Battery voltage.

[Gbrowncls55]

What should the voltage be on the battery on an R230 or any other car for that matter. Mine shows 10.9 with engine off at the cigarette lighter and 12.9 with the engine running. The CLS shows 11.9 with the engine off and 13.9 with the engine running. I only ask because on the R230 I get the "convenience services temporarily unavailable " note every morning. Its complicated by the fact that the R230 has two batteries. Any thoughts

 

[skippyjasper]

Couple of things to consider:
Voltage at the cigarette lighter is likely less than at the battery.
Typically the dash display value is 1/2 volt lower than at the battery.
Battery voltage after an overnight sitting wants to be 12.5 or higher.
Charging voltage should be 14.1-14.2ish, but that depends on an almost charged battery. So a depleted battery will bring down your charging voltage.

Your 10.9 value suggests a tired battery and/or the vehicle driven in short trips such that it never gets fully charged.

I have this happen with my diesel ML. Short trips will eventually show up as a labored start. I'll usually put it on the Ctec charger when I notice and starting returns to normal.

Skippy

 

[190]

10.9 volts indicates and almost completely flat battery so it seem unlikely to be an accurate measurement otherwise the car would struggle to start. 13.9 volts with the engine running is no great shakes either but there a couple of issues to bear in mind. This may sound a contradiction in terms but you only get an accurate indication of charging voltage once the battery has become fully charged. If the battery is severely depleted then the high charging current drags the charging voltage down. Contradiction or not you can only judge the maximum charging voltage by measuring it when the battery is fully charged.

Second thing is on old cars MB were notorious for setting the voltage regulator a touch on the low side at 14.0 volts. Even old flood lead acid batteries are perfectly happy at 14. 3 volts On a modern MB with the intelligent charging system you'll see 14.6 volts or even a tenth or two more.

 

[CaptainChaos]

12.9 with the engine running sounds low. It would be worth checking it directly at the battery rather than through the lighter. I have one of those gadgets too, very handy especially on an older car. FWIW my old Range Rover shows 13.9 when running and dips into single fingers at cold start up!

 

[Dutchbenz]

It's always worth doing a continuity check to make sure there is no loss between alternator and battery.
Check ground of the alternator by measuring volts between alternator casting and negative batterypost, check volts between alternator output and positive batterypost. The loss may be a few tenths max.
Tony.

 

[brucemillar]

Can I ask what you are measuring the voltage with and have you tried to calibrate with a known voltage? Try a household plug point and you should be seeing 240vac.

Assuming that your measuring device is good? Your battery terminal are clean. You have a good clean earth (very important).

Measure across the battery terminals where you should see:

Engine Off: 11.9 > 12.5 VDC
Engine On at idle: 12.5 > 13.x VDC
Engine 2.5rpm: 13.8+ VDC Much over 14.0 VDC could be too much suggesting an alternator issue. Anything under 13.8 would also suggest an alternator problem.

 

[grober]

On an R230 there are two batteries- the one on the front is a battery for the starter the second in the boot is for all the other onboard electrics. The "convenience services temporarily unavailable " would point towards the AGM battery in the boot being down on voltage. Check the date of manufacture- should be stampted/embosed somewhere on the top

 

[190]

Can I ask what you are measuring the voltage with and have you tried to calibrate with a known voltage? Try a household plug point and you should be seeing 240v.

That reminded me of a brexit issue Officially we are harmonised with the EU at 230v but the tolerance is 10% either way so the EU could stay at 220v and we could stay at 240v. I wonder if we will revert to 240v again.

 

[Dutchbenz]

What I measure in a householdplug depends on the time of the day, on a sundaynight I could measure 240 but a few hours later on mondaymorning when all the laundrymachines wake up it drops to 230... not really a reference.

 

[brucemillar]

Okay Okay. Maybe calibrate against something else apart from household plug point. My point was/is that measuring is only as good as the device you measure with.

 

[Gbrowncls55]

Thanks all. Starter battery is fine its the larger convenience one in the boot that has seen better days 7 years old according to date stamp. Will replace it shortly so I can have heated seats when I really need them!

 

[190]

To check my digital multi meter I gathered together half a dozen different ones at work and checked them all against each other. Not a true reference I suppose but if I discarded the highest and the lowest the rest including mine were within 0.05 volts of each other on the 20 volt DC range. Even the highest and lowest were only an little worse. None of them were very cheap £5 meters but they weren't all Flukes either.

