1967 Barracuda alternator upgrade question

[MObarracuda]

I’m looking at upgrading my original 35 amp alternator (see attached pic with orange valve cover). I have two choices of inexpensive round style square back alternators to choose from a 60 or 78 amp reman units.

I have several questions for FABO members that have completed the upgrade.

1) If I order a reman part# 201531 will I actually get a 78amps unit or will the reman company use consolidated parts and make them all 60 Amps?

2) I’m interested to know what is the max amp rating the Ammeter and standard wiring is rated for in my ‘67 Barracuda before having to make electrical upgrades (i.e.MAD ELECTRICAL bypass). If the answer is 35amps I’m going for the higher AMP rating alternator since I have to make the upgrades anyway. If you guys have installed 60amps Altenators and have no issues with the Ammeter and stock wiring than it’s 60AMP unit for me.

There was an allpar artical that states an option for 60amp alternator which came with different wiring (Improved Wiring for older Mopars). Sounds like the upgrade is needed with any alternator upgrade.

Alternator option 1

Remy 201531 (rebuild) From a
Volare 1978-1980 6cly through V8 that makes 78amps (picture 1)

Alternator option 2

AC Delco 19135769 from a 78 dodge D350 360 V8 truck that makes 60amps. (Picture 2)

I don’t have any major electrical upgrades installed on the car (running mechanical fan, modest aftermarket radio, orange box ignition, original dealer installed aftermarket AC, already completed headlight relay bypass). With the alternator upgrade I will also replace the old points style voltage regulator (VR) with a solid state VR and add wiring for the 2nd field on the square back alternator.

What would you do. 60 or 78 AMP upgrade?

 

[rumblefish360]

I’m in the same boat and a am considering a amp by pass route. It would just simply be easier IMO. And ultimately safer at the higher power level.

I don’t have an issue with an amp gauge with stock voltages.

I know a lot of people here tell tales of burnt up parts but I have never seen 1 example. Only claims. Not that I think it is impossible but ... still haven’t seen it.

I am also not so crazy as to install a 100 amp Alt. on a 30 amp gauge. That’ll jus burn up the gauge of the draw is ever needed.

 

[MObarracuda]

Hey Rumblefish,

Thanks for your reply. I don’t have the testing equipment but think it would beneficial if we could test the Ammeter to the point of failure.

I would have thought the Chrysler engineers would have specified a gauge where they only used up to 80% of gauges rated amperage to achieve a continuous duty rating. So, theoretically if the stock alternator made 35amp they would have specified wiring and the gauge for 42amps or more.

It would be nice if testing could be done to know how hot he gauge gets under continuous amperage load on the gauge alone fails to put all of this into perspective.

I’m going to go with the 78amp alternator and bypass the ammeter for for now. At some point I will send my gauge cluster to redline gauges for restoration and voltmeter conversion since I’m not aware of any better options.

 

[GMachineDartGT]

You can put a 200 amp alternator in, but it will only put out what is needed. In your case maybe 40 amps. No need to bypass the gauge. Add a 10ga wire from the alternator to battery stud on the starter relay. This will allow some current at the ammeter to alert you should it stop charging, and shortcut most of the current back to the battery.

 

[RedFish]

The same amp gauge and same size wiring was found in those vehicles with the higher output alternators. If one should leave the lights on/kill the battery, or have any of several scenarios where the alternator does do all it can do, the wiring or the amp gauge may fail. Jumper from alt to battery detailed above is the simplest solution.
Of course the wipers, blower, a/c, everything in the cabin will would still be routed through the amp gauge. Your headlight relays have reduced the total draw there. So it comes down to what you want to do versus what you must do.
I did convert my alt gauge ( and serval others ) to a volts gauge but my reason has nothing to do with the amount of current going through it. I see gauges as on scene reporters. None of them should be able to interrupt the story they are reporting. This amp gauge is the Clark Kent of gauges.

 

[Mattax]

All good points. Maybe it will help to explain alternator performance.

1. Alternator output will equal demand, as long as demand does not exceed the alternator's capability.
examples. Lets say the ignition draws 3 amps, and the alternator needs about 2 amps for the field circuit, so the alternator output is 5 amps.

