</font><font color="blue" class="small">( Gee Soundguy you aging my equipment here. I have a battery charger that is more of a trickle charger and I can't say it is more than 5 years old. I use on smaller batteries only like my 4 wheeler. But if I leave it hooked up it will drain the battery in a couple of days. Can't tell you what brand it is because I have abused it pretty good. It is 12v and only a 1 amp trickle.
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Gee.. I only can guess at why... If it has a diode in line with the output to rectify the current.. that diode.. if functioning properly shouldn't allow reverse current.
Here are some ideas: Rectifier is breaking down in reverse direction way too easilly... ( need new rectifier ).
There is a filter capacitor across the output and it is leaky. ( this does happen )
Sometimes there is a blead resistor across the capacitor to discharge it after the unit is energized. This will be after the rectifier, and yes, would allow the battery to discharge back through that resistor. If built like this... it is a shoddy design with no forward thinking.. as addition of another rectifier after this stage would prevent it from discharging the battery.. but would still let it discharge the capacitor.
I have also seen some chinsy designs that use a load resistor ( sometimes in combination with a zenir diode .. making it a shunt limiter ) as a form of limiter to 'preload' the charge circuit.. it is therefore never running open loop, as it always sees that load resistor. Again.. this could discharge the battery.. but it is a bad design.. addition of another rectifier would allow it to limit charge but not discharge the battery.
Generally most battery chargers especially trickle chargers don't use filters on the dc side, as it isn't really needed.. the voltage will come up steady even with half wave rectified voltage.
I would be interested inseeing the inside of that charger.. if you ever open it.. snap a pic so I can identify the type of charge circuit they have used.
In any event, you could add a germanium diode inline with the charging wires and it won't discharge back through the charger. You will see a .4 drop in charging voltage at the battery. If the charger is charging sufficiently higher ( 13.6 ), it shouldn't be a problem. Check the open circuit voltage the charger is produceing. Many will run up in the 15-16 range with no load. Measure just the output of the charger with no load. if you are charging at 13.6 or above, the addition of the germanium diode should still let the charging voltage be high enough to charge that 12 cell.
Soundguy
