# Battery tester(measure the internal resistance of a battery)

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#### wizpic

Hi all

I am thinking of designing and building a battery analyzer by measuring the internal resistance of the battery, The batteries are 6V and 250AH, and i want to use a PIC nd a LCD/GLCD to show data and battery voltage and may be temperature (internal)

I have hhave done plenty of searching on google but can not find what i am after,

Does any one know where i can find the info i.e schematics and stuff like that so i can make a start
OR how does one measure the internal reistance of a battery becuase a multimeter will not do this,

any help or info wold be nice

cheers

wizpic

#### IanP

Re: Battery tester(measure the internal resistance of a batt

Take a look at:
"Rapid-testing of batteries"

Regards,
IanP

The DC load test measures the battery's internal resistance by reading the voltage drops of two loads of different strength. A large drop indicates high resistance.

#### wizpic

Re: Battery tester(measure the internal resistance of a batt

Thanks for that, I have read it and it has give me some mor info

I woudl like to know of a circuit or a way to test the internal resistance of the battery as far has i understand it you have to send very quick sharp pulse to the battery to discharge it and then take some voltage mesaurements and then you can work out the internal resistance of the battery :?:

if some one can point me in the right direction i woud be thankfull

cheers

wizpic

#### IanP

Re: Battery tester(measure the internal resistance of a batt

This circuit: "BATTERY CHARACTERIZER" can be a good staring point ..
It can be found at:
http://www.vermontficks.org/pic.htm

Regards,
IanP

Kripton2035

### Kripton2035

Points: 2

#### wizpic

Thanks Ian that was a good starting point cheers
I have been doing a lot of reading, I have now got me a working circuit (sort of) carried out some tests and i need now to figure out what to do next

I want to use a pic to display the readings which is no problem with codiing but my signal i have got is -50mv AC, i have tried to use a bridge rectifier then boost the signal but doe nto seem to work,

How can i convert the AC millivolts in to dc and boost it to 0-5v so then i can do my calculations

any ideas ?

wicpic

#### IanP

Re: Battery tester(measure the internal resistance of a batt

To rectify such small signals you have to use an "active" rectifier, and an opamp-based peak detector can be a good candidate for this job .. see picture below ..
Then add another opamp-based stage which will scale and amplify this dc signal to 0-5V ..

Regards,
IanP

#### wizpic

Thanks Ian

I will look into this over the weekend if i get time with it been crimbo i the usaul runs to do before christmas

Well once again thanks for your help and have a good christams and a happy new year

wizpic

#### surfman

##### Newbie level 6
Re: Battery tester(measure the internal resistance of a batt

IanP said:
This circuit: "BATTERY CHARACTERIZER" can be a good staring point ..
It can be found at:
http://www.vermontficks.org/pic.htm

Regards,
IanP

Hi did anyone have compiled HEX for this project?

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