Visit our Popular Forums

FlyingCloud1937 · 27-01-2012, 14:35

ELECTRONIC FAILURE ANALYSIS HANDBOOK

17.2.1 Electrical Specifications
The performance and reliability of connectors relies on their electrical specifications.
Contact Resistance. Contact resistance in connectors is primarily the result of two factors:
constriction resistance, and film resistance. Constriction resistance is the electrical
resistance due to multiple single-point contacts at the interface surface. Film resistance is
due to microscopic film formation on the mating surfaces. Films, primarily oxides and
halides, resist the flow of currents. For the contact mating pair to provide useful electrical
conductivity, the oxide film has to be removed, allowing contact with the exposed metal.
Contact resistance between mating surfaces is one of the critical parameters in a connector
and is typically measured in milliohms (mΩ), or fractions of a milliohm, at specified
current and ambient temperatures. Contact resistance varies as a function of time and
depends on the size and shape of the mating contacts, contact material, number of prior
mating cycles, and environmental conditions such as vibration, temperature, moisture,
contaminants, and so forth.
Contact resistance can be adversely affected in a situation where the contact is only partially
inserted into the mating surface. A partially inserted contact, under maximum electrical
and environmental stress conditions, may eventually overheat, possibly resulting in
an ignition. Typical contact resistance and calculated contact power dissipation as a function
of contact current is presented in Table 17.1. Figure 17.2, derived from Table 17.1,
shows various connector parameters as a function of rated contact current for a family of
connectors with increased current-carrying capacity. Parameters include (1) contact pin
resistance, (2) calculated contact power at rated current, (3) specified contact diameter,
and (4) connector extraction force. It is observed that the parameters follow an approximately
logarithmic function, and that the contact pin resistance decreases with increasing
current, whereas the other parameters increase as a function of contact current. Calculated
contact power has an approximately straight-line relationship on a log-log plot. Dissipated
power level is approximately 0.20 W at 15 A, increasing to 3.7 W at 100 A, and further
increasing to 10 W at 200 A. Above 200 A, the contact power remains constant at approximately
10 W. Experience indicates that a typical off-the-shelf connector, operating at its
maximum specified rating of 15 A and dissipating over 0.4 to 0.5 W of power, may start to
overheat. At power levels of 0.8 to 1 W, this connector will rapidly overheat. If the dissipated
power level exceeds 1 W, the connector will go into thermal runaway, with contact
pin temperatures exceeding several hundred degrees and subsequent melting and ignition
of the plastic insulating material. Thermal runaway is discussed further Sec. 17.8, which
describes case studies (p. 17.47).

http://www.accessengineeringlibrary....9639_ar017.pdf

Fuss · 27-01-2012, 20:00

Hmmm, How can we sum up this thread which has got some very useful information in it.......

How can we sum this up...I dont have electrical marine engineers on my boat any more. My experience was that they sometimes tried to confuse me with electrospeak when the reality was that they had no idea themselves. I guess they figured it would make them look professional and convince me to give them the work. After my 2nd bad experience I stopped.
I sometimes worked with an real electrical engineer by trade who often said he did not know.... he knew the basics, he was very good.

**Dockhead** · 28-01-2012, 01:15

Quote:

Originally Posted by FlyingCloud1937

ELECTRONIC FAILURE ANALYSIS HANDBOOK

17.2.1 Electrical Specifications
The performance and reliability of connectors relies on their electrical specifications.
Contact Resistance. Contact resistance in connectors is primarily the result of two factors:
constriction resistance, and film resistance. Constriction resistance is the electrical
resistance due to multiple single-point contacts at the interface surface. Film resistance is
due to microscopic film formation on the mating surfaces. Films, primarily oxides and
halides, resist the flow of currents. For the contact mating pair to provide useful electrical
conductivity, the oxide film has to be removed, allowing contact with the exposed metal.
Contact resistance between mating surfaces is one of the critical parameters in a connector
and is typically measured in milliohms (m&Omega