2. Potential alternator power goes up with rpm. At a certain rpm, it reaches maximum.
Ratings can be done any way the manufacturer wants. It can be 90, 95%, or 100% max or whatever is convenient.
Here's some examples of the rpm curve for AC-Delco 15Si alternator. (I've not found a published curve for our alternators)

Alternator RPM on the graph is approximately 3 times crank rpm for a AMC Jeep 360, one application the 15 SI was used on.

However notice these graphs indicate they are for amperage out at 12 Volts. If that's true, then the amps on a system regulated at 14 volts will be less. In other words, at any given power output, the amps available can be made to look higher by rating at a lower voltage.
So an alternator rated at 12 Volts will have higher amp rating than if it was rated at 14 volts.

To give you some idea of the Chrysler roundback rating vs outputs -
The tests in the service manual are done at 15 Volts, engine speed 1250 rpm.
37 amp unit should put out 34.5 amps.
46 amp unit should put out 41 amps.
60 amp unit, should supply 51 amps.
At idle speeds, they will supply less power. At slightly lower voltage, they will supply a little more current.

The ammeter will indicate whenever the battery has to take over supplying power because the alternator can't keep up.* If you are seeing discharge on the ammeter under your normal driving conditions, then a higher rated unit may be better. If it only can't keep up at low rpm, then the max rating is less important than what the unit can do at low rpm. Sometimes higher rated units do worse at low rpm. In general, the newer (square backs for example) tend to be a little better at low rpm than the roundbacks.

The ammeter itself should only be seeing current flow when starting and when the battery is recharging. It is reasonably well protected by the fusible link. The link will melt first in any major overload. Problems occur with repeated moderately high current flows because the battery is doing extra work (that the alternator should be doing) and poor connections.

*Understanding Charging Systems with Ammeter

 

[rumblefish360]

Thanks to Mattax and GMachineDartGT.

I figured pretty much what you said above, that the Alt. would only put out so much (demand) but worried about maxing the gauge out of there was a problem. Like a bad regulator stuck in the charge circuit. I have one of those! LMAO! Seeing the Amp gauge peg at idle is an eye popper!

I am going to be installing an upgraded stereo with an amplifier. The future may hold more.

 

[Mattax]

I know a lot of people here tell tales of burnt up parts but I have never seen 1 example. Only claims. Not that I think it is impossible but ... still haven’t seen it.

I am also not so crazy as to install a 100 amp Alt. on a 30 amp gauge. That’ll jus burn up the gauge of the draw is ever needed.

Same here. The photo that 273Dart has posted in other threads, and I'm sure he's seen, is from a truck with a plow or winch. These are always wired to the battery. In fact, the draw from a winch can be so high only the battery could supply it. Wiring additional equipment to the battery becomes a problem with ammeter type charging circuit. Its that much worse when its stuff that can draw the battery down and/or requires constant recharging.

I would have thought the Chrysler engineers would have specified a gauge where they only used up to 80% of gauges rated amperage to achieve a continuous duty rating. So, theoretically if the stock alternator made 35amp they would have specified wiring and the gauge for 42amps or more.

The charging circuit was designed to handle high loads only for short periods. Starting and recharging. As the battery recharges, the current it demands gets less and less. So even if its 25 amps initially, in a minute or two its down to 10 and then 5 and finally 0 amps.

Continuous loads are where it gets in trouble. A car with A/C and lights and fan on sitting in traffic idling can end up running on the battery instead of the alternator. So the charging circuit is seeing continuous load, at lower voltage (12.5 instad of 14.5) therefore higher current draw, and the battery is getting drained. When engine rpms come up, the battery wants to be recharged and will take all the current it can, so again the ammeter and charge circuit are working hard.

The rest of the gages are on a voltage limiter.

 

[BillGrissom]

If the last photo is the alternator you presently have, it looks like it has 1 field wire (other brush is grounded), as was typical for round-back alternators, but some late ones (~1971) did have 2 field wires. If true, you will need to ground one of the field terminals on your new square-back to work with your older Vreg. Many many posts on this. If your battery stays charged, your alternator is sufficient. I still use the round-back on my 1965 Newport, w/ electronic ignition and TBI (electric fuel pump) and the battery stays charged over a week of driving.