# Power pluggged in, Flat battery



## Borisd0 (Jan 3, 2006)

My B574 2002 is laid up with 240v connected so I expected both engine & leisure battery to be full. I thought a engine run would be beneficial in this cold weather. The onboard voltmeter showed both batteries fully charged, however the engine battery was completely flat as verified with a meter across the terminals. 

Questions, 
Why did the panel voltmeter show 13.5v when the battery was flat? 
Why did the 240v connection not keep the engine battery topped up? 

Any thoughts gratefully received. 

Geoff.


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## DABurleigh (May 9, 2005)

If the battery is knackered then with a mains charger on it it will still show a good voltage but when you try to draw a couple of hundred amps for the starter motor there is no oomph (technical term with complicated units) to do the necessary.

I'd bet the vehicle battery is at least 4/5 years old?

Dave


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## Kees (Jan 15, 2009)

Hi Geoff

If the battery voltage (as read on the meter) was low whilst the mains was still connected and the panel reading 13.5V then it sounds like there must be a blown fuse between the charger and the battery. The panel is probably reading the "battery voltage" on the charger side of the fuse and is really indicating the charger voltage, not the true battery voltage. 

To a battery charger, a fully charged battery is the same as an open circuit, i.e. 13.5 volts but no current flow into the battery. If the fuse blows then the charger is unaware of this. If the panel monitored the battery voltage independently from the charger cabling then it would indicate the low battery voltage but this involves more cable so most motorhome manufacturers choose to save the money.

If the battery actually reads 13.5 volts (on the meter) when the mains is on then, as Dave said, the battery is probably knackered.

Hope this makes sense

Kees


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## Borisd0 (Jan 3, 2006)

Thanks for the two responses,

A few added comments,
The battery is 2 years old.
The battery was completely dead, I think the only load was the alarm and that had ceased to function. I never attempted to start it as no lights were on the dasah.

So far I like the the idea of a blown fuse from the on board trickle charger.
Now to try and find it!

Thanks,


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## sideways (Jun 2, 2008)

Was it a 2 year guarantee battery i,m sure they put time bombs in them usually for a week after warranty runs out.


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## wakeman (Nov 23, 2009)

Hi Geoff, I have been on a steep learning curve since buying my 1990 Hymer B644.

I had the same problem as yourself with dead battery when on mains hook up having not used her for a month or so, I had left the radio on standbye which was enough to flatten the Engine battery. I managed to get hold of a wirring diagram from Hymer all be it in German. I know a bit about auto electrics and when I studdied the diagram I reallised that on hook up only the leisure battery is charged.

Please see the post

http://www.motorhomefacts.com/ftopic-75825.html

In the next couple of days I will be fitting a bridging fuse as Clive suggests the only difference being I will also fit fit a diode so that the current only runs one way.

I hope that this helps maybe its different on the newer Hymers.

Les


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## drcotts (Feb 23, 2006)

Hi Geoff
Are you sure that your van is set up to charge both leisure and engine batteries. Even a smart charger will charge the leisure batt first and then the engine battery when the leisure is full. Rarely do they do them at the same time except driving.

If you put a volt meter across the engine batt when you think its being charged it should read 13.5 volts ish. If it reads 12.5 or less it isnt being charged.

Phill


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## Penquin (Oct 15, 2007)

drcotts said:


> Hi Geoff
> Are you sure that your van is set up to charge both leisure and engine batteries. Even a smart charger will charge the leisure batt first and then the engine battery when the leisure is full. Rarely do they do them at the same time except driving.
> 
> If you put a volt meter across the engine batt when you think its being charged it should read 13.5 volts ish. If it reads 12.5 or less it isnt being charged.
> ...


Unless you have a Battery Master fitted - then both are charged - that is the aim of the excellent battery master system.

http://www.outdoorbits.com/battery-master-p-32.html

An excellent bit of kit IMO,

Dave


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## EuropeanCampers (Mar 28, 2008)

wakeman said:


> Hi Geoff, I have been on a steep learning curve since buying my 1990 Hymer B644.
> 
> I had the same problem as yourself with dead battery when on mains hook up having not used her for a month or so, I had left the radio on standbye which was enough to flatten the Engine battery. I managed to get hold of a wirring diagram from Hymer all be it in German. I know a bit about auto electrics and when I studdied the diagram I reallised that on hook up only the leisure battery is charged.
> 
> ...


Les,

Geoff's bus is a similar vintage to mine and I would guess has the same Electroblok multi stage charging system. This does indeed charge both hab and engine batteries simultaneously when on hook up, the hab battery in a full 3 stage way and the engine battery with a float charge.

So Im guessing Geoff either has a knackered engine battery or a problem with the engine battery charge part of the circuit coupled with a continual drain on the battery from something like an alarm or Truma boiler frost valve.

Hope this helps.
Gareth


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