[RE-wrenches] Hidden corrosion caused catastrophic battery system failure
Ray Walters
ray at solarray.com
Sat Jan 21 12:05:02 PST 2017
HI Dave;
Based on the evidence, I might suspect a short in the inverter, or the
inverter was feeding a heavy load when the melt down occurred. I can't
see how a short at the battery would cause an inverter failure, unless
the melted lead caused the polarity to be reversed, or created a
positive grounded system. My theory is that the Catastrophic
Electronics failure may have occurred first, and then the subsequent
high current caused the battery melt down. If the resistance were high
enough at the battery terminal, then the current flow might have been
low enough to not blow the Fuse. 250 amps across a 6 volt drop at a bad
connection would not trip a breaker or trip the inverter LVD, but would
be 1500 watts of concentrated heat that is going to melt lead very quickly.
We had a case a couple of years ago, where we switched from our tried
and true Vaseline, to an anti-corrosion paste made especially for
batteries. We thought it was an "improvement". However, the grit in
the paste kept the connection from making full contact, and when we were
operating the inverters at full capacity, a battery terminal started
smoking. We shut the system down before the lead started melting, but
I'm sure that would have happened soon after. We cleaned the paste off,
redid all the connections with a complete coating of Vaseline, and now
*only apply the paste after the connection is tight, never to the
contact surfaces*.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 1/21/2017 8:52 AM, Dave Palumbo wrote:
>
> 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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