Alternator Amp Size?

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DustyEd

DustyEd

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My wife and I are in the process of replacing the old "incorrect" alternator on our '70 Duster 340 4 sp. non A/C. We know it should be the round back design for 1970. The car originally came with the 37 Amp alternator (Code 72 on the build sheet). The wiring will remain original along with the electronic voltage regulator. We will either be using the external "orange box" electronic ignition module or perhaps the internal PerTronix kit in the distributor.

Question #1 is whether we should stay with a 37 Amp alternator (which are harder to locate) OR can the wiring at the bulkhead, etc. handle a 60 Amp alternator (easier to locate) without ever having any issues with over heating/meltdown? Standard equipment, radio, etc., but does have an old 8 track tape player with vintage speakers.

Question #2 is whether to go ahead and use another square back design from 1972+ (easiest to find)? It's claimed they are more reliable and easier to service than the round backs.

Question #3 Does anyone have any experience/recommendation which PerTronix kit to use? There are 3 choices: Ignitor, Ignitor II, or IgnitorIII.

Thanks for the help.


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The firewall bulkhead plug from the battery has a fusible link on it, but I recommend both a larger alternator and a separate charge loop back to the battery with a fuse block in it and replacing the ammeter with a voltmeter. Here's some reference material on what you you want to do with your charging system and why the factory electrical becomes suspect with age.
Vintage Chrysler electrical repairs and updates
 
hey im new to A, im over here from C, but I have goofed with ALTs, so just trying to help out.
I don't know if you know about it or not, so I suggest studying the bulkhead / ammeter bypass by nacho RT / MADD enterprises.
also slant6dan covers a bunch of it about how to beef up the charging circuit and install fused protection etc - super cool dude.

the biggest stock roundback alt is 60a IIRC. realize you dont get this amperage output at idle. i think you can find a kit to get a roundback up to 75a iirc.

I am currently trying to retrofit a 5th ave 150amp ALT onto a 68 440.
once you add dual fans, elec fuel pump, 1000w amps, ipod chargers, etc. you cant even hold idle at a stopsign - not enough voltage to fire the coil and etc. forget about turning on the headlights or A/C or heater.

id recommend NOT trusting the stock wiring. I used 10ga originally, but will go to 2ga for 150a ALT.

also check out crackedback & slant6dan headlight harness mods - it offloads the whole headlight circuit from running thru the bulkhead 4 times . . .and the foot dimmer, and the dash switch.

try not to die -

- saylor
 
o I used the summit 8000005 (whatever number) dist + orange box kit for a 440. I changed from points. 10,000% difference. aside from disc brakes, maybe the best upgrade so far. do not hesitate.
 
DustyEd said:
My wife and I are in the process of replacing the old "incorrect" alternator on our '70 Duster 340 4 sp. non A/C. We know it should be the round back design for 1970. The car originally came with the 37 Amp alternator (Code 72 on the build sheet). The wiring will remain original along with the electronic voltage regulator. We will either be using the external "orange box" electronic ignition module or perhaps the internal PerTronix kit in the distributor.

Question #1 is whether we should stay with a 37 Amp alternator (which are harder to locate) OR can the wiring at the bulkhead, etc. handle a 60 Amp alternator (easier to locate) without ever having any issues with over heating/meltdown? Standard equipment, radio, etc., but does have an old 8 track tape player with vintage speakers.
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The 8 track should not add significant load but it would be good to figure out where the power for it is spliced in. If it had a big amp and you were cranking, that might be different. If you will be running it while the engine is off, that will also effect the answer.
Either alternator will work fine.
The higher output alternator, especially a squareback, may provide a little more output at idle. That's generally a good thing. You won't see the battery take over when sitting at a stop light or traffic with the headlights and wipers on.
The downside is yes it can put a higher load though the wires IF something calls for more power. About the only thing that will call for a lot of current is a drained battery. So if you ever have to get jump started, watch the ammeter and keep the engine rpms down so the charging current stays as low as you can get it.