, or fractions of a milliohm, at specified
current and ambient temperatures. Contact resistance varies as a function of time and
depends on the size and shape of the mating contacts, contact material, number of prior
mating cycles, and environmental conditions such as vibration, temperature, moisture,
contaminants, and so forth.
Contact resistance can be adversely affected in a situation where the contact is only partially
inserted into the mating surface. A partially inserted contact, under maximum electrical
and environmental stress conditions, may eventually overheat, possibly resulting in
an ignition. Typical contact resistance and calculated contact power dissipation as a function
of contact current is presented in Table 17.1. Figure 17.2, derived from Table 17.1,
shows various connector parameters as a function of rated contact current for a family of
connectors with increased current-carrying capacity. Parameters include (1) contact pin
resistance, (2) calculated contact power at rated current, (3) specified contact diameter,
and (4) connector extraction force. It is observed that the parameters follow an approximately
logarithmic function, and that the contact pin resistance decreases with increasing
current, whereas the other parameters increase as a function of contact current. Calculated
contact power has an approximately straight-line relationship on a log-log plot. Dissipated
power level is approximately 0.20 W at 15 A, increasing to 3.7 W at 100 A, and further
increasing to 10 W at 200 A. Above 200 A, the contact power remains constant at approximately
10 W. Experience indicates that a typical off-the-shelf connector, operating at its
maximum specified rating of 15 A and dissipating over 0.4 to 0.5 W of power, may start to
overheat. At power levels of 0.8 to 1 W, this connector will rapidly overheat. If the dissipated
power level exceeds 1 W, the connector will go into thermal runaway, with contact
pin temperatures exceeding several hundred degrees and subsequent melting and ignition
of the plastic insulating material. Thermal runaway is discussed further Sec. 17.8, which
describes case studies (p. 17.47).

http://www.accessengineeringlibrary....9639_ar017.pdf

Bravo - now finally some real and useful information.

What this boils down to is that a cheap connector should not be used at its full rated capacity. At 15 amps, there will be enough resistance to produce 0.5 W of heat, which is almost enough to make it start to overheat (not 3680 watts, and irrespective of what type of load is on the circuit - resistive, a motor, whatever - the only thing that matters is how many amps). If you overload it, it will go into thermal runaway as more heat is produced than can be dissipated. Maximum heat produced is 10 watts (again, not 3680), but 10 watts is enough to start a fire.

So the moral of the story, I think, is:

1. Use good connectors, not crappy Home Depot ones
2. Specify them so that they will not be loaded to full capacity
3. Crimp them properly with a good ratcheting crimped
4. Inspect them from time to time to be sure that they don't start to corrode.

Can we all agree?

transmitterdan · 28-01-2012, 03:00

Quote:

Originally Posted by FlyingCloud1937

Yes the came off the same boat.

There is a lot of information in the picture, just look at the labels. All of the loads that were of the restive type are burnt. Now look at the cable to the far right galley outlet.

Lloyd

They all came off high current loads (heaters, toasters, microwaves, etc.). It has nothing to do with "resistive type". A typical space heater of 1500W draws about 12-14A. Clearly these crimps were not tight enough for that load. Also, the wire looks a little small but I can't judge the gauge of wire. The crimps all look to be very poor. One even looks to be soldered which if so can cause its own problems. The common denominator looks to me like a poor electrician did this work.

Dan

**s/v Jedi** · 28-01-2012, 03:29

Quote:

Originally Posted by transmitterdan

They all came off high current loads (heaters, toasters, microwaves, etc.). It has nothing to do with "resistive type". A typical space heater of 1500W draws about 12-14A. Clearly these crimps were not tight enough for that load. Also, the wire looks a little small but I can't judge the gauge of wire. The crimps all look to be very poor. One even looks to be soldered which if so can cause its own problems. The common denominator looks to me like a poor electrician did this work.

