Charging?

[2ruble]

I replaced my battery with an AGM battery and also 80amp alternator last night, I didn't "charge" the battery after running around with just the battery running the vehicle because I figured the alternator would do it driving around for about an hour last night and the drive to work this morning. My question is that under throttle the voltmeter is coming up fine, above middle - at what I'm assuming is about 14v. At idle, on occasion, it would drop down to below middle, closer to what I'm assuming is 9-10. I can't remember if I had the heater on at idle or not, but that really shouldn't drop it I wouldn't think.

I tested last night after install, the battery was at about 12.32 after alternator install and under rpm it registered about 13.4, under load it dropped a hair, but stayed above 12.

It's an 89 bronco ii 2.9 with A/C (doesn't work) but the heater blows hotter than hell.

Ideas? Or I just haven't let it charge enough?

 

[RonD]

Reads like you have a problem

New battery should be 12.8 volts to 13v, at rest

5 year old battery 12.3v, near end of life

12.2v or lower is end of life, and cold morning, "click, click, click"

Since your new battery was drained, you can cut it some slack, but it should come back up to 12.8v after charging.

After startup battery voltage should show 14.5v or higher, under 15v
Alternator's voltage regulator puts out "recharging" voltage, 2+ volts, until battery is recharged, that could last 5 to 15 minutes, depending on battery's condition.
Then voltage regulator will switch to "maintenance" charge, 1 volt, to keep battery charged without "cooking it".

Once started the alternator provides all the power for the vehicle, recharging or maintaining the battery is a secondary purpose, battery can actually be removed from a running vehicle, it is no longer required by the electric system.
Battery's only purpose is to start the engine.

I would retest battery voltage
After is sits for an hour or longer, thats "at rest" voltage
Start engine, you should see 2+ volts more at battery, 14.5 to 14.9v
Increase RPMs to approx. 2,000 and hold it there, volts should go up and then drop back down to 14.5-14.9v, that's the voltage regulator working.
If startup voltage is lower, 13.5v, and then goes up to 14+volts with RPM increase then alternator has an internal problem

After driving for 10 minutes or so, don't shut off the engine and test battery voltage again.
Should be 1 volt above "at rest", so 13.5-13.8v, turn on all the lights and heater fan to high.
Voltage should drop and then come back up to 13.5-13.8v

If voltage drops and doesn't come back up then you have a failed field in the alternator.

Test alternator wiring
Key OFF
test B+, wire on the large stud/nut on alternator(you don't have to disconnect wire from alternator), should show battery voltage, exactly the same, if even slightly different then that wire has corroded connection at one end.

Remove 3 wire connector on alternator.
test Yellow wire, should show battery voltage, if not then blown fuse or fusible link

test Green wire, should be 0 volts
turn key ON, engine OFF
Green wire should now show battery voltage, that is your Battery Light wire, it is also the ON/OFF switch for alternator, so an important wire.
It runs through ignition switch and dash so can show slightly lower voltage, but .1 to .2v. not alot

In 1989 battery's Positive and alternator are connected at Starter Relay on the inner fender, one of it's larger studs is the power distribution point of the truck, so all power for the truck runs through that one connection, make sure ALL the wires connected there are clean, use wire brush or emory cloth to remove and corrosion on any wire ends.

Battery's Ground is equally important, make sure its connection to engine is clean(bare metal) and tight

DC voltage is like a ONE LANE circular highway, if everyone is driving at 80mph then every one can go 80mph, if there is road construction(corroded connector) which slows traffic down to 20mph then EVERY ONE has to slow down to 20mph
"Keep the highway open", clean those Grounds, lol.

 

[2ruble]

k, thanks, I'll check that this afternoon/tonight and report back

 

[Spott]

battery can actually be removed from a running vehicle, it is no longer required by the electric system.
Battery's only purpose is to start the engine.

This is absolutely untrue. Please do not suggest or mention this ever again, because it can easily damage PCM computers, on almost every vehicle from the past 3 decades.

Alternators generate "dirty" power with lots of voltage ripples and spikes in the DC waveform. An important function of the battery when the engine is running is to "smooth out" that power; the battery absorbs the spikes and fills in the low spots. The battery acts as a giant filter capacitor.

On pre-computer, carbureted vehicles, you could remove the battery while running, because everything was simple electro-mechanical devices (lamps, pumps, coils, solenoid valves) and tolerant of voltage fluctuations. People used this fact as a cheap-and-dirty method to test an alternator, but it was bad practice even then.

On a computer controlled vehicle, pulling the battery is just asking for trouble. In the best-case scenario, then the computer gets fluctuating power supplied to it, and in turn sends fluctuating power as the reference voltage to the sensors. The sensors don't care, but the values they report fluctuate proportional to that reference voltage, so the computer sees rapidly changing and even out-of-range values from all the sensors. It can't make sense of those values, and quickly shuts off the engine as a fail-safe. And that's the best-case results.

It gets even worse: Remember those spikes and ripples in the power from the alternator? Some spikes are bigger than others, and occasional spikes are big enough to fry some of the transistors in the processor in the PCM.

Additionally, just before you disconnect the battery, the alternator has a bit of load on it trying to supply that "maintenance charge" to the battery, and is supplying extra power. When the battery is disconnected, that extra power has no place to go, and spreads out through the rest of the electrical system, including the computer. This generates an extra-large voltage surge immediately, for a fraction of a second, before the alternator can readjust to the reduced load.

