lead acid car battery.

[xchcui]

Hello.

I know that when the alternator is charging the battery and the battery becomes fullcharged,the charging current should decrease to certain charging current value.If the current value is too high and doesn't decrease,it indicate problem in the battery(short cell for example).

I was checking the charging current of a no new,car battery(with clamp meter),while the alterantor charged it and i noticed that the charging current was not go down less than 1.2A(while the battery considered to be fully charged).I would like to know what should be the charging current range that should shows a proper battery?(or since it might depended on the capacity,then what should be the percentage range from the battery capacity)?
In my case 12v 55Ah lead acid car battery.
What is the maximum charge current that will indicate a good condition?
What charging current should a new battery usually give?
In my case 1.2A is 2.2% of the capacity of the battery(55Ah).
Is it ok?

Thanks in advance.

 

[SemiMan]

Quick question. Was your clamp meter calibrated for 0?

 

[xchcui]

Quick answer.Yes it was.

 

[magellan]

I'm no expert but if I remember right lead acid batteries require a float charge to compensate for self discharge plus a topping off charge. These are done at lower current levels and 1.2A sounds about right.

Also your voltmeter should read a slightly higher voltage than 12.5V on charging, a volt or so over resting voltage in order to overcome the internal resistance of the battery. The alternator also puts out a higher voltage than is needed, which is reduced by the voltage regulator. If your voltmeter only reads 12.5V then it's likely your voltage regulator or alternator aren't working or there's a problem with the cables.

 

[xchcui]

Thanks for your response.

The alternator is function properly and its output voltage is ok.
The question is not specific bout the condition of my battery or the alternator.
Also,it is not about the proper float charge and things like that.
It is more focus on the charging current(from the alternator) that i will see in the clamp meter(when the charging current is stabilized and doesn't decrease anymore)that will tell me that the battery is ok and there isn't any problem in the battery.
When the charging current stay high(regards to battery capacity),it is mean that there is problem with the battery,but i don't know the numbers and for that i am asking for an answer.
I need here an experience answer from experience person,since i am familiar with all the operation of the alternator and the battery but i need presice numbers.

 

[NoNotAgain]

You indicate that the alternator is supplying 1.2 amps with a fully charged battery.
Your electrical system is going to constantly going to provide current for fuel pump and computer operation as well as current for the fuel injectors.
I've got a Snap-On YA271 analyzer that is a carbon pile tester for the battery as well as checking alternator charging system out put.
Modern vehicles using electronic ignition, engine controls as well as the fuel pump typically require more than 10 amps to run all of the overhead devises.
Shunt the battery connection and see how much current the alternator is out outing.

 

[xchcui]

Thanks for the response,but as i mentioned before the alternator is fine,this is not the issue.I familiar with all the standard test to check the battery and the alternator,but again,this is not my question.
I mentioned that the alternator,in my case,charged the battery with 1.2A,when fully charged and doesn't decrease below that.I gave that example only for make my question clearly.The alternator provide at the beginning more current(before the battery full charged)and it doesn't have no problem to do that)and decrease until 1.2A and stand constant.
Of course,the alternator provide current to other consumers in the car,but this is not related to my question.
But,please,read carefully my first post and try to understand what is my question.

 

[SubLGT]

How did you determine the battery is fully charged?
How accurate is your clamp meter at 1 amp?

 

[magellan]

I understand, but since your charging system is working properly do you have any reason to suspect there is anything wrong? In that case the 1.2A you are reading as a constant could just be the normal trickle or topping charge into the battery to maintain a full charge under normal use. Unless you have a reason to suspect something is wrong it's probably working normally.

Establishing full state of charge accurately is not easy though and all current methodologies have their shortcomings. But unless you really think something is wrong the system is probably working okay even though it might be nice to know. But maybe one of the real EE's here knows and will comment.

