Hi,

Would I be correct in thinking that 14.2-14.5 is the nominal charging voltage? This is driving (engine speed ~1500RPM), no lights on, radio on, no particular electrical load (i.e. heater fan off, wipers off etc).

Just idling, it sits around 14.0-14.2?

Cheers,

D

Measure directly at the alternator to see if there are any losses in the connections between it and battery.

Red meter probe on alternator output stud (careful not to short to any nearby earthed metal), and black probe on alternator body.

Compare with reading across battery poles in same conditions.

There's a temperature dependency which means the value at alt should lower a bit as the engine (and so the alternator) get warm.

Yes, those numbers you quote are the nominal territory to be expected.

Absolutely true what @Breezy_Pete says, but remember (it happened to me after I forgot to plug the voltage regulator into the alternator) the amber light fault on the dash has different meanings: fault bulb or, for example, voltage regulator issue. So, if it is off, you are good. If one time it lights up, check the bulbs, and if they are all good, the next thing is the voltage regulator. If it does go wrong, there are possibilities that the ECU or the comfort unit can get fried due to exceeding voltage. In case you want to invest in VCDS, you will know about any faults (even those that do not have warnings on the dash, like the pressure sensor in the AC line if the AC gas is low).

As this is posted in Mk2 section, therefor assumed not to have smart alternator and EFB/AGM battery, I'd think that the voltage quoted to be a little high - particularly if constant.

Off for a little refresher course on old battery tech.

Taking a look at OPs profile, has both Mk2 & Mk3 - the voltages quoted would be as expected for Mk3 (with stop-start) but I would be checking voltage regulation if on mk2 and a constant figure.

I'd expect to see a maximum constant charge figure of 13.8 VDC and a floating charge 13.2 VDC on a standard L-A battery and alternator.

Yes @Warrior193 you're correct, i've seen the two fabia's

But With mine 2013 mk2 1.2 tsi cbza i have 14.2 V idling until the subwoofer kicks in and the voltage drops to 13.9 V. While driving I have to check. (Currently I have a Varta D24 battery with this spec: 60 Ah, 540 A).

Edited 15 May, 20251 yr by Jack25

Spec sheet of the aftermarket version of the voltage regulator on these alts: ARE3010 | Alternator regulators

Voltage set point is 14.5V.

2 minutes ago, Breezy_Pete said:

Spec sheet of the aftermarket version of the voltage regulator on these alts: ARE3010 | Alternator regulators

Voltage set point is 14.5V.

Can confirm that even on skodaparts, checking by the VIN, the OEM code that comes out if searched on the internet all says 14.5 V set point.

Thanks for all the responses.

It is a 2014 CBZA without stop/start (no AGM/EFB) and I would, also, have expected the voltage to be ~13.8V, hence my raising the question.

I know the Mk3 raises voltage to "load the alternator" under engine braking/overrun scenarios, maybe to reduce fuel consumption and add engine braking but I've not seen the Mk2 doing this. I had seen other posters saying they had ~14.5V so I wasn't immediately panicked about it.

I should have said but the voltage was read via OBD2, from the ECU (CM) and also from the OBD2 device (they both agreed, voltage wise). Since the ECU is connected to the battery, I thought that what it sees is maybe a bit lower than what the alternator is putting out (but same as the battery voltage) because of the voltage drop between alt and battery.

I've read that the maximum charging voltage for a lead acid battery is 14.7V so it is within that but I don't remember it being this high previously although I might be getting it mixed up with my Mk3.

If anyone else can confirm that the charge voltage is this high on their Mk2, that'd be appreciated, especially given that the car had a new battery yesterday after the problems with it not turning off with the ignition key (!) and I'd like to not be cooking the new battery.

Quick update. I just checked with a calibrated multimeter.

The OBD2 CM voltage is ~0.1V lower than the meter reading at the battery terminals (which I guess is the best point seeing as this is what the battery is being charged at). So, at least I can trust the OBD2 CM reading.

