able to do so for 45 minutes.
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#### sleemanj

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##### Re: Battery bank and solarrrrrrr
« Reply #5 on: September 27, 2018, 03:02:22 am »
Andreas Spiess did some videos on exactly the topic, you should watch them

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#### Zero999

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##### Re: Battery bank and solarrrrrrr
« Reply #6 on: September 27, 2018, 09:36:07 am »
Something is required to limit the voltage to no more than 4.2V per cell. The charging current should also be reduced, if the cell voltage is lower and if the cell voltage is below a certain level, it should be discarded and never recharged. The voltage thresholds for lower charge current and no charge can be found on the cell datasheets or through a search engine.

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##### Re: Battery bank and solarrrrrrr
« Reply #7 on: September 27, 2018, 01:58:10 pm »
Something is required to limit the voltage to no more than 4.2V per cell. The charging current should also be reduced, if the cell voltage is lower and if the cell voltage is below a certain level, it should be discarded and never recharged. The voltage thresholds for lower charge current and no charge can be found on the cell datasheets or through a search engine.

I used this battery http://www.ventor.co.in/lithium-ion-polymer-battery4000mah37v-p-478.html which have built in circuit. And after having built in circuit sill I need a circuit to limit voltage? I am using 4 battery (4000mah) in parallel to make it 16000mah.

Also, If it already has a built-in circuit then still it not get charged after getting discharge fully? If yes, what do I do to prevent this? What is the concept of the circuit?

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##### Re: Battery bank and solarrrrrrr
« Reply #8 on: September 27, 2018, 01:59:00 pm »
Andreas Spiess did some videos on exactly the topic, you should watch them

Thanks for sharing. It is so much informative:)

#### Zero999

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##### Re: Battery bank and solarrrrrrr
« Reply #10 on: September 27, 2018, 07:01:04 pm »
Your battery is only specified to be 4000mAh, at a discharge rate of 0.2C, which is 0.2*4000 = 800mA. A faster discharge rate will quite likely reduce the capacity somewhat. The maximum discharge rate is 1C, which would be a current of 4000mA or 4A.

The maximum charge current is 0.5C, which is 2000mA or 2A, so the solar panel should never output more than that current, otherwise it could damage the cell.

The recommended charge voltage is 4.2V, with 4.3V being the absolute maximum, so there needs to be a circuit which limits the voltage at that level.

Interestingly the cell is specified at 4000mA, with a lower cut-off voltage of 2.75V, but later on in the data sheet it recommends an under-voltage protection circuit which activates at no less than 2.8V. Perhaps this is 2.75V rounded up? I don't know.

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##### Re: Battery bank and solarrrrrrr
« Reply #11 on: September 28, 2018, 01:12:37 pm »
Your battery is only specified to be 4000mAh, at a discharge rate of 0.2C, which is 0.2*4000 = 800mA. A faster discharge rate will quite likely reduce the capacity somewhat. The maximum discharge rate is 1C, which would be a current of 4000mA or 4A.

The maximum charge current is 0.5C, which is 2000mA or 2A, so the solar panel should never output more than that current, otherwise it could damage the cell.

The recommended charge voltage is 4.2V, with 4.3V being the absolute maximum, so there needs to be a circuit which limits the voltage at that level.

Interestingly the cell is specified at 4000mA, with a lower cut-off voltage of 2.75V, but later on in the data sheet it recommends an under-voltage protection circuit which activates at no less than 2.8V. Perhaps this is 2.75V rounded up? I don't know.

So, this mean that
Charging current to battery which output's from the solar panel lies between : 800mA - 2A ( 0.2C - 0.5C)
Discharging current : 800mA - 4A (0.2C - 1C)
Am I right?
If yes, then can I use solar panel of 5V 1A ? Because I somewhere read that solar voltage is bit (around 1V) greater then battery voltage. Am I right?

#### Zero999

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##### Re: Battery bank and solarrrrrrr
« Reply #12 on: September 28, 2018, 08:41:26 pm »
Your battery is only specified to be 4000mAh, at a discharge rate of 0.2C, which is 0.2*4000 = 800mA. A faster discharge rate will quite likely reduce the capacity somewhat. The maximum discharge rate is 1C, which would be a current of 4000mA or 4A.

