charging system out put

[toyota62]

Hi Guys.
I am wondering what should be the maximum charging system out put for a 12v vehicle.(At operating temperature.)
Normally when vehicle is cold alternator pumping its maximum voltage/out put and as engine getting warmer system voltage drops.
I have seen some new cars pumping 15.20v.If you turn the head lights on then it regulate between 13.9v-14.5v.
Thanks.

 

[jldcol]

I have seen 16 volt capacitor in auto radios. These are elecrolytic power supply "cans". I think tolerance of +/- 10% is normal. That would mean at 14.4v+ some of these would start to get affected. I would like to keep alt volts below this in general. Your are correct that voltage is higher after a recent start, due to the battery voltage being low. I think if you lose the regulator you can get 40-50 volts out of alternator.

 

[The_Jeff]

It's also temperature regulated so when the headlights are on at idle and the voltage drops it's because the alt is running 100%.

Also the battery chemistry in GM cars needs a couple extra 1/10s of a volt to properly charge.

 

[toyota62]

Do you think these numbers are ok.
When car is cold 14.65V(With or with out load.)
At operating temperature 14.45V(With or with out load.)

 

[Quest]

With a fully charged, healthy battery, at idle w/o any additional load such as rear defroster, headlights and A/C on, you shall get approx 13.8VDC and this should be the "expected" norm.

When the battery is somewhat discharged and/or you are in a sub-zero temperature, it is not surprising to get 14.5VDC during charging (high idle).

I was once started a cold suzuki in -36C w/o block heater and no battery blanket on. Finally started it and the alternator was putting out in excess of 15.2VDC to recharge my exhausted battery. It went on like that for at least 30mins and the alternator was only a dinky lil Denso 45amp unit.

Q.

 

[brianl703]

Alternators (more specifically, voltage regulators) do not put out more voltage when the battery is discharged.

A discharged battery appears, to the alternator, as just another load. It doesn't know whether the extra, say, 30 amps it's putting out is because your battery is discharged or because you turned on the rear defroster.

There are some exceptions to this--some GM vehicles have a current sensor on the battery cable that is presumably used for feedback to control the charging voltage.

For other cars, given that most regulators have temperature compensation and that the temperature of the alternator is proportional to how much current it's putting out, one would expect that the voltage would actually decrease if the alternator is charging a discharged battery, and the voltage would decrease more if the battery is heavily discharged.

This is the behavior I've seen.

 

[brianl703]

Originally Posted By: eljefino

Also the battery chemistry in GM cars needs a couple extra 1/10s of a volt to properly charge.


That "maintenance free" battery chemistry (lead-calcium) appears to be standard for most car batteries now available, based on the response to an email I sent to Johnson Controls asking about the plate formulation of Duralast batteries.

Ford uses maintenance-free lead-calcium batteries, has been for years, but their regulators are set a couple 10ths of a volt below what GM sets their regulators. (14.8v vs. 14.6v, as I recall). The Ford setting apparently results in less water loss but may result in more sulfation.

 

[mechtech2]

Voltage regulators by design or by luck put out more when cold than hot.
Over 15V is rare, and is a little high.
14-14.5 with a high load at 2,000 RPM is good.

 

[GMGuy]

In general, you need to supply more than 13.8volts to the battery for it to take a charge. In a vehicle, GM's in particular you'll see 14.7v when everything is running.

New GM systems are taking a different approach and doing an (almost) completely computer controlled charge approach. They claim it is to increase the life of the battery-I suspect its more to do with eeking out another point in the mpg wars. Unless the demand is there, the alternator will put out 12.8ish volts. If demand increases, or the computer detects the battery charge state is low it will bump up the voltage. In the case of trucks/vans, tow-haul mode will put the system into full charge mode (14.7volts).



More than you ever wanted to know about lead acid batteries (the charging section):

http://jgdarden.com/batteryfaq/carfaq9.htm

Alex.

 

[toyota62]

Befor i did this modification to my alternator my charging system out put was 14.2V when cold and 13.8v when hot.

http://www.detomaso.nu/~thomast/alternator/

 

[brianl703]

Originally Posted By: GMGuy
If demand increases, or the computer detects the battery charge state is low it will bump up the voltage.


I've noticed that if my Saab 93 is idling for a while with a heavy electrical load (rear defroster), it'll increase the idle speed about 200RPM after several minutes. It doesn't do this without a heavy load, and it drops the idle speed instantly if the defroster is turned off.

Pretty interesting, because I know ambulances, police cars, and other vehicles with heavy electrical loads often have a similar "idle up" function, either factory or aftermarket.

 

[Busteck2]

unless you can full field the alternator and put it under load while watching an ammeter you cant know what the total output of the alternator is.

the regulator is exactly what its name implies, something that regualtes. it regualtes alternator output, commonly between 14 to 15 volts. but this number changes depending on battery state of charge/condition and the electrical load of the system and the speed at which the alternator is turning..

basically, if the car isn't killing batteries regualrly, or the battery is football shaped and smells like rotten eggs and the voltmeter is somewhere between 13 point something volts and 15 point something, its most likely OK and you need to look for other things to worry about..

 

[Busteck2]

when you get down to to brass tacks, you can only make electricity one way, that is by moving a conductor in a magnetic field.

then there are two basic ways to increase or decrease the amount of current you create in that alternator... you can turn the alternator faster or you can increase/decrease the strength of the magnetic field in the alternator.

since its an automotive engine, the possibility of that engine running at one constant speed is remote so the regualtor spends quite a bit of its life varying the amount of field current going into the alternators field windings depending on electrical load.

if that alternator spends too much time at engine idle speed with a heavy electrical load, it may start discharging the elctrical system as the output of the alternator is lower than the electrical load..

 

[mechtech2]

toyota - Clever Modification.

 

[toyota62]

http://www.necon.co.za/agcabatt.htm

 

[StevieC]

In my truck when it's a cold Canadian winter day and my truck has been sitting in frigid temperatures all night the most I have seen on my Scan Gauge is 14.5 Volts. When fully warmed up and in summer heat I have seen nothing less than 13.5, but usually sits around 14.0. Has been like this for the 150,000KM I have owned it.

I know from a previous car that one of the cells in a battery could be a tad flaky and cause wrong voltage readings. I have seen it cause 15V/16V readings and you replace the battery and its fine... Just a thought!