The Wonder of the Generator to Three-wire Alternator Upgrade

[FuzzyDriver]

With internet research I found that a Comet generator is good for about 30 amps. This charging current goes to the load-side of the ammeter so that you can detect charge/discharge conditions. A heavily discharged battery will draw nearly all 30 amps. This charge current passes through the firewall twice: path is generator/voltage regulator -> ammeter -> solenoid junction -> battery.
The alternator in a 1965 Comet is good for about twice that, 60 amps. I do not have a 1965 Comet to examine. Does someone with a stock-wired, alternator-equipped Comet know the gauge of the wire from the alternator to the ammeter? This wire is the heaviest wire coming from the alternator/voltage regulator (probably black-yellow). And then from the ammeter back to the solenoid (probably solid black)?
I'm certain that the wire gauge used was chosen by Mercury to be adequate for the maximum that the generator is capable of.
My concern is that if you have upgraded from a generator to an alternator, is the wiring adequate to supply the increased load capacity? Can the firewall "quick-connect" handle the current? What about the black-wire connector near the ammeter? Many who perform the alternator upgrade, use wiring diagrams for vehicles that do not have an ammeter. Using these diagrams, they take the ammeter out of the charge path (by hooking the alternator output directly to the battery). That's one half of the load issue, but any added, heavy loads (stereos and such) are still supplied through the black wire.
Confusing to people is that now the ammeter shows a discharge even when the alternator is charging the battery just fine. This is because the battery charge current (i.e., alternator current) is not passing through the ammeter, only load current is passing through.

When I got my 1964 Comet, whoever did the conversion must have been very confused. They did the common wiring diagram method of hooking the alternator output directly to the battery. And then they spliced the original generator output (white-black), now wired to the alternator output, to the voltage regulator output (black-yellow). The end effect of this was to create an alternate load path (around the ammeter).

[Lou's Comet]

A lot of people don't trust ammeters, also if you go from a 30 amp generator to a 60 amp alt the ammeter gauge also needs to be rated for the 60 amp, just like the wire. Prob why the previous owner took the ammeter out of the picture.


From page 116 in the Ron Francis catalog:

""DO NOT USE AN AMMETER!
WHY? Ammeters risk under-dash fires. It probably reads 30-0-30 or maybe 50-0-50? What amperage is your alter- nator? If it is more than the ammeter, say 100 amps or even 75 amps - you can understand how a low amperage gauge can’t handle what the charg- ing system can put out. You must not exceed the capacity of the gauge! External regulators give false readings to the alternator if there is any type of a bad ground. These style alternators are usually not capable of the extra amps most hot rodders want.
Running a cooling fan? Forget it.
To get a good reading from an ammeter, all juice must flow through it to sense and
indicate proper- ly. IF you don’t wire it prop- erly, there is no sense using it.
• Voltmeters tell you BEFORE the trouble.
• Ammeters tell you AFTER you already know there’s trouble.
• Ammeters cause too many false signals to the Alternator/Regulator resulting in over or under charging.
• Voltmeters will give improved Alternator efficiency.
Using a Voltmeter, rather than an Ammeter, eliminates the heavy cur- rent flow in the vehicle’s electrical system...a MUCH SAFER METHOD!""

Also here is a link to Autometer

https://www.autometer.com/blog/faq-post ... n-ammeter/

I have my old harness at my shop and could find the gauge of the wire for ya Sunday when I get back. But you might want to think about it before you start running 60+ amps thru a 50+ year old gauge in you dash.

Just something to think about,

Lou

[FuzzyDriver]

   I was interested in ensuring that the existing wiring traveling into/out of a Comet's cabin can handle 65 amps or so, but I appreciate your concern.
   Thanks for the copy-pasta. Where can I get this Ron Francis catalog? He doesn't seem familiar with the Comet ammeter, or even what an automobile's ammeter is for. But he certainly has a reactionary opinion to push out. Regardless of ammeter installation, the current supplying large hotel loads still passes through the firewall into the cabin via "quick connectors". So don't be thinking you're safe simply by not using your ammeter; it's that 60 year old wire you should ensure is safe.

