Last week I had to replace batteries as one went bad. Put the new ones in and a few days later was starting to crank slow again. Drivers side battery tested a little low so threw it on the charger, cleaned all the terminals and back in business.

Just want to make sure that I'm working with a healthy charging system. I went through some tests that I found in another thread. Do these values sound right?

Drivers Side Battery Engine Running All Accessories On 13.50V
Passenger Side Bat, Engine Running All Accessories On 13.54V
Alternator "Field Terminal" 6.4
Alternator "Field Terminal with battery voltage 13.6
Alternator Big Terminal 13.6
Between two field terminals 7.0

No Accessories on Engine Running
Drivers Side Battery 13.82
Passenger Side Battery 13.83
Alt Field Term 10.4
Alt Field Term 2 13.82
Alternator Big Terminal 13.82
Between Field Terminals 3.4

Engine Off
Drivers Side Battery 13.59
Passenger Side Battery 13.50
Alt Big Terminal 13.38
Positive Battery Terminal to Alt Case 13.50

I also did the test where I hooked a 12V light up to the alternator big terminal, grounded it to the case, then measured voltage from positive battery cable to big terminal on ALT. Value of 0.

We're supposed to be going out camping this weekend. Just don't want to end up with a dead battery if I can help it.

 

mine is usually around 14.0 - 14.2v with 2 amplifiers and lights on cruzing down the highway. Idle is around 13.6- 13.8v.

 

Your voltage when the engine is off seems too high. I thought it should be 12.8V.
And I see a little over 14 when idling on my trucks.
Did you check to see if you have a IOD somewhere?

 

Testing is much simpler than what you are making it .
Your not giving RPMs , the alt. needs more than just idle , to do its job .
You need to load test to know whats / what .
Check all connections to batteries [ both + & neg. ] at both ends [ to engine , ground , starter ] , and not forget the fusible links .

 

I don't understand what you mean by this??

 

I was just using the tests I found in another thread here.

The accessories being on should count for a load test should it not? Bright headlights, Driving lights, AC on full bore, Radio with Amplifier going.

I have checked all the connections and cleaned them up prior to doing any of the above.

What testing would you suggest?

Thanks

 

Most of the alt. are 120 amp.s , and all the accessories do not add up to that .
Its one of those things that if you do not have the right tools or knowledge you can not get a good test .
Try taking to one of the do it yourself parts houses , many will do testing , but again , they most likely are not good at diagnostics , but its a start .
It is common in these alt.s , that the brushes wear , making them a little weak .

 

You have a healthy alternator. What I look at is the voltage you measured between the field terminals and battery voltage. With 7 volts between the field terminals and the battery voltage at 13.5, your PCM is calling for a lot of current from the alternator. This may have been measured just after the engine is started.

With the field voltage at 3.4 and batteries at 13.8, the PCM has reduced the alternator output current to keep the battery voltage from getting to high.

The battery voltage measured just after turning off the engine will drift down to about 12.6 volts over a period of several hours.

All is normal and the way it should work.

 

I believe "bent valves" is correct on the analysis of the PCM voltage supplying higher (7 volts) when the alternator needs a higher charge on the batteries and PCM supplying a lower voltage (3 volts) when the batteries require less charge. The PCM is functioning properly and the alternator is suppling a correct charge at 14 volts to charge the batteries.

It sounds like everything is running normal as long as both batteries are reading close to the same and not like what was posted earlier. I don't think you can do much more than you already have to verify the charging and starting system. If the starter continues to spin and start properly when cranking than your batteries are holding a charge and the alt and PCM are functioning properly. The starter supplies a big load on the batteries so listen to how quickly it starts and if it starts quickly you are fine. If the starter takes longer to crank over you are beginning to see problems and then investigate the cause. Otherwise I'd say...Happy Camping.

I'd say keep watching your amp and volt gages and if your getting around 14 volts and you don't have a huge current draw you are good to go.

Keep us posted on any further results as you put some miles on it.

Dave

 

Thanks guys, I'll let you know how it turns out. appreciate all the replies