Resistor Too Hot Solder Joint Melt

[yanco]

I am using BA6219 reversible motor driver from ROHM. The Resistor connected to the BA6219 is 10 ohm 5 Watt.

The 10 ohm is connected to input of the 18 V unregulated adaptor which is supply to Pin 8 of the motor driver. The 7812 output is supplying 12 V to the rest of the circuit.

7812 is not hot. It is cold enough to touch.


18 Vin o-------------7812 --------
| |
| |
| R= 10ohm 5 watt
| |
| |
Pin7 Pin 8 of BA6219 Rohm Reversible Motor Driver


The Resistor 10 ohm is too hot until it melt the solder joint. I have try placing it vertical far from the PCB and also try using 50 ohm 5 Watt, it is also very hot. I can only touch the solder joint for 3 second.

If I change the resistor to higher value, like 100 ohm. The current to the BA6219 is too low. There is not enough energy to drive the motor. So, where is my mistake. Pls advice.

Thanks.
James

 

[schwarz]

Hi yanco ,
You were able to solve '7812 Get Hot / Vin Voltage Drop' yourself. I suppose this is the same circuit.

W=I*I*R gives me 0.7 A at 5W across 10 Ohms; at 2.5W it is 0.5A
What's current through 10 Ohms , it should be less than 0.5 A.
Since 50 Ohms is also 'very hot' there is something wrong with
driver or motor ( jammed).
Is 7812 o/p Volts OK ? Have you tried replacing BA6219 ?

Please confirm that even with hot resistor motor is being driven!
Good Luck.

 

[IRstuff]

Perhaps you need to heat sink and figure out the worst case power:

18^2/10=32.4W
18^2/50=6.5W.

You should have never had a 5W resistor in your circuit.

Since the 50 ohm resistor is also hot, perhaps your circuit is already fried and shorted out.

TTFN