That inverter will do just fine.

Dennis

-----Original Message-----
From: Rocket J Squirrel [mailto:camping.elliott@gmail.com]
Sent: Friday, January 27, 2012 5:25 PM
To: Dennis Haynes
Cc: vanagon@GERRY.VANAGON.COM
Subject: Re: Poor man battery testing

On 01/27/2012 06:42 AM, Dennis Haynes wrote:

"[...] a basic 400 watt unit will do the job [...] and the feature we want
is that it will shut off when the battery reaches 100% discharge
(10.5 volts)."

Something like this fine $20 item, perhaps?

<http://www.harborfreight.com/400-watt-continuous-800-watt-peak-power-invert
er-66814.html>

The other item is, "[...] an old style electric clock."

For the young-uns, ol' Dennis is referring to something like an old-school
AC-powered electromechanical clocks, the kind with a small synchronous motor
and a bunch of gears, something that churns away as long as power is applied
then just stops when it loses power--like a "Westclox" brand or similar
clock, but not a digital clock that plugs into the wall and goes dark as
soon as the power is cut off. However, electromechanical "digital" clocks
with the little physical painted flip-over tiles, like in "Groundhog Day,"
will work, too.

Now that's a bit harder. First stop, Goodwill!

--
Jack "Rocket j Squirrel" Elliott
Bend, Ore.
1984 Westfalia. A poor but proud people.
1971 "Ladybug"-brand utility trailer ca. 1972 from a defunct company in San
Clemente, Calif., now repurposed as The Westrailia.

Sent from my kitchen.

On 01/27/2012 06:42 AM, Dennis Haynes wrote:
> 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
>