DustyEd said:
Question #2 is whether to go ahead and use another square back design from 1972+ (easiest to find)? It's claimed they are more reliable and easier to service than the round backs.
Click to expand...
The squareback are easier to replace parts in. You can do most of it yourself if you wanted.
I see thats a squareback on there now.
All replacement units are a gamble. A lot of junk is sold over the parts counter - not just for our cars either. :(
If I was handed an original 1970 roundback in decent condition and a remanufactured 1973-75 squareback, I'd bet on the roundback being more reliable. However we rarely get that choice...

DustyEd said:
Question #3 Does anyone have any experience/recommendation which PerTronix kit to use? There are 3 choices: Ignitor, Ignitor II, or IgnitorIII.
Click to expand...
The plain Ignitor seems to be hands down the most reliable.
 
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The load the wiring will see depends on the the equipment.
The output rating of the alternator is its maximum potential.
For example:
If a pair of headlights draws 9 amps at 12.8 Volts, when the lights are turned on, 9 amps will flow from the battery to the lights.
If the same headlights draw 11 amps when powered at 14 volts, then when the lights are turned on and the engine is running, 11 amps will flow from the alternator to the lights.

There are a couple of weak spots on a '70.
Bulkhead connector and the column connector since it has the main power to the key switch, and back out. So the question of reliablility comes down to the condition of the terminals in those connectors in particular.
 
60 is really pushing it with stock wiring, 'specially as old as these girls are. They made a 45? 47? a if you could find one of those that would be a great compromise. THE THING IS, the typical volume rebuilders are shitheads. You never know what you are getting from those guys.

If you don't have a bunch of accessories, stereo, etc, added, a 37 will run just fine.......and did.......on thousands and thousands of cars 'back then.'

ANOTHER old ANNOYING story from the old days. When I had my 69 383 RR (this was about 71 spring) I was generally BROKE. The alternator in that car blew two diodes. I simply hacked them out of the circuit, and let it run with what was left. This likely turned a 35ish A alternator into about a 20 or less. And it introduced NOISE because the ripple was uneven. I left the radio off, that car at the time had NO other electronics. With a little "sensibility" the thing ran fine--for nearly a month--until payday
 
Personally I think the alternator output is made a bigger deal out of than it actually is. I ran a 100 amp alternator in my Challenger with the original stock wire harness for over 70k miles using the car as my daily driver. I had zero issues with the harness or alternator, including the original amp gauge. I ran halogen head lights and an aftermarket stereo with that set up, but that was about it beyond the original electric loads.

I run the same alternator in my Duster, although I have recently replaced my amp gauge with a volt gauge and installed one of crackedback’s bypass wires. My dual electric fan set up is run off of relays and pulls a pretty significant amount of juice. But I still had no issue with it running the original wire harness, which I probably ran as is with the added fan relays for at least 15k miles or more.

Check the amp gauge, check the bulkhead connector and make sure it all looks good. Clean it up, make sure the connections are tight. If the harness is in good shape it’ll be fine. If it’s all hacked up and altered by non-electrical type previous owners, probably not so much. If the original connections are loose, corroded, melted etc then again, not so much.
 
^^You were lucky and likely did not have big extra loads, and maybe you didn't drive in the winter much. Even "ma" knew the bulkhead connector/ ammeter were a problem. "She" offered what is known as "fleet/taxi/ police" wiring mod for optional 65A alternators. This was a mod that bypassed part of the bulkead connector by feeding through an individual grommet much like the tach wire or clutch safety switch wire did

In early 70's I bought a 440-6 RR from a good friend. (On a side note he's still alive.) He and I were both radio amateurs, and both of us had gear in the car. I ran a "trunk mount" UHF radio, all tubes, as well as a VHF partially solid state radio. Between the two of us "we" finished off the bulkhead connector and damaged the ammeter, mounted in the plastic Ralleye cluster. I "fixed" it by drilling out the connector terminals and running big wire straight through the connector.

And since then, I've seen a few more, even though I was never a "pro" mechanic.
 
The problem with mopar OEM alternators of this vintage is the crappy output at idle.

If everything is right, the alternator only puts out enough + a little overhead that items demand. One of the things that big alternators generally have is superior output at low RPMs.

On a stock alternator, one could always put a smaller pulley on it for better idle output. Just have to be careful regarding max RPM the alternator is capable of withstanding.
 
Think of things using watts and the voltage and amps feed that requirement.

