Draper led torch charging light remains on

[Mikezoe65]

As a postscript, after checking the presumed fully charged torch every day today it failed to work which must mean despite there being no red charging light there remains a small drain. I’ve now given up and ordered a new one which unlike the original is supplied with a charger. I’ve learned my lesson - not to grab the first charger from the drawer full of them that has a socket that fits but to check the output voltage too!

 

[Delta Prime]

In the future, if you have any questions about any subject of electronics, please do not hesitate to ask. Good luck to you.

 

[Mikezoe65]

PPS
Below is the underside of the pcb. Any comments?

 

[Delta Prime]

R3,R4 solder short, reflowed from excessive heat.
U1 (max smoke)
Solder balls, solder splatter.
Poor assembly.
For safety ,through away the PCB &
Keep the LED & switch for parts, if you like?

 

[Mikezoe65]

Not just yet! My new torch took about 7 hours of charging at around 1 watt (5v) before the red light turned green and so I charged the faulty torch the same rate for 7 hours (no charging light) and am testing briefly every few days. It could be that the torch remains useable ie holds its charge for as long as the new one. Time will tell.

 

[Delta Prime]

Not just yet

Do as you wish, you are being careful in my opinion 1 W divided by 5 V equals 200 mA of current. There is a process in charging lithium ion batteries first it is a constant current. There is your 200 mA then it changes to constant voltage charging to achieve 4.2 V full charge. The seven hours that it takes initially is for safety purposes and it is only done the very first time you charge your flashlight or torch or cell phone.
You’re dealing with the subject you do not understand. This is why you’re asking questions. I answer on the condition of being cautious,as to your well-being. Good luck to you.

 

[Mikezoe65]

Thankyou for a very detailed and considered response. You are quite correct that I’m new to led technology and wary of Li-Ion batteries in particular. I’m remain surprised - even a little shocked - that such a device is sensitive to the specification of the charger ie that whilst it is happy to face say a 5v DC output, why eg a 9v supply wouldn’t be equally satisfactory. Doesn’t the pcb have as a key role to protect the torch by accepting only what current it needs?
There needs to be a much greater education of the public about the need to tag all mains chargers to minimise the risk of hurriedly connecting (as I did) a 30v vacuum cleaner charger which happens to have the correct plug. When I did do so, the charging light came on but there was no indication of the damage being caused to the pcb.

 

[Harald Kapp]

Doesn’t the pcb have as a key role to protect the torch by accepting only what current it needs?

It does, but only within the limits of its specification. When the pcb is designed to accept a 5 V input, it is unreasonable to expect it to operate from 30 V.

There needs to be a much greater education of the public about the need to tag all mains chargers to minimise the risk of hurriedly connecting (as I did) a 30v vacuum cleaner charger which happens to have the correct plug. When I did do so, the charging light came on but there was no indication of the damage being caused to the pcb.

Welcome to the family. You're not the first making this experience.
I started long ago to even label my 5 V USB wall warts with the names of the associated devices as these wall warts come in different amperages.