Thanks for the response,but as i mentioned before the alternator is fine,this is not the issue.I
familiar with all the standard test to check the battery and the alternator,but again,this is not my question.
I mentioned that the alternator,in my case,charged the battery with 1.2A,when fully charged and doesn't decrease below that.I gave that example only for make my question clearly.The alternator provide at the beginning more current(before the battery full charged)and it doesn't have no problem to do that)and decrease until 1.2A and stand constant.
Of course,the alternator provide current to other consumers in the car,but this is not related to my question.
But,please,read carefully my first post and try to understand what is my question.

 

[WalkIntoTheLight]

If I ran my car 24 hours a day, I might be concerned about a 1 amp constant trickle charge. Otherwise, it's not doing any harm, so why worry about it?

 

[SemiMan]

With accurate temp you can fairly accurately set end of charge. Its a trade off between sulfation and water loss and oxidation.

Best question so far is how do you know it is fully charged ? Please explain.

 

[xchcui]

I try to explain what do i mean:
When charging a battery(partly discharge),at first(taking aside the first charging stage) it takes high current and slowly the current that it takes decrease,until a minimum current,that below that it doesn't decrease.This value that it doesn't decrease below that,should tell us something on the condition of the battery.if the minimum current is too high,this is mean that there is a problem with the battery(like short cell).
Now,the questions were:
What is the maximum charging current that should tell me that the battery ok?(or max percentage from the capacity of the battery)?
And what is the minimum current that i will get in a brand new battery?
The question is not necessarily about my battery,it was only for example/comparison.
I hope that it is clearly now.

 

[NeilP]

As has been mentioned, other ancillary devices use power.
Also it depends on the exact alternator voltage output. Even a fully charged battery will take current if you supply it with a high charge voltage. Basic electrics. If there is a PD then current will flow.

There is no one correct answer to what current is 'correct'. If you had a relatively small car battery and a big truck battery , both charged to exactly the same voltage, and they were both alternately connected to an alternator running at a precise voltage output, you would read a higher float current on the big battery than the small car battery. The big battery will have a lower internal resistance than the small, so for the same potential difference between battery voltage and alternator output, there will be a different current flowing.

When the vehicle is running, the battery is not really supplying any current to the car electronics, it is all coming from the alternator. So you are not measuring charge current at all at the moment, you are measuring current to run the car, with maybe a trickle of current passing through the battery, depending on car electrical 'idle load'

If you want to test this the only way is to remove the alternator and battery and build a rig to spin the alternator, probably from another electric motor. Then wire up the alternator. Basic old style alternator with built in regulator will have a large terminal for current out and a small terminal for battery voltage 'in' - usually via the charge warning light and ignition.

Alternatively, If you can find an old diesel vehicle like an old tractor with a manual stop cable to the fuel injector pump you can keep the engine running with the ignition key off. Then you would have to disconnect the alternator from the vehicle wiring loom and wire it up custom as before to ensure no vehicle ancillaries like clocks are drawing current.

Only then will you truly know how much current your fully charged battery is taking from the alternator. On some external regulator alternators you may then be able to adjust the alternator output to give zero current to the battery.

A Dynamo system will all have external regulators from my experience, and they can all usually be adjusted for output in relation to battery charge state.


Your alternator will be putting out 13.8 volt and even if 'fully charged' will continue to take some current.





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[magellan]

Thanks, NeilP, a very informative post on just how complex this apparently simple problem is. I have copied it into my "battery notes."

I just had one question. You said:

"Only then will you truly know how much current your fully charged battery is taking from the alternator. On some external regulator alternators you may then be able to adjust the alternator output to give zero current to the battery."

Let's suppose the alternator isn't putting out too much voltage and the voltage regulator is working okay and the battery is fully charged. (I realize "fully charged" isn't easy to determine accurately). But let's assume we have an accurate state of charge. Does a fully charged "resting battery" present anything in the way of a parasitic drain or load? Or does that basically amount to the float charge?

 

[SemiMan]

Keep in mind you are essentially in the absorption/float phase of charging which can take hours to finish ..... Hence why I asked how you know its fully charged. Odds are its not.

