Hi everyone, can you swap out a round back 2 wire alt for a 2 wire square back alt on a 64 barracuda without any modifications? Thanks for info
Round back to square back alt
- Thread starter Cuda 1964
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67Dart273
Well-Known Member
Just ground one brush and bolt it on, or take that opportunity to convert to a 70/ later VR which only requires one more wire
Some claim that some of the squarebacks draw more field current, but I've not had trouble with them thataway
Some claim that some of the squarebacks draw more field current, but I've not had trouble with them thataway
Just to be sure....
You're talking about the original single field wire "round back" alternator
And you want to replace it with a 2 field wire "square back" alternator.
The original round back alt was a two wire could have been a single field which was on a 273 64 Cuda would like to replace it with a powermaster 17519 two wire square back
Just some terminology....
2 wires on the round back means the charge wire and the single field wire.
Square back alternators have 3 wires, 2 field and one charge wire.
Some square back alternators have been modified by the manufacturer / remanufactured to internally ground one of the field wires so they can be used on an application that calls for a single field wire.
2 wires on the round back means the charge wire and the single field wire.
Square back alternators have 3 wires, 2 field and one charge wire.
Some square back alternators have been modified by the manufacturer / remanufactured to internally ground one of the field wires so they can be used on an application that calls for a single field wire.
I suspect anything from Powermaster will have draw more field current. Likely it will be 2 x the current the regulator was inteded to handle. Also if there are any problems or weaknesses in the circuits, this will magnify them.
In some applications, the size of the squareback will limit the travel for tensioning the bolt, and a shorter belt will need to be used. Not to mention, the increased output of the Powermaster unit may be more than the old 64 wiring can handle.
Output depends on demand. So the only increase in demand will be, or could be, the field current. On the other hand, at idle speeds, that increase can be the difference between having enough power to run the headlights, wipers, and brake lights without dipping into the battery.
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67Dart273
Well-Known Member
Another possibility is, that even if the field current allegation is correct, (and assuming one stays with the early VR) these modern replacement VRs have a pass transistor that may or may not be heavier duty !!! than the old electro-mechanical ones. THAT could go either way.
ANOTHER reason for "adding one more wire" and converting to the flat, 70 and later VR
ANOTHER reason for "adding one more wire" and converting to the flat, 70 and later VR
That's a mouth full, and the biggest problem with our old undersized wiring.
Add brighter headlights, stereo, electric fans, etc and zap/smoke!
Old underpowered alternator will just max out at 40 or so amps and things might just get hot!
It's not a problem until someone inadvertently adds load like electric fans. Or adds load to wires and connections that can't handle it
Even then, its not a zap! poof situation, more typically your slow burn (melt) scenario.
The alternator won't care other than it too may get hot from running at near maximum. The battery has a tremendous capacity and will cover for a while.
Lets go over the loads.
Here's what I've measured on my '85 AMC Jeep SJ (with Delco 12SI alternator so field current is internal)
The Delco alternator was rated 74 amps or later 92 amps. It only put out 27.4 amps. Why?
Because that's all the loads that were turned on or connected.
A 64 Barracuda will have about 2.5 amps for the ignition and about the same for the field. Lets call it 5 amps
Headlights will be about the same, 9 amps. A little less if using the original lamps, or the 35 W low beam halogens.
Parking and instrument lights will be less since it has no side markers. lets call it 5 amps for simplicity.
Heater fan will probably be the same or less. Lets call it 9 amps.
Total current needed driving on a cold night, 27 amps.
Well within the capacity of a '34 amp' alternator at high idle or driving down the road.
The one load not listed is battery recharging. If the battery wants 10 amps (such as after starting), then the '34 amp' alternator will not be able to do that at slow idle and run all the stuff listed above. I don't have slow idle measurements for maximum power capacity for any unmolested Chrysler alternator of this period. But it is not uncommon for A-body owners to comment on the fact that the ammeter will flick slightly toward battery discharge when at a stop light at night, especially with wipers or heater fan running. And yes rear brake lights add a few amps to the load.
