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Melted battery terminal
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user9253



Joined: 28 Mar 2008
Posts: 1263
Location: Riley TWP Michigan

PostPosted: Mon Jul 30, 2018 3:29 am    Post subject: Re: Melted battery terminal Reply with quote

If the battery manufacturer designed battery terminals which are not capable of carrying maximum battery
current, then why didn't both battery terminals melt? Equal current flows through both terminals.


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PostPosted: Mon Jul 30, 2018 4:35 am    Post subject: Melted battery terminal Reply with quote

At 06:29 AM 7/30/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

If the battery manufacturer designed battery terminals which are not capable of carrying maximum battery current, then why didn't both battery terminals melt? Equal current flows through both terminals.

But the thermal dynamics are not necessarily
matched . . . what are the relative heat
rejection pathways for the two terminals
and were the joint make-up pressures identical?

One generally designs most conductors to
have a lot of head-room for current vs.
risk of destruction. Recall my exhibit where
a 22AWG wire was shown to carry 20Amps without
putting either wire or insulation at risk?

These terminals were being operated a lot further
up risk-mountain than the manufacturer would
have suggested. Just because any particular
SVLA battery is capable of dumping huge currents
consistent with engine cranking doesn't mean
that it's a low risk application.

Consider the cross section of the failed
terminals with say the posts on top of a
car battery. Engine cranking currents on
most car engines is on a par with that required
to crank an aircraft engine. I've never seen
a car battery post melt . . . even with loose
terminals.


Bob . . .


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PostPosted: Mon Jul 30, 2018 4:52 am    Post subject: Melted battery terminal Reply with quote

I think he said that both did melt.
Charlie
On Jul 30, 2018, at 6:33 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
Quote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>If the battery manufacturer designed battery terminals which are not capable of carrying maximum battery current, then why didn't both battery terminals melt? Equal current flows through both terminals.--------Joe GoresRead this topic online here:http://forums.matronics.com/viewtopic.php?p=481942#481942http://wiki.matronics.com[/url]http://www.matronics.com/contribution


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user9253



Joined: 28 Mar 2008
Posts: 1263
Location: Riley TWP Michigan

PostPosted: Mon Jul 30, 2018 9:35 am    Post subject: Re: Melted battery terminal Reply with quote

It would be interesting to learn what the battery manufacturer has to say about
the melted terminal. Would they put the blame on pilot error or battery design
or poor connection or too small wire size or a combination of these?


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PostPosted: Mon Jul 30, 2018 9:57 am    Post subject: Melted battery terminal Reply with quote

Guys,
I think we've got some overthinking going on here. It really boils down to this: If you pull so much energy through a circuit that stuff gets hot enough to fail, the thing that heats up to its failure point first is going to fail first. In this circuit, that thing was a lead battery terminal.
    -- Art Z.
--
https://CheerfulCurmudgeon.com/"We do not see the world as it is. We see the world as we are."


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PostPosted: Tue Jul 31, 2018 8:02 am    Post subject: Melted battery terminal Reply with quote

At 12:35 PM 7/30/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

It would be interesting to learn what the battery manufacturer has to say about
the melted terminal. Would they put the blame on pilot error or battery design
or poor connection or too small wire size or a combination of these?

I suspect they would say, why was this battery
being used to crank so large an engine? Unless
a battery's sales literature speaks to 'cold
cranking amps' or some such, it's reasonable
to believe that hte battery was designed for
more pedestrian pursuits.

Waaayyy back when, there was an endeavor mounted
by a start-up that called themselves Bolder Technologies
out of Golden. CO. They started a next generation
of the jelly-roll SVLA cell that featured
very thin electrode sheets separated by
equally compacted layers of active material.

The cell was about the same size as a c-sized
flashlight cell. It was rated at about 1.1
Ah but had an internal resistance of about
1 milliohm. Short circuit current on this product
was over 1000 amps.

Clearly, this was designed to support the extra
ordinary demands of engine cranking. We saw
some samples at B&C about 1999. There were a
few products that exploited the cell's
features. One was a 'start stick' that showed
up at OSH a year or two. Show pilots were
using them to crank up and then leave behind
for the performance. But you only got ONE
chance to get her lit up . . .

The product had some problems. To achieve
those delivery currents, they had to make
1000A capable electrical contact along the
entire edge of an electrode sheet at both
ends of the jelly roll. Not easy. I think
there were issues with service life as well.

The company went TU and was bought out by
somebody in Malaysia I think. I'm seeing some
new offerings in the 'start stick' class
of product . . . costing $killo$. sure
hope the performance issues are fixed!
Then these new kids on the block may well
be lithium based.

https://goo.gl/yCJovM

Wow, $250 for a power cord . . . a bit
rich for my blood . . .

Dug around a bit on Bolder TMF. Found
some mentions all of which are 25
years old.

https://goo.gl/G11GRS

The TMF SVLA may well have been a flash in
the fires of history . . .

In any case, when a battery is INTENDED to
perform in the low duty cycle high drain
demands for engine starting, the engineering
data sheets will speak to that capability
with high draw time limits or other qualities
like cold cranking amps.

Many UPS/RV market batteries have been used
successfully in light aircraft but will
dance up to the edge of failure in hard-
start events . . .



Bob . . .


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Eric M. Jones



Joined: 10 Jan 2006
Posts: 559
Location: Massachusetts

PostPosted: Tue Jul 31, 2018 4:22 pm    Post subject: Re: Melted battery terminal Reply with quote

Tight connection are good to a point. After that, they can induce stress in the terminal...which was probably made of recycled crap anyway.

Stress cracking, leading to failure. Only my guess.


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PostPosted: Wed Aug 01, 2018 8:19 am    Post subject: Melted battery terminal Reply with quote

At 07:22 PM 7/31/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones(at)charter.net>

Tight connection are good to a point. After that, they can induce stress in the terminal...which was probably made of recycled crap anyway.

Stress cracking, leading to failure. Only my guess.

. . . or a simple failure to accommodate
differences in materials . . .

Lead has about 1/10 the compressive strength
of copper and still less relative to the steel
attach hardware. Electrical integrity of the
joint depends on reducing voids in the mating
surfaces as close to zero as possible . . . and
keeping them there.

Initially easy with the lead post . . . it's
like really cold peanut butter. Tighten up
the hardware until the terminal's willingness
to 'squish' brings the connection gap to
zero.

But you have a time-dependent problem not
unlike keeping the wooden propeller attach
bolts at their proper tension. They should
be monitored and perhaps re-tensioned.

Over time, vibration and thermal cycles will
produce a reduction in joint pressure. Not
so much on a wheel chair or un-interruptible
power supply. Once the pressure begins to
relax, joint resistance goes up which lays
the foundation for the observed failure.

Had the terminals on this battery been
periodically re-torqued or perhaps fitted
with Belville washers, this failure may not
have occurred. But we've seen hard starts
produce inter-cell connector failures too . . .

Bottom line: If the engine doesn't start in
a few blades, your antennae need to be on high gain
alert for the effects of extra-ordinary stress
on lots of hardware . . . not the lest of which
is the battery.


Bob . . .


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