Guidance needed for repair of 24 v. batt. charger:

Discussion in 'General Electronics Chat' started by PieroC, Sep 25, 2009.

  1. PieroC

    Thread Starter New Member

    Sep 16, 2009
    5
    1
    Hello Friends;

    I recently purchased a second hand 10 amp, 24 v. Schauer battery charger in "as is" condition and am now attempting to repair it. The silicon controlled rectifier was marked "bad" and had been clipped out of the circuit. (see attached schematic). This left the charger as a non-automatic, non voltage controlled unit requiring the use of a timer on the AC supply for safe charging. I have purchased a new rectifier and pop-riveted it to the heat sink assembly at the back of the charger.
    The old SCR had a scrap of blue wire still soldered to one terminal leaving me in no doubt as to that part of the reinstallation. I have soldered the blue wire which connects to the C2 capacitor of the control circuit board to one terminal of the new SCR. (see attached photos). From examining the old SCR, it's clear that there was a heavier gauge wire soldered to the other terminal. I'm not sure where this wire led and am flummoxed when it comes to this part of the hook-up. Here's what I don't understand: What is the schematic actually telling me about the re-wiring of the new SCR? In examining the actual wiring of the charger, it appears that the DC from the diode rectifiers is fed directly to the heat sink plate at the back of the charger. (top left in photo). From the heat sink, there is a heavy black wire which, when I bought the charger, was connected to the ammeter and on out of the charger to the + battery clip. From examining the schematic, I'm guessing that maybe the SCR is electrically connected to the heat sink by it's mounting stud and that the connection from the SCR to the ammeter shown on the schematic is this heavy black wire. On the other hand, my admittedly amateur reading of the schematic would lead me to believe that the connection from the SCR to the ammeter uses a terminal on the SCR, not the heat sink. HELP !!!

    pc
     
    james fulghum likes this.
  2. aad

    New Member

    Sep 22, 2009
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    0
    What type of SCR is it?
     
  3. PieroC

    Thread Starter New Member

    Sep 16, 2009
    5
    1
    The SCR is an S1070W S487
     
  4. loosewire

    AAC Fanatic!

    Apr 25, 2008
    1,584
    435
    Your diagram is very clear,the photos are clear,go back and look for snipped
    wires a use magifer if needed.See what you can see that has not been touched.
    Do you have diagram that new part came with. Eliminate the wires that have not
    been touched. look close for signs of sniped wires.Your diagram showed the the power out put going to charger lead
    thru ampmeter. Make a list of what you have according to diagram,then look close at others things.
    check diodes for shorts,check for ground shorts. I just made a post helping people
    show some things getting repaired,you came along at the right everyone should
    know how to charge there battery and repair there charger,Instead of going to engineering
    on paper in schools,doing the math part first.
     
    Last edited: Sep 25, 2009
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    A datasheet for an S1070W is available here:
    http://www.datasheetcatalog.org/datasheets/2300/365417_DS.pdf
    If that link doesn't work, click here:
    http://www.datasheetcatalog.com/datasheets_pdf/S/1/0/7/S1070W.shtml

    The S1070W is on page 6.
    From the diagram in the 5th column, left terminal is cathode, center & tab are anode, right terminal is gate. Looks like your gate is connected via the blue wire to the circuit board, but the cathode is not connected to anything.

    I can't see enough detail in the photos.
    There should be two wires coming from the black wire side of the ammeter, one of them going to the cathode of SCR1, the other going to the control circuit at R5. I think just the wire to the control circuit's R5 is connected.

    I don't know why there is a 'flying lead' connected to the heat sink plate to the upper left of the control circuit. Is there another spade connection on the ammeter where the black wire is connected? If so, I would remove that flying lead from the heat sink plate, connect it to the 2nd spade connection on the ammeter, and solder the stripped end to the cathode of SCR1.

    If you didn't use heat sink compound/thermal grease on the SCR, you really should use it. Radio Shack stocks little tubes of heat sink compound.

    Also, I would much prefer using a panhead screw with a locknut on SCR1 instead of a pop rivet. Pop rivets will expand and contract with heat/cooling, and you want to be certain that there is always a good mechanical, thermal AND electrical connection between the heat sink and the SCR.

    [ETA]
    The rectifier bridge is mounted to the bottom of the charger frame under the heat sink.
    The circuit breaker is that object mounted to the bottom of the charger frame close to the ammeter.
     
