Help with simple power converter issue

[bovine0001]

I bought this cheap drill which came with a power converter/plug which a wire went to a micro USB, which you plugged into the drill and charged it. I wanted to charge it off DC, so I cut off the converter and soldered a cigarette lighter charger with a resistor. covered it all up with heat shrink. This worked great for a short time but recently stopped working and the resistor has been getting real hot and smoking a bit.

I plan to look for a short, but should I put a small case, enclosure on the connection/resistor?

Thanks

 

[davenn]

Hi there
welcome to EP

I wanted to charge it off DC, so I cut off the converter and soldered a cigarette lighter charger with a resistor. covered it all up with heat shrink. This worked great for a short time but recently stopped working and the resistor has been getting real hot and smoking a bit.

so how did you determine that you could charge it from 12V with only a resistor in circuit ?
and how did you determine the value of this resistor ?

what sort of batteries are in the drill .... NiCad, NiMH ? LiPO ?

all have specific charging requirements that you have ( by your comments) probably ignored.
I'm not surprised something is getting hot

 

[Audioguru]

USB is only 5VDC. A lighter socket is 12VDC to 14.4VDC. A HUGE difference in power.
You are lucky that the battery did not explode or catch on fire.