Could this be early sign of battery at end of life?

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That's was my thinking "grease" I asked. He said "no" as the grease will eventually leak/leach out. Yep, grease does break down and separate, so that sounded right!

Hey, the guy may have been leading down a rabbi hole. The test would be use some silicone then test resistance. If resistance doesn't go up, it is good.
 
Sorry, I have got to disagree with what has been said. First a multimeter resistance test isn’t a good test as only a very small amount of current is used to get the reading, second point is that the main connection made is from the bolt itself, you are better of cleaning the threads and fitting a new bolt.
 
Interesting disagreement.

But consider it's not as easier or fast to clean paint out of threads as off body. And without sealing in some manner we're inviting corrosion.

What then would be a good test to see if use of silicone interfered with the connection?

What would you suggest as a sealant?
 
All you do is run a Tap through to clean threads, I have some electrical connection grease, it looks like vaseline. It was supplied via the parts department so not sure where or how to buy it, I would probably use vasaline/petrolium jelly. Best test is a voltage drop test, but I can’t see how silicone would affect it unless you apply it between the mating surfaces.
 
Julian Stead said:
All you do is run a Tap through to clean threads, I have some electrical connection grease, it looks like vaseline. It was supplied via the parts department so not sure where or how to buy it, I would probably use vasaline/petrolium jelly. Best test is a voltage drop test, but I can’t see how silicone would affect it unless you apply it between the mating surfaces.
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I interpreted it as applying it between the mating surfaces.
 
Best solution is not to clean the paint off the body in the first place, if you already have then fit the ground lead and tighten the bolt to torque, then apply the silicone over the top. The reason car manufacturers don’t use clean steel to make the connection is that it isn’t needed too and that corrosion will be a issue at a later date.
 
If someone removed my paint at the ground points I would be seriously annoyed. Aluminium or similar metal then yes I would clean, but mild steel panels need paint protection.
 
I've an issue grinding off good paint also. But on a connection that has bad paint, I'd give his suggestion a try. But would want to run some test first. I can't think of any other way, but to check resistance bare then with silicone.

The issue of corrosion on the cables working its way inside the connection & under the sheathing, is probable more import to us with our ageing fleet.
 
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Ground cable test is simple, voltage drop test under load, if the reading is more than 0.5v then change the cable and clean threads and bolt. If less than 0.5v then just spray with lithium grease and leave it.
 
2001LC said:
That it's probably time for the "Big Three Upgrade"

"He went on to say; good idea to check resistance of cable (off the vehicle), comparing to new cable. That if I see corrosion near lead, you can bet it's into/around wire strands and lead. This will increase resistance and must be replaced."

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Here's the full store:

This seem like a good thread to share something I just learned from a United Airline mechanic.

While on a flight to LA from Denver to buy The Black Knight (yes I name them) last week with my girlfriend, we got stuck in the very last row. She took window seat, while I the aisle thinking/hoping no one would take the center. Well, a guy 6'4" did, that couldn't get his knee to fit in, so I gave him my Knee space. We got to talking gear-head stuff the whole flight. He into diesel Mercedes and me into 100 series (what else). I gave you the above story, so you know where info comes from!

He told me in aircraft they have a tool that used to clean/grind under the ground/negative connection(s) on the air frame. They then add a dab of sealant to spot before bolting back on the the ground lead. They finish by cover assemble (Air frame, ground lead & bolt) with the sealant.

He said he's does same procedure on his car's. Cleans paint off from under leads on grounds and then seals. He's helped friends do the same, which cleared up electrical issues they had. He said the paint between lead & body metal increases resistance.

I asked "what is this sealant", he gave me a the name of this special aircraft sealant, but said I did not need it, that I could just use silicone sealant. That as bolt tightens, sealant squeeze out making a good contact and a perfect seal around the lead end.

He went on to say; good idea to check resistance of cable (off the vehicle), comparing to new cable. That if I see corrosion near lead, you can bet it's into/around wire strands and lead. This will increase resistance and must be replaced.
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A&P mechanics know their stuff! Have a look at section 4.0, page 17 (page 27 of pdf) https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980201283.pdf

Electrical bonding is no joke on aircraft, the entire airframe is a bond path to help protect it from lightening, a lot of composites even have conductive laminae worked in, bonding jumpers are all over air frames connecting everything together.... using some sort of chemical conversion coating on the surface, and then sealing, is standard OP in the aerospace world.
 