Take a 55 watt headlight. If you feed that light with 10 volts, it wants to draw 5.5 amps. Now feed it better voltage say 13.5 and the amp draw through the circuit is now 4.07 amps. Amps is what will cause the heat in the system. That why having sufficient sized wire and minimal voltage drop is important.
 
crackedback said:
Think of things using watts and the voltage and amps feed that requirement.

Take a 55 watt headlight. If you feed that light with 10 volts, it wants to draw 5.5 amps. Now feed it better voltage say 13.5 and the amp draw through the circuit is now 4.07 amps. Amps is what will cause the heat in the system. That why having sufficient sized wire and minimal voltage drop is important.
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Actually Rob this might not be true. You would likely have to actually measure this with instruments, because a tungsten filament has a temperature/ resistance curve. While the thing DOES increase resistance with increased temperature, there is no guarantee that the curve will follow the nominal wattage. The nominal wattage is just that.....an approximate figure at the design supply voltage, which "I'd hope" is 13.8--14.2V

But you are absolutely correct on "the idea", and the fact that undersize wiring and poor connections is just plain trouble.

My 70 RR had FOUR tail / turn/ stop bulbs, and yet used the same "damn small" wiring as an A body. I towed a trailer some with that car, and thought several times of trying to upgrade the wiring for the trailer. The trailer added FOUR MORE bulbs to the mix
 
Yes, it wants the 55 watts, but the voltage won't allow. More of the math of it.

Try lighting a 12 volt bulb with 6 volts, won't put out the lumens.
 
crackedback said:
The problem with mopar OEM alternators of this vintage is the crappy output at idle.

If everything is right, the alternator only puts out enough + a little overhead that items demand. One of the things that big alternators generally have is superior output at low RPMs.

On a stock alternator, one could always put a smaller pulley on it for better idle output. Just have to be careful regarding max RPM the alternator is capable of withstanding.
Click to expand...

Good points...Maybe that's why the rebuilt alternators have the 2 5/8" dia. pulley compared to the factory original stamped pulley at 3 1/4" dia. (P/N 2444478-single groove) in order to spin it faster at low engine rpm. I wonder what IS the max RPM these smaller pulleyed ones can handle? Probably just have to find out.
 
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Ir's been a while since I did my alternator, But I seem to remember from probably here that my 64 slant originally had a less than 30A output. I bought an alternator that tested at I think 90A, it came from a van with a wheelchair "elevator". So big output. I wired it directly to the battery through a fusible link. So the bulkhead charging load isn't there. I put in an electronic regulator at the same time. Of course, the alternator only shows discharge, and wont let you know if you lose charging. You could add a voltmeter to see if you're charging.
 
crackedback thank you for all the work you put in on the headlight harness mod. i totally copied it and it is beautiful.

you and nacho and slant6dan have contributed so much to the mopar collector we all owe you.

20191228_095056.jpg


@ anyone - see if your wires look like this near the headlight plugs - time to think about the crackedback headlight mods.

if you go read slant6dan, he explains the stock wiring is barely capable, as seen in this stock wire.

try not to die -

- saylor
 
saylor said:
crackedback thank you for all the work you put in on the headlight harness mod. i totally copied it and it is beautiful.

you and nacho and slant6dan have contributed so much to the mopar collector we all owe you.

View attachment 1715460985

@ anyone - see if your wires look like this near the headlight plugs - time to think about the crackedback headlight mods.

if you go read slant6dan, he explains the stock wiring is barely capable, as seen in this stock wire.

try not to die -

- saylor
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Hey Saylor,
Are you referring to the general design of the harness or the condition of the "wavy" brown wire?
 
THIS is what overheated connectors look like.
upload_2020-1-29_9-58-14.png


IF you drive at night a lot.
And if the car has newer headlights, then the odds are good that some connection(s) in the headlight circuit will have too much resistance for the load. There is a 15 amp breaker in the headlight switch itself. However it doesn't always trip in these situations because the current flow isn't quite that high.

One solution, a a good one, is to connect the headlights to the alternator output through relays. This eliminates the long route to the headlights and takes the load off the main power circuit. The original wires to the headlights are used to turn the relays on and off.

