Battery and charging

[Rapid Red]

Was reading thru some topics, on a Ford CD. Not looking for any particulars, just board. Spot a large amount of information with regards to the battery & charging system.

To say the least there is a lot going on there, quite a sophisticated design & its operation. That is one point, the second I want to point out. Starting the car letting it idle, and thinking one is charging the battery.

Is killing the battery, the car is running totally on the battery. The charging does NOT happen before 30 mph.

Interesting I'd say, for anyone having battery problems, and figuring out what's going on. Doing their own troubleshooting, for repair. I highly recommend spending 250 for a Ford CD, pages of information on the system, defined steps to isolate problems.

my .02

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[ORRadtech]

It's always been my feeling that the battery and charging system in cars has been poorly understood by most people. The more technologically advanced ICE vehicles become the wider the gap in understanding. For example the fact that the car needs to be told it has a new battery to optimize the system isn't all that well known.
EVs take it to another level entirely.

 

[Johnnybee]

Was reading thru some topics, on a Ford CD. Not looking for any particulars, just board. Spot a large amount of information with regards to the battery & charging system.

To say the least there is a lot going on there, quite a sophisticated design & its operation. That is one point, the second I want to point out. Starting the car letting it idle, and thinking one is charging the battery.

Is killing the battery, the car is running totally on the battery. The charging does NOT happen before 30 mph.

Interesting I'd say, for anyone having battery problems, and figuring out what's going on. Doing their own troubleshooting, for repair. I highly recommend spending 250 for a Ford CD, pages of information on the system, defined steps to isolate problems.

my .02

I find this hard to believe, since I have put a meter across the terminals when idling and always get something in the vicinity of 14.5V. So it’s got to be charging.

 

[KeyLime]

I find this hard to believe, since I have put a meter across the terminals when idling and always get something in the vicinity of 14.5V. So it’s got to be charging.

Agree. If the voltage across the terminals is higher than the battery resting voltage the battery is charging. Maybe not by much, but it can't be discharging. Current won't flow uphill against a voltage gradient.

An interesting experiment would be to turn everything on. Heat seats and steering wheel, cabin fan on high, all lights, etc. and then measure the voltage at the battery terminals. Maybe then you can exceed alternator idle output.

 

[nustang]

I find this hard to believe, since I have put a meter across the terminals when idling and always get something in the vicinity of 14.5V. So it’s got to be charging.

yep its charging at idle at that voltage, more of a trickle without amps behind it.

 

[Buldawg76]

Agree. If the voltage across the terminals is higher than the battery resting voltage the battery is charging. Maybe not by much, but it can't be discharging. Current won't flow uphill against a voltage gradient.

An interesting experiment would be to turn everything on. Heat seats and steering wheel, cabin fan on high, all lights, etc. and then measure the voltage at the battery terminals. Maybe then you can exceed alternator idle output.

If the cars alternator is sized correctly for the cars supplied equipment as in from the "factory" then the regulator in the alternator will adjust the charge rate according to load placed on the battery. Hence the amp rating for alternator output. Your car will come from the factory with an alternator that is capable of suppling enough amps to maintain a positive charge rate to the battery with all supplied equipment turned on for maximum load possible at idle.

It may only be barely above 13.5 volts at idle, but it will be charging.

I am a retired ASE master tech of 50 years in the business, and I can assure you your cars factory alternator is rated to output more amps than your cars system can draw.

BD

 

[HoosierDaddy]

I find this hard to believe, since I have put a meter across the terminals when idling and always get something in the vicinity of 14.5V. So it’s got to be charging.

Shhhhhh. Was going to use the 30 MPH minimum as a defense if I ever get ticket for too fast in school zone, parking lot, etc..

Judge, I had to go 30 or risk battery going dead and stranding me on side of the road.

 

[KeyLime]

I am a retired ASE master tech of 50 years in the business, and I can assure you your cars factory alternator is rated to output more amps than your cars system can draw.

BD

I'm trying to remember off the top of my head but I think the Mustang Alternator is 175 Amps max output. You could almost TIG weld with that. You're right, pretty hard to run out of juice even at idle.

 

[Buldawg76]

I'm trying to remember off the top of my head but I think the Mustang Alternator is 175 Amps max output. You could almost TIG weld with that. You're right, pretty hard to run out of juice even at idle.

Yea was not sure what the amp output is buts it's not your old 32 amp muscle car alternator for sure. 175 sounds about right for all the electronics in cars today. Heck my Lincoln mig welder is only 140 amp.

BD

 

[Postal Bob]

Is killing the battery, the car is running totally on the battery. The charging does NOT happen before 30 mph.

If that was true, then after you jump start a car with a dead battery, and remove the jumper cables, the car should immediately turn off.
Now I don't disagree that at idle, the battery is hardly charging. But at idle, the car is certainly not running on the battery.

 

[Buldawg76]

If that was true, then after you jump start a car with a dead battery, and remove the jumper cables, the car should immediately turn off.
Now I don't disagree that at idle, the battery is hardly charging. But at idle, the car is certainly not running on the battery.

Exactly, if the alternator is not working with a dead battery the car may run for a minute or two after jump starting but will quit running once the battery loses its little bit of charge it got from jumping it off.

BD

 

[ice445]

If that was true, then after you jump start a car with a dead battery, and remove the jumper cables, the car should immediately turn off.
Now I don't disagree that at idle, the battery is hardly charging. But at idle, the car is certainly not running on the battery.

Yup, the only issue with starting the car, idling it for like 15-20 minutes, and then turning it off thinking you "charged" the battery, is that yeah, at idle it charges, but it's probably not going to charge enough to replenish the 400-500 amps you just pulled to run the starter. So do that enough and the battery will end up deceased.

 

[Rapid Red]

If that was true, then after you jump start a car with a dead battery, and remove the jumper cables, the car should immediately turn off.
Now I don't disagree that at idle, the battery is hardly charging. But at idle, the car is certainly not running on the battery.

The charging system circuit excites @ 2k, below that thresh hold it's using the battery.

 

[Buldawg76]

Yup, the only issue with starting the car, idling it for like 15-20 minutes, and then turning it off thinking you "charged" the battery, is that yeah, at idle it charges, but it's probably not going to charge enough to replenish the 400-500 amps you just pulled to run the starter. So do that enough and the battery will end up deceased.

BD

 

[KeyLime]

The charging system circuit excites @ 2k, below that thresh hold it's using the battery.

The charging system needs current to the alternator rotor windings to energize. The initial current comes off the battery and then after it powers up the alternator provides its own excitation current. It has nothing to do with engine rpm. You can size the alternator pulley as fast as you need at engine idle to meet maximum demand. Obviously you don't want it spinning at warp speed when the engine is at red line rpm, so there are some limitations. Some alternators are the permanent magnet design. I think, but not certain, that they don't require any current to the rotor. They self energize as soon as they rotate.

In the old days generators were a problem. The have a much lower output at low rpm as compared to an alternator. Sizing the pulley to provide enough current at engine idle while not moving so fast at red line that that it would over speed and self destruct was challenging.

Think of this. If your scenario is true, a 6MT Mustang would need to be moving at better than 73 mph in 6th gear (2000 rpm) to energize the alternator. 72 mph for the A10.

Don't confuse engine rpm with alternator rpm.

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