Yes, your cable is designed to take the design current of the vehicle. The best test is to test this by putting everything on, headlights, demisters etc and crank the engine over. If there is resistance in the cable it will cause a voltage drop, as I x R = V. You are measuring V(volts) with a multimeter, so to measure the Voltage drop across a single cable all you do is put your probes on each end. Now the circuit begins at the battery so put your black lead on the negative and put the red cable on the chassis ground point or any clean chassis point and then turn everything on that you can, take a reading whilst turning the engine over, cranking the engine over is not so important with the chassis ground but it does no harm. If the reading is over 0.5v then there is to much resistance causing a voltage drop. You can move the red lead to the motor and check the motor ground in the same way. This tests the cable in the most accurate way as it shows how it deals with the current it is designed to take.

The lead is so big and short then you would expect to see 0.1v or less but the manufacturers set a guide of 0.5v allowance.

Voltage drop tests was the only approved method that a multimeter was allowed to be used by the European manufacturers I was trained by.

Resistance checks for sensors

Test lamps are good for voltage or voltage drop method with a multimeter.
 
2001LC said:
Load test,,,, on a cable?
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Yup, there will be some resistance, more if the cross section is reduced due to corrosion...but it will be pretty small...I'm not sure if household multimeters would be able to reliably measure such small values though. may need some fancy Fluke stuff ;)
 
Julian Stead said:
Why are we talking aeroplanes
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because he was talking about the skybus mechanic who told him about sealing the bonding jumper... I just wanted to add to it, and nasa docs are cool... and I am a nerd....and I like metal tubes with wings (look at my avatar hahaha)
 
Ps, if you want to check that the ground connection points are good and not just the lead then move the red lead on to a good ground point close by, as in if you test the motor ground then put the red lead on to a clean bolt next to the ground point to confirm.
 
@Julian Stead good info thanks. Couple questions for you on this.

1. How did you come up with the 0.5v allowance voltage drop? Is it in the FSM?

2. Do you know of any chart or diagram that may show allowable voltage drop to wire size with length of wire factored in?
 
Julian Stead said:
Yes, your cable is designed to take the design current of the vehicle. The best test is to test this by putting everything on, headlights, demisters etc and crank the engine over. If there is resistance in the cable it will cause a voltage drop, as I x R = V. You are measuring V(volts) with a multimeter, so to measure the Voltage drop across a single cable all you do is put your probes on each end. Now the circuit begins at the battery so put your black lead on the negative and put the red cable on the chassis ground point or any clean chassis point and then turn everything on that you can, take a reading whilst turning the engine over, cranking the engine over is not so important with the chassis ground but it does no harm. If the reading is over 0.5v then there is to much resistance causing a voltage drop. You can move the red lead to the motor and check the motor ground in the same way. This tests the cable in the most accurate way as it shows how it deals with the current it is designed to take.

The lead is so big and short then you would expect to see 0.1v or less but the manufacturers set a guide of 0.5v allowance.

Voltage drop tests was the only approved method that a multimeter was allowed to be used by the European manufacturers I was trained by.

Resistance checks for sensors

Test lamps are good for voltage or voltage drop method with a multimeter.
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Very informative, thanks @Julian Stead

When I ask the A&P; "what resistance I should look for to determine if a given cable/wire is a good or bad" He said they compare to a new one in the shop, that they have in stock. Well if I had new in stock that would be nice, but I don't.

This automotive industry standard acceptable test may not be as sensitive, but should be very helpful.


Somebodyelse5 said:
because he was talking about the skybus mechanic who told him about sealing the bonding jumper... I just wanted to add to it, and nasa docs are cool... and I am a nerd....and I like metal tubes with wings (look at my avatar hahaha)
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Cool stuff! Read through, gives me high level of confidence this A&P was be genuine in his advice he gave me.
 
0.5v was specified by the manufacturers when on a training course. People where mis diagnosing circuits using multimeters on warranty claims so the master techs had to go for training on techniques that was a approved method to get the claims through. There was no chart, just that 0.5v was the maximum, this goes for all circuits. The cable calculations are done by the manufacturer and as long as you use the designed current then this works out. As in if you are testing a light circuit, you turn the lights on, testing the starter motor, you turn the motor over.

The cable calculation will be worked out from design current and lenght of run of cable, which is irrelevant to us as that has been calculated to give a voltage drop of less than 0.5v
 
As an alternative to voltage drop measurement: 4-wire resistance measurement is a common method to measure low resistances accurately (such as airbag initiators etc, please do not try at home!). Found a good video that describes the method for ground cables (below). If you were to measure the resistance between the negative battery terminal and the engine block and/or frame, you can determine the quality of the cable + clamping in one shot.

 
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