you talk about the basics of electrics But you don’t seem to understand that the battery can only supply current when the system voltage drops to below that of the battery.

 

no matter how many consumers are being put on, I have never seen the voltage of a car with the engine idling drop to the point where the battery is being used. 

Seen does not mean doesn't happen.

I've never seen Australia but I know it exists :P

34 minutes ago, SuperbTWM said:

no matter how many consumers are being put on, I have never seen the voltage of a car with the engine idling drop to the point where the battery is being used. 

I can show you that at lunchtime (I think).

Edited 14 February, 20197 yr by Wino

That would be a good test.

But also, can you check to see if the idle increases at all?

 

I succeeded, but had to try pretty hard. From a 12.79V starting point (before unlocking car) the lowest reading I could get was 11.59V. That was with lights on and full beam, heated rear window, blower on 4, wipers front and rear and (probably importantly) the auxiliary PTC heater on full, which was a retrofit, so slightly unfair as the petrol engines/alternators don't usually have these heaters.

DVM is wired directly across battery posts.

 

Idle speed I didn't really look at until the end of the experiment, which was at just under 900rpm I'd say, maybe a little higher than I'd expect at that time after a cold start.

If I remember I'll try the same thing when I get home with warm engine this evening.

 

 

 

 

I did repeat this when I got home, and remembered that if I put the A/C on I could get the rad fans spooled up too, and the result was that without using the retro-fitted PTC heaters, I struggled to get the voltage to dip below 12.8. I did just about manage it, but it took everything I could think of including hazards on and brake lights on to get there.

Idle speed seemed to stay within 10% of normal 700ish.

 

So actually my conclusion is that with factory installed equipment only, I support the idea that all the power will be coming solely from the alternator when the engine is running.

 

Newer cars may differ.

4 hours ago, Wino said:

 

So actually my conclusion is that with factory installed equipment only, I support the idea that all the power will be coming solely from the alternator when the engine is running.

 

 

 

I'm gonna have this one then, cheers  

 

Any more takers? I might see how my van copes tomorrow, it has a 2000w inverter in the back and I just so happen to have a kettle......

20 hours ago, SuperbTWM said:

 

I'm gonna have this one then, cheers  

 

Any more takers? I might see how my van copes tomorrow, it has a 2000w inverter in the back and I just so happen to have a kettle......

Did you even read his post?

14 minutes ago, abaxas said:

Did you even read his post?

Yes, he proved my point exactly

On 14/02/2019 at 17:50, Wino said:

 

 

So actually my conclusion is that with factory installed equipment only, I support the idea that all the power will be coming solely from the alternator when the engine is running.

 

Newer cars may differ.

 

Did the OP recode for the new battery?

On 14/02/2019 at 17:50, Wino said:

 

So actually my conclusion is that with factory installed equipment only, I support the idea that all the power will be coming solely from the alternator when the engine is running.

 

Newer cars may differ.

 

Nearly there but not quite!

 

A potential difference in an electrical circuit is needed for current to flow. This is measured in Volts and current flow in amps.

 

The reduced voltage you measured is a reaction proportional to the current flow / draw from the consumer devices active at the time of measurement. On these micro hybrid vehicles, this will be mostly from the battery until such time the system senses that the voltage is low or the current draw is too great for the battery alone to support without damaging it. The alternator is switched in and out to recharge the battery as a result. Engine speed does not affect alternator output unless stopped. Regen braking uses the rotation of the engine off-throttle to capture the kinetic energy of the vehicle through the alternator instead of burning fuel. 

 

For a battery to charge, a potential difference in the circuit needs to be greater than that of the voltage of the battery so that current can continue to flow. Hence a charging output from the alternator on the electrical circuit no higher than 14.8v, battery voltage will settle at 12.8v open circuit for an AGM (depending on specific gravity of the acid). That difference of 2v allows a small current to flow in the circuit for a period of time ensuring the battery is always able to be fully charged.

 

The principle operation for a vehicle battery is to provide the high rate current flow the starter motor demands. It can sustain this rate for approx 250 seconds before being fully discharged to 6v. It’s secondary operation is to provide electrical energy for connected devices and as a byproduct smooth out the electrical system absorbing electrical spikes and irregularities. 

 

Repeated short engine run times kill batteries as there is never enough time to put back the electrical energy that has been borrowed previously.

 

jeez! Did I write that? I need a lie down or a life. 

Edited 16 February, 20197 yr by BigEjit

If you believe this - "engine speed does not effect alternator output unless stopped"; You need to check your own understanding.  It affects the current that the alternator is capable of delivering considerably; hence the experiments of high load at low revs to explore whether the system can cope without using battery charge.  My car is not a micro-hybrid, by the way.

 

Whatever charging governance is used, if the voltage across the battery terminals is at or above its fully charged resting voltage, the load current is being supplied wholly by the alternator.

