How to limit current ?

[rcmeca]

I have quite a few power adaptors 240volts (Australia) for my electric planes,I would like to lower current eg 500mA to at least 100mA ,as to slow charge the battery packs(NiMH).Is there a simple way of do this? Regards Mark.

 

[Nigel Goodwin]

Add a series resistor, the value depends on the exact output of the supply, and the battery voltage. This doesn't give a constant charge value, but there's no need for that.

 

[rcmeca]

Thanks Nigel for a quick reply,excuse my ignorance I have just started to study electronics,is a series resistor a single component or a series of different resistors.Thanks

 

[stevez]

Mark - google on "series resistor" and you'll likely see some great explanations w/diagrams that help to clarify things. You might view the battery you are charging as one resistor - and you would add another resistor in line (in series) with the battery.

 

[Hero999]

Look for ohms law, then you can calculate the required value.

Normally you don't have to worry about current since the appliance will just draw what it needs, LEDs and most battery chemistries are the exceptions to the rule.

 

[RODALCO]

Don't forget the lamp in series, This can be very well used to limit the current and voltage to charge battery packs.
For example use a 12 volts 3 Watt or 5 Watt or wattever wattage you need to limit the maximum current in the circuit.
The beauty of the lamp is that you have an optical indication of the charging current.

I use this way a lot to slowly recover 12 Volts substation batteries which have been discharged for a while.
After a while the 12V 21 Watt lamp gets dimmer when the batt voltage increases, then take the lamp out and leave the 12 volts charger connected to fully charge up the batt.
This process may take a few days, bear in mind that these are deap cycle batts 12 volts 100 Ah or bigger.

 

[rcmeca]

Thanks Guys for your help, Stevez I found those web sites and out comes the calculator,Rodalco great info I too have deep cycle batteries which I use to power an electric outboard which sometimes I push too hard.Thank you again everyone this is a great community. Regards rcmeca . PS Found this site which would be helpfull to someone new to electronics ,**broken link removed**.