With the engine first started and "on choke" (elevated RPM), the meter reads 14.4 or 14.5 and the CM reads 14.3V or 14.4V.

After 30s or so, the engine idles at normal speed and the meter reads 13.9/CM reads 13.8V.

if I rev it up, it raises to the ~14.5V (meter/CM).

if the alternator setpoint is 14.5V, this all sounds correct, if maybe a couple of 0.1 or 0.2V too high at the battery.

Voltage regulator should make the output voltage independent of rpm, so not sure what's going on there. Suggests that alt isn't able to output enough current at low revs to maintain its setpoint, with minimal load. Possible indication of too-short carbon brushes.

What mileage on car?

Edited 15 May, 20251 yr by Breezy_Pete

What do you mean by CM?

20 minutes ago, Breezy_Pete said:

Voltage regulator should make the output voltage independent of rpm, so not sure what's going on there. Suggests that alt isn't able to output enough current at low revs to maintain its setpoint, with minimal load. Possible indication of too-short carbon brushes.

What mileage on car?

About 70,000 miles.

CM = Control module (OBD2 terminology) = ECU.

I did find this, which supports what I measured :

Expected battery voltage (for lead acid)

• Idle (~800 RPM): Voltage starts around 13.5V, which may be just enough to maintain the battery.

• Cruising (~2500 RPM): Voltage rises to 14.3–14.4V, ideal for charging.

• High RPM (>3000 RPM): Voltage is capped at 14.4V by the voltage regulator to prevent overcharging.

Trust me.

Can your OBD diagnostic thing look at measured values of things in real time?

If so try to find a channel in engine ECU that shows alternator load percentage. (I'd look up which using VCDS on our Roomy, but it's in bits while I change the front pipe at the moment).

Monitor at idle and higher rpm. It shouldn't max out at idle and cause the output voltage to be pulled down, unless you have a lot of loads switched on.

I do! Is 70k miles a bit low for the alternator brushes being worn?

My OBD2 can measure in real time but there is no alternator load % unfortunately.

@briscaF1 Anyone near you with VCDS?

Are you anywhere near me? Swindon or Oxford?

70K does sound low for worn brushes, I would agree. Nevertheless it would be interesting to see what the alt load is showing at idle.

Roomster running again so I had a quick look at VCDS on the alternator load subject.

Initially found - by searching - a measuring block entry called 'alternator load' but that read 0 no matter what.

Then just looked down the looong list of advanced measuring values until I spotted 'generator load'. That's the one.

First pic, just radio and blower on 1.

Second pic, radio plus blower fan on max.

Third pic headlights added.

I'll pop out in a bit and measure voltage across battery posts in last condition, like I should have done at the time!

Edited 15 May, 20251 yr by Breezy_Pete

To my disappointment I saw the voltage across batt terminals dip to 13.8 in that last high-load condition at warm idle, popped up just above 14 with a few revs. Room for improvement there.

11 hours ago, Breezy_Pete said:

To my disappointment I saw the voltage across batt terminals dip to 13.8 in that last high-load condition at warm idle, popped up just above 14 with a few revs. Room for improvement there.

How do I get hold of VCDS?

I checked again last night on the drive home. At idle, just after engine start, the battery voltage (at CM) was 13.9/14.0V. When driving home, at 1500-2500 RPM, the voltage was generally around 14.1-14.4V so I wondered if it had been elevated before because the battery was brand new, not very charged and still charging to capacity. There didn't seem to be any increase in voltage in engine overrun, like there is on my Mk3.

Anyhow, with the engine running at about 1100RPM, and the battery voltage at about 14.1V, if I put the radio/heater fan/rear demister on sequentially, the voltage dropped to 14.0V so I think it is handling load OK.

I'm less worried about it now since it isn't sitting around 14.5V all the time.

VCDS is available from a few distributors in the UK.

I've used Ilexa.co.uk recently and found them excellent.