Chevy Nova Forum banner

21 - 33 of 33 Posts

·
Registered
Joined
·
304 Posts
i know nothing about electrical, but there has to be a measurable test for this using one car and testing the multiple locations? maybe?

would what Chevy II Guy experienced should show something of a good initial result, then a result that would degrade over time as his alternator got toasted? say, during initial connection he was at 100%, three weeks later 50%, 6 weeks later 0.5% with a roasted alternator. or do electrical issues not show in such a way? as in they go from 100% to zero, and that's it? i am using generic non-actual, no units numbers for my simple brain, so go easy on me, please.

just would rather have a scientific test with actual data rather than "mine works fine" which is what kind of where i am at--mine works fine. but does it really? and will my alternator fail over time?

i am fascinated by this subject, sorry for my electrical ignorance and rambling. would also like to avoid alternator issues.

-Rusty
 

·
Registered
Joined
·
9,845 Posts
One other thing, I originally had my battery (in the trunk) grounded to the rear subframe. I have welded in subframe connectors so I figured this was a good path. I could start my car with no problems. However, I was burning up alternators. Upon getting my 3rd alternator replacement under warranty, I went to a alternator/starter rebuild shop and asked a few questions. I described my problem to him and he immediately said, "this sounds like a ground problem." I then ran the ground battery cable to my transmission and have not had a problem since.
Interesting - when you are running your engine, the alternator is the mother of all grounds. All current runs through he case of the alternator and the battery ground has little to do with anything. A bad connection means reduced current, which would not be a condition of burning up an alternator.
 

·
Registered
Joined
·
9,845 Posts
i know nothing about electrical, but there has to be a measurable test for this using one car and testing the multiple locations? maybe?

would what Chevy II Guy experienced should show something of a good initial result, then a result that would degrade over time as his alternator got toasted? say, during initial connection he was at 100%, three weeks later 50%, 6 weeks later 0.5% with a roasted alternator. or do electrical issues not show in such a way? as in they go from 100% to zero, and that's it? i am using generic non-actual, no units numbers for my simple brain, so go easy on me, please.

just would rather have a scientific test with actual data rather than "mine works fine" which is what kind of where i am at--mine works fine. but does it really? and will my alternator fail over time?

i am fascinated by this subject, sorry for my electrical ignorance and rambling. would also like to avoid alternator issues.

-Rusty
One thing to think about is the number of trunk mounted battery installations that are working just fine with a ground attached to the rear frame, probably about 99%. As in any fix-it thread it's the failures that drive the conversation.
Most electrical problems in old cars stem from bad connections, and by physically manipulating the wiring, either by replacing wires or inspecting and adjusting wires, you may fix the problem. If you do multiple connections at one time you have no idea which one was the faulty one. If you want to know what the actual problem was, do one connection at a time.
A good school for how to wire a rear mounted battery is your local boneyard. Look at how guys who design this stuff for millions of cars do it. Find a car with a rear-mounted battery, like a BMW, Volvo, MBZ, Saturn, Jaguar and see how they run the cable, what size cable do they run, how they insulate the cable, how they ground the battery, etc.
 

·
Registered
Joined
·
1,065 Posts
Interesting - when you are running your engine, the alternator is the mother of all grounds. All current runs through he case of the alternator and the battery ground has little to do with anything. A bad connection means reduced current, which would not be a condition of burning up an alternator.
With a bad ground, the alternator thought the battery was low and worked at 100% and kept burning itself up.
 

·
Registered
Joined
·
34 Posts
With a bad ground, the alternator thought the battery was low and worked at 100% and kept burning itself up.
I have personally repaired many vehicles over the years with bad alternators, odd conditions ect that all came back to the same thing, guys with trunk mounted batteries that decided to cheat and not run the negative cable to the block or bellhousing. Sure the factory on many vehicles does it and gets away with it quite well, my 2010 Camaro being 1 of them. However I stand by and always will that any car (esp old) that was not equipped that way from the factory gets it done right. And by right I mean 2 cables ran side by side and anchored every few feet at the most by insulated clamps, that way I know for a fact that even though there may be issues with any build a voltage issue due to bad ground wont be one of them.
 

·
Registered
Joined
·
355 Posts
I spent 7 years writing service diagnostics for GM and 20 years as an electrical engineer at Chrysler, along with building many cars in my garage and 6 years as the BCM/RF hub/battery/alternator/cable release engineer on the Viper program and I'm still learning things from Mike Goble! Thanks for doing the math.
 

·
Registered
Joined
·
9,845 Posts
With a bad ground, the alternator thought the battery was low and worked at 100% and kept burning itself up.
This doesn't make sense on many levels.

