Bigmikey65

So my ‘70 W-30 runs fine driving around town - until I turn the headlights on. Once I turn the headlights on the car stalls approximately 10 minutes later. It will then not restart until 40 minutes later - seems like the battery is drained. This is very frustrating. I’ve had the alternator out of the car and tested - it’s good. Brand new battery yesterday. Fresh build. 37 amp stock alternator. The car runs in idle with the headlights off. The car stalls after 10 minutes with the headlights on. The alternator belt is tight. The battery cables are properly installed. I checked all the alternator wiring. It only stalls with the headlights on. I noticed that my idle might be a little low - it’s at 650 rpm in neutral. Car is a 4 speed. Motor is a fresh build - to stock specifications. Could the issue be that the idle is too low ? Was looking forward to taking her to her 1st show tomorrow but….

droldsmorland

What is the running voltage with & without the lights on?
Was the battery load tested?
Parts can test OK when cold and decay as they heat up.
Was the alternator tested under load? Was it tested by a knowledgeable person or a big box wanta be?
What is the condition of the battery cables? Clean your grounds to include both ends of the secondary (large) battery wires.

Fun71

Is this an internally regulated alternator or an extermally regulated version?

fleming442

I would suggest a CTEK charger at minimum. Put a voltmeter on it, rev it up and see when the voltage rises. It probably won't crack 13v until 3000 rpm-ish. Most don't charge at idle, and you can't expect an alternator to recharge a low battery, unless you're going for a very long drive during the day without the lights drawing.

Bigmikey65

Put a Volt Meter on it. The amps steadily decrease with the headlights on at my present idle of 650 rpm. When I increase the idle to 850 rpm the Volt Meter shows that the system is charging as normal. The alternator is a stock 1970 37 amp alternator with an internal voltage regulator. The alternator was rebuilt by a man who has been exclusively in the alternator business for 49 years. I took it back to him and tested under load - it worked as it should. Properly. The battery was load tested. My battery cables are brand new. I am thinking that my idle needs to be increased to 800 rpm. I believe factory stock is actually 750 rpm. I probably should have had the internals upgraded to 55 amps. Is it possible that the problem is a low idle ?

droldsmorland

When it stalls will the starter crank but the engine will not re-fire for ~40 mins? Y or N
If in fact it cranks over have you verified spark?
Points or HEI?
You say the voltage VDC (not amperage) falls off while you're watching it? This indicates a charging system problem to me.

Please provide some basic data:
-Battery surface charge VDC before doing anything =
-Battery VDC "drop" while cranking =
-Battery/alternator running VDC lights off =
-Battery/alternator running VDC lights on =
-Battery group size & CCAs =

It worked for 50 years with 37amps, doubtful that 18 more will fix the problem.
Another 100 rpm at idle wouldn't hurt anything but it is not the root cause.

fleming442

Sounds like it's working perfectly fine 🙄

Bigmikey65

When the car stalls it will not crank. It then started after sitting for 40 minutes.

Points

At 650 rpm idle the car runs fine - good voltage reading. At 650 rpm idle with the lights on the car will drain the battery and stall.

At 850 rpm idle the car runs fine. At 850 rpm with the lights on the voltage is normal.

I should upgrade the internals to 55 amps but in the meantime is a 650 rpm idle too low ? Has anyone had this issue with this alternator setup ?

olds 307 and 403

It may just be too low of an idle and there may be a short or maybe a bad ground on your headlights. You can upgrade those alternators to more like 80 amps, both internally and externally regulated alternators, which will make a noticeable difference. Especially if you have an upgraded stereo or other electronics added, more amperage, as long as it doesn't exceed the alternators cooling ability, is always a good idea. I find the 10SI 100 amp alternators never last. About 80 amp or less, are without issue. Pretty sure it is just too much heat generated. My Summit 80 amp 10 DN externally regulated alternator worked great without issues for at least 5 years. I am now running a CS series serpentine 105 amp alternator in my 70S.

Fun71

That is lower than the factory spec for idle speed.

droldsmorland

Mike,
I need numbers to be able to help not "normal" Normal tells me nothing.
Fill in the blanks after the = signs above.

If it will not crank once it stalls you have a charging or starting system problem.

Steve

Koda

I personally am wondering about how it can die, not start, then magically be able to 40 min later. Is this dead battery style starting, like no starter at all, or weak starter on a hot, overtimed engine, whurr<nothing> start?

If it's the latter, I think you have a bad alternator, bad starter, bad cables or some combination.

fleming442

Bad starter.

Olds64

x2

Next time it happens use a rubber mallet and rap on the starter a few times. Not starting when hot could be a classic heat soak issue.

fleming442

Fixed that for you..... aka "Ford starter tool 775B"

Bigmikey65

Battery is reading 12.6 volts when car is off.

14.3 volts when car is running with no accessories.

When I turn the headlights on - that’s when the volts start to drop to around 11 and the car shuts off.

Without the headlights on the car runs fine.

When I try to start the car after it stalls it sounds like it does not have enough power to turn over. There are no clicking sounds. The car will start about 40 minutes later - can the battery regenerate itself in that time ? The battery is brand new. This is the 2nd brand new battery in the car. The starter is the stock unit - it was recently rebuilt.

Everything in the car is either new or rebuilt.

When I get a minute I’m gonna increase the idle to 800 rpm and see if that helps the problem.

Battery is a group 24 with 600 CCA.

I know the car calls for a Group 27 but I don’t believe that’s part of the problem.

joe_padavano

Both of these are normal.