You don't need a particularly expensive meter to test battery voltage. How you use it is vastly more important to get an accurate result.

 

[Stratman]

The biggest differences I found between my Maplin Gold meter and the Flukes we had at work were the quality of the leads (the Fluke's were much more flexible and less likely to tangle) and the Flukes survived being treated like they belonged to somebody else, which they did. I take care of my Maplin and it's still going strong decades later.

Accuracy wasn't a problem. As 190 says, any decent meter will be plenty accurate enough for anything we'll throw at it.

 

[imkaz]

What should the voltage be on the battery on an R230 or any other car for that matter. Mine shows 10.9 with engine off at the cigarette lighter and 12.9 with the engine running. The CLS shows 11.9 with the engine off and 13.9 with the engine running. I only ask because on the R230 I get the "convenience services temporarily unavailable " note every morning. Its complicated by the fact that the R230 has two batteries. Any thoughts

Those voltages seem low. The CLS seems to have the right voltages. With car running alternator should be outputting 14 volts even with Aux battery unplugged. With car asleep voltages for both batteries should be about 12.6 volts, aux voltage if AGM should be a bit higher but definely more than 12.6V.

Best way to check is leave battery disconnected or out of car for 1 day and check voltage, if its too low you need to replace it, but I think check the alternator first because below 12V while engine is running doesnt sound right.

 

[markjay]

Try using 2 devices to see if they agree between them.... the second device can be one of these (scroll down through the list):

https://tinyurl.com/yauxlkfn

 

[markjay]

And is you are particularity stingy....:

https://www.amazon.co.uk/dp/B0092KVYGI/?tag=amazon0e9db-21

£1.41 with free UK delivery.... can't argue with that

(Ahmmm.... that's the one I got)

 

[Stratman]

Having done a little research on t'intertubes I've come to the conclusion that Mercedes are a little 'stingy' when it comes to battery voltage. I used the hidden COMAND menu* to display it when on a trip yesterday, after it had put back the energy used to start the engine it gradually settled at 13.6-7, which agrees with my digital multimeter.

It is possible to increase the alternator voltage but it's a bit of a bodge (lift off the earth tag of the regulator and put a highish current diode between it and earth) and I won't be doing it.

*Select radio or system (anything but nav really) on COMAND

Simultaneously press Mute, 1 and 3 and hold for several seconds until the display changes

Select 'Versions'

Scroll down to second page and select 'infos'

Voila!

 

[m80]

Couple of points,
we didn't actually harmonise with Europe to drop to 230volts 'AC'. It is considered with the tolerance allowed in supplies the overlap covers their desire for harmonisation. We are still effectively 240 volts nominal.
Leads Direct | What is the difference between UK voltage and European voltage

Checking a meter at 240 volts 'AC' for accuracy doesn't mean that it will still be calibrated accurately at 12 volts 'DC'.

As long as not kerknackered I would trust a cheapo meter to give ok results at 12 volts, and even a Fluke will one day be kerknackered. How do we know at the point of testing unless we have a known supply voltage to compare with?

The point of reading a lower voltage at such as a ciggy lighter only applies if, it has a bad and high resistance connection to it, or there is a load through it.
Volt drop is a product of load, assuming resistivity and source voltage are constant.
Any difference should only be slight, perhaps 0.2 volts.

Before writing off any low voltage producing battery, especially at this time of year, I would attempt to connect a battery recondioning charger. CTEK have the best name but I'm using the Aldi (sounds to be similar to Lidl) charger for about £14.

 

[MarcusRomer]

My W204 is charging at 15.2 volts, this doesn’t sound normal as sometimes when starting the car its labouring to start. A company has offered to diagnose the problem at £80. I feel that I should just replace the alternator as the car is a 61 plate and it’s never been changed.

Does anyone feel this could be the best move as an alternator at this age could fail again and spending £80 every time is not cost effective?

 

[grober]

Could be several things- depending on the alternator it may have replaceable voltage regulator/brush pack which would be a cheap repair if it's that. Why not consider a reconditioned alternator rather than a brand-new one at least half the price. Try your local Bosch auto electric agent and see if you can negotiate a combined fault finding/replacement deal?