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Repairing battery charger by transistor doubling

By on November 18, 2015
Repairing battery charger by transistor doubling








Battery charger Model KCA-1220  came to my shop last week in dead situation ,I opened the cover  hoping it is a matter of blowing fuse, noting was I expected ,

charger board

I carried on checking till I come to transistor power Q1 :2SC3320 was short. I looked to the datasheet  I found (VCEO=400V, IC=15A, IB=5A).

Unfortunately I found nothing can replace it in my drawers . the only transistor I have with big number is BU508A, but this transistor is only 8A.( VCEO=700V, IC=8A, IB=2.5A)

Just I would like to mention that I could not find the original part in the local market , and because of the political instability in our country , making an order through the internet became more difficult.

Anyway ,I made comparison to the two transistors datasheet , they look similar , the only difference is their current rating .

transistor layout

double transistor

I decided to make 2 of BU508A  in parallel to increase the current rating , this idea comes to my mind , because I have came cross many circuit which designed on this base.

I made it and it works..



This article was prepared for you by Muftah H Shawish from Misrata Libya. He has more than 25 years experience in troubleshooting and repairing of  industrial systems, electronic control system, temperature controller, motors drives and automotive control unit. He was a BET graduate, currently work as a manager of electrical repair dept in Libyan steel company and also run his own electronics repair shop.

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  1. Andre Gopee

    November 18, 2015 at 9:02 am

    Excellent job. Learn something new each day. Thanks for sharing.

    • Muftah Shawish

      November 18, 2015 at 7:55 pm

      Thanks for encouraging words Andre.
      best regards

  2. Jim

    November 18, 2015 at 9:48 am

    Hi Muftah I would think that the back of the transistor should be mounted to the plate with a screw so it would be able to use it's current rating and stay cool, instead of heating up the other transistor. Wires can be made to the leads. But enough said good work on the fix. Jim from USA

    • Muftah Shawish

      November 18, 2015 at 7:59 pm

      Hi Jim,
      you are right about heat transfer, it would be much better if transistors be erected as you advice, thanks for good comment.
      best regards

  3. Mangala

    November 18, 2015 at 1:00 pm

    Great job. Thanks for sharing.

    • Muftah Shawish

      November 18, 2015 at 8:14 pm

      Thanks for your words Mangala.
      best regards

  4. Albert van Bemmelen

    November 18, 2015 at 4:16 pm

    Hi Mr.Muftah. Sorry to hear that components are less available
    in your country.
    If your solution works it is exactly the same as when 2 Diodes
    are placed in parallel to increase the max current.
    Although in case of placing more Transistors in parallel
    they often also use extra Emitter and/or Base resistors
    to equalize the currents over all transistors used.
    Such transistor enhancements are made to many linear Power Supplies
    with for instance an uA 723 controller in its circuit were the max
    current is increased by switching more identical power transistors
    parallel. Because every transistor still can have another Hfe they
    would be unequally charged and actuated in their Base and with as
    result different currents in Collectors/Emitters.
    But I guess you here would have too little space to obtain such a modification.

    • Muftah Shawish

      November 18, 2015 at 9:17 pm

      Hi Dear Albert,
      Thanks for your comments, up to now i received no complains from my customer.. it should work , the only problem it may comes up because of accumulated heat from the two transistors, this may cause problem if the charger used continuously.
      best regards

  5. Hicham

    November 18, 2015 at 7:11 pm

    Great Dear MUFTAH, my remark only it could be better to make the second transistor in contact with the heat sink but i appreciate your common sence who let you solving problem without original part. Excellent job keep it up.

    • Muftah Shawish

      November 18, 2015 at 9:22 pm

      Hi Dear Hicham,
      Thanks for your comments... now getting the original parts in my country is taking too much time. it is good for us to use some alternative solutions.
      best regards

  6. sandeep C

    November 18, 2015 at 8:00 pm

    Good work. Thanks for sharing.
    Sandeep C

    • Muftah Shawish

      November 18, 2015 at 9:23 pm

      Thanks Sandeep c for your words.
      best regards

  7. George

    November 18, 2015 at 8:12 pm

    Great repair. As to sharing the load you could match the gain of the re;acement transistors so they would be able to share the loaSorry to hear about the problems getting parts. One can only hope that things will get better.

  8. George

    November 18, 2015 at 8:15 pm

    Great repair. You could either buy matched pair transistors or match them yourself utilizing hFE function on a meter.
    Sorry to hear about the hard time getting parts. Let's hope things get better.