This is not normal. Are these stock(ish) headlights and not some 8.3 gigawatt aftermarket pavement melters? If so, figure out where the dead short is that is sucking the power from the system. I'm assuming the voltage drop occurs with the car running? If so, where are you measuring voltage? What happens to voltage if you put the headlights on with the car not running?

Vintage Chief

14.3V at the battery car running suggests ALT is working fine. From your 1st post onward it appears you have an issue with your headlight circuit either the Switch or wiring. I’d check your headlight circuit.

Bigmikey65

Headlights are stock-ish - nothing fancy.

Looking at my notes - the battery actually read 13.4 volts with the car turned off.

I am measuring voltage at the battery.

The voltage drop occurs with the car running.

The voltage reads 12.8 with the car off and the headlights on.

Vintage Chief

If you’re running aircraft runway landing lamps you should replace with standard automotive headlights.

Vintage Chief

What happens when IGN SW is ON, but car not running when you turn headlights ON? Voltage drop?

Bigmikey65

I’ll check that Norm.

Bigmikey65

Is it possible that the alternator is making enough voltage at 650 rpm to keep the car running but there is not enough voltage at 650 rpm to run the headlights ?

Obviously this is where my issue is.

Another thing I think I need to check is how fast the battery voltage drops with the car off and the headlights on.

Vintage Chief

You’re supplying 14.3V to the battery car running - you just said that.

Bigmikey65

Correct Norm.

At 650 rpm and the headlights on - the voltage starts to drop until the car stalls. Approximately 5-7 minutes.

When I increase the idle to 800 - 850 rpm there is no voltage drop with the headlights on. The car runs normal.

Vintage Chief

Did a 1970 W-30 come stock OEM w/ an internal ALT VR?

Bigmikey65

The stock 37 amp alternator has an internal voltage regulator.

My alternator checked out fine when I took it out and had it bench tested.

Vintage Chief

Interesting…

Vintage Chief

Sure sounds like a little peanut (37A) ALT for a W-30. Why are you idling at 650 RPM. That sounds ~ 200 RPM too low isn’t it? This car have AC or no AC? I would suspect no AC?

truckman5000

It's something that's heating up too much.

positive to starter resting on block, heating up, current draw, then only supplies enough power to the starter cold.

It's not a power issue It's a current pass through issue. and since it works when cool, it's a power to starter issue.

Vintage Chief

I don’t suspect the ALT is bad, you’re supplying 14.3 V

Vintage Chief

I believe you’re onto it.

droldsmorland

Mike before we go any further turn the RPMs up to 750-800 and report back.
Please fill in the blanks, after RPM is turned up. (hit the "quote box in the lower right and simply fill in the blanks)

-Battery surface charge VDC before doing anything = 12.6 is OK,13.4 is even better.
-Battery VDC "drop" while cranking = _____
-Battery/alternator running VDC headlights off = 14.3
-Battery/alternator running VDC headlights & high speed blower on =______<----KEY DATA at 1, 5 & 7 min intervals at ~750-800RPM
-Same as above with just parking lights on = ______
-Battery VDC headlights on engine off = 12.8
-Battery VDC parking lights on Engine off = _____
-Battery VDC headlights on engine off x 5 minutes = ______
-Battery group size & CCAs = 24/600 CCA

The factory alternator should be able to handle FULL system load at rated idle speed.
Once you have adjusted the RPMs and filled in the blanks we will start to dive in deeper.

This device will load test, surface test, and alternator test. A good tool to have, not much money:
https://www.schumacherelectric.com/p...y-load-tester/

Bigmikey65

So I increased my idle to 800 rpm and here are the readings with the car RUNNING :

Headlights ON and Heater Fan on High = 13.2 - 13.4 Volts

Headlights OFF and Heater Fan on High = 14.3 Volts

Headlights OFF and Heater Fan OFF = 14.4 Volts

Headlights ON and Heater Fan OFF = 14.0 - 14.2 Volts

I left the car running for 20 minutes with the headlights ON with no change in Voltage.

Is it possible that the stock 37 Amp Alternator does not produce enough volts at a lower than recommended idle speed to maintain battery charge with the headlights on ? Yes, this is an old alternator, but it was rebuilt by a professional who solely rebuilds alternators for a living. On the bench the alternator performed as it should. The headlight bulbs are stock voltage.

After a lot of head scratching and work I think I might have found the answer to my problem.

Thank you for all your help - I am definitely open to further questions/suggestions.

droldsmorland

Headlights ON and Heater Fan on High = 13.2 - 13.4 Volts...this is low. Barely above battery surface charge.
Full load at rated RPM should be 14.0-14.2. You don't have a full load yet...wipers, brake, reverse, interior lights, defogger etc

I still think the alternator is weak. Or a connection is bad taking the alternator to its knees. Does it sound loaded and does it get warm fast?

truckman5000

I think it's the tail light bulb.......that draws current after 30 minuets suddenly......that's gutta be the issue......

Let's talk alternators
Car turns on?
You must have a 2,000kw sound system, and a off road light bar mounted on the roof......or ?

droldsmorland

Good point. Don't joke I've seen bad bulbs and bad sockets do strange **** like this.
This outer fringe stuff is at the tail end of root cause analysis, but it is there. Let's keep it simple until the simple stuff is ruled out.

68post

I'm curious as to whether all of the grounds are intact and of the original size or larger/smaller ?
Be careful with all the low voltage running that you don't blow the fusible link, it's happened to me on a vehicle that had a crank pulley larger to slow down the accessory drag.

fleming442

I agree, but we've already been assured that everything thing is good and 37a is plenty big because that's what the engineers designed to last 10 years.

dragline

Glad you found your problem. Just wondering if a different alternator pulley diameter would allow you to run @ 650 rpm and maintain proper voltage.