The maximum charge current is 0.5C, which is 2000mA or 2A, so the solar panel should never output more than that current, otherwise it could damage the cell.

The recommended charge voltage is 4.2V, with 4.3V being the absolute maximum, so there needs to be a circuit which limits the voltage at that level.

Interestingly the cell is specified at 4000mA, with a lower cut-off voltage of 2.75V, but later on in the data sheet it recommends an under-voltage protection circuit which activates at no less than 2.8V. Perhaps this is 2.75V rounded up? I don't know.

So, this mean that
Charging current to battery which output's from the solar panel lies between : 800mA - 2A ( 0.2C - 0.5C)
Discharging current : 800mA - 4A (0.2C - 1C)
Am I right?
If yes, then can I use solar panel of 5V 1A ? Because I somewhere read that solar voltage is bit (around 1V) greater then battery voltage. Am I right?
The voltage still needs to be limited to 4.2V. Connecting the 5V solar panel directly to the battery will cause it to overcharge, resulting in damage.

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##### Re: Battery bank and solarrrrrrr
« Reply #13 on: September 28, 2018, 10:15:13 pm »

The voltage still needs to be limited to 4.2V. Connecting the 5V solar panel directly to the battery will cause it to overcharge, resulting in damage.
[/quote]

Thanks, will do this. It clear my doubt
« Last Edit: September 29, 2018, 11:40:13 am by radhika »

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##### Re: Battery bank and solarrrrrrr
« Reply #14 on: September 29, 2018, 08:54:10 am »
Hello,
As according to our discussion Charging current is decided as 1A to charge the battery and voltage is 4.3V. I build circuit as shown here https://postimg.cc/GTbYfXVv
I got 3.9V as the output voltage but I want 4.3V. Also, I got 1A as output from the circuit to charge the battery. What to do to get 4.3V as the output?

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##### Re: Battery bank and solarrrrrrr
« Reply #15 on: September 29, 2018, 08:57:02 am »
Hello,
As according to our discussion Charging current is decided as 1A to charge the battery and voltage is 4.3V. I build the circuit as shown here https://postimg.cc/GTbYfXVv
I got 3.9V as the output voltage but I want 4.3V. Also, I got 1A as output from the circuit to charge the battery. What to do to get 4.3V as the output?

The base terminal of transistor get switch On when connected to the Arduino PIN and this complete the circuit.

#### Zero999

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##### Re: Battery bank and solarrrrrrr
« Reply #16 on: September 29, 2018, 03:32:35 pm »
Hello,
As according to our discussion Charging current is decided as 1A to charge the battery and voltage is 4.3V. I build circuit as shown here https://postimg.cc/GTbYfXVv
I got 3.9V as the output voltage but I want 4.3V. Also, I got 1A as output from the circuit to charge the battery. What to do to get 4.3V as the output?
What represents the battery and solar cells in that circuit?

All I see is a 5V linear regulator, connected to a 5V supply, with a transistor short circuiting the output and the regulator limiting the current.

You'd be better off selecting the adjustable LD1117 and using resistor values to give 4.2V out. Don't aim for 4.3V, as the battery will overcharge if the component tolerances make the actual voltage higher. Refer to the schematic on page 24 of the data sheet. If R1 = 120R and R2 = 300R, the output voltage will be 4.2V.
https://www.st.com/resource/en/datasheet/ld1117.pdf

The only issue with the suggestion above is what happens when it's dark? The battery will discharge via R1 and R2 and could also try to flow back through the regulator into the solar panel. A Schottky diode could be connected between the regulator circuit and the battery, but it would drop a small voltage so the battery will take much longer to charge. The voltage of the regulator circuit could be adjusted to compensate for the diode loss, but then there's a risk of overcharging the battery, as the diode will drop a much lower voltage, when the current is low.

Another possibility is a shunt regulator made with a transistor boosted shunt regulator IC, such as the TL431. Refer to the schematic in figure 31, on page 24 of the data sheet. Connect the circuit directly across the battery terminals, with a Schottky diode in series with the solar panel, to prevent back-feeding. If R1 = 8k2 and R2 = 12k, the output voltage will be 4.2V. The transistor needs to be rated to dissipate about 5W, which means it will require a decent heat sink.