Battery voltages accuracy as displayed on control panel

[DavidG58]

We have an often too clever for its own good Hymer S800, the control panel allows me to view hab and can battery voltage and also current being drawn

We are driving through France in very cold weather and having had issues previously do all I can to avoid flat cab batteries

Our cab battery on our Mercedes chassis was changed 2 years ago

So, point of my thread, battery level for cab often shows 12.3 - 12.5V in morning, seems low to me

Today’s ‘scare’ and reason for post I checked this morning we had a typical 12.5V but out of interest asked Bev to watch display when I turned ignition on, just to panel lights on. Bolts dropped to 11.7 on display

Bev didn’t know how bad I thought that was and the engine turned fine and started first time

So is this actually OK, is the display probably wrong or did I just get lucky?

 

[Richard n Ann]

Does it show too low when charging? It should be 13.8 and sometimes up to 14.4v

 

[DavidG58]

Does it show too low when charging? It should be 13.8 and sometimes up to 14.4v

Both read around 13V on charge even very accurate 14.4V initially on hab batts for gel setting

 

[Manic]

The analogue gauge on our 2001 B584 is not very accurate always shows lower than when checked with voltmeter in one of the 12volt outlets.
Shows 12.2 when it’s 12.7ish.

 

[Reallyretired]

I have volts on the panel, on the solar controller and on a socket I needed an led indicator on but didn't have one so put an led voltmeter on which I did have. They disagree with each other around 0.2v the panel one always being lower than the other two. Best put a accurate multimeter on then you will know how accurate the panel meter is. My panel meter generally shows 13.6v on charge while it is actually 13.8v.

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[DavidG58]

My real concern was that at 11.7V it would be too low to start

But I will look at doing volt meter checks, but battery is a bugger to get at under passenger floor

 

[tonyidle]

My real concern was that at 11.7V it would be too low to start

But I will look at doing volt meter checks, but battery is a bugger to get at under passenger floor

A cig lighter socket will do.

 

[Richard n Ann]

We have an often too clever for its own good Hymer S800, the control panel allows me to view hab and can battery voltage and also current being drawn

We are driving through France in very cold weather and having had issues previously do all I can to avoid flat cab batteries

Our cab battery on our Mercedes chassis was changed 2 years ago

So, point of my thread, battery level for cab often shows 12.3 - 12.5V in morning, seems low to me

Today’s ‘scare’ and reason for post I checked this morning we had a typical 12.5V but out of interest asked Bev to watch display when I turned ignition on, just to panel lights on. Bolts dropped to 11.7 on display

Bev didn’t know how bad I thought that was and the engine turned fine and started first time

So is this actually OK, is the display probably wrong or did I just get lucky?

The voltage will drop if the glow plugs are on, could it be that?

 

[DavidG58]

A cig lighter socket will do.

I have a voltage indicator that goes in a cig lighter, I guess there could still be inaccuracies but if they agree it suggests they are right

 

[DavidG58]

The voltage will drop if the glow plugs are on, could it be that?

I can test that tomorrow by seeing if voltage goes back up when glow light goes out

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[grumfy]

David
What you describe are exactly the same symptoms exhibited by my two year old Concorde. Even down to the too clever for its own good control panel and systems. Maybe ignorance would be bliss but I cannot stop fretting after having a flat battery recently. I do not have any answers so will watch your thread with interest.

 

[WillH]

11.7 would be near normal for when you start the engine, any load causes the voltage to drop, i.e. glowplugs, starter motor. An accurate reading can only be made perhaps 10 mins after the load has been removed as the voltage recovers after load. 12.5v could be fully charged depending how accurate your meter is. Are you overthinking this?

 

[WillH]

Bear in mind an accurate, laboratory, voltmeter will cost over £100, how much do you think a MH manufacturer will pay for a simple readout?

 

[autorouter]

Our cab battery on our Mercedes chassis was changed 2 years ago

Check that the connections on the thin EBL voltage sense wires are clean and undamaged, and the 2 amp fuses are not corroded or blown.

