Measuring battery charge 1

[WTRVS]

Is there an easy way to calculate the effective charge of a battery? For example a 7,2 Ah UPS battery. When I connect a resistor, is the voltage drop an indicator of the charge level or do I need the voltage drop rate in function of time?

Is there a formula to calculate this?

Thanks

 

[MikeHalloran]

For the typical UPS lead-acid battery, the voltage can give you a reasonable estimate of the charge state, provided you also know the temperature.

For most other battery chemistries in use today, voltage is not a reliable indicator; you have to measure the current in/out over time.

ICs specific to battery management have existed for some time. It would probably be helpful to read the app notes for any you can find.



Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

Google: lead acid battery state of charge

...and start browsing. Tonnes and tonnes of good info.

This assumes that your UPS uses a lead acid battery (most do).

 

[Zogzog]

Specific gravity would be the best true indicator I would think

 

[MiketheEngineer]

How do the cheap battery testers you can buy at Radio Shack work??

 

[MikeHalloran]

I have an RS battery tester for single cells.
It appears to be just a voltmeter. It does not appear to apply any load other than what it takes to drive the galvanometer.
When measuring NiMH and alkaline cells, it consistently reports as 'good', cells that have been declared totally dead by two digital cameras and by my AA LED Maglite.

IOW, it's not a very good tester, even for ten bucks.


Mike Halloran
Pembroke Pines, FL, USA