Battery Chargers

[RayS]

While invistigating a small problem in the wiring of my van, I got to measuring battery voltage etc. The van is 3 years old fitted with BCA Power Centre 2 unit of which the book says can be left charging the battery continuosly. Found that with everything - including the charger switched off and siconnected from mains (of course) there is a small current flow from the battery into the caravan somewhere. It is about 90 milliamps, so noting too serious. This happens whether the illuminated charger swithch on the BCA unit is On or Off. I am pretty sure nothing else is connected - the current is too small for a bulb or any other dc device I have.

Does anyone know whether such a small reverse current is usual for such chargers - i presume there may be a back path through the rectifiers - or would have been in the good old days of plate rectifiers - not sure about soldid state stuff.

Any views much appreciated.

 

[ProfJohnL]

Hello Ray,

90mA is far too much for leakage through a rectifier circuit, so it suggests that something else is drawing the curent,. Do you have an alarm system? or a car radio with a permanent feed?

Can't offer any more without actually cheking the caravan

Sorry.

 

[gary]

I wonder how good your multimeter is as it has to put some load on the circuit and 90ma seems reasonable?

 

[Zbungle]

I wonder if either (or both) a caravan radio is fitted which draws a tiny amount of current for its memory and/or the Status aerial amplifier is switched on, which also draws a small amount of current.

Just a thought as I am often guilty of overlooking the obvious.

 

[ProfJohnL]

I wonder how good your multimeter is as it has to put some load on the circuit and 90ma seems reasonable?

Hello Gary,

Ray has probably used a multimeter to measure the quiescent current from the battery. The multimeter when used in this mode will not add any addition current load as it sits in series with the current, but the meters internal Resistance will marginally reduce the current flow.

So his measurement of 90mA is still excessive, and indicates that something is drawing about 1.8 Watts of power.

 

[ianfionarandall]

Could there be a relay in the system somewhere that continues to operate?

 

[Pete4]

If you have a volt meter fitted to the 'van, this will draw a current.

 

[ProfJohnL]

Hello Pete,

PLesae see my comment to Gary's posting. Yes a volt meter will draw some current but 90mA is far more than reasonable for such an instrument. Even a moving iron meter shpuld not draw that much!

 

[RayS]

Hello Gary,

Ray has probably used a multimeter to measure the quiescent current from the battery. The multimeter when used in this mode will not add any addition current load as it sits in series with the current, but the meters internal Resistance will marginally reduce the current flow.

So his measurement of 90mA is still excessive, and indicates that something is drawing about 1.8 Watts of power.

I used a digital voltmetwer which should have a very high impedance, so this can probably be ruled out.

Checked all lights and radio off (and not on standby), nothing else 12v. in the van. Disconnected all mains circuits too, as thought there might just be a return path through 12v negative to earth.

But thanks for the ideas - it's quite easy to overlook things when working outdoors in the cold . Ray

 

[RayS]

Thanks to everyone who has replied - I am now wondering whether the current I saw was prehaps from smoothing capacitors in the power pack/charger unit. I did measure immedaiately after disconnecting the mains, so this is possible. I will try it again with sufficient time delay to make sure these (assuming there are some) are well discharged.