The battery voltages are measured by the EBL via separate 'sense' wires. These are relatively thin wires that go from the EBL directly to as near the battery as possible.

The hab battery has a larger main fuse, 20 or 30 amps, and a smaller 2 amp fuse just next to it for the voltage sense wire. There's a similar one for the cab battery.

The negatives are not fused, and run all the way to the battery negative terminal. The reason that separate sense wires are used is to avoid inaccuracies due to voltage drops in the current-carrying wires.

Bear in mind an accurate, laboratory, voltmeter will cost over £100, how much do you think a MH manufacturer will pay for a simple readout?

In my experience cheap meters that are not obviously faulty are surprisingly accurate. They will usually tell you whether the voltage is for example 12.5 and not 12.6 or 12.4. I have checked several meters against accurately calibrated meters at work, and they have always been at least this accurate.

 

[DavidG58]

I think it could be true to say I am overlooking things, if a little harsh, my technical ability almost peaks at reading the display although I carry a multi meter the thought of tracing wires leaves me in a sweat

For example when looking for a fault on our toilet flush I managed to create a dead short with my wedding ring, luckily only blowing a fuse

Some things in life I have found are best left to those that know what hey are doing

Update on my volts today, controller display of cab batt volts at rest 12.5V turned on ignition to glow plug stage 11.7V rising back to 11.9V when glow plug light went out, then a rather scary 10.8V when the starter turned the engine

But start it did, this might be another case of too much information, without the display I would be unaware of the numbers and all the while it starts I don’t think I will worry

The sun is just coming up here 30 mikes north of the med in France life is good

And we have RAC European cover

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[funflair]

Morning David 10.8 when the starter kicks in is no big deal as it is taking a big chunk of amps to turn over that lump of an engine, 12.5 before you start the process of heating up and starting is a good level of charge so just enjoy your break and don't worry about it. Ours starts with as low as between 12 and 12.2 on the battery before I turn the key

Martin

 

[autorouter]

But start it did, this might be another case of too much information, without the display I would be unaware of the numbers and all the while it starts I don’t think I will worry

The voltage of a battery is only a good indication of its state of charge under very specific conditions. There must be no output load, and no charging input. In addition it must be left in the no load/charge state for a few hours.

As you have seen, the voltage of a fully charged healthy battery varies greatly when under load, and when being charged. 10.8 volts when starting is in fact quite good, I wouldn't be surprised at 9 volts on a cold morning.

That's the reason people use a battery monitor device that continuously counts the charge in and out of the battery, and doesn't rely on just the battery voltage. Maybe your EBL does that already for the hab battery. Having said that, these devices are rarely fitted to a starter battery.

 

[Dare_Devil_Dennis]

What was the (very cold) temperature? you may have answered your own question.

For guidance purposes for battery monitoring, the battery voltage (and current capacity) is normally quoted at 25C. At very low temperatures, you can expect lower off charge voltages.

The fact that it cranked and started is a good indicator that the vehicle battery is ok.

The Hab batteries, if warmer (where are they/is it?), will likely indicate higher voltages. But to compare like for like you need to disconnect or switch off the charger.

For peace of mind, you need to get the battery to "normal" temperature and take more readings, or get it tested properly by someone who knows what they are doing and is not trying to sell you a new battery.

Good luck
Dennis

 

[PhilandMena]

Martin has nailed it. Big draw when starting so only right the reading drops of the scale.

 

[Xabia]

I installed a Victron battery monitor in my Hymer, it’s more accurate than the DT201 panel.

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[pappajohn]

My real concern was that at 11.7V it would be too low to start

When actually cranking the battery voltage can be as low as 9v....but it still starts.

Ign on, not running, there's a lot of background gubbins (relays, ECU etc) sucking power.

Volt meters/gauges/dials are only as good as the component parts...cheap Chinese crap will never be as good as an expensive quality meter.