Dan

I didn't want to bring that up but 100% agree. I think the common denominator among these failures is the crimps done by the same installer.

The resistive load thing... if there is such a thing as a "clean" load then it is resistive. I could be made to believe that an inductive or capacitive load creates a problem with a terminal, but not for a resistive load.

But none of this has anything to do with the IT. This is not really the thread to try to ban crimp terminals from boats. Back to soldering gauge 4/0 battery cables?! No way lol.

ciao!
Nick.

**Dockhead** · 28-01-2012, 03:48

Quote:

Originally Posted by s/v Jedi

I didn't want to bring that up but 100% agree. I think the common denominator among these failures is the crimps done by the same installer.

The resistive load thing... if there is such a thing as a "clean" load then it is resistive. I could be made to believe that an inductive or capacitive load creates a problem with a terminal, but not for a resistive load.

But none of this has anything to do with the IT. This is not really the thread to try to ban crimp terminals from boats. Back to soldering gauge 4/0 battery cables?! No way lol.

ciao!
Nick.

I have had nothing but problems with soldered terminals on cars and boats. In my youth I did not trust crimped terminals -- probably right, since at that time I had never even seen a good crimp tool

So I took crimp terminals and soldered the wires into them -- thinking it would be top best practice.

Well, those joints all failed because of vibration. And I inherited some soldered terminals on my boat which also failed due to vibration.

According to everything I have read, a really good crimped terminal is better than any other type.

I have a good ratcheting crimp tool, but I'm always looking for something better, and am willing to pay almost any price.

I am also on a constant search for better crimp terminals. The last batch I bought from the electrical wizard at Cowes -- they were expensive and he swears by them, but I am still skeptical, and still looking for better ones -- and don't care what they cost.

No crimped terminal done by me has ever, in my experience, ended up looking like one of those depicted by Lloyd. But I am careful making them, and scrupulous about not overloading them. Also, I use 230v and 24 v power, which requires half the amps for the same power as 110v and 12v, which I avoid.

**s/v Jedi** · 28-01-2012, 04:09

Yes, soldering wire creates a hard spot that leads to failure where a crimp survives.

That is why I question Loyd on vibration causing failures with crimp terminals. But he has gone back to his game of ignoring that and just throwing out random bits of new info. Last time he wanted engineers with oscilloscopes come out and test genset waveforms and later also shore power waveforms.... for a broken fan in a charger. He now claims he solved the problem before I did... the path of discussion leads to nowhere. I got PM's from other CF engineer members with the same experiences and we just let it go. Only problem is that unknowing readers might interpret that the wrong way.

I think I will put this on my blog instead and just post a pointer on CF. Just did that with something else and that works much better.

cheers,
Nick.

**GordMay** · 28-01-2012, 05:20

Greetings and welcome aboard the CF, transmitterdan.

Maine Sail · 28-01-2012, 05:22

Quote:

Originally Posted by Dockhead

I have a good ratcheting crimp tool, but I'm always looking for something better, and am willing to pay almost any price.

AMP Aerospace Certified (when used with AMP PIDG terminals) - They will however exceed US Mil-Spec pull strains when crimping other terminals such as Molex & FTZ (I do not and will not use Ancor terminals personally). I've load tested these tools myself to be sure... With a 12GA wire and yellow ring terminal they beat the next closest ratcheting crimper I own by about 60 pounds of pull strain..!

For example a 12GA wire in a yellow ring will not allow pull out to about 190+ pounds of force, this well exceeds even the US mil-spec. The Mil Spec MIL-T-7928 tensile requirement for this same terminal & wire is actually 110 pounds..

**Dockhead** · 28-01-2012, 06:16

Quote:

Originally Posted by Maine Sail

AMP Aerospace Certified (when used with AMP PIDG terminals) - They will however exceed US Mil-Spec pull strains when crimping other terminals such as Molex & FTZ (I do not and will not use Ancor terminals personally). I've load tested these tools myself to be sure... With a 12GA wire and yellow ring terminal they beat the next closest ratcheting crimper I own by about 60 pounds of pull strain..!

