Date: Sat, 28 Jan 2012 08:56:37 -0500
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Poor man battery testing
In-Reply-To: <018c01ccdda1$160bd890$0200a8c0@PROSPERITY>
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The main advantage of the inverter method is the automatic shut off at 10.5
volts. Makes for some repeatability and you do not have to watch.
Dennis
-----Original Message-----
From: Scott Daniel - Turbovans [mailto:scottdaniel@turbovans.com]
Sent: Saturday, January 28, 2012 4:30 AM
To: Dennis Haynes; vanagon@GERRY.VANAGON.COM
Subject: Re: Poor man battery testing
how about just power the high beam headlights with the battery ...
using that for a load ?
----- Original Message -----
From: "Dennis Haynes" <d23haynes57@HOTMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, January 27, 2012 6:42 AM
Subject: Poor man battery testing
Deep Cycle battery capacity load testing.
Theory: Deep cycle batteries need to be tested differently than the normal
tests used for starting batteries. The major consideration is that a deep
cycle battery needs to be able to deliver power for a longer period of time
whereas a starting battery is called upon to deliver a very large amount of
power for a short period of time. Deep cycle batteries are rated in total
Amp/hours over some period of time, usually 5,6, or 20 hours. This is
critical to understand as the effect is not linear. Also it is important to
note that a longer, lower current draw will actually bring the battery to
lower state of charge as the cut off voltage is approached. There are many
variables to battery performance and test results but we will want to do is
come up with some repeatable procedure. Ultimately you will want to try this
on a new battery after 10-20 cycles to get a baseline. Then at some
periodic interval you test again to determine the health of the battery.
The Tools: The basic tools will be to get a 12 volt to 120 volt inverter.
One with metering would be real nice but a basic 400 watt unit will do the
job. The inverter will be used to supply a load and the feature we want is
that it will shut off when the battery reaches 100% discharge (10.5 volts).
Next we want an old style electric clock. We can set the clock to 12:00 when
starting the test and when the inverter shuts off we will be able to see how
long the battery lasted. Next we will need a load. Regular light bulbs can
provide us with a known load. The watts to be determined by the battery
capacity we wish to test.
The method: We need to know the battery rated capacity and decide the test
method we want to use. The 5 hour test provides very good test results.
Note that a battery is not considered failed if it can deliver 80% or more
of its rated capacity. As such if the battery is still going at 4 hours at a
full load we may choose to stop the test to avoid needlessly wearing it. So
let say we have a battery rated 100 A/H for 5 hours, we want a load of
100/5=20 A/h load. 20 A/H X 12 V is a 240 watt load. So 240 watts of light
bulbs will in theory give us the load we need. Now we need to keep in mind
that the battery rating is based on Amps. As the battery voltage goes down
current needs to increase if we are to maintain the same power. Real load
banks compensate buy increasing the load as the voltage drop to maintain a
constant current draw. The inverter may also do that to some extent. Add the
inverter looses and other variables and we need to use a slightly lower
load. For our test purpose for this size battery lets use2-100 watt bulbs
for a 200 watt load. Again, after you do this once you will have a base line
so just use the same equipment for the next test so you get a trend.
For the test you want to start with the battery fully charged. If inclined
take specific gravity readings of all the cells. If some cells are low try
on equalization charge to bring them up. On large motive power batteries we
sometime do long term constant current charges to get the acid out of the
plates and if needed we also do acid adjustments to get the cells back.
Anyway after the battery is fully charged we want to let it sit to dissipate
that surface charge and be at room temperature.
So we will connect the inverter, clock, and light bulbs. Be sure to have the
bulbs in real sockets, lamps, a drop light etc. broken glass and glowing
energized filaments do not make for a good day. With the clock set to 12:00
turn the inverter on with the load. Now let's see how long it keeps the
lights on. You may want to take voltage readings before starting the test,
(open circuit), when the load is turned on, and then every hour. This will
also give you a lot of information.
Dennis
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