1. The battery ground was sufficient to start the car. This is when the battery is providing 100+ amps to the starter and Kirchoff reminds us that all current must return to the source. There must be a good ground connection to pass that current, and the starter is grounded to the block. This means that the block is a good ground, and whatever the block is grounded to is a good ground as well, followed by whatever the battery is grounded to.
2. Once the engine is running, all current returns to the case of alternator. The alternator senses the voltage at whatever point the sense line is connected to and controls the voltage based on that sense point. It doesn't single out the battery as a specific load that needs more voltage, at this point the battery is just another load. The alternator will supply current to the battery based specifically on the difference in voltage between the alternator output and the unloaded battery voltage, which moments before had been sufficient to start the engine.
3. It takes just a few minutes to restore the battery to full charge. If you supply 100 amps for 5 seconds to start your car, it takes about 30 seconds at 16 amps to restore the charge. Beyond that, the current goes to a trickle.
4. A faulty connection, by its very electrical nature, reduces the current in a circuit. It would defy every law of electricity to assume otherwise. .
5. How does the ground that was sufficient to pass 100+ amps when you turned the key suddenly disappear and become insufficient to maintain a trickle charge to the battery?
 

·
Registered
Joined
·
9,845 Posts
I have personally repaired many vehicles over the years with bad alternators, odd conditions ect that all came back to the same thing, guys with trunk mounted batteries that decided to cheat and not run the negative cable to the block or bellhousing. Sure the factory on many vehicles does it and gets away with it quite well, my 2010 Camaro being 1 of them. However I stand by and always will that any car (esp old) that was not equipped that way from the factory gets it done right. And by right I mean 2 cables ran side by side and anchored every few feet at the most by insulated clamps, that way I know for a fact that even though there may be issues with any build a voltage issue due to bad ground wont be one of them.
A couple of points:

1. No one in this thread is advocating against running a separate cable as a return line.

2. To what would you attribute success of the vast majority of rear mounted battery installations that use the steel of the body as a return line, whether OEM or home-built? I have built many cars as well, and used the frame as a return successfully 100% of the time.
 

·
Registered
Joined
·
34 Posts
If these cars were originally equipped with trunk mounted batteries and engineers determined how and where to properly put the grounds (as I explained with my 2010 Camaro) then my thinking may be a bit different. But they were not and when re-engineering something that's in most cases over 50 years old my feeling is to go the extra mile. And with problems I've addressed regarding this issue I always let experience be my guide. We put tons of money into these cars for things that in most cases are more about looks (I'm really guilty on this lol) then why not just spend a few extra bucks on something that may negate a problem sooner or later. Regardless some of us may just have to agree to disagree and since the thread is pretty much beat to death I'm out.
 

·
Registered
Joined
·
1,065 Posts
This doesn't make sense on many levels.

1. The battery ground was sufficient to start the car. This is when the battery is providing 100+ amps to the starter and Kirchoff reminds us that all current must return to the source. There must be a good ground connection to pass that current, and the starter is grounded to the block. This means that the block is a good ground, and whatever the block is grounded to is a good ground as well, followed by whatever the battery is grounded to.
2. Once the engine is running, all current returns to the case of alternator. The alternator senses the voltage at whatever point the sense line is connected to and controls the voltage based on that sense point. It doesn't single out the battery as a specific load that needs more voltage, at this point the battery is just another load. The alternator will supply current to the battery based specifically on the difference in voltage between the alternator output and the unloaded battery voltage, which moments before had been sufficient to start the engine.
3. It takes just a few minutes to restore the battery to full charge. If you supply 100 amps for 5 seconds to start your car, it takes about 30 seconds at 16 amps to restore the charge. Beyond that, the current goes to a trickle.
4. A faulty connection, by its very electrical nature, reduces the current in a circuit. It would defy every law of electricity to assume otherwise. .
5. How does the ground that was sufficient to pass 100+ amps when you turned the key suddenly disappear and become insufficient to maintain a trickle charge to the battery?
I gave you my hypothesis. What is yours? When it was grounded to the frame, it would start the car but it burned up multiple alternators. When I moved the ground to the transmission (from the frame) I have not had any charging issues since. Why would it do this? I don't claim to be an electrical engineer. I just have seen first hand what works reliably ALL the time and what can work but can also degrade over time and cause you problems later. A while back, I called American Auto Wire when I rewired my car. They highly encourage people to run a separate ground cable to the motor but stop short of telling people not to use the frame, due to the fact it is hard to tell some people it isn't a best practice when sometimes you can get by with it.
 

·
Registered
Joined
·
1,065 Posts
"Your steel frame rail is a very poor conductor of ground current. The American Autowire All Copper Grounding Kit eliminates the framerail as a conductor by using three grounding boxes connected by 6 gauge copper cable." This was taken from American Autowires's website.
 

·
Registered
Joined
·
9,845 Posts
Where to begin...

My first impression is that this is a company selling products to guys with little electrical knowledge or experience. Their products look and work well, but some of the claims are misleading or contrary to what one would do to assure the best ground path. You would definitely use something like this in a car with a poor or non-conducting body. I see that the large cable is about a foot long before they go to the 6 gauge. Are you going to ground your system within a foot of the battery? Is 6 gauge wire sufficient as a ground for your starter? If you have a steel car I see this as a $200 fix to a $2 problem. I also understand that there are guys who see $200 as just a drop in the bucket of their $40K build and it looks very good, but for old cheap guys like me, I can do a lot of other things with that $200. I also understand that if you are building cars for a living, appearances are very important.

Let's look at what is true with the AAW statement. True - steel is not one of the best conductors of electrical current, as I have shown in previous posts, about 1/8 the conductivity of copper, but it is not a 'poor' conductor. This includes the iron in your block and the steel in your alternator bracket. In your Nova, the original battery cable went from the battery to a piece of ferrous metal. The vast majority of problems in this circuit are caused by a faulty connection at this interface by paint, corrosion, loose bolt, etc. It's the same case with a rear mounted battery - the vast majority of problems are caused by a faulty connection on either end of the battery cable or the cable from the frame to the block.

There is no separate category of current delineated 'ground' current. Kirchoff's laws of current apply everywhere in the circuit, so the current at the positive post of the battery is always equal to the current at the negative post.

The current carrying capacity of any conductor is directly related to cross sectional area, hence a 14 gauge wire will carry less current than a 10 gauge wire. This is basically how a fusible link works, the smaller wire can't carry as much current as the larger wire and burns up. Look at a fuse from your fusebox, the center of the fuse has less CSA than the ends, and this is where the fusing takes place.

Electricity will take every path available between two points of different potential. If I put a 16 gauge wire in parallel with my 1/0 battery cable, it will conduct some of the current in a ratio inversely proportional to the resistance. 16 gauge wire has 40 times the resistance per unit of length than 1/0 cable, so about 1/40th of the current would go through the 16 gauge wire.

When you attach a ground wire to a steel frame rail in your car, the current is not confined to the rail. It courses through any and all conductors attached to the rail that afford a current path to a place of different potential. All crossmembers, the other frame rail, the floor, the sills, the body panels, roof, pillars, anything connected by conductors. For safety's sake I hope all this metal is securely welded together, like they did when these cars were new. The CSA of this steel return path is orders of magnitude larger than any dedicated wire you might run, so why would you eliminate it as a path of conduction? If I felt the need to add a separate ground wire in the system, like the setup above, I would add it in parallel to my existing path, thus increasing the current carrying capacity 100% of the time.

One of the things that most interests me in these threads is how the 99% of the properly working installations get swamped by the 1% that fail. As an engineer, when you design a circuit and 99% of them work and 1% fail, you do failure analysis. I look at the rear mounted battery as a good example of how this principle would work. Years ago, when guys started moving their batteries to the trunk for better weight distribution, some guy did it wrong. He didn't properly route and insulate the positive cable and he had a fire. A little failure analysis at this point might reveal that he stretched the cable over a sharp edge or laid it on the headers, etc. Using good electrical practices during the installation would have prevented this problem. Instead, he now installs a relay in his trunk, re-wires his starter circuit, and now everyone believes that if you don't have a relay in your trunk your car will catch on fire. If you go to the junkyard and inspect an OEM rear battery installation, one of the millions produced by various manufacturers, you will find properly engineered cable installations and no relays.

Addressing your particular alternator problem, I didn't participate in the process, so I don't really know what happened. One of the problems with electrical troubleshooting is that a simple tug on a wire may remove a problem without you even knowing it. A loose connection is made whole for the time being and you can't replicate the problem.
What were the symptoms when you burned up your alternators? Output voltage? Excess current? Where would this current go? Kirchoff says that all the current leaving the alternator must return through the case, which is bolted to an iron block or a steel bracket. All the current that is distributed through the system must come back through the ground connections. A bad connection in the ground system will not increase the current in the system, it will reduce it. Why would the ground connection be sufficient to start the car but insufficient to run the system at a greatly reduced current?
 
21 - 33 of 33 Posts
Top