For example a 12GA wire in a yellow ring will not allow pull out to about 190+ pounds of force, this well exceeds even the US mil-spec. The Mil Spec MIL-T-7928 tensile requirement for this same terminal & wire is actually 110 pounds..

That looks like a serious bit of kit. So you recommend this AMP crimp tool and what kind of terminals? Molex? FTZ? But not Ancor?

Maine Sail · 28-01-2012, 06:41

Quote:

Originally Posted by Dockhead

That looks like a serious bit of kit. So you recommend this AMP crimp tool and what kind of terminals? Molex? FTZ? But not Ancor?

I am not necessarily "recommending them" as they are grossly expensive. They are what I have chosen to use for rings, which are what I crimp most..

Personally I like to see any tool that can meet or exceed the US MIL-T-7928 and I know these tools can do that. I personally feel the ABYC spec for crimp terminals is a joke, but that is just my own personal preference. For example ABYC wants 35 pounds for 12GA wire and the US Military wants 110 pounds.... Big difference...

The tools shown will exceed even the US Mil-Spec and that makes me very comfortable when putting my name on that termination.

For factory made heat shrink, the vast majority of my terminations, I generally use FTZ as they are very consistent, but Molex and AMP also make excellent and consistent terminals and I use those too.

For insulated terminals I use AMP PIDG terminals.. Keep in mind these two tools only crimp rings or forks. The one on the left only does Yellow and the one on the right, only Red & Blue.

You'd need another tool for butts unless you want to slightly modify them by removing the terminal stops for forks and rings. I try to avoid friction fit connectors at all costs, but sometimes it just can't be avoided..

I generally steer away from Ancor because I find the quality & consistency of the terminals is like going to Vegas, kind of a gamble. You never know what supplier is supplying the product to them this week vs. last. Ancor does not make their own stuff, they are nothing more than a re-brander and re-packager and the terminals are anything but consistent, in MY experience.. They don't even make their own wire. They are a "brander" not a manufacturer..

Companies like Molex, AMP and FTZ are quite consistent and seem to have considerably better quality controls in-place than I find Ancor does. Nothing against Ancor I just want "consistency" in a terminal, which I don't find they offer when compared to companies like AMP, Molex or FTZ among others...

**Dockhead** · 28-01-2012, 06:48

Quote:

Originally Posted by Maine Sail

For heat shrink I generally use FTZ as they are very consistent, but Molex and AMP also make excellent and consistent terminals. For non-insulated I use AMP PIDG terminals.. Keep in mind these tools only crimp rings or forks, you'd need another tool for butts unless you want to slightly modify them by removing the terminal stops..

I generally avoid Ancor because I find the quality & consistency of the terminals is like going to Vegas, kind of a gamble. You never know what supplier is supplying the product to them this week vs. last. Ancor does not make their own stuff they are nothing more than a re-brander and re-packager and the terminals are anything but consistent in my experience.. They don't even make their own wire. They are a "brander" not a manufacturer..

Companies like Molex, AMP and FTZ are quite consistent and seem to have considerably better quality controls in-place than I find Ancor does. Nothing against Ancor I just want "consistency" in a terminal, which I don't find they offer when compared to companies like AMP, Molex or FTZ among others...

Great advice; thanks.

transmitterdan · 28-01-2012, 06:57

I agree 100% with Maine Sail about the tools and brand name terminals. Another point about tools is that the tool ideally should be "calibrated" to ensure it is making proper crimps. Some lesser crimpers will change performance after several uses. I had one from Harbor Freight that was useless because of this. In a production environment, high quality crimp tools should be checked every 6 months or yearly minimum. Most of us don't have a way to calibrate a crimper. Maine Sail's suggestion for doing a simple pull test will help determine if the crimper and terminals are compatible and working correctly.

Dan