What Is This Ammeter Doing?

[JG71B]

Can someone tell me if too small of a battery would make my ammeter gauge do this at idle, no accessories are on. I just find it odd. It moves a tad bit more that way when I turn the lights on. It's a 650 CCA battery but I put in it about 2 years ago that a buddy had sitting around unused for nothing. Goes briefly to the charge side until it's running for a couple seconds and then to the middle and then where you see it it stays pretty much. I've checked grounds replaced the wiring harness for the engine (383 car) a couple years ago. Everything works....it's just a bit odd to me is all. Thanks in advance

 

[4vnut]

Voltage regulator?

 

[R413]

Discharge. A bad battery can do that, to small a battery will not do that.

 

[493 Mike]

Perhaps it's just a calibration issue. Try a voltmeter.
Mike

 

[RJRENTON]

Discharge. A bad battery can do that, to small a battery will not do that.

Yes....a partially sulfated battery will react this way.....batteries will sulfate over time due to non use.....
BOB RENTON

 

[JG71B]

Yes....a partially sulfated battery will react this way.....batteries will sulfate over time due to non use.....
BOB RENTON

It's 3-4yr old battery by its date but, I understand new is meaningless these days, for a while now. Voltmeter looks good off and while idling. I plan to bypass it anyway here soon

 

[RJRENTON]

It's 3-4yr old battery by its date but, I understand new is meaningless these days for a while now....

Time is not relevant....it's more a function of use or not....it's due to chemical reaction of the batteries components...lead, lead dioxide and sulfuric acid during the charge/discharge cycle...
BOB RENTON

 

[Bee1971]

I would bee more concerned with your oil pressure gauge

 

[Bee1971]

At idle , what is your volt meter readings at the battery

 

[Dragon Slayer]

So a bad battery sulfated over, with provide more current to the loads? So it presents a higher voltage than normal to the Voltage regulator? Causing VR to to lower current to the alternator field so that Alternator voltage stays low? I am asking, because it does not sound right to me?

The ammeter is mechanical, and if current flows from battery to the loads it reads in the discharge range.
Normally after sitting and then cranking to start the car, the battery is somewhat drained, especially in an older battery. The ammeter will go to the charge side after starting because battery voltage is low and the VR is telling the alternator to raise voltage so that battery can be charged while also feeding loads.

You can take it to an auto store and they will load test battery and alternator in the car, let you know what's going on.

 

[Tman100]

I’d check the alternator. If it charges at 1000 rpm or so and used to charge at low idle could be a burnt diode in the diode trio. If the rectifier is only working at 66% it can cause this issue. If you have a fancy battery tester you can check this. Otherwise most decent shops can check this in about 5mins.might not be your issue but I’ve come across this a couple times.

 

[SlinktRR]

I haven't seen that, mine will sit at 0 after start up unless it hasn't been on the tender for a while. As long as the charging voltage is correct with a multimeter I wouldn't be concerned. My 800cca battery is 11 years old now and acts like brand new...the secret is to put it on a battery tender whenever it's in the garage. 12.6 volts if off the charger for awhile, 12.85 volts fresh off the tender with negative disconnected.

 

[RJRENTON]

So a bad battery sulfated over, with provide more current to the loads? So it presents a higher voltage than normal to the Voltage regulator? Causing VR to to lower current to the alternator field so that Alternator voltage stays low? I am asking, because it does not sound right to me?

The ammeter is mechanical, and if current flows from battery to the loads it reads in the discharge range.
Normally after sitting and then cranking to start the car, the battery is somewhat drained, especially in an older battery. The ammeter will go to the charge side after starting because battery voltage is low and the VR is telling the alternator to raise voltage so that battery can be charged while also feeding loads.

You can take it to an auto store and they will load test battery and alternator in the car, let you know what's going on.

An automotive storage battery operates on chemical reactions. It doesn't absorb volts and current but converts the applied current to change lead sulfate (from the chemical reaction of lead, lead dioxide and sulfuric acid to lead,lead dioxide to increase the specific gravity of the acid and to put the lead compounds back on their respective plates...aka charging the battery. As a battery ages the respective plates become polarized, inhibiting their ability to accept a charge or to furnish energy...cranking the engine. All the while producing the 12 volts at the terminals, which is the result of the pure chemical reaction of lead, lead dioxide and sulfuric acid (the chemical reaction is 2.0 volts per cell X the number of cells) REGARDLESS of the battery's ability to furnish any significant cranking energy. This condition is referred to as sulfation....which may be convertible by long slow charging...1-2 amps at 12.5-13 volts over several days to possibly re-polarize the positive and negative plates...this method may be successful. One would measure the specific gravity of the acid as the gravity will increase as the battery accepts the charge. A fully charged battery will have a specific gravity of 1.260 to 1.270 corrected for temperature as measured with a hydrometer. The gravity will decrease as the battery supplies energy to its connected load; charging increases the gavity of the acid. A battery is a chemical reaction device that is capable of supplying or consuming energy that can go either way. It's that simple...it's an electrochemical device, whose effectness decreases over time...or polarization. The battery must be charged at a slightly higher voltage to overcome any internal resistance and to orignate the charge reaction...it's approx 13.5-14.5 volts. Just my opinion of course....BOB RENTON

 

[Dragon Slayer]

Bob, You did not answer the question. The ammeter doesn't lie. The battery is sourcing the loads, and the alternator is not. If the alternator and VR are GOOD. That means they are seeing a high voltage from the battery and the battery is running the car.

