Hello,

I wanted to charge a 12V battery. When charger wasn't plugged in, I accidentally connected the wrong polarity, so two diodes got burnt by 10.8V from the battery. Please see attached pics.

Charger details; Output = 13.8V 500mA. Diodes are in series, connected between transformer and output wires.

Would anyone know/guess what diodes would they are be please?






Thanks in advance.

 

Any diode such as 1N4001 to 1N4007 will be fine.

 

hi zahmuh,
I see there are 2 other diodes alongside the blown two.?
That indicates a full-wave bridge.
Are there any markings on the unblown two diodes.?
E

 

Trace out the circuit. If the 4 diodes form a bridge, then you can read the marking on the other diodes to see what was used originally.

ak

 

Thanks for all prompt replies guy, highly appreciated.

Markings on those two are darkened, so not sure if those two are blown as well. I think I should use two of 1N4007 one and check first, to see if other two are blown as well, but which way is the current flow side for both? On the other two, they are on opposite side to each other.

Now Maplin is closed down. It's been a very handy store for these stuff. Any other stores where I can get electronic stuff, do you know?

Cheers

 

hi zak,
I use this company for hobby bits, reasonable shipping costs.
https://www.bitsbox.co.uk/index.php...result&search_in_description=1&keyword=diodes
E

 

Hello,

Other companies to look at could be:
https://www.esr.co.uk/index2.htm
https://www.rapidonline.com/?ra_source=domain-redirect&ra_source_value=rapidelectronics.co.uk

Bertus

 

The title of your thread mentions a diode for reverse polarity protection, but that doesn't work for a battery charger, since the current direction for a normal charge is the same direction when the battery is reversed.
So for reverse protection, you can add a fuse.

 

Hello,

I wanted to charge a 12V battery. When charger wasn't plugged in, I accidentally connected the wrong polarity, so two diodes got burnt by 10.8V from the battery. Please see attached pics.

Charger details; Output = 13.8V 500mA. Diodes are in series, connected between transformer and output wires.

Would anyone know/guess what diodes would they are be please?

View attachment 152853


View attachment 152854

Thanks in advance.

There's a couple of ways you can do a reverse protection diode - each has its own pros & cons.

The parallel or shunt protection diode must not be used without a fuse. if you use a big enough rectifier - it might not fail short circuit in the time it takes the fuse to blow. You also have to make sure other components like PCB tracks can stand the short term fault current.

The series protection diode has a forward volt drop penalty - about 0.7V for silicon and just under 0.2V for Shottky barrier.

A lot of people are using MOSFETs for series protection diodes with even lower Vf - Everyday Practical Electronics have used it in a number of projects and may have devoted an article to how it works.

 

The series protection diode has a forward volt drop penalty

As I noted in my previous post, a reverse protection diode provides no protection for a battery charger since a reversed battery draws current in the same direction as the normal charge current.