Re: (ET) New here, E15 and E12

["David Roden" <etpost drmm net>]

On 24 Sep 2021 at 13:47, joeaverage frontiernet net wrote:

> How much abuse can these batteries take?

It sounds like you may be undercharging your batteries.  Or, they're not 
in 
very good shape and have low capacity.  It's not at all unheard of for a 
neglected or mistreated battery to be murdered in 2 years, or less.

I would start by giving each battery a full charge independently with a 
known-good 6 volt automatic charger.  You can also charge them in 12 volt 
pairs, but because of the way ETs tap their batteries, that's not as good.

Then try again.

I would next check specific gravity in each cell, using a good quality 
hydrometer.  The floating ball type is pretty iffy.  For the best, I 
recommend a good quality temperature compensated glass float type.  For a 
cheaper hydrometer, E-Z-Red makes a reasonably accurate and more durable 
one with a pivoting float inside a plastic case.

With all batteries individually charged and equialized (continue charging 
at a low rate for about 24 hours), measure SG in each cell.  A fully 
chaged 
good cell will measure 1.260.  An SG of 1.225 or more is OK.  Below that 
it 
gets dicey.

1.260 = full
1.225 = 75-100%
1.190 = 50-75%
1.155 = 25-50%
1.120 = 0-25%
<1.120 = dead flat and likely to freeze this winter

Note especially any cells that are significantly lower than the others.  
Equalize that battery for another 24 hours and try again.  Continue this 
until the low cell gets close to its brothers, or until it won't rise any 
further.

It's also a really good idea to test each battery individually for 
capacity, and replace any that don't produce at least 100 amp hours (a 
standard capacity golf car battery is rated 120 minutes @ 75 amps, or 150 
amp hours).

If you have access to a commercial battery capacity tester you're all set. 
 
Charge each battery individually as above and test. 

A capacity testeri is just a means of applying a known typical load.  For 
golf car batteries that's usually around 75 amps.  A commercial tester 
will 
be automated to one degree or another.   It measures the amp hours 
produced 
from full charge until the battery falls to 5.25 volts (1.75 volts per 
cell), with the voltage measured while the load is connected.  

There are a couple hacky DIY substitutes for The Real Thing.

You can make your own 6 volt dummy load tester.  It won't be automated so 
you'll have to time the test yourself, and monitor the battery voltage on 
load and stop the test when it falls to 5.25 volts.  You calclulate the 
amp-
hours by multiplying the average current by the decimal number of hours 
from full to flat.

A cheap way to make a dummy load is to harvest the coiled nichrome wire 
heating element from an old 120 volt, 1500 watt space heater, stretch it 
out, cut it in eights, and parallel the 8 segments.  You can make 
connections to the segments with crimp lugs, and bolt them to ceramic 
standoffs on a heatproof base.  

Now you have a resistor of about 0.15 ohms. At 6 volts that will draw 40 
amps - not ideal, but good enough.  Just make sure that you blow air over 
it, and use a contactor in series that can handle at lest 50-75 amps *DC*.

An easier capacity tester hack uses a cheap ~1000 watt 12 volt power 
inverter, a load of around 750 watts (250 watt heat lamps are great for 
this), and an old fashioned plug-in electric clock (check local thrift 
stores).  

The advantage of this method is that it's automated, so you don't have to 
babysit.  The disadvantage is that you have to use 6v batteries in series 
pairs.  The capacity that you measure for the pair is effectively that of 
the weaker of the two batteries.  You can pinpoint the stinker(s) by 
repeating the test with differently-paired batteries.

The automation relies on the fact that most power inverters will shut down 
at low battery (~10.5 volts for a 12 volt battery).  Plug the heat lamps 
into the inverter, along with the clock.  Connect the inverter's input to 
a 
series pair of 6 volt batteries.  Set the clock to 12:00:00 and start 
everything up.  

When the inverter shuts down, at least one battery is flat.  To calculate 
the amp hours it yielded, divide the power rating of your load in Watts by 
120 to get amps, then divide by the efficiency factor of your inverter 
(0.8 
for an 80% efficient inverter).  Now you have the approximate initial 
battery current.  In reality the current changes over discharge, but that 
number is usually close enough.

Convert the clock's hours and minutes into a decimal hours quantity (1h 
20m 
is 1.33 hours).  Multiply hours by amps calculated above to get amp-hours.

Once you have the amp-hour capacity of each battery, replace any that are 
egregiously low.  A standard golf car battery when new produces 150 amp 
hours at 75 amps.  Traditionally it's considered fully depreciated when 
it's down to 80% capacity, but for ET purposes 100 amp hours is probably 
still OK.


David Roden - Akron, Ohio, USA

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