    • Muftah Shawish

      November 18, 2015 at 10:02 pm

      Hi George,,, i think the DC gain of the two transistors is not much different... thanks for your nice words my friend.
      best regards

  9. Paris Azis

    November 18, 2015 at 10:05 pm

    Hello Muftah

    The idea of paralleling transistors is always good and accepted if there is no alternative of using a replacement like the original. But in such a case I agree with the comments of Albert and George below. You should either use two absolutely matched BUs (this needs picking them up from a multitude of them in an available stock and after measuring their Hfe parameter) or (in your case) use any pair of them but using current sharing resistors in their emitters, before their common connection.
    This will cure any asymmetric current flow through them due to their different Hfe parameters, which in turn (given that the transistors are mounted on the same heatink and in similar way) will ensure that they will have the same operational temperature (and finally this is what we need to take care of).
    Anyway, I hope that you have chosen those transistors with the closest Hfe parameters to each other!

    Best Regards

    • Muftah Shawish

      November 19, 2015 at 2:55 am

      Hi Paris,
      Thanks for your informative reply, regarding the thermal drift due to differences in characteristics of transistor, I am keeping the charger under test and I will take this fact in my consideration, I will make the new connection and adding the ballast resistors for equalizing the current.
      Best regards

  10. Humberto

    November 18, 2015 at 10:11 pm

    Great repair Mr. Muftah, in my country many techs use that method of connecting two transistors in paralell. I have the same trouble than you in obtaining some spare parts and devices due to political restrictions.

    • Muftah Shawish

      November 19, 2015 at 3:00 am

      Hi Humberto,
      Thanks for your comment, our problem is how to transfer small amount of USD, the visa card is restricted to prevent misuse by some bad people.
      hopefully thing will get better soon.
      best regards

  11. Parasuraman S

    November 18, 2015 at 10:29 pm

    Good Job! Paralleling transistors is something I have never tried. Good input and I learnt something new today from you. Very valuable info. Good Luck and all the best.

    • Muftah Shawish

      November 19, 2015 at 3:03 am

      Thanks for your comment Parasuraman S, we all learn something new each day of our life.just keep trying.
      best regards

  12. Emmanuel

    November 18, 2015 at 10:36 pm

    thanks for the post, am really gaining from your post

    • Muftah Shawish

      November 19, 2015 at 3:06 am

      Hi Emmanuel,
      Thanks for your words, i am happy that what i have shared was informative to you my friend.
      best regards


    November 19, 2015 at 1:16 am

    Good repair job Mr Muftah,KEEP it up.THANKS for SHARING.

    • Muftah Shawish

      November 19, 2015 at 11:32 am

      Thanks BHUPENDRA THAKUR for your regards

  14. Maazị

    November 19, 2015 at 2:17 am

    Thanks for posting, Mufta. learnt something new today.

    • Muftah Shawish

      November 19, 2015 at 11:34 am

      Thanks Maazị, my best regards

  15. thanh chelseabun

    November 19, 2015 at 2:55 am

    it's worked but was it tested at maximum rating?

    • Muftah Shawish

      November 19, 2015 at 11:37 am

      Hi thanh,
      thanks for comment, about testing , the charger is under test for some days.
      best regards

  16. Ulises Aguilar Pazzani

    November 25, 2015 at 11:52 am

    nice thinking Sir

  17. Jestine Yong

    November 30, 2015 at 7:47 pm

    Comment by George:

    Therefore " Both of them will be running much hotter then is allowed. and both will overheat, and consequently blow.

    My way would be , to drill another mounting hole on the same heat sink, mount second TR on new place, and just run fly leads to first transistor.
    Another thing is to separate bias to the transistors, by inserting two 10 ohm resistor into basess.
    Or by separating their outputs by heawy duty resistor 0.1 or 0.33 ohm, inserted into line of Emitters.

    Thank you ,,,George

  18. Juwel

    May 27, 2016 at 7:37 am

    Would anybody post the transistor lists[spec] of Ring RCB320 Battery charger ?
    One of the transistors missed from circuit board from corrosion.
    Thanks ahead.

  19. quy

    August 9, 2016 at 11:33 am

    How much is Kca1220?

  20. kris

    January 4, 2019 at 2:13 am

    I wish you pice for youre wonder full country there was a time when people from my country poland was working in youre contry as a street bilder in 80's last century good luck my frend !!!!


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