[RE-wrenches] Hidden corrosion caused catastrophic battery system failure

Sat Jan 21 07:52:07 PST 2017

Hi Chris,

I don't have any pictures myself, the Backwoods email included a photo of a
corroded bolt and a clean assembly which I've snipped and attached.

Off the Wrenches list I have had a conversation with another wrench who
shared his successful methods which I will share here.

<< The issue I remember from before on this thread was do you put the
material between the lug and post or outside of it?

And I'm not sure from the article if it was put on between or outside?

Personally I've done between and  never had a problem. Yes I've seen
corrosion around the lug, but take the lug off and its clean.   Outside
seals the corrosion in, inside prevents it from forming IMO.

However, if the bolt got lose, it would generate heat, which would melt out
any and all material, creating oxidation, more heat and away you go to
failure mode.

Also the photo doesn't show split/lock washer.  I think its really important
as the lead does flow over time, so no matter how tight you make it,  it
will loosen up over time especially with higher currents/heat.

The lock washer will buy you some time before needing to retorque the
fasteners.

 I'm curious about the damage mode to the inverter and all that.  I don't
understand how a short on the battery would destroy all the electronics?

I've gone to a battery angle grinder with flappy wheel to prep the terminal
posts. - fast. >>

My response to him.

I wondered about the failure of those big expensive components too, but I
have never had a dead short for more than a split second at the batteries (a
few misplaced cables when working too quickly are easily dealt with). I have
been installing a catastrophic class T fuse between the battery bank and the
DC distribution center breaker also.

I would always buff the cable ends with a green scrubbie and file the
battery terminals to remove any corrosion and then lightly coat all
surfaces,  including all the hardware thoroughly (incldng lock washer), with
petroleum jelly before assembling and tightening (very tight - tight as I
could without breaking the hardware, lead starts to compress). I've been
very happy with doing it this way for 30+ years. Learned much of this from
Peter Talmage and Rob Wills here back east as well as from Richard Perez
(RIP).

 Dave

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of cwarfel
Sent: Saturday, January 21, 2017 9:54 AM
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] Hidden corrosion caused catastrophic battery
system failure

Hi David, do you have any pictures of this that could be shared?  Chris

On 1/20/2017 12:52 PM, Dave Palumbo wrote:

Following is an entry from a Backwoods Solar email that I received today. I
would like to share this as a teachable point for RE techs not familiar
enough with proper battery bank care and as a reminder for those of us with
years of storage battery experience. 

I have underlined the two issues in the Backwoods email copied below my
bullet points to highlight the teachable issues.

.         Checking wiring connections: Check not only for tightness but also
for temperature. There are two simple methods that work well: #1) Use an IR
Thermometer to ensure all connections are of a similar moderate temperature.
#2)  Use your fingers to check temperatures. I'm practiced at this second
method because inexpensive IR thermometers were not available when I began
to care for storage batteries. I simply use my bare fingers (with a light
coating of petroleum jelly) to wiggle test each battery cable at the battery
terminal. Fingers are sensitive enough to gauge proper temperature. I have
easily found several warm or hot connection points over the years caused by
loose or corroded hardware. Do this as preventive maintenance every time you
water the batteries or bi-monthly with sealed cells. Corrective measures
(tightening, or taking apart and cleaning, or replacing, and reinstalling)
are taken immediately when a warmer than usual connection is identified.

.         It is not recommended by most veteran wrenches to use any
"anti-corrosion paste" on the terminal connections. This has been discussed
a few times over the years on the Wrenches list. Most of us have found that
a thin coating of petroleum jelly (Vaseline is one brand) does the best job
of protecting against corrosion while still allowing some visual inspection.

from Backwoods Solar 1/20/17.  << This past summer Backwoods had a visit
from one of our retired co-workers, xxxxx.  While it is always good to have
friends visit, the circumstances for his dropping by were less than ideal.

A small, catastrophic failure had led to the loss of a battery bank, two
inverters, and a voltage converter.  Ultimately, the failure was traced back
to a single nut and bolt in the battery bank cable connections, that had
developed hidden corrosion over time.  Corrosion causes resistance to the
flow of electricity, which in turn generates heat.  With enough corrosion,
and enough current flow, the amount of heat generated can be sufficient to
melt battery terminal connections; which is exactly what happened in xxxxx's
case.  The melted metal flowed between the negative and positive terminals
of his industrial battery, causing a high power short that was beyond the
capabilities of any of the circuit protection, resulting in the damage to
the equipment.

Now keep in mind, xxxxx is one of the more detail-oriented people we've had
here at Backwoods.  The discipline of a military background, along with
critical thinking of an engineer, were still not enough to overlook one very
tiny detail.  xxxxx does his mechanical maintenance on a routine schedule;
checking for tightness in wiring connections, cleaning accumulated spray off
battery tops, cleaning out dust and spider webs, and keeping his battery
terminal posts coated with anti-corrosion paste.  This is not the type of
person you'd expect to see such a failure.

So what happened?  It all boiled down to the battery terminal connections.
What xxxxx had NOT done, was dissembled the nut and bolts from the battery
terminals and cables to check for internal, hidden corrosion.  It had been
about 6 years since he had done that level of inspection.  When previously
reviewed, the hardware had been thoroughly inspected, cleaned, and
re-assembled, and then coated with anti-corrosion paste on the exterior.  In
one of the 16 nut/bolt pairs, a small bit of contamination or moisture must
have been left trapped inside.  Over the course of the next six years, the
corrosion grew, contaminating the entire connection; but was NOT visible
externally at all! >>

Best regards,

Dave

David Palumbo 

Independent Power LLC

462 Solar Way Drive

Hyde Park, VT 05655

802-371-8678 cell

802-888-4917 home

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-- 
Christopher Warfel, PE
Entech Engineering, Inc.
401-466-8978
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