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Charging a Li-ion Battery of 25.9 V and 5.5Ah

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phrbob93

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My aim is to develop a charger of a Li ion Battery of the following specification
voltage 25.9V
capacity 5.5Ah
i dont know how much cell it contains..nor i am having any document where i could find this.
i want to charge it by the means of energy conservation.. for that i selected a piezoelectric charging system by shoes..it can charge a standard Duracell 9V battery of capacity about 500-600 mA
now how much time and battery of such 9V require to charge that Li on Battery of 25.9V?
 

SunnySkyguy

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You can't whip milk into butter with a wet noodle.

Nor can you get 5.5Ah or 142Wh ( 5.5Ah*25.9V ) from a 5.4Wh 9V primary battery ( 0.6Ah *9V)
 

erikl

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25.9V means 7 cells (of 3.7V) in series. If you can load a 9V accu, you could perhaps load 2 Li-ion cells in series, if you can secure that each of them are limited to ≦ 4.2V .

It is recommended to load Li-ion cells with at least C/10 (usually C/3). This would mean you'd have to load each 5.5Ah cell with at least 550mA. Loading Li-ion cells with lower current than C/10 is not reasonable nor effective.

If you actually can load a 9V accu with 550mA (must be rather big shoes ;-) ), this would mean 30h load time for 3 * 2 Li-ion cells in series + another 10h for the 7th cell. So your shoes have to walk for at least 40 hours for a full load!
 

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Some students made piezo insoles for shoes. They charged two tiny series 8mAh 3.7V Li-Po button cell batteries with 1.92 million steps (200 days at 10,000 steps per day).
Your huge battery will take centuries to charge.
 

erikl

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what if i use multiple number of 9V battries?
Then divide the number of hours by this multiple number. So for multiple number=4 you need 4 shoes to walk (close together - perhaps a big animal?, carrying the Li-ion accu + electronics) for 10 hours. Provided that these piezo shoes can actually deliver 9V @ 500-600mA, each.
 

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Then divide the number of hours by this multiple number. So for multiple number=4 you need 4 shoes to walk (close together - perhaps a big animal?, carrying the Li-ion accu + electronics) for 10 hours. Provided that these piezo shoes can actually deliver 9V @ 500-600mA, each.
could you explain me that on what biases you are saying that i need four 9V batteries and together they would take total 10 hours to charge the 25.9 V battery ? i need some more detail
 

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what if i use multiple number of 9V battries?
A piezo provides an extremely low current when it is stepped on. If each shoe has a piezo in it then the extremely low current occurs only in pulses for half the time. An Energizer 9V Ni-MH battery is 175mAh.

There are many videos of piezos in shoes producing electricity in you tube. Here is one: https://www.youtube.com/watch?v=FGQ_7fMXBf8
The guy walked for 15 minutes with a piezo beam on one shoe. The piezo drove an energy harvesting module that was charging two AA Ni-Cad cells. It lighted an LED flashlight but maybe for only a few seconds.
They calculate that 30 minutes of walking can produce enough energy to light one LED for one minute. The graph of current showed a peak of 6mA which might be the LED current.

Another video had a piezo in a shoe rectified with a bridge rectifier and charging a capacitor. It was calculated that the energy harvested was so low that it would take 182 million steps to charge a little cell phone battery.
 

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*
If LiPo has I*t= 5.5Ah then energy storage is V* I*t = 25.9V*5.5Ah = 142Wh > x3600= 511,200 W-s= Joules


By comparison your 9V primary battery is only
9V *0.6Ah *3600s/h =19,440 Joules

Thus your LiPo ( ignoring charger type inefficiency ) will take 511,200/19,440=26 times longer charge time with 26x more energy storage.

This example using PZT sensor created 1W peak and 0.25W average at 1 footstep per second or an average energy of 0.25 Joules

If each step was 1m, then you would need to walk 511,200 x2m if only on one foot to fully charge the LiPo cells.

Always analyze specs before you try to design something
and start with an energy source, converter and load to identify where all the losses are . THis is called a power budget spec. ( simple list)

Do you think you can walk 1000 km to charge up the battery? i.e. Round trip from Mumbai to Ahmedabad or roughly from Toronto to New York City and Google says you can make the round trip walking in 204 Hours ( not counting stops) ;)

Next consider another power source and battery size and make a list of specs.
a priori for any good design
 

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I think the OP sees little kids running around and having shoes with bright LEDs flashing with each step. Aren't the LEDs in the shoes powered by a battery and not by a piezo?
 

erikl

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could you explain me that on what biases you are saying that i need four 9V batteries and together they would take total 10 hours to charge the 25.9 V battery ? i need some more detail
Instead of loading the cells timely in serial manner (s. my post #3 above), you then could load them (timely) in parallel.
 

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Erikl says "load' but he means to say "charge".
Four 9V batteries in series produce 36V which is much higher than you need.

Somebody said that a 9 battery has a capacity of 600mAh but that is for an alkaline battery that cannot be re-charged. The capacity of an Energizer 9V Ni-MH battery is only 175mAh. the 5.5Ah battery you talked about charging has a capacity that is 31 times higher. Then you need millions or billions of shoes with piezos inside.
 

phrbob93

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ok i think i have to skip the idea of charging using Piezo
and, now i am thinking of doing it using generator which will generate the voltage by means of paddling
but i have no idea that what specification of motor i need.. and i have to develop a charger which must have the following feature
a) Over Voltage Protection:
b) Output Reverse Protection: The charger will be cut off when the battery polarity is
wrongly placed.
c) Short Circuit Protection: The charger will be cut off automatically when a short circuit
is detected.
d) LED indicates the charging status.
e) Built in IC to cut off power automatically when the battery is fully charged

please suggest me some circuit diagram according to my need
 

phrbob93

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*
If LiPo has I*t= 5.5Ah then energy storage is V* I*t = 25.9V*5.5Ah = 142Wh > x3600= 511,200 W-s= Joules


By comparison your 9V primary battery is only
9V *0.6Ah *3600s/h =19,440 Joules

Thus your LiPo ( ignoring charger type inefficiency ) will take 511,200/19,440=26 times longer charge time with 26x more energy storage.

This example using PZT sensor created 1W peak and 0.25W average at 1 footstep per second or an average energy of 0.25 Joules

If each step was 1m, then you would need to walk 511,200 x2m if only on one foot to fully charge the LiPo cells.

Always analyze specs before you try to design something
and start with an energy source, converter and load to identify where all the losses are . THis is called a power budget spec. ( simple list)

Do you think you can walk 1000 km to charge up the battery? i.e. Round trip from Mumbai to Ahmedabad or roughly from Toronto to New York City and Google says you can make the round trip walking in 204 Hours ( not counting stops) ;)

Next consider another power source and battery size and make a list of specs.
a priori for any good design
ok i think i have to skip the idea of charging using Piezo
and, now i am thinking of doing it using generator which will generate the voltage by means of paddling
but i have no idea that what specification of motor i need.. and i have to develop a charger which must have the following feature
a) Over Voltage Protection:
b) Output Reverse Protection: The charger will be cut off when the battery polarity is
wrongly placed.
c) Short Circuit Protection: The charger will be cut off automatically when a short circuit
is detected.
d) LED indicates the charging status.
e) Built in IC to cut off power automatically when the battery is fully charged

please suggest me some circuit diagram according to my need
 

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