Should I use 500E 5W resistor ?

[milan.rajik]

Should the 500E resistor in this circuit be 5W type ? It is a battery charger circuit. 500E is used to trickle charge.

0.3E I have used 5W. 4A will flow to charge a 12V 6Ah battery. Should the 500E also be 5W because it is only used for trickle charging.

 

[esp1]

hi,
In the worst case where the 500E has say 18V across it, the current thru the 500E is 18V/500 = 36mA, which only 0.65 Watts.

With a 12V battery on the output of the charger there is only 18V -12V = 6V across the 500E, which is 12mA, so thats < 0.1Watt.

I would fit a 0.25W 500E

Eric

 

[hamid159]

no,it shouldn't be 5W....for example if your input is 18V and battery is charging at 13V,then 18-13/500= 10mA current will flow through it.So,its power should be >0.05W..

 

[milan.rajik]

But I think Battery charging is done at 14V 4 Amps.

 

[hamid159]

i fear,you will damage your battery if you charge it at 4A... 4A is much greater for 6Ah battery....
anyway,0.3E resistor should be greater than 5W ( about 8W or 10W )...

 

[milan.rajik]

0.2W 10W is not available. What next value of resistance can I use which is 10W type. Should I use 2 X 0.1E 10W in series ?

 

[hamid159]

yes,you can use it,,now equivalent will be 0.2E,So,now power rating for each resistor should be greater than 1.6W...you can also use 2 x 0.1E of each 5W rating

 

[milan.rajik]

So, Can I use a 18V 2 Amp or 3 Amp transformer with a bridge circuit for charging power supply ?

 

[hamid159]

which battery you are using? lead acid?

- - - Updated - - -

see this...**broken link removed**
you can use the first circut...it has current limit,which will not damage you transformer or lm317or battery....

 

[milan.rajik]

I am using a 12V 6Ah or 10Ah Gel battery.

 

[milan.rajik]

In the first circuit at this page what is the wattage of resistor named see text. I have set charging current to 600 mA. so 0.6/0.6 = 1E resistance. What should be wattage 1/4W, 1/2W, 1W, 5W ?

**broken link removed**

 

[Borber]

Do you know this equations

P=(I^2)*R or P=(U^2)/R

?