Completed Project Replacing the rectifier in a vintage car battery charger?

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
Hi everyone,

My battery just died yesterday (actually left the lights on). Took it out for charging today but my new automatic charger for detect such low voltage to begin the charging process. So, I had to hook it up to my great old Lucas charger (attached pic below) but only to notice there was no defection in the ammeter. I checked with my multi-meter and found the output was like just 0.24V, opened the case and checked the transformer an it was fine. Looks like a blown rectifier-selenium rectifier I guess (pic below). After a futile search found these rectifiers are no longer available, so finally got a KBPC2510 metal bridge rectifier. I've installed it on the battery charger and measured the out put at 6V and 12V setting gave me 6.9V/11.9V open circuited and when connected to the battery the outputs rose from 6.8- 8V for 6V battery and 14-15.8V for the car battery as it got charged .

Is this because of the metal bridge rectifier? I haven't had the chance to measure the volts with the old rectifier before. Are these voltages bad for these battery?
 

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debe

Joined Sep 21, 2010
1,390
The old Selenium rectifiers are not very efficient. The new bridge rectifier is the reason you are getting a higher voltage. Probably a little high a voltage. Be great to get a flat battery charged up quicker, you would just have to keep an eye on the voltage & turn it of when it starts to get near 15V.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
The old Selenium rectifiers are not very efficient. The new bridge rectifier is the reason you are getting a higher voltage. Probably a little high a voltage. Be great to get a flat battery charged up quicker, you would just have to keep an eye on the voltage & turn it of when it starts to get near 15V.
I just let the battery voltage get sufficient and then I put it back in the automatic charger to do the remaining work. a friend of mine who is a mechanic told me a 12V/15CP flasher bulb in series might act like a power resistor and get the job done.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
You usually have to add a high power resistor in series to closely mimic the characteristics of the selenium one. They stink when they blow.

You cam check www.batteryuniversity.com for care and feeding if batteries.
I was thinking of using 12V 15CP flasher bulb in series since I don't have a spare power resistor with me now.

That awful stink!! I remember that when I last used the charger like 4 years ago. It was nasty but it never crossed my mind it was the rectifier dying.
 

ian field

Joined Oct 27, 2012
6,536
Hi everyone,

My battery just died yesterday (actually left the lights on). Took it out for charging today but my new automatic charger for detect such low voltage to begin the charging process. So, I had to hook it up to my great old Lucas charger (attached pic below) but only to notice there was no defection in the ammeter. I checked with my multi-meter and found the output was like just 0.24V, opened the case and checked the transformer an it was fine. Looks like a blown rectifier-selenium rectifier I guess (pic below). After a futile search found these rectifiers are no longer available, so finally got a KBPC2510 metal bridge rectifier. I've installed it on the battery charger and measured the out put at 6V and 12V setting gave me 6.9V/11.9V open circuited and when connected to the battery the outputs rose from 6.8- 8V for 6V battery and 14-15.8V for the car battery as it got charged .

Look between the fins - Lucas kept the same form factor for a while after introducing hermetically sealed rectifiers.

Not sure if they started as early as germanium, but silicon is very possible.

If it actually was selenium - read the other replies.

If it was silicon units bonded onto the fins; your KBPC can slot straight in.

Germanium isn't impossible - can you strip it down and see if any individual rectifier elements survived? A DMM diode check will sove the mystery.

Germanium has a lower forward volt drop than silicon, but ISTR: it had more dynamic resistance - if you have to replace the lower Vf of germanium, Shottky barrier is probably easier to source - but they come in low reverse voltage ratings, so watch out!!!

Is this because of the metal bridge rectifier? I haven't had the chance to measure the volts with the old rectifier before. Are these voltages bad for these battery?
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
I'll try dismantling the old rectifier today and find out if it is a selenium rectifier. I thought of taking it apart first but have heard selenium is kinda poisonous. So, gave up that idea till now.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
Me too. It's one of those smells you just can't forget. Almost as nice as black powder in the morning.
That rotten egg smell is nasty. Found my grandpa's really old Bosch 6/12V 8A charger plugged it today and tried charging a battery, rectifier gave it magic smoke and smell!:D
 

Ylli

Joined Nov 13, 2015
1,089
I'll try dismantling the old rectifier today and find out if it is a selenium rectifier. I thought of taking it apart first but have heard selenium is kinda poisonous. So, gave up that idea till now.
Won't suggest taking the Selenium Rectifier apart. As you say, Selenium is toxic.
 

tcmtech

Joined Nov 4, 2013
2,867
I'll try dismantling the old rectifier today and find out if it is a selenium rectifier. I thought of taking it apart first but have heard selenium is kinda poisonous. So, gave up that idea till now.
Don't chew on it and then make sure you wash your hands with soapy water (don't lick them clean) when you're done playing with and you will be fine.
 

ian field

Joined Oct 27, 2012
6,536
Don't chew on it and then make sure you wash your hands with soapy water (don't lick them clean) when you're done playing with and you will be fine.
Absolutely - trace amounts of selenium are included in some multi vitamin tabs - water will kill you if you swallow enough.............

Lucas carried on with that style of construction after they introduced hermetic rectifiers - any there will be easy to see, and you can just replace the whole thing with a modern rectifier. In this context; I can't see any useful purpose in dismantling a selenium stack, but its not the apocalypse some people are suggesting if the remains are disposed of sensibly. There are *MUCH* more dangerous things in electronic components - and a few of them got exempted from RoHS.

If its silicon - just bung in the KBPC and forget it - selenium or germanium replacement might need a current limiting resistor added - this has been pretty much covered on existing replies.
 

GopherT

Joined Nov 23, 2012
8,009
Won't suggest taking the Selenium Rectifier apart. As you say, Selenium is toxic.
Oh my god! Am I supposed to wash my hair after I use Head and Shoulders Medicated shampoo?

Active Ingredient Selenium Sulfide 1% Inactive Ingredients: Water, Ammonium Laureth Sulfate, Ammonium Lauryl Sulfate, Glycol Distearate, Cocamide MEA, Ammonium Xylenesulfonate, Sodium Citrate, Fragrance, Dimethicone, Cetyl Alcohol, Sodium Chloride, Citric Acid, Sodium Benzoate, Stearyl Alcohol, Disodium EDTA, Hydroxypropyl Methylcellulose, Methylchloroisothiazolinone, Methylisothiazolinone, Red 4.
 

Ylli

Joined Nov 13, 2015
1,089
Oh my god! Am I supposed to wash my hair after I use Head and Shoulders Medicated shampoo?
You are not inhaling Selenium dust when you wash your hair. Or, and if you want, why not play with that Mercury that came out of the broken tilt switch. It's fun stuff.
 

GopherT

Joined Nov 23, 2012
8,009
You are not inhaling Selenium dust when you wash your hair. Or, and if you want, why not play with that Mercury that came out of the broken tilt switch. It's fun stuff.
Every time one of those little soap bubbles bursts, it creates an aerosol that is easily aspirated. I'm so confused - dandruff or life?
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
536
Every time one of those little soap bubbles bursts, it creates an aerosol that is easily aspirated. I'm so confused - dandruff or life?
You could try showering with a gas mask on:D.JK.. Maybe it ain't that serious or else it would have been banned.
 

ian field

Joined Oct 27, 2012
6,536
That rotten egg smell is nasty. Found my grandpa's really old Bosch 6/12V 8A charger plugged it today and tried charging a battery, rectifier gave it magic smoke and smell!:D
Rotten egg is hydrogen sulphide - selenium decomposition is more like rotten fish.
 
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