Diagnosing charging system health '70 Barracuda EFI

[Mopsquad]

Hello all,

I have the EFI dual TB 426 hemi conversion running pretty well.  Using a laptop, you can see lots of data.  One thing that I'm monitoring is the battery voltage. 

The battery is the red cap OEM looking modern battery.  Cold it measures about 12.4v

With the car running, initially I see 13.1v (verified with laptop and voltmeter).

With the car idling up to 30-45 mins, the voltage drops to about 12.6v and stabilizes.  Flicking on the headlamps, fog lamps, the voltage does not drop.  The lights flicker slightly but do not dim.

I've always thought that the alternator produced voltage should be 14-14.4v

What are your thoughts everyone?

TIA

Steve

[1 Wild R/T]

Have you done a bypass circuit taking the bulkhead connector out of the charging system?

[Mopsquad]

Have you done a bypass circuit taking the bulkhead connector out of the charging system?

Not sure exactly.  I did remove the ballast resistor and tapped into the two wires to supply the EFI and MSD - the 12v on and 12v crank.  Taped up the remaining wires. 

[1 Wild R/T]

Run a 8 ga wire from the stud on the alternator to the stud on the starter relay....   Doing this will make your Ammeter no longer read the charge so it will show discharge most of the time.... Personally I disconnect the black lead on the back of the ammeter & move it to the post with the red wire... Then the meter doesn't read at all, next add a volt meter, whether you get one that plugs into the cigarette lighter or whatever other method but that will be your way of knowing what the charging system is doing...


You should also consider relays for your headlights....  Take all the major loads away from the bulkhead connector, the car will be more reliable & less likely to catch fire....

[YellowThumper]

I chased a similar gremlin on mine for a long time. Ammeter was already bypassed. It ended up being the wire that feeds 12v to the voltage regulator for it to read charge requirements. My charge volta gf es always varied from high to low. Never consistent. I believe it was said this is the blue wire. To fix issue I just used it to trigger a relay that fed clean power to vreg. All is now rock solid.
Issues lie somewhere in bulkhead and ignition switch. I would suspect something similar as it changes after time. Surmising wiring is getting hot and resistance changes.

Good luck.

[1 Wild R/T]

I chased a similar gremlin on mine for a long time. Ammeter was already bypassed. It ended up being the wire that feeds 12v to the voltage regulator for it to read charge requirements. My charge volta gf es always varied from high to low. Never consistent. I believe it was said this is the blue wire. To fix issue I just used it to trigger a relay that fed clean power to vreg. All is now rock solid.
Issues lie somewhere in bulkhead and ignition switch. I would suspect something similar as it changes after time. Surmising wiring is getting hot and resistance changes.

Good luck.

If the blue wire gets low voltage the regulator should raise the voltage so you should have been getting high readings, not low....   A ground problem at the regulator can cause a low voltage reading....  Using a relay like you did should be a very clean signal for the voltage sensing...  Relays are very useful when you understand them...

[YellowThumper]

  yes I did have that backwards.
However I will surmise the low V is heat aka resistance issue.
IIRC it was your input that got me corrected.

Thanks.

[Mopsquad]

 Thx for the replies everyone.  The electrical system, specifically the charging/regulation is out of my wheelhouse. Did I interrupt a charging prompt by eliminating the ballast resistor circuit?

[1 Wild R/T]

Thx for the replies everyone.  The electrical system, specifically the charging/regulation is out of my wheelhouse. Did I interrupt a charging prompt by eliminating the ballast resistor circuit?

You didn't eliminate it, you bypassed it.... That's not effecting your charging...  First & formost add that 8 ga wire I previously mentioned & then retest your voltage....

[Chryco Psycho]

What alt are you running ?
Sounds to me like it may not produce enough amps , it is definately not producing enough at idle which is why you are losing voltage idling , woth all of the systems you are running for the EFI system , fuel pump , computer etc you need more alt output .
Does the voltage rise to 14.3 when you bring the RPM up to say 1500 or so ? If so you woud be ok driving but sitting in traffic you will run the battery down .

[Mopsquad]

What alt are you running ?
Sounds to me like it may not produce enough amps , it is definately not producing enough at idle which is why you are losing voltage idling , woth all of the systems you are running for the EFI system , fuel pump , computer etc you need more alt output .
Does the voltage rise to 14.3 when you bring the RPM up to say 1500 or so ? If so you woud be ok driving but sitting in traffic you will run the battery down .

Thx, I'll try the 8 ga wire. Regarding alt. I believe it's stock.  I'll try revving it up and see what volts it goes to. Btw. Here's a pic of my gauges. Disregard the high temp reading it was Friday and it doesn't read properly on fridays. Lol.  The amp is near the 'C'.

[Mopsquad]

Run a 8 ga wire from the stud on the alternator to the stud on the starter relay....   Doing this will make your Ammeter no longer read the charge so it will show discharge most of the time.... Personally I disconnect the black lead on the back of the ammeter & move it to the post with the red wire... Then the meter doesn't read at all, next add a volt meter, whether you get one that plugs into the cigarette lighter or whatever other method but that will be your way of knowing what the charging system is doing...


You should also consider relays for your headlights....  Take all the major loads away from the bulkhead connector, the car will be more reliable & less likely to catch fire....

Too clarify. Which stud on the alternator and which stud on the starter really?

[Chryco Psycho]

The large stud on the Alt  with the 1/2" nut & the start relay , 1 wire from the positive battery terminal bolts to the relay

[Brads70]

Run a 8 ga wire from the stud on the alternator to the stud on the starter relay....   Doing this will make your Ammeter no longer read the charge so it will show discharge most of the time.... Personally I disconnect the black lead on the back of the ammeter & move it to the post with the red wire... Then the meter doesn't read at all, next add a volt meter, whether you get one that plugs into the cigarette lighter or whatever other method but that will be your way of knowing what the charging system is doing...


You should also consider relays for your headlights....  Take all the major loads away from the bulkhead connector, the car will be more reliable & less likely to catch fire....

Too clarify. Which stud on the alternator and which stud on the starter really?

main power/battery stud on alternator, and for the starter relay ,the one that is connected to the battery. Alternatively you can go from alternator stud right to the battery if you prefere.   I'll throw my hat in with those that highly recommend doing this mod. Relays for headlights too ! Member "crackedback" made me a nice tidy kit to  wire up my headlights to relays . @crackedback
If your running a stock output alternator it will not be up to the task with modern add ons.    I've been running a  high output alternator from here for 5 plus? years now with no issues. https://www.qualitypowerauto.com/catalog.php?item=557   Others have adapted cheaper solutions using various stock components. https://www.manciniracing.com/search-results.html?query=alternator%20kit#query=alternator%20kit

[crackedback]

I'm not far from you over in Indio.

I build the 6 and 8ga charge wires with a fusible link.  Try to make them stealthy as well.   Simple to install.  I may have an ad up here somewhere.

Where are you tapping the system for your EFI?    Battery or starter relay on our mopars is a horrible spot with the factory charging system.

Let me know if I can help.