Choosing the right alternator

[69_bad_bird]

Hi all, I'm not the best when it comes to electrical, but I'm looking to get a new alternator since the one on the car bit the dust. I'm not certain what amperage it was but, I'm pretty sure it was a 60a alternator and it belonged to my old setup. The accessories on my 69 Road Runner it has dual electric fans, and MSD electric ignition. Do I get a higher amperage one or is 60a okay? The car idles at around 700RPM. I believe the old alternator struggled a little bit keeping everything charged up. Any help and recommendations would be greatly appreciated. Thanks.

 

[Kern Dog]

Great question.
I have no electric fans, no electric fuel pump or a high power stereo but....
I do run a vacuum pump for the brakes. At idle, the system is at around 10 volts with the A/C or heater fan motor spinning and the headlights on. My Volt meter does show better charging as rpms increase but still behind average with the HVAC system and lights on.
I'd like to hear of an alternator that charges better at idle speeds. I have a stock 60 something amp alternator too.

 

[Nacho-RT74]

Any alt able to feed all the car demands as posible at iddle speed to reduce the power demand to the batt (meaning discharge on ammeter)

iMHO, an alt able to give no less than 45 amps iddling, but more the better. Myself will be pointing out to a 100 amps alt able to give up to 65 amps iddling… for a STOCK car on electrics, except for the halogen Sealed Beams.

A stock 60 amps alt could be on maybe 25-30 amps iddling, depending on pulley size and the actual iddling speed.

Small pulley helps to increase alt speed so better power output at engine iddling.

With all the discussions around this, I’m still surprised you still need to hear of an alt with better charging results Kern.

 

[Kern Dog]

It seems that the rebuilders default to the smallest pulley for the parts store rebuilt units.
I already have one of those.
If I'm driving in the daytime with no A/C on, the volt meter shows 13+ even at idle while pressing the brakes. It is when I have the headlights on, the A/C and brake lights on when the numbers drop below a comfort level.

 

[Nacho-RT74]

Sure, you are increasing the load demand at night with the same output level source

And if it rains things become even WORST… wipers sucks A LOT.

Trust me… i have being a REAL DAILY DRIVER of my Charger. Under hard driving conditions

 

[HEMI-ITIS]

Sounds more like a weak voltage regulator. I have a one wire 100 amp GM alternator.

 

[Crackedback]

Hi all, I'm not the best when it comes to electrical, but I'm looking to get a new alternator since the one on the car bit the dust. I'm not certain what amperage it was but, I'm pretty sure it was a 60a alternator and it belonged to my old setup. The accessories on my 69 Road Runner it has dual electric fans, and MSD electric ignition. Do I get a higher amperage one or is 60a okay? The car idles at around 700RPM. I believe the old alternator struggled a little bit keeping everything charged up. Any help and recommendations would be greatly appreciated. Thanks.

You really need to do an assessment on what your amp draw is at idle with accessories running. That should be about the minimum output at IDLE. You'll need to get a slope chart and see how the alternator performs at lower rpm's. Higher output alternators usually put out more amps at lower RPM.

The old school mopar alternator output at idle generally suck. Nowhere close to required for even a totally OEM car with headlights and heater blower motor running.

 

[radical rob]

Call John at power master. They can help. I run one of their 175 amp units

 

[1 Wild R/T]

My solution... Just moved this from my spare engine mock up to the car today... Toyota Land Cruiser alternator... Max output, 110 Amps, Max output at idle? 95 amps...