A '70 Duster came with 6012 headlamps, nominally 40 watt low, 50 watt high beam.
These were often replaced with later 6014s, which are 50 watt low, 60 Watt high.
or sometimes H6014 (Halogen) which were 55W , 60 Watt.
However another replacement halogen that is now more common is the H6024, with only 35 Watt low beam and 55 or 60 W high.
 
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DustyEd said:
Good points...Maybe that's why the rebuilt alternators have the 2 5/8" dia. pulley compared to the factory original stamped pulley at 3 1/4" dia. (P/N 2444478-single groove) in order to spin it faster at low engine rpm. I wonder what IS the max RPM these smaller pulleyed ones can handle? Probably just have to find out.
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The alternator pulley is more or less matched to the other pulleys, crank in particular, for that application.
The replacement ones are whatever they feel like installing because they could buy in quantity for cheap.
A puller is needed to remove the pulleys. To install, the case must be seperated and a press used to install them. That's not as difficult as it sounds unless the pulley dimensions are wrong.

Skim through this for photos
Alternator repair, a little show and tell.

All alternators have low output at low rpms. So yes the correct pulley set is very important.
For example, here's an max output test of a later '78amp' squareback that Nacho got with a replacement.
upload_2020-1-29_11-39-0.png

That is ALTERNATOR RPM.
The specs in the shop manual are usually to test at 1250 engine rpm.
Sometimes, higher rated alternators have worse low rpm performance. It depends on the details of how they are built.
 
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My Duster 340 was converted to electronic ignition in the mid '70s with the addition of the external ECU module (orange box) (mine is actually blue) and the 4 spade ballast resistor (1971 and up).

Does anyone know if I can go back to using the standard/original (1970 type) 2 spade ballast resistor whether I install the PerTronix electronic ignition kit in the distributor or stay with the existing external type ECU (orange box) mounted on the fender?
 
DustyEd said:
My Duster 340 was converted to electronic ignition in the mid '70s with the addition of the external ECU module (orange box) (mine is actually blue) and the 4 spade ballast resistor (1971 and up).

Does anyone know if I can go back to using the standard/original (1970 type) 2 spade ballast resistor whether I install the PerTronix electronic ignition kit in the distributor or stay with the existing external type ECU (orange box) mounted on the fender?
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Any reason you want to go to the Pertronix? I have one in the shop right now and I'm not all that impressed. Maybe after I spin it up I will be, but the Chrysler distributor is pretty hard to beat.

About the original question..I'm on the fence about a bigger alternator. Modern ignition boxes use a good amount of power and I suspect at lower RPM's I'm no powering the box enough.

I'm not all that anxious to bypass the ammeter if I can avoid it.
 
yellow rose said:
Any reason you want to go to the Pertronix? I have one in the shop right now and I'm not all that impressed. Maybe after I spin it up I will be, but the Chrysler distributor is pretty hard to beat.

About the original question..I'm on the fence about a bigger alternator. Modern ignition boxes use a good amount of power and I suspect at lower RPM's I'm no powering the box enough.

I'm not all that anxious to bypass the ammeter if I can avoid it.
Click to expand...

I'm considering the PerTronix just because a friend likes how his engine bay looks original, other than the 2nd wire from the distributor to the coil. If there's a performance advantage with it, that would be a plus. However, if the external ECU (orange box) is more reliable I would lean in favor of it. I really think the external ECU and extra harness is widely used and accepted for engine bay appearance in these cars. Would you agree?

I also would rather not bypass the ammeter. The only addition to my car's system is the 8 track player and the radio would be off when it's used, obviously.
 
Orange boxes haven’t been crap for two decades. If you get one that doesn’t break up over 5k go play the lotto.

I went PerTronix in my Challenger, worked great. Better than the chrome box even.
 
hi !

you don't HAVE to throw out your ammeter but you do need to check it (now right now yes now) and make sure its connections are high n tight. also do study the wiring diagram and understand how the ammeter is right smak in the middle of everything. you can offload most current from it with the above mentioned wiring methods. it wont read perfectly perfect but you don't have to delete it completely and can keep the stock look.

I happen to drive a rusting pile of metal so I promptly threw it as far as I could out into the woods and then joined the wires together with a strong splice.

if you are pushing old man status like me, you may remember seeing melted dash gauges is why.

try not to die -

- saylor

p.s. mom said go with the orange/blue box ignition
 
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