Go Down

Topic: 100mA battery discharging circuit (Read 1 time) previous topic - next topic

fatality

im want to build a discharging circuit using arduino to discharge a 300mAh 8.4v NiMh cell. been doing some research on the web for weeks now and stumbled upon a constant current sink circuit using tl431. The circuit is on page 8 of the datasheet
http://www.100y.com.tw/pdf_file/38-ON-TL431,NCV431.pdf

before building the circuit i would like to get some suggestion from fellow arduinians. Do i have to use high wattage resistor for Rs? or is there any better or easier way to discharge a battery at 100mA??

MarkT

You can calculate the dissipation in the resistor very simply - P = IV, V = IR, therefore P = I^2 R.  Most standard through-hole resistors are rated for 0.25 to 0.6W depending on exact type.  For a 2.5V reference and 0.1A discharge that means a 25ohm resistor which is 0.25W, so should be OK (it will run hot).  You could use 4 100ohm resistors in parallel to get 25 ohms and a lot less heating.

But back to the original issue - this rate of discharge means something has to dissipate 8.4 x 0.1 = 0.84W (in the circuit you give it will be mainly the transistor, necessitating a power transistor with perhaps a small heat sink.

A far simpler solution is an 82 ohm 2 or 3W power resistor (1W would be enough but again would be pretty hot).  Battery voltage is fairly constant (till discharged) and thus a resistor will be a constant current sink in effect.

Be careful not to let the battery over-discharge, this can drastically reduce the life of most rechargable batteries.
[ I won't respond to messages, use the forum please ]

Go Up
 


Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

Arduino
via Egeo 16
Torino, 10131
Italy