   The Comet ammeter has no electrical connectors, so current flow through it is not a safety risk. It's needle deflection comes from electromagnetic coupling (i.e., a magnet near a wire carrying current). The wire loop running through the "quick-connects" along with the quick-connectors themselves are susceptible to high-current damage, but the ammeter itself is not. You can verify this by looking at the back of a Comet instrument cluster.
   I tested mine by running a test lead from my meter through the loop on the back of the ammeter and powering a headlight with my bench power supply.
   Just FYI, I did this test setup because I neglected to note which direction the cable went through the loop when I took the cluster out. If you run the wire through the loop backwards, the ammeter's readings will swap.
   The 1965 Comet has an alternator and ammeter. I found on the internet that this alternator is 60 A capable. Previous owner put a GM 7127-3AV alternator in my Comet, which is good for 65 A.
   Three-wire alternators, as I understand the vernacular, are not externally regulated. I've read a lot of articles describing "three-wire" alternator installation and they all are referencing alternators with internal regulators; such is the 7127-3AV put into my Comet by the previous owner.

Running a cooling fan? Forget it.
To get a good reading from an ammeter, all juice must flow through it to sense and
indicate proper- ly. IF you don’t wire it prop- erly, there is no sense using it.

   This is not correct. An auto's ammeter is not wired to normallu display current flow through all loads. If yours is, you don't have it "wired prop- erly". The ammeter is wired to display current into/out of the battery. In normal operation, the alternator is supplying loads along with whatever charge the battery is currently needing. This is why (again, in normal operation) your ammeter should show a slight charge (i.e., keeping the battery charged) even if you have all hotel loads turned on. If your cooling fan is wired so it can't run when the engine is off (i.e., like your water pump fan) then it's not a concern, either (for the same reason).

• Voltmeters tell you BEFORE the trouble.
• Ammeters tell you AFTER you already know there’s trouble.
• Ammeters cause too many false signals to the Alternator/Regulator resulting in over or under charging.
• Voltmeters will give improved Alternator efficiency.

   As an experienced technician and thinking things through, I'm not sure if any of this is true.
   An ammeter tells you immediately if your alternator fails because all loads immediately start passing through the ammeter as opposed to voltage which goes down gradually as the battery discharges. Got a big battery? Voltage might go down quite slowly.
   Ammeters do not give any signals to the alternator. They display battery current.
   The difference in alternator efficiency is the difference in heavy-gauge wire resistance times whatever current is flowing to the battery (not to loads - ammeters have nothing to do with load current when the alternator is suppying the loads). Are we talking about nano-watts here?

[Lou's Comet]

   I was interested in ensuring that the existing wiring traveling into/out of a Comet's cabin can handle 65 amps or so, but I appreciate your concern.
   Thanks for the copy-pasta. Where can I get this Ron Francis catalog? He doesn't seem familiar with the Comet ammeter, or even what an automobile's ammeter is for. But he certainly has a reactionary opinion to push out. Regardless of ammeter installation, the current supplying large hotel loads still passes through the firewall into the cabin via "quick connectors". So don't be thinking your safe simply by not using your ammeter; it's that 60 year old wire you should ensure is safe.

https://www.ronfrancis.com/

If you click on the request a catalog link it will let you download or view it. I have used his wiring harness's for years without a problem

  The Comet ammeter has no electrical connectors, so current flow through it is not a safety risk. It's needle deflection comes from electromagnetic coupling (i.e., a magnet near a wire carrying current). The wire loop running through the "quick-connects" along with the quick-connectors themselves are susceptible to high-current damage, but the ammeter itself is not. You can verify this by looking at the back of a Comet instrument cluster.
   I tested mine by running a test lead from my meter through the loop on the back of the ammeter and powering a headlight with my bench power supply.
   Just FYI, I did this test setup because I neglected to note which direction the cable went through the loop when I took the cluster out. If you run the wire through the loop backwards, the ammeter's readings will swap.
   The 1965 Comet has an alternator and ammeter. I found on the internet that this alternator is 60 A capable. Previous owner put a GM 7127-3AV alternator in my Comet, which is good for 65 A.
   Three-wire alternators, as I understand the vernacular, are not externally regulated. I've read a lot of articles describing "three-wire" alternator installation and they all are referencing alternators with internal regulators; such is the 7127-3AV put into my Comet by the previous owner.

I really didn't want to mess with the old gauges on my 65.
I took my factory gauges out and installed new Stewart Warner gauges and rewired the car with a Ron Francis harness. The old harness was rough. Also installed a ford 1 wire alt
https://www.summitracing.com/parts/PWM-77491

Running a cooling fan?
To get a good reading from an ammeter, all juice must flow through it to sense and
indicate proper- ly. IF you don’t wire it prop- erly, there is no sense using it.

