Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
1970 Fury Alternator and Battery Charging Considerations
There has been a lot of discussion about alternators, bulkhead problems, ammeter bi-pass and the addition of heavy load options such as upgraded headlights, audio systems, etc. I�ve decided to try and clear the muddy waters as much as possible by taking you through the wiring on my 70 Fury which should be fairly representative. To make my diagram fit your car you will have to look at the wiring diagram in your Shop Manual and renumber the bulkhead pins to match your year.
The OEM system on my '70 Fury looks like this. A wire runs from the Battery stud on the alternator to bulkhead pin #16. The alternator has two Field studs, one runs to the Field pin on the regulator and the other goes to a splice (which Mopar calls the #1 splice). Four wires are spliced, one from the alternator Field, one to the ignition ballast resistor, one to the ignition pin on the regulator and one to bulkhead pin #12.
On the dash side of the firewall, the wire connected to the #16 pin goes to another splice which Mopar calls the Master Splice. Two wires from this splice go to the fuse panel and via fuses and breakers supply virtually all circuits. Two special circuits also connect to this splice, the headlights and the ignition switch. Finally a wire from the splice goes to the ammeter. From the other side of the ammeter a wire runs to bulkhead pin #28.
Back on the engine side, a wire runs from the bulkhead pin #28 to the battery stud on the start relay. Finally from the battery stud on the starter relay a fusible link runs to the battery.
Back on the dash side, the wire from bulkhead pin #12 runs to another splice. This splice joins wires from the ignition switch, key-in buzzer, dual brake warning lamp, oil warning lamp and hidden headlight door motor.
Ok, so how does it all work?
With no key in the ignition, 12 volts will be found on one side of the ignition switch. This voltage is from the master splice via the ammeter, via pin #28, via the fusible link from the battery.
Now put the key in the ignition, do not turn to start, just to the run position. In the run position the 12 volts now goes from the ignition switch to the splice connected to pin #12. From there 12 volts appears at the ballast resistor, the Ignition pin of the regulator and the Field studs on the alternator, one Field directly from the #1 splice and the other from the Field pin on the regulator.
Looking at the ballast resistor, one side has 12 volts from the #1 splice; the other side has a wire connected to the coil and a wire connected to bulkhead pin #11.
Also note that 12 volts from the battery via the master splice, via bulkhead pin #16 appears at the alternator Battery stud.
The 12 volts on the splice connected to bulkhead pin #12 also causes the Brake Warning Light and Oil Warning Lamp to light.
Ok, turn to start and the following happens. The start contacts on the ignition switch pass 12 volts to bulkhead pin #11 to put 12 volts on the coil. Another ignition contact connected to bulkhead pin #31 and on to the Ignition stud, passes 12 volts and the relay pulls in, spins the starter and turns over the engine. The rotating engine turns the distributor to make and break a ground connection to the other post of the coil. This fires the plugs and the engine starts. When you release the key back to the run position, the starter stops and the 12 volts disappears from bulkhead pin #11 which feeds the coil. However we still get battery voltage via the master splice through the ignition switch to the splice connected to bulkhead pin #12. However the 12 volts now has to pass through the ballast resistor to get to the coil. This means there will be a voltage drop and the coil will not see 12 volts but probably 10 volts or so.
While all this neat stuff is happening the motor started spinning the alternator and the regulator is busy making sure the voltage at the #1 splice is regulated. Note the voltage at the #1 splice is coming from the alternator battery stud, via bulkhead pin #16, via the master splice, via the ignition switch, via the splice to bulkhead pin #12, to the #1 splice.
Now assuming our regulator is set for say 14 volts, the couple of volts we were losing across the ballast resistor are now working in our favor, the coil doesn�t get the whole 14 volts, it gets about 12 volts. People with shorted ballast resistors fry coils. People who don�t read instructions when wiring up electronic ignitions usually burn expensive toys.
Anyways the alternator is happily pumping out 14 volts via Bulkhead pin #16 to the master splice where it is distributed to all the various toys and lights. None of this current load passes through the ammeter or the battery. When you turn on the radio, the 12 volts goes into the radio and the return path is to the dash ground, to the body ground, to the engine ground strap to the well grounded to the engine alternator. You must ensure all of these ground connections are clean and tight.
Now since we just used the battery to start the engine it will have lost some charge. Power will pass from the master splice through the ammeter to bulkhead pin #28 and on to the battery via the fusible link. The length of this path is about 7 or 8 feet and the resistance of this path will create a voltage drop proportional to the current flowing down the wire. Note that the 3-wire alternator regulates at the Master Splice so the charge wire path is from the splice to the battery. For those who have converted to a 1-wire alternator the path is longer running from the alternator stud all around to the battery. The 3-wire charge wire length is specifically designed to simply and automatically limit charging rate and to avoid boiling the battery dry. When the battery has completely charged it will settle to 14v as the charging current drops to zero. If you turn off the engine when the battery is fully charged and put a voltmeter on it, you will measure about 14 volts. However after a few hours the battery will settle and stabilize at 12,6 volts.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
This segment looks at voltages and the effects of dirty connections.
Note the circuit from the alternator Battery stud, via bulkhead #16, via master splice, via ignition switch, via the splice connected to bulkhead pin #12 and the #1 Splice are all connected and all should be at the same voltage. And, that voltage is set at the #1 Splice, so what�s the big deal?
Well the big deal is every joint, connector, piece of wire and switch contact have some resistance and will create little voltage drops. The current through the wire from the alternator Battery stud, via bulkhead pin #16 to the master splice will work against the resistance along the path and create a voltage drop. So what? Well the current from the master splice via the ignition, via splice connected to bulkhead pin #12 to the ignition will also cause another voltage drop. No sweat, the regulator will jack up the alternator output until the ignition is back to 14 volts. Well actually the #1 Splice and that will be dropped to 12 volts by the ballast resistor before it gets to the coil.
Since our cars are getting on in years, they might have a little dirt in the bulkhead.
For instance, bulkhead pin #12 is dirty and it is dropping 2 volts. What happens? The 14 volts our alternator is pumping out is only 12 volts by the time it gets to the #1 Splice. But the regulator doesn�t like that, cranks up the alternator to restore our 14 volts.
Great, the regulator is happy, but we start to fry bulbs because our alternator is pushing 16 volts to the master splice. Even the battery tries to accept more charge. It can�t but since the voltage is now over 14.4 volts the electrolyte starts to breakdown pump out hydrogen.
Not good!
If bulkhead pin #16 is also dirty and dropping another 2 volts, the regulator will see the drop and crank the alternator up to 18 volts. The system will stabilize with the under dash wires at 16 volts, the regulator at 14 volts and the alternator at 18 volts.
Probably not long before the alternator self destructs.
I might add at this point, in 1978 before I parked my Fury the alternator was flaky. I�d pull the alternator, clean and check it. Never any problems found so I�d re-install and it work for a few days and then nothing again. Over a month or so of alternator war, I replace the alternator twice, regulator once and fiddled and fussed with it to no avail. Finally I parked it in my back yard and it essentially sat there for 18 years. When I pulled the front fenders I discovered the bulkhead connector. I dug out the wiring diagram and started looking at the pins and found pin #16 had been running so hot it actually melted a hole in the bulkhead block. Fixed that and my charging system worked perfectly.
I can�t stress enough how important it is that the bulkhead connector pins be in mint condition and sealed from dirt and moisture.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Now that we understand how the three wire, remote sensing, alternator used in my 70 Fury works, how do we make it bigger?
If we decide we want a gazillion watt audio system that draws 50 amps we need a bigger alternator and we need to look at wire sizes and ground sizes. If the OEM alternator is rated for 30 amp we need to get a new one rated for at least 80 amps. Since we know more toys will appear, go bigger, but not too big. Alternator selection is more complicated than just amps, their output varies with rpm. Some generate lots of amps down at idle speeds, some don�t. If you select the wrong type, your audio system sound will vary with speed. The regulator simply can�t maintain the regulated voltage if you draw heavy current at low rpm. If the voltage at low rpm is say 11 volts, then the battery will try to make up the difference. Get stuck in traffic for a while and your alternator will overheat and your battery will slowly discharge.
Good alternators which will produce lots of current at low rpm are not cheap.
Ok assuming you have found the perfect alternator. If it has a Battery stud and two Field studs, it is a three wire remote sensing type and you may have to buy a matching voltage regulator. I say may because the Fields are controlled by voltage from the regulator and as long as they don�t draw current your OEM regulator should work. But make sure because each alternator is different.
If the new alternator has only a Battery stud, it is internally regulated. So only connect the wire from bulkhead pin #16 to the Battery stud and you can disconnect your existing regulator. The two wires running to the #1 Splice that used to go to the alternator Field stud and regulator Ignition pin are no longer needed. Insulate the ends since they will be live and wire tie them out of the way.
Start the car, your new alternator should be working perfectly!
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Now, where to connect our 50 amp toy? You absolutely don�t want that kind of current flowing through the bulkhead, so the connection point needs to be somewhere between bulkhead pin #16 and the Battery stud on the alternator. You don�t want to run a ton of wires to the alternator stud and you can�t just splice it into the existing AWG 10 wire going to bulkhead pin #16.
You need to buy a buss block which in simplistic terms is a big bolt, usually copper, that you connect a bunch of wires to. It�s a fancy name for a splice. You can get ones with a copper bar with lots of studs on which you can connect wires. If you plan to have electric fans and/or high powered headlights, get two. Now before you go shopping, consider what will be connected to these bus bars. Will the devices require fuses or fusible links? Say yes since you really don�t want to burn up your ride when an amplifier shorts out.
So you better get a bus bar that has a weather protected box and has some way to mount fuses, breakers, fusible links and maybe some relays. Go to a wrecker and look at the power distribution boxes used in modern cars. They use relays for some circuits, breakers for others and lots with modern spade type fuses. These can be repurposed easily to connect your toys. When you get the box, get as much of the harness as you can, you can use parts of it for your circuits.
Ok assuming you�ve got one or two of these distribution boxes, mount them where they will be handy. These boxes will have stud to connect to the alternator, connect the stud to the alternator Battery stud using battery cable. The battery cable must be stranded with a high strand count so that it is nice and flexible. It should have factory pressed spade lugs on each end. Route the cable such that at the alternator end it can�t get near the manifold. Now you need to ponder how to route the cable to make the jump from the engine to the body or firewall. These parts are moving with respect to each other and that will flex the cable. You want as little cable flex as possible. Since the motor moves from side to side and not up and down, its probably best to route the cable down the top of the engine and up onto the firewall. You will need to play around to get the best location. Just remember this cable, if shorted will output the full capacity of your alternator.
If you have a second distribution box up on the rad support for fans and/or headlights, run another big cable from its battery stud around the fender to the firewall and the battery stud on that box. This wire doesn�t need to be battery cable because the rad support loads will not be huge. In any case, both cables must be large enough that at full amperage load they drop minimal voltage since you want your distribution box(es) to be fixed at 14v.
Now reroute the AWG 10 wire from bulkhead pin #16 to the bus block.
At this point check your ground straps, add a few extra ones and make sure all are tight and clean.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Ok the power side of the system is complete, what about the battery charging circuit. The OEM circuit is fine the way it is, or is it? Well if your alternator selection was done correctly, the alternator should be able to supply sufficient current (power) at idle to run all the toys and maintain the bus voltage at 14 volts. If this is true, and will always be true, then the OEM circuit is fine. However, we are not perfect and neither are alternators. If the alternator can�t keep up to the load, the battery will jump in and start pumping out amps. These amps will pass through bulkhead pins #28 and #16 to get to our bus. We don�t want to push those bulkhead connections, so we will bypass them.
Disconnect the wire from bulkhead pin #28 at the starter relay, tape the end very securely and cable tie it against the harness. Run a new 8 foot length of AWG #10 from the starter relay to the new bus on the firewall. You may need to get creative to use up the extra length, just don�t shorten it or you�ll screw up your battery charge rate. The existing fusible link should stay in place between the starter relay and the battery.
Batteries accept charging current only when the voltage on the posts is higher than the sum of the cell voltages. If the voltage difference is 1 volt, the internal resistance of the battery will limit the current to some value. Increase the voltage difference, the charge rate increases. Essentially the extra resistance of our 8 feet of charge wire acts to reduce the voltage difference and slow the recharge down, thus avoiding heat and gassing.
A common mistake, people assume that if they change from a 30 amp alternator to a 100 amp alternator their battery will charge faster. Nope! And that�s why the AWG 10 wire and fusible link are still sized correctly.
And by the way, your ammeter is now dead and no longer a worry.
|Since the charge circuit no longer passes through the bulkhead, the only critical connector to worry about is good old #16. On my car I noticed that bulkhead connector pin #25 was unused, so I took pin #16 apart, replaced the wire ends and moved them to location #25. Recall my #16 slot was basically a black hole and it was easier to relocate the pin than replace the whole bulkhead connector. If you are worried that #16 is still heavily loaded, unwrap the wire that we abandoned from pin #28 and route it over to the new bus. This will split the load between pins 28 and 16 but it will cause your ammeter to bounce around. Do not reconnect it to the starter relay. That would put it in parallel with our new 8 foot charge wire and effectively cut its resistance by 2.
Now before you start ripping things apart, get a wiring diagram for your car and draw your own diagram similar to mine. Your bulkhead pin numbers probably will be different. Use your diagram to verify where the wires actually are on your car. Unless you are the first owner, you may find interesting surprises. Since Ma Mopar knew what she was doing, any modifications you find should be carefully examined to see that they don�t cause problems. While you are at it, clean every connection you find. Don�t forget the grounds. One car restoration problem is over zealous application of paint between bolted together body panels. If you paint all the mating surfaces you will have ground problems, so get some braided copper strap and some crimp on terminals to make some short ground straps. Use these jumpers between panels placing the straps across joints behind or under so they don�t show. Alternately run a bunch of ground wires in a harness and physically ground each light assemble, etc. and not rely on body grounds at all. I�m leaning toward a grounding harness, easier to do and easier to trouble shoot.
Joined: Thu May 01 2008, 11:15AM
Location: Chicago,IL
Posts: 2868
Polaraco wrote ... It's not rocket science
It may not be, but there have been a lot of people on here confused and posting info that is only 1/2 correct at best. Clear posts like this from professionals do nothing but make this a better place for everyone.
Good job Bill! Had to wait till I had a quiet moment to read through it all. True, most of this can be gleamed from the wiring diagrams, but I know many people see all those lines and go snow blind.
One minor addition. When the voltage drops happen due to resistance, that energy has to go somewhere. That somewhere is HEAT. Which is what causes the meltdowns, fires and other general calamities. It is impossible to over stress the importance of keeping ALL electrical connection points clean and tight. Dielecetric grease is one part of this, it will keep moisture and dirt out of the connections. I use it on just about every electrical contact point- Bulkheads, blades, harnesses, and even light bulbs. Ever had to remove an exterior bulb with needle nose because it corroded in the socket??? Goes along with my theory on anti-size and threads, but that is another topic!