Have I a duff battery
 

I took the battery off the car and put it on charge for a few days in the garage.
As soon as I took it off charge I measured the voltage and it was 12.8v, another battery that had been off charge for about a week measured 13.2v.

The above was about 3 or 4 days ago, I have just measured the suspected duff battery again and it is 12.57v. Not a lot of drop but as it was 12.8 when it came off charge I am suspecting it is duff.

Your thoughts please. If you too think it may be duff I will take it back and the shop can try a drop test.

macafee2

I wouldn't say the voltage you have measured necessarily indicates a duff battery.

I would put a mild load on the battery for a while and recheck the voltage. An old 55W 12V headlamp bulb consumes nearly 5Amps and makes a good test load.

At say 2 minutes, what would I expect to see voltage wise?

macafee2

I would put the bulb on for 30 minutes. This will remove approximately 2.5Ah of charge from the battery which will have a capacity of around 70Ah for a 096 type when new.

You should get at least 12.5V which would indicate that the battery is at >90% fully charged.

If it drops to less than 12.5V, the battery is not as healthy as it should be.

What was the measurement or conclusion in the end?

Result, undecided about the battery. The voltage seemed not to drop any further, always staying above 12v. I am wondering if the fault is on the car. I kept a headlight bulb connected for well over an hour as suggested but the voltage stayed above 12.
I have just taken the battery off charge and it is showing 13.04v.

macafee2

ok thanks, I'll test it again in the morning

macafee2

An old way that the AA used to test batteries was to charge by running the engine for 5 mins , then disable the engine by pulling a fuse so that the car would crank but not start. Crank the engine for 15 seconds and listen to the cranking speed , and if it starts to drop , the battery is unserviceable . That is a live drop test and is pretty conclusive.

I can try that. What fuse to remove, fuel pump?
15 seconds continuous cranking seems a long time, I just timed it my goodness that is a lot of cranking

macafee2

The 15 second cranking test was reasonable when most people were driving around in 1.3L or 1.6L petrol cars. A 2L diesel engine requires a lot more cranking current due to the higher compression. The starter solenoid as well as the starter motor would be in danger of overheating over 15 seconds.

Personally, I would never crank an engine on one of my cars for more than 5 seconds, which will feel like eternity when doing it.

A local garage will do the equivalent high-current drop test for little more than beer money!

With the sensitive electronics on most modern cars these days why would you risk a crank test when for not a lot of money you can get a drop / load tester that will determine the condition of a battery

https://www.machinemart.co.uk/p/clar...E&gclsrc=aw.ds

Agreed.

I normally listen to the vigour with which a battery cranks an engine and replace the battery if it is getting a little tired. I consider this really important on say the Twintop where if the battery is depleted the roof and window drop-down/up-lift etc. could loose adjustment settings.

The older batteries get relegated to use with 12V LED floodlights for use when working on cars, lawnmowers, etc.

You would normally hear it slow within 5 seconds if it was duff and I never blew a starter motor. They eventually equipped the patrol force with Midtronic battery testers which gave the member an informed choice of whether to replace the battery or take a risk :shrug:

measured the voltage and it is showing 12.8 which is pleasing

macafee2

some days after

macafee2

The important thing to note with the old type simple test is volt drop over a specific time from a reasonably, ideally fully charged battery, the cranking speed can be an indicator, but can be affected by engine faults.

First rule of thumb when testing battery, cranking, charging, in fact anything electrical on vehicle systems.........start with a fully charged or as near as battery, hence the engine running bit, obviously at the roadside the only way to get some semblance of a charge in it and would be approx. 15 mins at a high idle..............you can't do a cranking test with a flat, or very low battery !



This system was used, had to be used, back in the day but time has moved on, thankfully.


The resistive drop test is OK but doesn't tell a full story and on rare occasions when instructions haven't been followed, can cause a bit of fun with a bang from the battery.


My Midtronics battery tester does the following from connection to a battery, asks if it is on the car or off, asks if the test is being done on a remote jump start post or battery terminals, warns if the croc clips are making a poor connection, shows the ambient temperature, asks the type, regular, spiral etc, asks the capacity and if SAE, DIN, JIS etc, then if it's happy performs the test.


It will show as battery good, needs replacing, or simply recharging, if the volts are too low at the start it will tell me to charge then retest, if on the vehicle it will ask for the engine to be started, via a jump pack/leads, run at a high idle then say when to shut down, switch on headlights to remove the surface charge then when removed re-test.


