[KYHAM] Battery Lesson Learned...help needed

[wa4qal at ix.netcom.com]

Tyler Allison wrote:

> First the story...it's long.
> 
> I've been running a 12VDC battery system for about a year. It powers my
> ham radio equipment, my weather station and my home network (cable modem,
> hubs, wireless routers, etc).  It ran off (2) two 12V Everstart Deep Cycle
> Marine Trolling motors I purchased at Walmart.  I was very careful, I
> thought, about reading as much as I could about proper wiring, wire size,
> etc.  I hooked them up with black and red 6 gauge wire. Thicker that it
> needs be..I think. Everything was hooked up to an Everstart 2/10/20 amp AC
> charger that has auto-shutoff (green light) when everything is fully
> charged. I put the batteries in the garage since I'd read some conflicting
> stories about the risk of non-sealed batteries in the living area of the
> house.

The deep-cycle batteries are good.  Those are a lot better suited to supplying 
power for such operations than normal "starting" type batteries.  The starting
type batteries are designed for delivering a high current burst of power for a 
short period.  Repeatedly deep cycling starting batteries usually results in a
fairly short life.

I show 6 gauge being good for 65 amps, ***IF*** the voltage drop is low
enough that it doesn't affect the equipment being operated.  It has a
resistance of .3951 Ohms per 1000 feet.  So, if you installed your shack
50 feet from the batteries (and, remember, this isn't linear distance, but
wire distance, which will have to take into account all of the bends and
diversions that the wire follows), this is 100 feet of wire (50 feet for the 
positive side, 50 feet for the negative side).  If you were pulling the maximum
current of 65 amps, then the voltage drop would be 2.6 volts, which may or
may not be a problem.

The lesson here is that it is not only the current carrying capacity that has to 
be taken into account, but also the voltage drop at the maximum current.  This
can come into play with house wiring for especially long runs, but it's more of
a concern with 12 volt circuits due to the reduced voltage drop margins.

> Okay now the 'lesson learned'
> 
> About 5 to 6 months ago(?) I noticed that I was never seeing the green
> light (auto-shutoff) when I would check on the batteries. I use to. I can
> see the charger everytime I pull in the garage. I figured it was just
> because I was pulling more amps than the charger could provide when I had
> it on the low 2amp trickle setting. So I pulled the manual out to double
> check and it seemed to read that I would be safe to put the charger on the
> 10amp settings since my batteries were large enough to handle the higher
> current (75AH each). So I flicked the switch to 10amp and thought nothing
> of it. I noticed that the green light still wouldn't come on but I thought
> maybe that had to do with the constant flow of current and it would
> 'never' show full. I took some readings while the batteries where under
> load with my amp/volt meter and everything looked normal.

Indicators usually mean something.  Of course, all too often they indicate
that something has failed, at which point, it's too late to do any recovery,
although prompt action can prevent further failures.  
 
> Anyway....more of the story.
> 
> In preparation of hooking up these batteries to a solar panel I wanted to
> cleanup my wiring. I installed circuit breakers, an on/off box, the works
> in my basement. I tested all the wiring, unplugged the batteries from up
> in the garage and installed them in the basement. I hadn't seen any
> problems in the garage so I figured after a year it was safe. (Lesson
> Learned)

No, no, no!  Lead acid batteries are outdoor animals (or, at least, garage
animals) [2].  I learned that the time that a lead acid battery I had in my 
shack "boiled over", and dumped a six foot diameter puddle of sulfuric 
acid on the floor.  That was not fun to clean up.

[2] You do have some minor concerns about outdoor batteries freezing
in winter, although it takes some VERY cold temperatures to freeze a 
charged battery.  It takes more moderate temperatures to freeze a 
discharged battery, though.  If a Lead Acid battery does freeze, it will
usually crack the case, and allow the electrolyte (Sulfuric Acid) to run out.

Plus, if you've ever been even somewhat close to one that has exploded,
you know that you don't want one in your house.  I had the battery on my
truck explode one morning (due to a manufacturing defect that allowed 
one of the internal connecting straps to fuse while I was cranking the truck,
which detonated a hydrogen explosion inside the battery)[1].  From inside
the cab, it sounded about like an M-80 going off (and, that was with the
hood closed and all of that sound proofing between the cab and the
engine compartment).  

[1]  And, of course, this happened at the worst possible time, while I was 
2500 miles from home. 

> This morning my wife wakes me up with "can you smell that? I think we have
> a gas leak". Oh great! Just what I need on a monday morning.  I
> immediately told her it didnt smell like gas to me. It smelled like rotten
> eggs, not what I remember natural gas smelling like.

Natural gas is naturally oderless.  But, because so many houses were blown
up because of gas leaks, and because so many people were killed, the gas 
companies add a very smelly chemical to the natural gas to allow leaks to be
easily detected.  I think this chemical is Ethyl Mercaptan, or maybe one of
the other Mercaptans.  Mercaptans are notoriously smelly.

