My 70 Chevelle SS big block has started to overcharge. After a 30 minute drive, enough pressure builds in the battery to blow the caps off.

I put a Summit 80 amp chrome alternator on a couple years ago. The external voltage regulator (electronic) is a couple of years old also.

Is the capacitor that was connected to the old mechanical regulator still needed?

The factory amp gauge has not worked in the 3 years I have had the car.

Any suggestions besides just replacing the voltage regulator?

Thanks!!

Denny,
Yes, your regulator is very likely blown...or there is no connection between the regulator and the alternator. Without regulation, the alternator has lost its reference voltage and is therefore charging at full output, thereby overcharging your battery. At first blush it sounds like a perforated regulator transistor in the electronic regulator.

Before I bought a regulator though, I'd do a quick check the integrity of the ground and the wires at the B+ junction block near the battery, and the integrity of the reference ground wire at the regulator, and the integrity of the B+ connection at the horn relay junction block. Integrity check means disconnect the wires from the lugs, wirebrush or otherwise THOROUGHLY clean them all and reconnect. Clean means shiny metal on all contact surfaces, and tight fitting properly torqued nuts and bolts at all critical grounding and B+ lug points.

Next, I'd verify that the alternator has a good low impedence connection to the block (no corrosion at the bolt heads, etc.) Just clamp your jumper cable negative lead to the alternator and to your battery negative, making sure they are both well shined and good clean connections.

Now, using your handy digital voltmeter, check the voltage for minute changes in B+ as you connect and unconnect the Jumper cable. Even a .2 volt change means you have a suspect ground at the alternator. remove bolts and buff or wire brush them on the contact surfaces. Ditto for the alternator body.

Next, check your charging voltage after you do these integrity checks and compare it to the previous reading with engine running. If it is the same (probably over 14.7 volts?) Your regulator is blown.

After installing the new regulator, and BEFORE you fire up the car, connect your voltmeter in the AMPS mode between the regulator's plastic connector and the spade lugs in the alternator. (i.e. put the DVM in amp mode in series with the regulator and the alternator. Why? SOMETHING blew that regulator. Make sure you don't blow your new one! Have an assistant start the car, as you measure the current draw there, being ready to have them quickly shut the car off at your command if the current draw is more than 1 amp.

Current draw should be something less than about 1 amp. If it is significantly more, there is a problem with your alternator's rectifier circuit. It is drawing too much current through the regulator, causing the regulator to blow. Once it blows, the alternator then runs away and overcharges your battery.

Cheers,

CBG
Cheers,

Thanks for the info. Could you clarify the procedure for the alternator ground test?
1. Connect jumper wire between alternator case and battery (-)
2. Check voltage between battery (+) and battery (-) with voltmeter?
3. Is vehicle running during this check?
4. Connect and disconnect jumper wire and look for any voltage deviation?

Charging Voltage Test
1. Check with meter at battery (+) and battery (-)
2. What is the desired voltage range?

With regulator disconnected, alternator will charge at full output?

Is there a way to check diodes?

Thanks!!

Denny,

My answers below.

1. Connect jumper wire between alternator case and battery (-) YES - this has one purpose. It is to quickly and positively establish a good ground between your alternator case and your system ground. It is quick, easy and temporary. That's the only reason to do it this way. Easier that taking out the bolts, wirebrushing, etc...if they don't need it why bother. This test will tell you that in less than a minute.

2. Check voltage between battery (+) and battery (-) with voltmeter? YES - ESTABLISH YOUR BASELINE SYSTEM B+ VOLTAGE. SHOULD BE ABOUT 12.7-12.9 volts NOT RUNNING ABOUT 13.8-14.2 VOLTS RUNNING.

3. Is vehicle running during this check? YES DURING THE GROUNDING TEST IT IS RUNNING. BE CAREFUL NOT TO STICK YOUR HANDS IN THE FAN OR BELTS! :-)

4. Connect and disconnect jumper wire and look for any voltage deviation?YES - ANY CHANGE IN VOLTAGE WHEN YOU CONNECT AND BREAK THIS TEMPORARY GROUND WILL ESTABLISH THAT YOU HAVE A POOR GROUND TO YOUR ALTERNATOR. NOT COMMON, BUT POSSIBLE. IF IT IS THERE, FIX IT FIRST BEFORE GOING ON TO TROUBLE SHOOT THE REGULATOR.

Charging Voltage Test
1. Check with meter at battery (+) and battery (-)
2. What is the desired voltage range? 12.7-12.9 NOT RUNNING, 13.7-13.9 RUNNING.

With regulator disconnected, alternator will charge at full output? NO IT WILL NOT CHARGE AT ALL. IF THE VOLTAGE DOES NOT DROP BACK DOWN TO THE 12.8 READING WHEN YOU DISCONNECT THE REGULATOR, YOU HAVE AN ALTERNATOR PROBLEM.

Is there a way to check diodes? YES- DIODES FLOW CURRENT IN ONE DIRECTION ONLY. USE YOUR DIODE CHECK FEATURE ON YOUR METER. THE READING SHOULD BE VERY LOW (.200 or less) IN ONE DIRECTION AND HIGHER IN THE OTHER (1.750 IS NOT UNUSUAL) IT DEPENDS ON THE DIODE. NO READING EITHER WAY MEANS THE DIODE IS OPEN. SAME READING BOTH WAYS MEANS IT IS SHORTED. IF YOU DON'T HAVE DIODE CHECK, USE YOUR OHM METER. SHOULD BE LOW IN ONE DIRECTION, HIGH IN THE OTHER.

Let me know how it goes. I'm betting it is the regulator.