circuit board battery chargers???

[new guy]

I have circuit boards that are fed 120vac and are supposed to charge a 4.8vdc battery and also ring a 6vdc 1/2 amp bell. If the 120vac goes off the battery is supposed to supply power for the bell and emergency lighting (two small 6vdc bulbs). The problem is when the 120vac is there the battery terminals only read 4.75vdc. And when the 120vac is not there the voltage at the bulbs is only 1.79vdc, (very dim bulbs) but the bell rings well. If I disconnect the battery the battery terminals on the circuit board will read 8.5vdc. I have tried 2 new circuit boards with 2 new batteries and the same readings exist. the 120vac feed is constant at all tests. I think the battery should be 6vdc and the reading at the battery terminals with the 120vac connected should be higher than battery voltage in order to charge the battery. Then when disconnected drop to battery voltage (6vdc) to light the lights brightly and ring the bell. What do you guys think? The part manufacturer swears they are the correct parts?? Is there a bench test of the transformers on these circuit boards?

[MrAl]

Hi there,


Do you have a schematic or can you examine the board and draw one up?

If we have a schematic we can tell you right away either what is wrong or what needs to be
changed to get it to work correctly. Without a schematic it is very hard to determine what
could be happening unless someone else has that exact same board.

I believe you are right however when you say that the voltage to charge a 6v battery must be
above 6v in order to charge it.

[dobrien]

You can also place a milliampmeter between the positive battery and the charger.
Then connect the unit to 120 vac and see if a current flows to charge the battery
and what the discharged curren. The chargeing current should be about 1/10 of the
battery capacity is. You can also place the manufacture and model number here.