How to measure AMP battery

Discussion in 'General Electronics Chat' started by sendbad, Mar 13, 2015.

Jan 8, 2015
43
1
hi
i have a lithium battery 3,7 volt
Unknown number amps
How can i know her ah number

or her amper
thank you

2. Papabravo Expert

Feb 24, 2006
10,340
1,850
Discharge the battery into a known load, then measure the current and the time.

3. Dodgydave AAC Fanatic!

Jun 22, 2012
5,158
772
have you got a picture of the battery?

Roderick Young likes this.

Jan 8, 2015
43
1
when i measure the current using mulltimetr not gev me Fixed number
Different numbers and then disappear

Oct 2, 2009
12,643
3,457

6. MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
I'll bet you are shorting the battery by connecting the ammeter across it without a series load resistor....

Jan 8, 2015
43
1
Does not have data
just 3,7 volt

8. Papabravo Expert

Feb 24, 2006
10,340
1,850
Then Ohms law tells me that you do not have a FIXED and CONSTANT load. An ammeter is a very low resistance, and could be damaged by doing what you did. Pick a resistor that will give you say 50 milliamps.

3.7 Volts / .050 Amperes ≈ 75 Ohms

The ammeter in series with the resistor goes across the battery terminals. Just to be extra safe estimate the power dissipated by the resistor as

(.050 Amperes)^2 * 75 Ohms ≈ 187.5 milliwats

So a quarter watt resistor will get warm but not explode.

Jan 8, 2015
43
1
resistance value 20 om

10. Dodgydave AAC Fanatic!

Jun 22, 2012
5,158
772
what is the number on the battery
?

Jan 8, 2015
43
1
series load resistor 20 om shorting the battery

so what Suitable om using

Jan 8, 2015
43
1
l
li-ion 18490 3.7 v
jo1.f18490ro4 340 13 12

thes all data in battry

Jun 22, 2012
5,158
772
14. MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
I'm guessing that size is about 1500mAh.
If 20Ω (180mA load current) pulls that battery down immediately, then it is totally discharged, and needs charging before you do any more tests.

Jan 8, 2015
43
1
i will do it