Hi Folks!
I have found a blown resistor in a battery charger. Is anyone able to help identify what value is should be replaced with?
Pictures of the circuit board back and front attached.
Many thanks in advance!

stv

 

hi stv,
Welcome to AAC.
What is the AC input voltage on that charger PCB.?
E

 

Can you take it out and see if the other side is ok so we can read it, at a guess it could be 47ohms?

 

hi stv,
Welcome to AAC.
What is the AC input voltage on that charger PCB.?
E

Hi Eric, the PCB is connected to a 240v wall plug. I’ve added a picture of the writing on the plug.
Thanks so much!
stv

 

Can you take it out and see if the other side is ok so we can read it, at a guess it could be 47ohms?

Hi Dave,
The resistor is scorched all the way around so none of the bands are readable unfortunately.
Thanks for your help.
Perhaps I should just try a 47ohm resistor?
stv

 

Don’t do that! We now know the voltage and current output if the power supply. If yoy can tell us the battery voltage, we can compute the resistor.

 

Hi Dave,
The resistor is scorched all the way around so none of the bands are readable unfortunately.
Thanks for your help.
Perhaps I should just try a 47ohm resistor?
stv

We need to know what voltage the battery is, the charger says 14V battery and outputs 17.4V, so it's possibly dropping 3V ...so 47 ohms will give you a current of 63mA.
You need to check the diodes to see if they are not blown too

 

I am going to guess the battery is NiCad given the simplistic charger. And it is a 0.1C trickle charger, i.e. it takes about 12H for a full charge.

 

Perhaps I should just try a 47ohm resistor?

It's a 5% tolerance resistor, so the significant digits can only be 43 or 47. If you could make out the 3rd band, that would tell you if it's 4x, 4.x, 0.04x.

What is the capacity of the battery being charged? It must be a NiCd, probably being charged at 0.1C because there's no charged detection.

 

Thanks for the responses! Here’s a pic of the battery. It’s an aftermarket battery.

 

Thanks for the responses! Here’s a pic of the battery. It’s an aftermarket battery.

That's not a very good charger for a 14.4V NiCd battery. Fully charged, it would be 16.8V and the adapter is only outputting 17.4V. You'll lose 1.4V in the bridge rectifier, so there's not much voltage left to charge the battery.

Did the charger burn up because you tried to charge a bad battery, or one with a low voltage?

I'd try a 47 ohm 3W resistor. Charging a dead battery would make it dissipate 6W. It would be okay down to around 5V.

 

That's not a very good charger for a 14.4V NiCd battery. Fully charged, it would be 16.8V and the adapter is only outputting 17.4V. You'll lose 1.4V in the bridge rectifier, so there's not much voltage left to charge the battery.

Did the charger burn up because you tried to charge a bad battery, or one with a low voltage?

I'd try a 47 ohm 3W resistor. Charging a dead battery would make it dissipate 6W. It would be okay down to around 5V.

Thank you! I’ll try that.