Low alternator charge at idle

[Kern Dog]

I have noticed that my alternator often fails to keep up when I'm at idle with the headlights and A/C going.
The car.....

I have a rebuilt 63 or 65 Amp alternator, whatever the highest one was for these cars.

If I am idling with the headlights on and the basic stereo on, it isn't terrible. Maybe 11.5-12 volts? At 1800 and up, the rate jumps to the 13.0 and up range. Cruising at 70 mph and 2200 rpms, it is solidly in the 13.7-14.0 range whether I have headlights on or not. I do have relays for the headlights, bought from FBBO member CrackedBack.
There is something about the A/C though. That fan motor really sucks the juice. At stoplights at night, headlights on, A/C going and brake lights on I'm dropping below 10 volts. I have no electric fans or fuel pump drawing power so why is it dropping so much? Can a stock alternator be rebuilt to put out more power at idle?
Randy/ 1 Wild R/T suggested this:

These brackets allow the use of a Toyota based Denso 60 amp alternator. That is lower than stock but it probably puts out more power at idle. I'd need something with a 2 groove pulley since the A/C compressor needs 2 belts to avoid slippage.

I'm not looking to jump right into this, I'm just testing the waters,
If you have dealt with the low output at idle, what did you do?

 

[Nacho-RT74]

Is amazing with all the threads about that I know you have read still thinking on this LOL. THERE IS NO WAY a stock alt holds all the loads with accesories at iddle. Hence why the bulkhead burns with the constant back and forth loads between batt and alt.

Yes, the A/C blower is the biggest load sucker on the car. Is able even to burn the fan lever selector on 73 and lates A/C control units that took me to install a relay system, one to every blower speed (4 in total if we count the heater speed)

Is wishing stock look and no brackets deal.. Tuff Stuff 100 amps. (There are 120 units at this moment too)

This is the cheaper source I have found on the web. I whish exactly this one for me but I have a lot of priorities right now to cover right now, and since my Charger is in pieces in Venezuela yet I think will take some time to take care of this


Alternator Tuff Stuff Performance 8509DP - Pace Performance Parts

Sure they are squareback alts, not completely correct for your 70 thought, but at least 80% correct look. 100% if you don’t look at the rear case LOL.

Long time ago a member of dodgecharger.com board found me a local shop on his area able to tune up the alt for a bigger capacity output but the quote was pretty much similar to this price (plus double ride for the alt) On those days tuff stuff wasn’t on market yet, just Powermaster.

JFYI… the quickstart shop upgrade kits are not really efficient. Already tried one.

 

[Nacho-RT74]

I posted the casted original finish, but chromed and black are available at the manufacturer website. Personally I’m not a big fan of “fashionist” finishes.

(I think I was editing my post yet while you “thanked” my reply)

 

[Kern Dog]

Hmm....

I have no ammeter. The alternator charge wire runs to the starter relay in my car. There is no charging voltage going inside.
The instrument panel is a Dakota Digital.

I should also mention that I have aftermarket Air conditioning too.

 

[Don67Satellite]

I installed a Powermaster 17519 100A to replace my old 60A that had issues. Chrome, but looks like a Mopar alt. I also run relays on the headlights. Don't have AC yet, but it powers all the stock stuff, heater blower, aftermarket gauges, Progression Ignition and I am at 14.5V at idle. If I recall the tag that came on the alt (they test them before shipping) it can put out up to 73A at idle if necessary, so I never seem to drop below 14.5V. I almost put the Tuff Stuff 8509RCSP (also chrome) in but the Powermaster arrived first, so it got the gig.

 

[Kern Dog]

Thanks Nacho and Don.
I have always relied on factory type alternators that I buy rebuilt from the major auto parts stores so I'm not as familiar with the aftermarket units. It would be good to have something that fits stock brackets so if I have a failure when on a road trip, I'd have an easier time finding at least something to get me on the road again.

 

[twecomm]

Another current draw would be the clutch on the compressor.

 

[Gold Rush]

Your stock 65 amp alternator does all you want off idle so why spend the $$$ for more unused capability. Yes some modern units put out better at idle but how often do you set idling... As you said until the a/c is used the levels are OK so maybe an idle speed boost while a/c is on is the answer. Does your engine have the idle kick up solenoid? If so you might make sure it is working and adjusted high enough. If you don't have one, they are available and easy to install.