    Last edited: Sep 25, 2009
  6. loosewire

    AAC Fanatic!

    Apr 25, 2008
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    Thanks Sgt. You are always there,new golf cart drop in motor appox $600. Thanks
    Again.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    [hijack]
    Ouch! :eek: Well, about 1/10 the cost of a new one. Regards to your son. But let's not do this to our OP; as this is their thread.
    [/hijack]
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    I don't think there is anything special about the SCR. I would guess any SCR with a PIV rating of maybe 50V or higher and a forward current rating of 15A continuous (or higher) can be used.

    If I was rebuilding it to use myself, I would probably replace all the caps and diodes on the control board because you don't know how stressed they are. Wouldn't cost much. The only thing you can't fix is if the transformer has problems but probably not too likely.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    From our OP:
    OK, good deal. Give it a shot, I think you're on the right track.

    If the original SCR was also pop-riveted to the heat sink, that is probably why it failed.

    Since the entire aluminum heat sink plate will be "live", make certain that no part of it can touch the case. Otherwise, if you happen to set it on a metal part of the vehicle in which the battery is being charged, you will cause a short through ground.

    Aluminum oxidizes (corrodes) after prolonged contact with air. You want to make certain that the area around the pan head screw doesn't oxidize. A quick blast of white lithium spray or a dab of wheel bearing grease will help to slow that down.
     
  10. PieroC

    Thread Starter New Member

    Sep 16, 2009
    5
    1
    Thanks to all of you who wrote in re: my charger repair question. SgtWookie in particular. What an incredible resource this site is!!
    Yes, the original SCR was riveted to the heat sink. I have the new one BOLTED on with thermal grease as recommended. The guy at Radio Shack gave me a tube for FREE!! I ran a lead from the SCR cathode to the ammeter and on out to the battery clip and the charger is now working perfectly!!

    pc
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Great news, and congratulations!

    Your detailed description of the problem, providing a schematic, and images of the "as-is" configuration were an enormous help towards solving the problem. It is seldom that we have a brand-new member that provides sufficient information in the first couple of posts to be able to get to the area causing the problem(s).

    What kind of vehicle do you have that uses a 24v battery? The only types I know of are military, fire, and military aircraft.

    A few things that you should know about lead-acid batteries:
    If you charge them too rapidly (using high current), their internal temperature rises, which shortens their life due to the increased chemical activity. The best thing to do is to keep them charged to capacity at low current, low temperature.
    At 77°F internal temperature (measured at the positive terminal), float voltage (once charged) should be about 26.74v for maintenance.
    Lead-acid batteries need to be occasionally "stirred" by slightly overcharging for a period of time occasionally.
     
  12. PieroC

    Thread Starter New Member

    Sep 16, 2009
    5
    1
    First off, to answer your question re: what type of vehicle do I have which uses a 24 volt battery, please see the attached photo or, for more pics + text, go to:

    http://picasaweb.google.com/PicoCantieni/EVTrike51509#

    I'm no where near considering myself an expert on lead acid batteries and welcome any and all tips, lore, advice, ect. I have found lots of good info. on the web. I have a pair of 12v. Interstate golf cart batteries rated at 155 ah. The batteries cost enough that I'm being pretty careful to treat them as well as I know how. Never leaving them discharged for any length of time and trying not to drain them too low.
    At present I have two chargers. One is the 1984 Schauer which I just repaired. It will charge at 10 to 15 amps and is voltage controlled to anywhere between 16 and 30 v. Right now I've got it set on ~28v. This charger is supposedly "fully automatic" and temperature conpensated, i.e. one should be able to leave it on the battery pack almost indefinitely as a maintenance charger. It's not one of those fancy three stage chargers you can buy nowadays and I don't leave it hooked up after the charge rate drops to about 2 amps. I'm guessing that if I turned the voltage down a bit it would probably work as a maintainer. I believe 28 v. is a bit high.
    My other charger I just bought recently off of Ebay. It's a Lester 25 amp with a timer. This charges a bit quicker and the timer gives some peace of mind that I won't boil the electrolyte. By the time the ammeter gets down into the 1-2 amp area, the voltage is about 30. My present rule of thumb based on experimentation is one hour of charging for each 10 miles driven but I keep a pretty close watch on the charge process.
    I believe I read somewhere that a good rule for charging rate is to keep it at about 10% of the amp hour rating on the battery. With that in mind, I guess the Schauer might be more "heathy" for my battery pack than the Lester.


    pc
     
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