lead acid car battery.

[magellan]

Thanks, NeilP. Great info and very helpful. I was hoping a real pro would weigh in here as I'm just a somewhat well informed amateur.

 

[magellan]

Thanks, Matthew, I was wondering about the difference between a typical auto battery and a deep cycle type and your explanation really helped.

As it turns out we have a medium sized electrical generator and its starting battery is a deep cycle one as it sits outside in the cold next to the house.

 

[NoNotAgain]

Deep cycle batteries aren't designed for starting engines. They don't produce high current levels required for running a starting motor.

You'd be better off wiring a trickle charger into your system to keep the battery up to voltage during storage. They also sell battery blankets to keep them from freezing during times of non use.

My generator operates on 24 volts for starting (a four cylinder diesel engine) and uses two group 27 batteries wired in series.

 

[NeilP]

Thanks, NeilP. Great info and very helpful. I was hoping a real pro would weigh in here as I'm just a somewhat well informed amateur.

Well lets hope so !!

My knowledge is based on use of lead acid batteries and the repair of cars and tractor electrical systems, from 1950's Series 1 Landrovers up to 'semi modern ' 1990's vehicles.

Also some answers based on basic electronics knowledge.

 

[tripplec]

Well I will quickly point out a few thing. First if you recall your high school physics a Lead acid battery is a 2.2V cell & you have 6 in that battery hence it delivers 13.2VDC at its native charged potentional. Rarely do we see that due to real world load and/charging of the package.

At voltage of 13.8VDC is what is used as the standard rating for equipment operating voltage however in a good operating system your vehicle and equipment is getting 13.9VDC -14.5VDC from most alternators. This will vary slightly on the state of the battery if its very low or nearly fully charged since the alternator voltage regulator is adjusting output accordingly based on voltage alone!! Not capacity, a 6 year old battery with working (not open or shorted cells that take some charge still generate the same 2.2VDC internally) and the alternator cannot be aware if the AMP/HR capacity is there at all and it the worst case amount to a very big capacitor which depletes itself with a small load if a charging source is removed. The only way to determine the capacity is assessing the electrolyte which is essentially a sulphuric acid fluid mixture base. When the battery is at full charge the Specific gravity of each cell is at 1275- 1285 at the highest or gassing starts.

Many of today vehicles adjust the end voltage based on temperature and an increase of .25 - .5VDC which may end up at 14.25DC to 14.7VDC in the winter which is common to bring the battery to the fully charged level and conversely lower in the summer as its not needed and extends the life of the battery. If you have a dash voltmeter you may have notice this in various seasons.

The current is controlled by the design of the regulator to maintain the battery which is what the alternator is designed to do. It is not designed to charge or recover a weak battery although many people expect it to since the current can be excessive going through it. Its intent is to keep the battery up to scratch and power your equipment.

A quality smart charger is required to bring the battery up to scratch not your auto store charger either. NOCO makes excellent multi step smart chargers. See a listing on http://www.geniuschargers.com/products

NOTE: A weak battery or dying one will have a few cells very low specific gravity reading or all low and irregular levels severely limiting the amount of current you can draw from it.

 

[NeilP]

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?

Because the alternator will have the highest voltage, it will be higher than the battery, even when fully charged. So in general the alternator will be supplying all the current for all devices. Not always true, but generally. If you start taking huge current loads, then the alternator will then supply up to its maximum along with the battery, but an idling alternator will probably not be able to supply all the current requirement. So when the device ( big audio system / vehicle winch / massive halogen spotlights etc) cause a voltage sag, this pulls the alternator voltage down, it tries to keep up, but then the battery starts supplying current. Some times this is not enough either. Think of people with huge car audio systems, even with big alternators (80-100 amp) and batteries they often fit capacitors near to the power amplifiers to supply transient requirements that the alternator / battery system can't supply.

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.

This has got me thinking...ummmm Possibly in an ideal system, and if you are assuming all the current from all the car devices is flowing back via the chassis earth to the alternator. But variances in resistance of earthing connections, slightly corroded or poor crimps, paint and corrision between earth ring connectors and chassis, nothing is guaranteed. In the harsh environment of a car


I am finding it difficult to find simple way to explain how I am seeing it. But most of the items on the car including the alternator are all earthed via the chassis. The alternator earth, is going to be via its mounts and via an earthing strap to the chassis, potentially higher resistance than other wiring paths. Having difficulty getting my head around that.

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

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.

If you are merely trying to determine a problem with a battery by measuring idle charge current I'd say you are over complicating things.
Better ways are:
A load tester that measures overall voltage sag of the battery when a know load is drawn through a heating coil.
Hydrometer that measures electrolyte Specific Gravity...temperature compensation required. You test each cell.
Resting cell or battery voltage.
Older batteries you could check the voltage of each individual cell, not possible now, so the SG is your best guide.

Thinking further as to why you want to know this, if it was for long term automated battery condition monitoring yes, you could use the fully charged idle current back to the battery , then this could be done. Because, yes, a faulty battery would draw more current, than a new battery, assuming all other thing safe equal.
it would need to be built so as to not start monitoring for maybe the first ..I don't know, 5- 10 - 15 minutes after engine start, to give enough time for the alternator to top up the battery again after starting. Would probably also want to put some time averaging on it too.

 

[NeilP]

Many of today vehicles adjust the end voltage based on temperature and an increase of .25 - .5VDC which may end up at 14.25DC to 14.7VDC in the winter which is common to bring the battery to the fully charged level and conversely lower in the summer as its not needed and extends the life of the battery. If you have a dash voltmeter you may have notice this in various seasons.

