Battery health tesing

Atthough I mentioned a simplified method of battery test, once you
understand the procedure, you can measure the battery voltage under load and
after the initial few seconds, you can plot the discharge voltage vs time.
So, if in five minutes, the voltage drops .03 volts, we know the voltage
drop is linear, so in 60 minutes the voltage will drop 12 x .03 or .36
volts.

As Andy mentioned, it can be computerized.

Interestingly, the ability to hold a charge also means the resistance to
change. So, if you see a battery on the shelf and put a charger to it and
the voltage soars instantly to full voltage, it is bad.

Once you understand what is happening, you can usually tell if a battery is
good within a few seconds, and know the projected life in a minute or less -
all with minimum equipment. A lttle knowledge gets you a long way. In
fact, you can often hang a auto lamp across the battery with a digital
voltmeter and watch the voltage drop. The less drop, the better the
battery.

Colin

"COLIN LAMB" wrote in message
ink.net...
In fact, you can often hang a auto lamp across the battery with a digital
voltmeter and watch the voltage drop. The less drop, the better the battery.

That is exactly how I have been doing it for years, and I have never found
a need for anything more fancy. For small gel cells, (as are used in gliders) I
use a digital voltmeter and a 50-watt sealed beam light. For larger batteries,
I use a commercial load tester that you can buy at NAPA or any similar auto
parts store for about $50.00 US.

Vaughn

Vaughn wrote:
"COLIN LAMB" wrote in message
ink.net...

In fact, you can often hang a auto lamp across the battery with a digital
voltmeter and watch the voltage drop. The less drop, the better the battery.


That is exactly how I have been doing it for years, and I have never found
a need for anything more fancy. For small gel cells, (as are used in gliders) I
use a digital voltmeter and a 50-watt sealed beam light. For larger batteries,
I use a commercial load tester that you can buy at NAPA or any similar auto
parts store for about $50.00 US.

It sounds like you are effectively doing an internal resistance
measurement. Do you have chart of volt drop, load, and good/ok/bad
decision for various size batteries? I've not seen that sort of thing in
battery data sheets, so I assume you have to develop the numbers
empirically.


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Eric Greenwell
Washington State
USA

"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