Battery health tesing

wrote:

I'm wondering if there's a simple or straightforward way to test an SLA
battery for general condition. Or a device I can buy that sucks a
charge out of a battery over a few hours and reports its actual
amp-hour capacity?

I've built Peter Nyffelers amperehour tester:

http://www.ppc.ethz.ch/~peny/sf/ah_test.html

The simple circuit is easy to build out of standard components.

It discharges the batteries with a fixed constant current until the voltage
is down to 10.5 V then it switches the battery back to the charger.

With a discharge current of 1 A the timer shows the capacity in ampere
hours.(at 1/2 A multiply by two).

This tester is convenient when you take care of a lot of batteries:
- Charge battery (I do this with a second charger)
- Connect the battery
- Reset the hour meter
- press the discharge button
- The next day the battery is fully charged and the hour meter shows you its
capacity.

Sometimes it is possible to revive tired batteries with a few cycles of
discharge and recarge (use a smart 3 phase charger).
If 5 cycles don't help you can give up.

George

Georg, what is the "M1 Elapsed Time Meter"? This looks like a simple
enough project but I'm not sure I can identify enough of those
components (ask me about software!). I do know how to handle a
soldering iron though...

"Eric Greenwell" wrote in message
...
It sounds like you are effectively doing an internal resistance measurement.
Exactly. I find that internal resistance is a great measure of the health
of a battery.

Do you have chart of volt drop, load, and good/ok/bad decision for various size
batteries?
No, but I usually consider any drop over a volt or so to be suspect
(assuming an appropriate load for the size of battery). In my work, I often
have the advantage of having identical batteries to compare against each other.

I've not seen that sort of thing in battery data sheets, so I assume you have
to develop the numbers empirically.

True, but for auto-sized batteries the tester I mention (a very common
type) comes with markings that make a great starting point.

Vaughn