 

[hunt2elk]

I switched my cars over to the Toyota 4 Runner Denso style internally regulated alternators. I did it for a different reason however. The high output (15-15.3 volts) that all of the new electronic voltage regulators for 1969 and older put out. I did buy the bracket kits from AR Engineering, but some guys are just adding a couple different spacers to the OEM setup and getting it to work. Night and day difference in how these Denso's charge. Even at 800 rpm, they are putting out the correct full voltage. I had the Denso's tested before installing, and they actually put out more than 70 amps. I couldn't be happier with the upgrade.

 

[twecomm]

Take a load off and install these.. https://www.holley.com/products/electrical/led_lighting/retrobright/parts/LFRB125

 

[69hemibeep]

In my Valiant I have a power master and with the A/C on high, condenser fan on turn signal on my brake lights will bring it below 12v at idle in gear. Think I'll change the stop bulbs to LED. The test sheet that came with the alternator shows they don't put out that much at idle.

 

[AR67GTX]

I largely cured dim headlights and low voltage at idle with the AC on (with stock alternator) with adding an idle solenoid on the carb and retuning my distributor to run 17/18 degrees initial advance + manifold vacuum on the vacuum advance. But your car is so modified that you may be fighting different issues.

I recently had issues with my system voltage dropping to around 10 volts when I switched the AC on. I had recently installed a rebuilt alternator and finally I put the old one back on and the problem was solved. I think the rebuilder might have missed a bad diode or something on the other one.

 

[Sinitro]

Take a load off and install these.. https://www.holley.com/products/electrical/led_lighting/retrobright/parts/LFRB125

Key point of LEDs is they do well on current rather than voltage so no wiring or relays are required. The retro-brights draw less than 10
amps about a 1/3 compared to OE incadescents..

 

[threewood]

Go Denso or go home. Much cheaper option. And yes, you can install it with factory brackets by adding two 5/8" spacers. And they are internally regulated so you can gut or ditch the regulator on the firewall. Installing one requires the addition of ONE additional wire direct from the alt to bat +. You will need to do some research on which ones have a double pully.

Running, it will hold 14v with accessories running. Below, installed on my 69 GTX 440...

 

[cosgig]

Is anybody worried about the higher amperage of the newer style alternators against the factory original wiring? That’s always been the knock for the earlier cars, especially the A bodies that used the paltry 38a alternators. Not saying Kern doesn’t have a wiring upgrade, and even a new dash and underhood harness from Classic may negate this worry, but I just wanted to bring it to light in case it’s still a concern.

 

[Gold Rush]

Current pulled (not pushed) through old wiring is always something to be aware of. As long as some really power hungry drain is NOT being added that usually in not an issue. Think of the alternator as a huge source of current. It will only supply the amount required by the loading device. A 38 amp alternator or 138 amp alternator will supply the same amount of current through a wire supplying a dome light.

 

[1 Wild R/T]

Couple things.... As far as concerns about wiring, Greg has the charge wires through the bulkhead bypassed same as I do & many others who don't want to experience an under dash meltdown...

On the dual pulley Denso... I've done a few, the spacing of the grooves is usually different than Mopar so what I've done is press the dual groove pulley of the Mopar & throw it in my lathe, five minutes later it bolts on the Denso & you 100% know it's correct....

 

[72RoadrunnerGTX]

Hmm....

I have no ammeter. The alternator charge wire runs to the starter relay in my car. There is no charging voltage going inside.
The instrument panel is a Dakota Digital.

I should also mention that I have aftermarket Air conditioning too.

The Tuff Stuff 9509DP is rated at 130amps and is a direct bolt-in replacement for the pictured application. Running them on several factory style A/C cars without significant voltage drop at idle speeds with all loads running. Have a Dakota Digital dash in one of them as well along with a total of 400 watts (low beam 2x80 watts, high beam 4x100watts) of Hella lighting.

 

[gtxdana]

Powermaster 7019

Powermaster makes a retro roundback alternator which is what I have for the GTX. The test sheet shows it puts out 71 amps at idle and 108 amps at the top end. I had good luck with a couple of other Powermaster products which is why I went with this alternator. That, and it looks somewhat correct for a 1970 alternator.

I used a Powermaster one wire alternator on one of my other cars which has a high electrical load with EFI, sound system, amp, A/C, radiator fans which draw over 40 amps on the high speed, etc., and it will stay at 14 volts in gear at 750 RPM.

 

[Crackedback]

Factory alternators stink for output at low RPM's. A factory 38-40 amp alternator is not putting out max output at idle. Slope is important as is minimum output.

Even stock loads like you mention, AC, Blower motor, headlights, basic OEM electrical necessities overrun the factory alternator output at idle.

I run Denso alternators off a four-runner/pickup. Like Randy, take the pulley off, spin it up and machine off the offset step to get alignment.