Nice, thanks for that, you learn something new every day..No surprise really but i never knew that ...not had experience with modern electrics. To me a modern vehicle is a 1982 long wheel based Toyota Landcruiser , and it is probably 15 years since I looked at the alternator on that, that system was an alternator with separate rectifier and regulator pack.

 

[xchcui]

...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

And what current we will see if there is a shorted cell?will we see higher float current?

...The 1.2 amps on the battery is fine for an automotive storage battery...

So,what is the maximum amps for an automotive storage battery,that it still considered fine?(or the max percentage amps value from battery capacity)?

 

[WalkIntoTheLight]

If you're that worried about your car battery, why not just take it to a garage and have them run a load test on it? Most will do it for free.

 

[NeilP]

And what current we will see if there is a shorted cell?will we see higher float current?

Yes but no idea what. The cell will be shorted or failed for some other reason, so the overall pack voltage will be at least 2 volts lower, that it should so the voltage difference between the overall voltage and the alternator will be larger than normal. The alternator will sense the lower voltage, so attempt to compensate and ramp up its output voltage to try and charge the battery, So you have an unknown voltage difference between battery and alternator, combined with an unknown internal resistance of the battery. But simply the higher voltage will try and drive the charge current higher, but to what, no idea.
A standard basic Lead acid bench charger often has high low and boost settings, as thou change the settings all that is happening is that the open circuit output voltage is being increased, to push more current through the battery, if left un attended these will boil a battery dry. Follow the link earlier and get your self an intelligent CV charger with built in battery diagnostics

So,what is the maximum amps for an automotive storage battery,that it still considered fine?(or the max percentage amps value from battery capacity)?

Do you mean max charge amps? No idea to be honest, I have quick charged good truck batteries at 40 amps or more, but I 'd not leave it like that un attended. A quick 5 minute host at high current..OK if yu have to ..but with anything not good for the battery, risking buckled plates.
It is going to depend on battery manufacturer and battery type. You will only know for sure by checking battery suppliers data. I'd certainly not leave any battery charging over night on anything more than a couple of amps.

 

[xchcui]

Thanks for all the responses.
I didn't got the numbers that i was looking for,but it seems that the thread became very informative and might be very useful for other members.

Thanks

 

[NoNotAgain]

I've got one of the big Snap-On service station chargers. Low, medium, high and boost start @500 amps. The analog timer makes sure that the current gets shut off so that you don't cook the battery. The cables also have a reverse polarity protection showing correct hookup.

With the new AGM batteries you have to charge them slowly or they'll blow the tops off. They cant vent the hydrogen gas off fast enough the small vent and safety valve they use The AGM batteries look like a 6 pack of beer.

 

[magellan]

It's a small engine by most standards, certainly nothing requiring the cranking power required to start a Diesel engine with its high compression ratio. When I said "medium" I was referring to a medium sized one intended for residential use. It's a 17kW Generac and will power the most critical stuff in our home but not the whole house.

Deep cycle batteries aren't designed for starting engines. They don't produce high current levels required for running a starting motor.

You'd be better off wiring a trickle charger into your system to keep the battery up to voltage during storage. They also sell battery blankets to keep them from freezing during times of non use.

My generator operates on 24 volts for starting (a four cylinder diesel engine) and uses two group 27 batteries wired in series.

 

[NoNotAgain]

An excerpt from Deka batteries on starting verses deep cycle verses the hybrid battery tech.
"Dual Purpose Deep Cycle/ Starting Service
Dual purpose batteries are ideal for applications that require starting and deep cycle service. They deliver powerful cranking amperage for easy starting, and low amp draw service for reliable auxiliary power.
Dual purpose batteries are a perfect compromise between the unique demands of starting service and deep cycling, low amp draw service."

 

[SemiMan]

Deep cycle batteries aren't designed for starting engines. They don't produce high current levels required for running a starting motor.

You'd be better off wiring a trickle charger into your system to keep the battery up to voltage during storage. They also sell battery blankets to keep them from freezing during times of non use.

My generator operates on 24 volts for starting (a four cylinder diesel engine) and uses two group 27 batteries wired in series.

With the exception of Gel batteries this is factually wrong. Most deep cycle batteries have plenty of starting current.

 

[SemiMan]

I've got one of the big Snap-On service station chargers. Low, medium, high and boost start @500 amps. The analog timer makes sure that the current gets shut off so that you don't cook the battery. The cables also have a reverse polarity protection showing correct hookup.

With the new AGM batteries you have to charge them slowly or they'll blow the tops off. They cant vent the hydrogen gas off fast enough the small vent and safety valve they use The AGM batteries look like a 6 pack of beer.

AGM batteries will accept a higher charge rate than any other lead acid battery. If you are venting gas with AGM then you are grossly overcharging.

 

[SemiMan]

We seem to be missing that the battery is likely NOT fully charged. It may be close but probably not.

Flooded batteries like a bit of "overcharge" to prevent sulfation.

C/40 which is indicated is high for a constant float but most modern maintenance free can recombine a fair amount of gas. Car have parasitic loads these days and that also needs to be topped up on discharge.

FYI, most old or worn batteries will have less float current as the internal resistance is higher.

Neil, those voltages suggest undercharged or worn batteries.

Semiman

 

[NoNotAgain]

With the exception of Gel batteries this is factually wrong. Most deep cycle batteries have plenty of starting current.

Argue with Deka not me. Read their recommendation yourself.

 

[SemiMan]

Marketing not facts. Read the spec sheets.

 

[magellan]

Yes. Awesome responses which are very informative and helpful.

Thanks for all the responses.
I didn't got the numbers that i was looking for,but it seems that the thread became very informative and might be very useful for other members.

Thanks