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ChargerKG
Active Member
Hey Electricians, I just replaced the alternator in the '65 Dart with this cheapo from NAPA. Ad states it is 60 Amp. It is a round back 2 wire. I am running the original single wire set up with one field terminal grounded. This is not cutting it. New Pre-1970 VR from Standard Electric Made in USA. Electronic Ignition, Orange box.
So output fluctuates quite a bit. Sometimes up to 18 volts reading at battery when cold. As the VR warms up it settles down to 13.5 to 14 volts but still have wild swings of output, flickering dash lights. Driving around after hot, stock amperes gauge might show discharging for 30 seconds then back to positive. From what I have read Electronic Ignition should use the later Electronic VR with the 2 wire set up. I want to keep the Electronic Ignition and use of stock Amp gauge. Have read a lot of posts about this but nothing about such erratic behavior. Any suggestions are welcome.
So output fluctuates quite a bit. Sometimes up to 18 volts reading at battery when cold. As the VR warms up it settles down to 13.5 to 14 volts but still have wild swings of output, flickering dash lights. Driving around after hot, stock amperes gauge might show discharging for 30 seconds then back to positive. From what I have read Electronic Ignition should use the later Electronic VR with the 2 wire set up. I want to keep the Electronic Ignition and use of stock Amp gauge. Have read a lot of posts about this but nothing about such erratic behavior. Any suggestions are welcome.
The amp gage is only showing whether and how much the battery is charging or discharging.
With a transistorized version of the VR, there will be no noise from the points, so your ECU is not in danger.
The fluctuation is probably one or combination of several possibilities:
1. High current draw alternator rotor. Do a search for 'field current draw' Your new alternator's rotor may be 2 or 3 times higher than the factroy designed for. It may also make a stronger magnetic field that breaks down more slowly. I don't know for sure. But 7+ amps instead of 2-3 amps is a big difference if that's what's going on.
2. Alternator's 'turn on' rpm is higher than a factory alternator and pulley. new alt's usually come with new pulleys. if the diameter is larger, then the alternator turns more slowly at any given rpm. At slow idle this means it may not be turning fast enough to produce power, at the same time it's rotor may be sucking 7 amps from the battery.
3. Battery capacity is getting low.
Since you have the older style VR, measure the V right at the regulator's input. If its not the same as the V at the battery or at the alternator's output, then that's at least part of the problem. In other words if the Regulator is seeing 13 Volts because there is high resistance in the alternator's output connections and the alternator is actually producing 18 V, the VR doesn't know that. Ther voltage drop will get worse during high current demand. For example immediately after starting the battery will suck maybe 15-20 amps (look at the gage) for recharging. Once its done recharging, then its essentially zero amps.
With a transistorized version of the VR, there will be no noise from the points, so your ECU is not in danger.
The fluctuation is probably one or combination of several possibilities:
1. High current draw alternator rotor. Do a search for 'field current draw' Your new alternator's rotor may be 2 or 3 times higher than the factroy designed for. It may also make a stronger magnetic field that breaks down more slowly. I don't know for sure. But 7+ amps instead of 2-3 amps is a big difference if that's what's going on.
2. Alternator's 'turn on' rpm is higher than a factory alternator and pulley. new alt's usually come with new pulleys. if the diameter is larger, then the alternator turns more slowly at any given rpm. At slow idle this means it may not be turning fast enough to produce power, at the same time it's rotor may be sucking 7 amps from the battery.
3. Battery capacity is getting low.
Since you have the older style VR, measure the V right at the regulator's input. If its not the same as the V at the battery or at the alternator's output, then that's at least part of the problem. In other words if the Regulator is seeing 13 Volts because there is high resistance in the alternator's output connections and the alternator is actually producing 18 V, the VR doesn't know that. Ther voltage drop will get worse during high current demand. For example immediately after starting the battery will suck maybe 15-20 amps (look at the gage) for recharging. Once its done recharging, then its essentially zero amps.
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ChargerKG
Active Member
Thanks Mattax, Battery is great and pulley is stock diameter so I am going with your possibility #1. Will compare V at VR vs. Battery tonight. Man, those headlights are bright at 18V 
KG
KG -