Edited 16 February, 20197 yr by Wino

I did with a Midtronics IDR-10 data logger for 3 weeks. Even our Mk2 Fabia is not affected by varying revs. 

What was your logger measuring, voltage I suspect. No-one's saying that alternator voltage output varies with engine revs.

 

https://www.researchgate.net/figure/Characteristic-curve-of-the-alternator_fig1_228584123

Edited 16 February, 20197 yr by Wino

Measures circuit volts and amps in fraction of a second intervals as well as a bunch of other user selectable channels.

 

 

I think you will find that charging in micro hybrid schemes is complex and uses SOC (state of charge) and HOC (health of charge) as its prime parameters in determining how much the alternator pushes out. Voltage is largely irrelevant unless at the extremes.

58 minutes ago, xman said:

I think you will find that charging in micro hybrid schemes is complex and uses SOC (state of charge) and HOC (health of charge) as its prime parameters in determining how much the alternator pushes out. Voltage is largely irrelevant unless at the extremes.

 

Are you talking to me or BigEjit there?

 

Would you agree with this sentence?

5 hours ago, Wino said:

Whatever charging governance is used, if the voltage across the battery terminals is at or above its fully charged resting voltage, the load current is being supplied wholly by the alternator.

 

6 minutes ago, Wino said:

 

Are you talking to me or BigEjit there?

 

Would you agree with this sentence?

 

I am talking to everyone. Although I'm not following this thread and haven't spent much time reading all the posts in detail, there seems to be a lot of "voltage" and "current" talked about. I too tended to think in terms of the old 14.3 v alternator output and battery charging to 100% but those days are long gone, as I found with my dabbling with a multimeter on my new Superb and subsequent research.

 

Micro hybrid operation is shortly if not already the mandated minimum in latest EU regs. i.e. stop/start and energy recovery. Soon the regs will be that you won't be able to disable stop/start in new cars.

 

With current sensors everywhere, particularly on the battery, the ecu can demand whatever current it wants, its a current demand and not a voltage demand.

 

Not sure if this demand is controlled open loop or closed loop however.

 

Judging from my Superb, the EFB battery can run very warm, and voltages are all over the place as a result. EFB and AGM batteries have significantly different characteristics compared to old school batteries. Charge acceptance in particular.

 

I better stop there, I have an annoying habit of rambling on too long....

Didn't want to commit to a disagree then? Or were you trying to day that in amongst all the "ooh its so complex".

2 minutes ago, Wino said:

Didn't want to commit to a disagree then? Or were you trying to day that in amongst all the "ooh its so complex".

Resting voltage is not really relevant. The battery is being dynamically used and the voltage at which charge acceptance occurs varies with many things, including temperature, and what level of charge/current has recently been demanded or dumped (second by second).

 

But if it makes you feel better, I'll commit to a maybe, depends..,.

 

Told you I am prone to rambling.....

If the battery has an open circuit voltage of 12.8 V, then connecting it to a circuit (such as an alternator and some load) that is also at 12.8 V will not cause any current to flow into or out of the battery.

Maybe a better to combine the above is:

Due to the requirements of start stop engines there is 'free in cost' engineering advantage that allows for slightly lower fuel consumption in testing while is almost every conceivable situation offers no difference to the consumer and, even thought, consumable wear (battery) may be slightly increased, the effects are so far within margin on error as to be irrelevant. All via a few lines of code.

 

On 16/02/2019 at 12:07, xman said:

With current sensors everywhere, particularly on the battery, the ecu can demand whatever current it wants, its a current demand and not a voltage demand.

 

 

 

But as BigEjit has reiterated for me, no matter how complicated the battery management, voltage and current are linked. You can't just demand current to go into a battery without the voltage driving it there. The same way you can't get current to come out of a battery without the voltage dropping below it so i'm not really sure what you are trying to say? (other than modern cars with start/stop are a lot more complicated than a cars of old with a standard battery)

 

 

 

 

Edited 17 February, 20197 yr by SuperbTWM

On ‎13‎/‎02‎/‎2019 at 16:32, teescom09 said:

Normal use is NOT short journeys or being parked up for long periods of time....

Tell that to the millions of car owners.

 

A lot of the cars in my area don't get used day-to-day. Most people commute into London via public transport. Their cars only get used during the weekend, often just for short shopping trips.

My parents live next to their work, they use their car about once a week for 3 miles trip to shopping.

My wife currently looking after baby, use her car twice a week for a few miles to take baby to activities or meet ups.

 

Short journey and/or being parked up for a week or two is normal use-case for many cars. Daily long 10+ miles commute is not normal use for many people. Car batteries only lasting 4 years is a shamble, my 4 year old EV drive battery is still holding 90% of its original capacity, and I floor it (80kW maximum draw) at a lot of traffic lights.