   This is not correct. An auto's ammeter is not wired to normallu display current flow through all loads. If yours is, you don't have it "wired prop- erly". The ammeter is wired to display current into/out of the battery. In normal operation, the alternator is supplying loads along with whatever charge the battery is currently needing. This is why (again, in normal operation) your ammeter should show a slight charge (i.e., keeping the battery charged) even if you have all hotel loads turned on. If your cooling fan is wired so it can't run when the engine is off (i.e., like your water pump fan) then it's not a concern, either (for the same reason).

• Voltmeters tell you BEFORE the trouble.
• Ammeters tell you AFTER you already know there’s trouble.
• Ammeters cause too many false signals to the Alternator/Regulator resulting in over or under charging.
• Voltmeters will give improved Alternator efficiency.

   As an experienced technician and thinking things through, I'm not sure if any of this is true.
   An ammeter tells you immediately if your alternator fails because all loads immediately start passing through the ammeter as opposed to voltage which goes down gradually as the battery discharges. Got a big battery? Voltage might go down quite slowly.
   Ammeters do not give any signals to the alternator. They display battery current.
   The difference in alternator efficiency is the difference in heavy-gauge wire resistance times whatever current is flowing to the battery (not to loads - ammeters have nothing to do with load current when the alternator is suppying the loads). Are we talking about nano-watts here?

I don't know a lot about ammeters, from what I have read and the fact that they are no longer used in cars/trucks I took mine out and updated it to a volt meter when I replaced the wiring and alt.

I do have a 65 and I do have the old harness and alt, at my shop so if ya want I can find out the gauge of the wire for ya this Sunday.

Here is a link that determines wire size by length of wire and amps.

https://info.waytekwire.com/wire_sizing

Lou

[tomb22]

You would be better off getting yourself a one wire alternator with a internal voltage regulator. Hook this alternator directly to your battery. Bypass your ammeter and install a voltage gauge. Hook up the voltage gauge so that it has power when the car is on. When the voltage gauge reads 14 volts, you know that the alternator is working.
Tom

[Boss/Cyclone]

I am running the one wire alternator in a ford case in 3 of my old cars including my 65 Cyclone. I run a heavy cable, like a shorter starter cable, from the alternator to the power side of the solenoid and they all have worked perfectly for decades.

[Lou's Comet]

I agree with Boss and Tom,

Buy anyhow, I stopped by my shop and the wires you are asking about are 10 gauge. They are black/ yellow stripe and black with red stripe. They are the thickest wires, other than batt cables.

But I don't think my alt was 60 amp. The factory shop manual says it is either 38 amp or 42 amp. The Factory brochure states, introduced on 65 Comet 27% more electrical 38 ampere alt. So I am thinking it came with 38. Not sure where you got the 60 amp spec.

Hope it helps!

Lou

[FuzzyDriver]

Lou,
You are right about the original '65 Comet alternator. Not sure which store I got 60 amps from, but these stores don't seem to mind selling you a "replacement" alternator that would cook your wiring if you loaded it down. 60 amps? pfffh! Summit has a 140 amp "replacement" listed for a 1965 Comet. How is this a safe replacement? Even their replacement alternator disguised to look like a generator is 90 amps.

Thank you for checking your harness for me. I appreciate it.

Oh, and thanks for the link to Ron Francis' site! Seems like a good place to order electrical items from.

Michael

[Lou's Comet]

Lou,
You are right about the original '65 Comet alternator. Not sure which store I got 60 amps from, but these stores don't seem to mind selling you a "replacement" alternator that would cook your wiring if you loaded it down. 60 amps? pfffh! Summit has a 140 amp "replacement" listed for a 1965 Comet. How is this a safe replacement? Even their replacement alternator disguised to look like a generator is 90 amps.

Thank you for checking your harness for me. I appreciate it.

Oh, and thanks for the link to Ron Francis' site! Seems like a good place to order electrical items from.

Michael

No problem Michael.

I have installed more than a few Ron Francis wiring harness's over the years and never had a problem with any of them.
And your right there are stores that don't care if you are getting the correct parts. I am lucky to have a local mom and pop auto parts store that has been in business for 40+years that I buy from.

Lou

[Joe Travers]

I run a plain-Jane Otter Zone one-wire 45A on my '63. Only draw that isn't stock is the MSD ignition system.

My son ran into a lot of problems when he started piling on draws in the last Mustang we built together.
Electric fans and stereo amplifier were the worst. IIRC, he ended up w/ 60A unit to handle all of that.

Joe