427 Contemporary Cobra - Charging Issue

[TheBDP]

First-time post here...

'66 427 Side Oiler Contemporary Classic (CCX34026) - Registered as a 99

I can't seem to find the root cause of a charging issue, and looking for pointers on where I might want to start.

The original alternator was bad from purchase(tested at a local Auto-Zone) -
I purchased a new Powermaster 150 AMP, and swapped it out.

Gauges now show it charging. But when I throw the battery tender on, it's showing a 60% capacity after about a 30-minute drive. Drops to about 30% after an hour's drive. I'm worried it'll die on the road.

No documentation is available from the original build, so looking for any pointers on where I should start chasing this gremlin at. Fuses look fine, and I have no idea if this car has ever had a fully charging system or not.

I'm pretty mechanical, and good with my hands, but I'm not too proud to admit when I don't know something. Any help would be greatly appreciated. Trying to avoid taking it to a pro, if it's something reasonably straightforward.

I don't have access to a lift, which seems to be my most consistent issue with the car. I can't seem to get under it to access everything.

[mrmustang]

Originally Posted by TheBDP

First-time post here...

'66 427 Side Oiler Contemporary Classic (CCX34026) - Registered as a 99

I can't seem to find the root cause of a charging issue, and looking for pointers on where I might want to start.

The original alternator was bad from purchase(tested at a local Auto-Zone) -
I purchased a new Powermaster 150 AMP, and swapped it out.

Gauges now show it charging. But when I throw the battery tender on, it's showing a 60% capacity after about a 30-minute drive. Drops to about 30% after an hour's drive. I'm worried it'll die on the road.

No documentation is available from the original build, so looking for any pointers on where I should start chasing this gremlin at. Fuses look fine, and I have no idea if this car has ever had a fully charging system or not.

I'm pretty mechanical, and good with my hands, but I'm not too proud to admit when I don't know something. Any help would be greatly appreciated. Trying to avoid taking it to a pro, if it's something reasonably straightforward.

I don't have access to a lift, which seems to be my most consistent issue with the car. I can't seem to get under it to access everything.

How old is the battery?


Bill S.

[Tommy]

Here's what I expect to see if everything is working correctly.

• All electricals and engine off, 12.8 volts at the battery
• Engine on at idle, 12.8-13 volts at the battery
• Engine on at 1500 RPM or higher with no accessories on, shortly after engine start 13.5-14.5 volts at the battery
• Engine on for more than ten minutes with no high draw accessories, 13-14 volts at the battery

If you don't see numbers very similar to these it is likely a problem with the battery, alternator or voltage regulator (if you have one separate from the alternator). The first thing I'd do is fully charge the battery on a charger and check it (with nothing attached to it) after a few hours. If its less than 12.8 volts, that's likely the problem. . . . If the battery tests good but the other voltages are low, its likely the charging system.

[TheBDP]

The battery is only a year old, but it's showing 11.9, and max capacity of 30% on the charger after 3 hours of charging. I'll swap this out in the morning and see if this is the culprit.

Appreciate the quick reply guys. Hopefully, this is it!

[Tommy]

If the battery is the problem, be sure to look for a reason it failed so soon. For example, it might have been overcharged or it might have gotten too hot.

[DanEC]

11.9 volts on a battery that you’ve attempted to charge is not good. You should see at least 12.4 to 12.8 volts. I think that battery has issues. But there could be other issues too with the voltage regulator or alternator.

[mrmustang]

Originally Posted by Tommy

If the battery is the problem, be sure to look for a reason it failed so soon. For example, it might have been overcharged or it might have gotten too hot.

This AM I was thinking perhaps a bad voltage regulator, which could also cause the battery to overcharge, thus creating the issues the OP is having.

Bill S.

[panteralee]

Start the car and measure the voltage across the battery. If the alternator is charging, the voltage will read higher than what the battery reads with the car not running. Either it is charging or it isn't. That will eliminate the alternator. report back once you do this.

[mvanhorn8893]

I also had an issue with the voltage regulator when I tried installing the original style voltage regulator and I wound up switching to a solid state voltage regulator that looked similar. If you need the wiring diagram I can email you the manual and my wiring notes.
My dash charge indicator light goes out when it is properly charging.

mvanhorn8893@gmail.com

Mike

[kitcarbp]

So the first thing i noticed is youre quoting the 11.9 V reading from your battery tender volt meter. Have you used a dvom across the bat terminals to check the battery no load ( key off) voltage ? Same 11.9v result? Dash volt gauge the same? Just to validate your tender reading.
Forget about the battery tender for the moment. As others have said, a good battery should be 12.4-12.8V depending on its health with no load on it. Starting up the engine using the same dvom on the battery will read a higher voltage at engine idle. How much higher will depend on the voltage regulator setting or type and the alternator health. Generally the charging voltage at the battery should be above 13.5V and can be as high as 14.0 V ‘ish depending again on the voltage regulator and or alternator health. My voltage regulator on my Ford 3G alt is set at 14.5V. You should also check the battery voltage with engine off with the battery loaded and measure the voltage at battery again. Key on and headlights on are a good load test with battery still in car. The engine cranking voltage is the best test. Under load will tell the real story on battery health. You should see loaded voltage about 11-12V. I re-learned this last weekend.
My no load voltage at battery was 12.6V yet when I turned the key, nothing worked, as if the main fuse was blown. I started checking down stream of the battery the first 30 minutes , wasting time!. Then I went back to the battery to measure voltage with about 6 amps load ( key on) at the battery, and discovered the voltage was 2.0V. Loading testing revealed the issue. The battery was dead as a door nail. It was 8.5 years old and owed me nothing.