Discussion in 'Radio Circuits, Repair & Performance' started by WA6MHZ, Mar 13, 2013.

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  1. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    One of the better and more affordable Battery boosters was the W4RRY model. But it seems they have long gone out of business, and no schematic or data exists that I can find on the net or anywhere.

    Mine worked flawlessly for years, but now it is blown. Not sure which part is bad, but they were so cheap from Digikey I ordered multiple parts of each and will just shotgun all the Silicon in the circuit. Troubleshooting Switching PS's is very difficult. I suspect one of the power FETs are bad.

    Here is the circuit board out of the case.


    The tricky parts of it are the 3 coils and the Transformer. It is conveniently made out of lamp cord wire to handle the current.

    I scored an inductance meter and measured the inductors. I have no idea what the torroids are. Powered iron or Ferrite? no way to tell. But here is the inductance as measured.

    L1: 5 turns on a 13mm core: 40.18uH
    L3: Same 36.84uH
    L2: 5 BIFILAR turns on 21mm core: 143.4uH

    T1 is a very tricky transformer. Here is a pictoral of how I figured it was wound. Also given is inductance from each wire to the other.

    The main regulator is a SG2525A regulating pulse width modulator. The Data sheet doesn't show any applications anywhere near what this is.

    The Power Fets are STP36NF06 N channel 60V 30A fets.
    The Power Diode is actually 2 diodes. MBR2535CTG with both cathodes connected together.

    Here is an approximate schematic of How I can figure it out.


    Not too complicated. Reproducing it would require figuring out the fancy torroids and the transformer torroid. If I could discern what kind of core it is, the windings could be replicated.

    I will do an ORCAD drawing of it when the boss is out of the office someday.

    The parts are on order from Digikey, and I am most anxious for them to come, as my Car Icom 706 is off the air till then. Hopefully the new parts won't blow. If they do, then there is a problem! Hmmm.......
  2. W9GB

    W9GB Ham Member QRZ Page

    ST makes the SG2525 Voltage Mode PWM

    SG2525 Datsheet, includes Test Circuit

    Here is a 500 W SMPS schematic (2003) that uses the SG2525 PWM.
    Was this used in the HP Color LaserJet 8550-PS (power supply)?

    This is the DEL400 subassembly -- using the SG2525.
    Last edited: Mar 13, 2013
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Why would you need to reverse engineer it ? You could just build a better one.

    Looks like simple PWMs.

    Wonder if W4RRY had a patent on using that lamp cord ?

    You should check before you build one.
  4. WB3BEL

    WB3BEL Ham Member QRZ Page

  5. KF5FEI

    KF5FEI Ham Member QRZ Page

    If it appears to be oscillating, it's likely one or both of the schottky diodes have failed. They will check good as diodes, but not work in-circuit.
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Give up on that solid state crap, its not very rugged.

    Get a Dynomotor.
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    I agree.

    It is most likely a bad FET , because of the lack of a proper heatsink, and proper fusing.

    I do believe...
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    If it is NOT oscillating it is not working. You may have it backwards, for a PWM.

    Diodes Short, until they let the smoke out and open, if not fused properly.
  9. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    The failure mode is as follows:
    With no load (battery not connected to the output), there is Zero current drain.

    With the battery hooked up, it draws about 9 amps even though the battery is topped off
    at 13.8V and drawing negligible current. That is why it was blowing fuses. It draws WAY too much current when enabled, but no current when not enabled. So I don't think it is the diode, but the power FET.

    I also wasn't satisfied with the poor heatsinking on the power fets and diodes. Think I Greatly beef that up in my repair, with lotsa heatsink compound. New parts will be in next week. Sent by UPS ground, as 3 day and next day were WAY too pricey!
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I like the Dynamotor idea.

    Key down...wheeeeeee! And watch the headlights go dim and these days, probably half the electronics in the car fail.:p
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