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Author Topic: Sensing battery voltage without discharging it.  (Read 1128 times)
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silvabelbr
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« on: December 10, 2007, 01:12:39 01:12 »

Hello,

What would be the best method of sensing a 3 volt lithium battery without discharging it.

thank you.
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programmer_100
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« Reply #1 on: December 10, 2007, 02:30:26 02:30 »

Hello,

What would be the best method of sensing a 3 volt lithium battery without discharging it.

thank you.

Give us some more information about what you are doing, eg Do you just want  to detect if the battery exists or do you wish to measure the voltage.


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creatv
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« Reply #2 on: December 10, 2007, 09:07:18 09:07 »

Hi,
you can use TEA1041T, it's very small circuit and low consume.

Creatv
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dideco
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« Reply #3 on: December 10, 2007, 11:00:11 11:00 »

Hi,

There may be a circuit which turns on for some miliseconds for some miliseconds and then turns off. Some CMOS integrated circuits consumes almost nothing to be used for this purpose such as CD4538 monostable.

Or, there may be a microcontroller which wakes up and turns on a transistor circuit to power itself, measures and then turns off, keeps itself powered with a capacitor until next awake...

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btkd
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« Reply #4 on: December 10, 2007, 12:46:19 12:46 »

You can use manual switch like in Dell laptops battery level indication.
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darksky
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« Reply #5 on: December 10, 2007, 01:53:52 13:53 »

Depends on the chemistry of the battery.  Some have a flat voltage then fall off rapidly.

An idea is to use an algorithm- a timer to determine background discharge then count events when woken up and chunks of energy used during wakeup.
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computer
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« Reply #6 on: December 11, 2007, 09:59:02 21:59 »

Hi!

You always will have some discharge when you do measure, but you can minimize it using a circuit that can perform measures within a time basis. For example: 1 measure per day. It's a good idea estimate the current drain of the whole circuit to calculate this time basis.

Other option is to built a brown-out detect circuit, if you just want to know if the voltage is below a certain trip point.

[]'s
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belinao
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« Reply #7 on: December 12, 2007, 03:47:01 03:47 »

if you have an extra power supply for the amp ops they will surely be the best option, just use a buffer configuration and that will probably do
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edi14_10
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« Reply #8 on: July 19, 2008, 06:51:53 06:51 »

how if the battery is been used to supply the controller or something else. for example, how can i measure the capacity of the battery that been used in a robot? I'm using a Li-ion battery 7,2V. in other word, how can i know wether the battery is empty, half charged, or full charged?
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borberk
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« Reply #9 on: July 19, 2008, 07:42:11 07:42 »

Q(charged)=I(charge)*t(charge) if I is not a constant use integral
Q(left)=Q(charged)-I(discharge)*t(discharge) if I is not a constant use integral
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edi14_10
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« Reply #10 on: July 20, 2008, 05:19:33 17:19 »

so, how can i measure the capacity in a battery if that battery has ever been used? maybe if i want to apply that equation, i still have to know the battery capacity rite?
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