The test results show volts at start of test, expected capacity and actual available capacity, state of charge and state of health of the battery, important bit these two, because you can have a battery that show say 12.6v so presumed to be good but the capacity has dropped from what it should be say 800A to 380A.


Whilst charging on the vehicle it will do a charging test, volts, look for diode ripple and so on.


It will also do a cranking test showing cranking speed, amps being pulled, volt drop etc. and from this to an experienced eye the condition of the starter motor can be determined to a degree, such as the odd one where the armature bearings are worn allowing it to rub on the magnet, modern sintered magnets or on the stator pole pieces.


Costs a bit but worth it's weight in gold.


But like any test equipment from a DVM upwards, only as good a the user.

Back in the day, (late 1960s buses) our Leyland Leopards would take several minutes continuous cranking in cold weather, followed by a clouds of acrid smoke.

Rubbish design from the 1960's compared to what exactly ? :shrug:



Fast tickover compared to idle tickover to put a charge into a nearly flat battery is the same you say.


Can I suggest you experiment on your suggestions with a modern alternator with both a voltmeter and an ammeter connected.


Then come back to report that the amps produced is exactly the same at both idle and a high idle.


Volts is only half of the story :shrug:

Up to the late 1970's most vehicles did not charge the battery well at idle. Motorcycles did not at all. When Honda launched the CX500 V-twin in 1978, they made a huge thing of the fact that its alternator charged the battery even at idle.

I dont do well reading a lot of material like that. I'm not good at technical reading, I just cant take all the information in.

macafee2

A bit technical in parts but otherwise not bad.


Remember when you said......... " Fast tick over to put a charge into a nearly flat battery is no better than just letting the engine tick over.--The modern alternators will hold 14.4 volts even at tick over.-- "


And I said .........."Fast tickover compared to idle tickover to put a charge into a nearly flat battery is the same you say.

Can I suggest you experiment on your suggestions with a modern alternator with both a voltmeter and an ammeter connected.

Then come back to report that the amps produced is exactly the same at both idle and a high idle. "


Could I suggest you read the PDF, taking note of Fig. 3 and Fig. 7 where you will find that there is a noticeable increase in current output at higher idle ( fast ) speeds

Did you hope to initiate a discussion on the basis of the paper? If so, to what end?

The term output is ambiguous. Whilst alternators have a relatively constant voltage output vs engine RPM, their current output is related to the RPM by curve that roughly has the form of Imax(1-e^-(k*RPM)). The maximum current output is available at around 2500RPM.

It is the current that carries charge from the alternator to the battery meaning that the charging rate is dependent on RPM roughly in accordance with the shape of the above formula's curve.

But the report doesn't show what you say, quite the opposite, the charts / graphs, 3 & 7, I mentioned previously actually how low the output, in amps is at low engine revs



Talking about the difference in pulley sizes is irrelevant, the article and graphs are talking about output at engine speeds, RPM, not at the alternator rotor speed, RPM.


You are comparing apples with oak trees !


MSS explains the voltage, current thing excellently.

Look at the first graph on page 172.

Read the title underneath it.---It says alternator speed.---:duh:



PS. I'm sure everybody has heard of --"oak apples"--Lol.

Plus, you've left a word out in your first sentence.

[QUOTE=Ducati750cc;2910403]A bit technical in parts but otherwise not bad.


Remember when you said......... " Fast tick over to put a charge into a nearly flat battery is no better than just letting the engine tick over.--The modern alternators will hold 14.4 volts even at tick over.-- "


And I said .........."Fast tickover compared to idle tickover to put a charge into a nearly flat battery is the same you say.

Can I suggest you experiment on your suggestions with a modern alternator with both a voltmeter and an ammeter connected.

Then come back to report that the amps produced is exactly the same at both idle and a high idle. "


Could I suggest you read the PDF, taking note of Fig. 3 and Fig. 7 where you will find that there is a noticeable increase in current output at higher idle ( fast ) speeds

Just found your post.

Five amps is a reasonable regulated charge rate both by the alternator or a battery charger.
Any more than that and the battery will start to overheat and lose water vapour from the electrolite.

The level of electrolite will start to fall reducing the amount of the plate taking part in the chemical action. Capacity is therefore lowered by overcharging.

On the car the battery is shielded from engine heat by having a casing around it. Engine heat too can cause vapour loss making the battery less efficient.---:shocked:

I believe you are looking at the capabilities of an alternator and not what it is actually doing when in a controlled operation on a car.

It's a bit late now but I'll see if I can make it less enjoyable for you tomorrow. :laugh:

The best! :snowball1::snowball1::snowball1: