Hi I'm repairing a maxi-mouse street amplifier that a friend fried some components on when he changed the batteries ... I've replaced the rectifier and one of the 4.7 resistors which burned out ... that leaves just the green led to change as it's open.... the ac input is 20vac .... the LEDs are 5mm and the amp runs on 2x6v batteries... my question is what tolerance does the LED have to be as I see they seem to go from 3v up to 12v ... the LED goes out when fully charged .... if anyone can give me a quick explanation of how the charging system works that would be really useful and informative should there be another fault in this circuit ... I read somewhere it was about the voltages being equal at some points on the circuit ... thanks in advance ... Andrew

 

LEDs are generally speaking not voltage devices but current devices. You connect an LED in series with a resistor to a voltage source. The resistor is chosen to limit the current. I can operate an LED from 400 VDC if I choose the correct resistor. I can also operate it from 3.3V, again by choosing the correct resistor.

 

This charger led just measures the voltage drop across the 4.7 ohm resistor when powered by AC, any Green led with 10 to 20mA will do.

 

Thanks to you both the replies ... I've ordered some LEDs ... Congratulations Dave on the Premier Title .... Liverpool have been my second City favourite team since the last days there of the great Bill Shankly ... I've followed them through all the highs and lows ever since .... hope there's many more to come . As the LED measures voltage drop to show the battery is fully charged does this mean that the circuit shuts down and the batteries are no longer receiving a charge or is it necessary to unplug the charger as soon as the LED goes out to protect the batteries from overcharging ? ... I imagine its safe to leave in as the design of this amp is incredibly well thought out .... a real work of art ..... it really is a beautifully functional amp .... all the best ...

 

You can leave it on charge continuously, the regulator is a 5-30V adjustable one.