motor runs for a while

[hirenn]

hello !

i have connect a +5v dc motor with 600mAH Li-ion fully charged battery in series with 100 OHM resistor

motor takes 60mA without load

my motor rotates only for 40 minutes instead of 6 HRS

why it happens ? and please tell me solution for that

thanks

 

[Audioguru]

You forgot to say the "average" voltage of the battery or how many "3.7V" cells it has.

Maybe it has 2 cells and averages 8.4V, or has 3 cells for 11.1V or has 4 cells for 14.8V.
But since the motor needs 5V then with 60mA in 100 ohms producing a voltage drop of 6V the battery average voltage is probably 11.1V.

600mAh should power the motor for about 10 hours. Maybe your battery or charger are no good.

 

[barry]

1) Have you verified that your battery is actually totally discharged?
2) Have you verified that the motor draws only 60 mA for the entire 40 minutes?
3) Is the battery actually specified for 600mAH with a 60mA load? The amp-hour rating depends on the load. Just because the battery is rated 600mA-H does not mean it can supply 6,000,000 amps for 100nS.

 

[Audioguru]

The Thunder Power 325mAh/70C battery for my radio controlled model airplanes is Lithium. Its maximum current is rated at 22.75A!
It can easily deliver 3.25A for 0.1 hour (6 minutes) and probably deliver 6.5A for 2 or 3 minutes.

I forgot to say that if the Lithium battery is very cold (way below freezing) then its capacity and maximum current are much less than the ratings.

 

[hirenn]

actually, i used nokia mobile phone battery,
it's 3.2V and 600mAH,
i track current continuously, motor take 6oma upto 40 minutes
when motor stop running, i measured voltage of battery, it was 2.1v around

any idea. . .

 

[Audioguru]

A Lithium rechargeable battery cell has a voltage that is 3.2V when it is dead. Its voltage is 4.2V when it is fully charged and the charging current has dropped to a low amount. Then its average voltage is 3.7V when it is about half-charged.
If you allow the voltage of a Lithium battery cell to drop below 3V like you did then the battery cell is ruined and will perform poorly like you see.

A product like a cell phone that is designed to use a rechargeable battery has a charging circuit inside that properly limits the charging current, limits the voltage to 4.2V and continues charging until the charging current drops to a low amount, then the charging circuit is disconnected. Another circuit in the phone measures the battery voltage and disconnects the battery when its voltage has dropped below 3.2V.

A Lithium battery that has its voltage below 3V should not be charged because then it might explode or catch on fire. The charging circuit in a product will not attempt to charge a Lithium battery cell that has a voltage below 3V.

 

[hirenn]

so, by using 4.2v(fully charged) and 600maH Li-ion battery for run 60mA and +5v DC motor upto 10 hrs , what i have to do?
any circuit or guidance for that?

 

[Audioguru]

Your battery is ruined and should be replaced.
Do you have a charger made for it or will you charge it in your phone?
You must not allow the voltage to drop below 3.2V.

 

[hirenn]

it means my battery will not work upto 7 hrs, then how can rotate my motor upto 7 hrs from 4.2V 600 mAH Li-ion battery

 

[barry]

There's some other issue here. It's not that the battery is damaged, it's that it,presumably, supplied less than a tenth of the expected ma-H. Unless, of course, the battery was damaged to begin with. You should be able to draw 60 mA for 7 hours from a 600mA-Hr battery. I still don't know the point of putting that resistor in series with the battery, though-that's just going to waste power. Unless your goal is to waste power. 60 mA through a 100 ohm resistor will drop 6Volts. Is that really what you want to do????

But, wait a minute. You say you've got a 5 volt motor connected to a 3.2 volt battery? And a 100 ohm resistor in series with all that?? I'm surprised your motor ran at all.

 

[Audioguru]

A lithium rechargeable battery is ruined when it has its voltage over-discharged below 3.2V only one time. If it has been over-discharged more than a few times then it is destroyed.
If it has been stored fully charged for more than a few months then it is ruined and is destroyed if stored fully charged for more than 1 year. New batteries are shipped to a user half-charged.

Maybe the battery is a cheap Chinese fake 18650 cell bought from ebay:
https://www.youtube.com/watch?v=eOshOXcSkDA

 

[Surender Reddy]

if the motor run continuously, the battery voltage reduce slowly.
After certain time the battery is not able to provide the sufficient voltage (min voltage) to the motor,
but the battery contains voltage (which is not able to drive the motor).