Between that initial large voltage surge caused by the battery disconnection, and the many other voltages spikes generated by the alternator, there's a significant chance that you can damage or destroy the engine computer.

Disconnecting the battery while the engine is running is like playing Russian Roulette with your engine computer.

Please do not ever suggest or even mention the possibility of removing the battery while the engine is running, because you will have the blood of dead engines on your hands.

 

[2ruble]

If it makes anyone feel any better... I wasn't going to disconnect the battery... lol. But I'll be using his testing methods... unless someone has something against those, lol

 

[RonD]

I wasn't suggesting removing the battery from running engine.

Point being made was the battery's 12volts is no longer being used because system voltage is now above 13volts so voltage is flowing into the 12volt battery not out of the battery.

And you are right, it was never was a good idea on any vehicle, year really doesn't matter.
And it was a popular test to remove Negative battery cable with engine running to test if alternator was working, lol, people still do that, and you could damage newer electronics doing that IF alternator was not working.

Jump starting a battery now is also dangerous to the vehicle being jumped and the jumping vehicle BOTH.
Newer "smart charging" systems will react badly to jump starting.

 

[2ruble]

So, checked before leaving work and the battery at rest was 12.8-12.9; started and it was 14.3. Went ahead and put it under load and it was about 13.9 and held. Drove home, which was a two hour drive today, and tested. At rest (engine still on), it was holding at 13.8-13.9, held rpm about 2k and it held 14.3ish. Put under load (lights, high beams, hazards, heat on high) and it gradually dropped from 13.9 to 12.9 and would have kept going - took about 30 seconds to make that drop. Left the load on and held rpm at about 2k and it jumped right back up to 14.3 and held around there. Turned off load and engine and checked at rest (engine off) and it dropped from 13.0 to 12.9 and stayed steady.

 

[RonD]

That drop at the end is a concern.
If alternator is new then take it back

It reads like 1 of the 3 fields in the alternator is not working.

An Alternator generates AC voltage from 3 field coils in the case of the alternator, each field has 2 diodes that change the AC to DC volts.
The control of the output voltage is done by the voltage regulator, it sets the volts being sent to the rotor, if voltage regulator sends rotor 8voltsDC then output volts(at idle) 14voltsDC, just an example.
As RPMs increase so will the output volts, so voltage regulator is there to prevent overvoltage that will damage "12volt" electrics, and "cook" a 12volt battery, limit is about 15volts, 9volts to rotor
So voltage regulator is setup to limit high voltage output, this sets a limit on how much voltage it can send to the rotor.
Just after starting the battery is drained so voltage regulator sets high rotor voltage to recharge battery along with powering the vehicle electrics.
Yours should have been 14.5v or higher after startup

When you lose a Field coil, you don't lose 1/3 of the voltage, that's because the voltage regulator can increase rotor voltage to compensate, BUT................at low RPM, idle, even at max rotor voltage the alternator output will drop to 13volts or less.
Common sign of this is "dimming headlights at idle", lol, no that is not normal, no car maker would put in an alternator that couldn't maintain 13.5volts at idle with all stock electrics on.

So your drop in voltage at idle with all electrics on and the fact you get a voltage increase when RPMs are increased means voltage regulator is at max volts to rotor at that time and at low RPMs it can't hold the 13.5v needed.

 

[wildbill23c]

That drop at the end is a concern.
If alternator is new then take it back

It reads like 1 of the 3 fields in the alternator is not working.

An Alternator generates AC voltage from 3 field coils in the case of the alternator, each field has 2 diodes that change the AC to DC volts.
The control of the output voltage is done by the voltage regulator, it sets the volts being sent to the rotor, if voltage regulator sends rotor 8voltsDC then output volts(at idle) 14voltsDC, just an example.
As RPMs increase so will the output volts, so voltage regulator is there to prevent overvoltage that will damage "12volt" electrics, and "cook" a 12volt battery, limit is about 15volts, 9volts to rotor
So voltage regulator is setup to limit high voltage output, this sets a limit on how much voltage it can send to the rotor.
Just after starting the battery is drained so voltage regulator sets high rotor voltage to recharge battery along with powering the vehicle electrics.
Yours should have been 14.5v or higher after startup

When you lose a Field coil, you don't lose 1/3 of the voltage, that's because the voltage regulator can increase rotor voltage to compensate, BUT................at low RPM, idle, even at max rotor voltage the alternator output will drop to 13volts or less.
Common sign of this is "dimming headlights at idle", lol, no that is not normal, no car maker would put in an alternator that couldn't maintain 13.5volts at idle with all stock electrics on.

So your drop in voltage at idle with all electrics on and the fact you get a voltage increase when RPMs are increased means voltage regulator is at max volts to rotor at that time and at low RPMs it can't hold the 13.5v needed.

Ron is spot on with his information. My 88 B2 charging system is sort of there. At above idle I have 14.2V, but at idle you can watch the voltage slowly drop. I have confirmed that 1 field in my alternator is in fact bad, and have ordered a replacement alternator, hopefully its here by next weekend.

Its not going to hurt anything running it this way, just remember that charging under load may be a problem at idle. So with lights on heater running, etc. you may not have enough juice to charge the battery if you don't drive very far at a time, keep a trickle charger handy to keep it topped off until you can replace the alternator. I've been looking into picking up a portable jump box just in case, and of course for other portable power usage as well.