 

[xchcui]

When the vehicle is running, the battery is not really supplying any current to the car electronics, it is all coming from the alternator. So you are not measuring charge current at all at the moment, you are measuring current to run the car, with maybe a trickle of current passing through the battery, depending on car electrical 'idle load'

Why not?

If i check the current at the wire that connected between the negative pole and the car's body,the clamp meter shows ONLY the charging current for the battery.
If you check the current at the wire that exit from the alternator,the clamp meter shows the current to all the other consumers included the charging current.

There is no one correct answer to what current is 'correct'. If you had a relatively small car battery and a big truck battery , both charged to exactly the same voltage, and they were both alternately connected to an alternator running at a precise voltage output, you would read a higher float current on the big battery than the small car battery. The big battery will have a lower internal resistance than the small, so for the same potential difference between battery voltage and alternator output, there will be a different current flowing.

In my question i mentioned that the charging current may be different on different battery capacities ,as you said.Because of that,i asked:

since it might depended on the capacity,then what should be the percentage range from the battery capacity)?

So,the answer can be explained by percentage.

The purpose and the idea of my question is to find by this measument problem in the battery.
If you have a shorted battery the minimum current will be higher than a proper battery of the same capacity.If they have different capacities so the comparison can be in percentage.

If my question is not clear enough,please,tell me.I feel that you miss the main point of my question and maybe it is related to how i wrote the question.

 

[NeilP]

Well pretty much all batteries from my understanding do have some self discharge, even if that period is measured in years.

It all depends on how accurate you are trying to get.
If for now we are assuming that the fully charged battery was charged by that particular alternator, I am sure with accurate enough measuring kit you would read a small flow to the battery even when fully charged. But again that will depend on alternator design. The old Lucas Dynamo systems used to have a cut out relay as part of them. You used to have to clean the points and set the air gap. So a system like that would supply no current until the battery voltage dropped back down to the cut in voltage.
Not sure if modern alternators all work the same or if some cut in/out like and old Dynamo reg.

But I'd say yes, even a fully charged battery, when connected to an alternator, you will still see some current flow. The disconnected resting voltage of a 6 cell lead acid is always going to be lower than the alternator output.

I have just checked 6 lead acids in the workshop, here, all good condition, all fully charged. Off the Chargers and disconnected from any load, for time period of any where from 4 hours to about 2 weeks.
Their voltages range from 12.38 to 12.45 volts
As soon as you put one of those in a vehicle, the alternator tries to keep them up to 13.8 volts, which is not their natural state.So current will flow.

Once the alternator has got the battery up to 13.8, it can be classed as fully charged, but it will be trying to return to its resting state, so s small float current will still flow. Probably going to be in the Milliamp region


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[mattheww50]

Several points. The charging voltage is determined by the voltage regulator for the alternator, which is not only sensitive to voltage, but temperature as well (low temperatures raise the voltage).

The 1.2 amps on the battery is fine for an automotive storage battery. Keep in mind that you have a choice when designing the batteries. The choice is between tolerance for deep discharge, and toleratence for overcharging. Deep cycle batteries tolerate deep discharge quite well, they don't tolerate overcharging anywhere near as well. So these batteries are suitable for applications like trolling motors and RV's. Automotive storage batteires are designed to tolerate overcharging quite well, they don't handle deep discharge very well at all. Most AGM batteries are designed for overcharging as well.

The only way to accurately determine if a lead Acid cell is full charged is to measure the specific gravity of the electrolyte.

 

[magellan]

xchucui,

You mentioned a shorted battery. If you have a shorted battery, or even just one of the cells is shorted, with the engine and alternator off your voltmeter will read less than 12.5V. That's a lot easier than trying to figure out the isolated charge current to diagnose a battery problem. I'm sure you already know this. Of course if your battery problem is more subtle than just a shorted cell then we're back to the more complicated situation you and Neil wrote about.

 

[NeilP]

V tm


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