The classic "rotten egg" smell is usually Hydrogen Sulphide, which is poisonous, 
and can be lethal in all but the smallest quantities (Plus, is has the notorious 
effect of desensitizing the nose, so that you don't realize that you may be 
inhaling a fatal quantity!).  

> We go hunting around the house and the smell is definitely stronger in the
> basement. She heads off to call Cinergy because she swears it's a gas
> leak. I think it's probably a sewer backup or something. The smell doesn't
> seem stronger in any one portion of the basement. Which seems odd to my
> mind.
> 
> As a professional troubleshooter/investigator at work my mind starts
> recapping what has changed that day.  DING DING DING! I moved the
> batteries into the basement. But they arnt suppose to vent...I know they
> CAN but they arnt suppose to.  A quick check of the batteries.  WARNING
> SULPHURIC ACID label on them. Sulfur has a rotten egg smell. *sigh*

If the battery was spewing out Hydrogen Sulphide, which is the chemical 
usually associated with the "rotten egg" smell, then it was seriously sick.

> I use my main on/off switch (hey it works!) and turn off all power in and
> out of the batteries. I touch the batteries, ooh my goodness are they hot.
> I had felt the batteries when they were in the garage mind you, they were
> hot but the garage was 90+ degrees at the time...I didnt think anything of
> it.
> 
> I get out my amp/volt meter and test each battery. One shows 13.03 V the
> other shows 9V. What the heck?!?!  13.03V is correct but 9V?!?
> 
> I move the batteries up to the garage again and try and charge each
> battery individually.  The good battery takes a full charge and the
> battery charger shuts off and shows green.  The 9V battery charges for
> 30minutes while waiting for the Cinergy guy to show up.  It never makes it
> passed 12.6 before I turn off the charger. By the time I test the battery
> with my volt/amp meter the volts have dropped to 11V and are quickly on
> the way down. I let the battery sit for another 10 minutes and the voltage
> has dropped down to around 9V again.
> 
> Okay..so I have a dead battery.
>
> But I don't know why I have a dead battery.

Usually what happens is that a cell will short.  This may happen because of
debris being shedded by the plates bridging a pair of plates and shorting
the cell, or because of the debris accumulating at the bottom of the cell, 
filling up the dead space there, and shorting a cell.   It may also happen 
because the plates warp, possibly because of overheating, and touch, causing
the cell to short.  

Once a cell has shorted, that drops the battery voltage from the nominal 13.2 
volts to 11 volts.  This will cause it to hog the current from the charger, and 
may, depending upon the design of the charger, cause the charger to pump 
even more current through the battery.  This excessive current overcharges 
the remaining cells, and may cause them to over heat or to shed material from 
their plates, which may cause more cells to short.  Additionally, the over 
current can also electrolyze the electrolyte, decomposing the water into 
Hydrogen and Oxygen, which forms a violently explosive mixture.  Plus, the 
water that's electrolyzed out reduces the volume of electrolyte, which 
increases the current density in the cell even more.  The combination of low
electrolyte level (which means that only part of the plates are covered), the  
severe electrolysis and violent bubbling, and the increased heating of the
decreased plate area can cause bad things to happen to the remaining cells.

If another cell shorts, then the voltage drops to 8.8 volts (2.2 volts per cell +/-
a bit), which would explain the 9 volt reading.  And, this can cause that 
battery to hog even more of the current, and for the charger to pump even 
more current into that battery.  

You didn't indicate if these were sealed batteries or not.  It might be interesting
to pop the inspection ports to check the electrolyte levels (but, remember that
there's sulfuric acid in there, and probably a goodly concentration of Hydrogen
gas and Oxygen!).

Also, when a cell shorts on one of the batteries, think what the current that the
other battery will be supplying into that battery with the shorted cell.  Let's see,
13.2 volts minus 11 volts divided by the internal resisance of the batteries, which
is somewhere around .001 Ohms...

> I drew a picture of the physical wiring of my system.
> http://www.allisonhouse.com/battery.jpg
> 
> Could the way I had the system configured been the cause of the damage?

I've seen some designs that use paralleled batteries to have isolating diodes
between the batteries so that a shorted cell on one of the batteries doesn't cause
the good batteries to dump their charge through the bad one.  Of course, you
need a goodly sized handful of very high current diodes to accomplish this, and
you need a charger that understands the .7 volt diode forward drop (and, a load
that will tolerate the .7 volt diode forward drop and still operate correctly).

> Any thoughts on what happened?

Shorted cell(s).

> ps: Cinergy guy showed up. I didnt tell him about the batteries until he
> did his check. He swears no gas leak. He asks if I have any punctured
> 'things' in the basement. I mention I was charging car batteries. He says
> "that's what that smells like".  *sigh*

Hopefully, you won't be billed for a service call (Maybe he had enough of a 
chuckle that he'll write it off.).

> -Tyler
> KI4BUM
> 

Dave
WA4QAL