Alternator & Battery Charging

[Alan in AZ]

2013 Limited.

My battery seems to be fully charged (by steady state unloaded voltage measurement anyway - will load test tonight) and it has never exhibited any issues in operation - everything works just fine.

However my recent addition of while driving battery monitoring shows that after a 'cold' start the alternator starts immediately and regulates to approx 14.5v charging voltage. This is quite normal I think. within 10-<15 minutes this drops down to a float level but the float level seems to be approx 12.9v, - above battery voltage but not by much. It then occasionally switches back to approx 13.5v rate but mostly stays at about 12.9v.

This float level seems too low..?. We are talking ambient temperatures of around 85F (its cooled off here a lot recently).

I see no functional issues with the battery - so I wonder?:

Does the alternator get controlled by the car in a smart way to manage fuel economy? does it monitor charge current somehow to know the battery is charged to reduce charge time (it seem to be well charged). Issue is if its doing this now - is it charging for even less time when its really hot?

I'm just surprised at these results. I'd have expected charging at 14.5v for maybe 15-20 mins slowly dropping to approx 13.5-6v for constant charging. With some reduction of both levels as the ambient temperature climbs high but only reducing by maybe 300-400 mill-volts...

Now I know most alternators on most cars are very dumb and are self contained and just regulate to a set voltage with aggressive temperature compensation to act as a time constant and rely on alternator temp as a proxy for battery temp - so a vary basic system. This assumes wide battery tolerance to mild overcharging.

What are the controls on this alternator - exciter for startup, remote sensing?, regulator voltage control? - charge on-off (e.g. low float/high float).

Anyone? can't seem to find much on this alternator, but it looks to be a pretty generic model.

Alan

 

[peterk9]

2013 Limited.

My battery seems to be fully charged (by steady state unloaded voltage measurement anyway - will load test tonight) and it has never exhibited any issues in operation - everything works just fine.

However my recent addition of while driving battery monitoring shows that after a 'cold' start the alternator starts immediately and regulates to approx 14.5v charging voltage. This is quite normal I think. within 10-<15 minutes this drops down to a float level but the float level seems to be approx 12.9v, - above battery voltage but not by much. It then occasionally switches back to approx 13.5v rate but mostly stays at about 12.9v.

This float level seems too low..?. We are talking ambient temperatures of around 85F (its cooled off here a lot recently).

I see no functional issues with the battery - so I wonder?:

Does the alternator get controlled by the car in a smart way to manage fuel economy? does it monitor charge current somehow to know the battery is charged to reduce charge time (it seem to be well charged). Issue is if its doing this now - is it charging for even less time when its really hot?

I'm just surprised at these results. I'd have expected charging at 14.5v for maybe 15-20 mins slowly dropping to approx 13.5-6v for constant charging. With some reduction of both levels as the ambient temperature climbs high but only reducing by maybe 300-400 mill-volts...

Now I know most alternators on most cars are very dumb and are self contained and just regulate to a set voltage with aggressive temperature compensation to act as a time constant and rely on alternator temp as a proxy for battery temp - so a vary basic system. This assumes wide battery tolerance to mild overcharging.

What are the controls on this alternator - exciter for startup, remote sensing?, regulator voltage control? - charge on-off (e.g. low float/high float).

Anyone? can't seem to find much on this alternator, but it looks to be a pretty generic model.

Alan

Not sure if my post on the Explorer's Smart Charging system will answer any of your questions.

http://www.explorerforum.com/forums/showthread.php?t=302522&highlight=smart+charging

Peter

 

[Alan in AZ]

Peter -Well maybe...

What I see is that after warm up the voltage drops to the low float level. After that time: on the over-run the voltage rises again from 12.9 - >13.5 (and it's very repeatable - with a small delay). The effect of this will be to increase alternator load on the engine - so I guess it acts as additonal engine drag (while also charging the battery a bit more).

That's the only way I see it could do what you noted anyway (absent some kind of multispeed alternator clutch) and it seems that is exactly what I am seeing. Presumably the ECU must tell the alternator to do this since it can't tell if you are in overrun or not on its own.

Once you accellerate again or even just start to maintain speed - the voltage drops back down again quite quickly.

Now the 12.9V float level means the battery is not discharging - but realistically it isn't really charging either - it will take absolutly forever to charge at that voltage (and will never reach a full charge that way).

It seems to me the only way this can be considered "~normal" is if the car knows for sure the battery is already very well charged - I'm interested to know how it can know that?

Seems to me it must monitor charge current directly under different conditions, and possibly also tests the battery voltage after starting & before the alternator starts up.

BTW if you continue over-run decelleration e.g. under braking all the way to a stop - you get the increased voltage all the way until just before you stop then it drops again at idle. This happens right around the point the overrun fuel cutoff must end in order to maintain idle - so maybe the two are directly related?

Alan

 

[peterk9]

I don't know what the story is on these batteries. There are posts where a batteries have been replaced within a week of picking up the EXplorer. I believe one member is on their 3rd battery. I am on my second one. It was installed at the end of March and now I'm seeing the same warning message pop up on the screen when I turn the ignition off. "Battery saver program OFF. Please turn off ignition or start car." The radio goes off right away instead of waiting for the door to open. It sat in the garage all weekend but was fine after parking it on Friday. I'm curious as to how much of a constant drain there is on a battery in the Limited. I guess I'll throw the trickle charger back on it in the morning.

Peter