You and one other stated that a bad battery can do this. I am asking how. Not how a battery works. My battery in a 70 RR is pushing 10 years old, is never put on a tender because it does not drain when sitting for weeks. It will crank the motor and it takes a few cranks to get fuel back into the carb. When it starts, I am showing a higher current from alternator to the battery. After driving a few minutes, the ammeter goes lower but clearly shows the alternator supplying the loads.

I agree with other that a diode in alternator, or VR may have issues.

 

[marksmopars]

Amp meter measures current magnitude and direction, this one says current is flowing from your battery, bottom line. Why is discussed above in some detail I think.

 

[Don Frelier]

1. Why is your oil pressure so low? (Or is it just not working)

2. What happens when you raise the rpm to 1,500-2,000 with no other changes?

 

[SlinktRR]

JG71B, put a meter on it when running, should be charging around 14 volts with good VR. Then shut off and measure what the voltage is on the battery terminals after sitting for a while. Post your readings.

 

[Don Frelier]

JG71B, put a meter on it when running, should be charging around 14 volts with good VR. Then shut off and measure what the voltage is on the battery terminals after sitting for a while. Post your readings.

I don't think it will be that high at idle, especially if the ammeter reading shown is accurate

 

[RJRENTON]

Bob, You did not answer the question. The ammeter doesn't lie. The battery is sourcing the loads, and the alternator is not. If the alternator and VR are GOOD. That means they are seeing a high voltage from the battery and the battery is running the car.

You and one other stated that a bad battery can do this. I am asking how. Not how a battery works. My battery in a 70 RR is pushing 10 years old, is never put on a tender because it does not drain when sitting for weeks. It will crank the motor and it takes a few cranks to get fuel back into the carb. When it starts, I am showing a higher current from alternator to the battery. After driving a few minutes, the ammeter goes lower but clearly shows the alternator supplying the loads.

I agree with other that a diode in alternator, or VR may have issues.

My answer is related with semantics....and your understanding.....the current flow to/from the battery thru the ammeter, excluding the innitial starting load, where only the recharging current is measured via the ammmeter is a simultaneous event. After starting, the ammeter, in addition to the battery, supplies the power to operate the vehicle, thru a parallel circuit arrangement of the battery and the alternator. There is no discrete point where the combined source is defined, as to which source is measured and the other source is not. If the alternator output does not match the load requirements, the bulk of the energy will come from the battery and the ammeter will reflect the current source, as the alternators output increases, the ammeter will reflect its contribution as a more positive current flow. The excess power will be available to charge the battery due to the starting load imposed on the battery. If the battery is or is becoming sulfated due to its age, the battery voltage may decrease due to its ilability to accept the charge, even though the alternator is at its maximum capability or the voltage regulator may be commanding maximum output. Its important to remember and realize that all batteries do not age at the same rate....it's exceptional that your battery has lasted 10 years without any intervention. But its all related to manufacturing technique, materials, including QC standards and actual operating conditions...vibration, temperature extremes, abuse, maintenance, etc. There are alternator issues that could be involved; specifically an open diode, low output current capabilities and worn out brushes for the rotating field both of which can effect ithe alternator's output to react to the innitial and connected load, including the battery and its ability to be recharged quickly. There are no one cause but a compilation of all factors involved......
BOB RENTON

 

[Dragon Slayer]

I don't think the wiring chart agrees with you. The alternator feeds through the bulkhead connector directly to a splice that feeds various loads including the ignition switch Battery feed. If you start the car, and disconnect the battery the car would still run. From that splice the alternator power goes to one side of the amp meter. The other side is the battery side going to the bulkhead and via fusible links connects to the battery. Granted it is a parallel circuit except the amp meter tells you whether battery is discharging or charging by measuring current direction and amplitude.

So back to your statement that a bad battery that is sulfated will cause the amp meter to show the battery discharging. Meaning running the loads because current flows out of the battery into the junction that the is feeding the car loads. While I recognize a damaged battery may not want to charge, I question how can it source current into a junction that is most likely at a higher voltage potential. The only way that happens is that the sulfated battery creates a high voltage condition and does source current. But apparently doesn't die or prevent starting.

Bad battery can present normal voltage when unloaded. Voltmeter reading. But once you load a bad battery, voltage drops way low and it can not source current to a load. If some how this condition acts like a diode and resist current flow into the battery, the amp meter would read neutral. The dead battery can't support a load by sourcing current.

Now I may be missing something here, which is why I question the answer it is the battery. But by his amp meter reading that battery is sourcing 10+ amps most likely and a bad battery can't do that. Now a bad alternator, or VR and that is exactly what you would see. Good battery starting the car and then sourcing current to run everything. Draining the battery over time. So at some point the battery will be drained and unable to source the start current requirement.

Now maybe he has a defective amp meter, or it is wire opposite. But as shown with an operating system, that battery is sourcing the load.