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Thread: NiCad charger getting hot

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    Supporting Member Randall's Avatar
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    NiCad charger getting hot

    OK, so not a music related question, but my Ryobi cordless NiCad charger gets hot just sitting there plugged in with no battery in it. I opened it up and the power transformer is too hot to keep a finger on. It is pulling 3.6mA, that doesn't seem like much does it? It charges OK, and I don't see anything obvious, I wonder what's up? Would not want to start a fire, but don't want to have to buy a new one. Would you trust it?

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    It's weird, because it WAS working fine.....

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    Supporting Member The Dude's Avatar
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    I wouldn't think a charger would get that hot with no load/battery. Have you looked at the guts? There can't be that much to a simple charger.

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    Supporting Member Randall's Avatar
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    Nothing looks unhappy. The PT passes the neon bulb test. Diodes all seem OK. Perhaps for giggles I will replace the electrolytics, the big one did measure as a short in circuit a couple of times, then it looked OK, not sure why.

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    It's weird, because it WAS working fine.....

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    Supporting Member The Dude's Avatar
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    Those Samxon caps aren't the best quality (mildly put). It wouldn't surprise me if one was leaky.

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    Supporting Member Randall's Avatar
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    That's what I am thinking Dude, can't hurt to order some replacements.

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    It's weird, because it WAS working fine.....

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    Supporting Member eschertron's Avatar
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    Is the PTC device (thermistor?) laying down on top of another component? It looks like a simple jumper under it, and I'm wondering if the thermistor should be sensing a component, or standing up and measuring free air temp.

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    Supporting Member The Dude's Avatar
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    I see thermal paste on the bridge rectifier, so it must mount to a heat sink. I'm guessing the thermistor butts up against that heat sink when the thing is put together.

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    Old Timer tedmich's Avatar
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    NiCd??

    Those bats are OBSOLETE!

    Eventually they will take no charge and charger will die trying. Sadly Ryobi makes no adapters like these
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    My dad just adapted all his old NiCd over to Li ion but his drill goes so fast he cams out everything when trying to drive, so I got him the 3 speed 20V driver

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  9. #9
    Supporting Member Randall's Avatar
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    The BR and the X0405 thyristor are the components mounted to the heat one sink. They are not real close together. I don't see a thermistor.

    "Those bats are OBSOLETE!"

    Tell that to the 40 -50 year old satellites that are still running on NiCads. They can be rejuvenated, I just did it to a "dead" Ryobi 18v battery. Totally dead, wouldn't even turn my drill after 1 hour on charger. Put the battery in the charger with red light on, unplug/replug the charger several times, surging the cells until the grren light comes on. Now a dead battery charges up to 20v, and holds a charge for days. How's that for obsolete?

    Now if I can just get this charger to cool down, I'm good for another few years.

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    It's weird, because it WAS working fine.....

  10. #10
    Supporting Member The Dude's Avatar
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    Thermistor is the yellow device marked PTC on the circuit board.

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  11. #11
    Supporting Member Randall's Avatar
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    Oh. I assumed it was just a cap. It is bent down, but not touching a small diode D9. I wouldn't think that would be the root of the problem here, could it?

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    Supporting Member The Dude's Avatar
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    I wouldn't think so, but anything is possible. You could test it with a hair dryer if you like- PTC, so resistance should increase with temperature. Does it locate near the heat sink as I conjectured?

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    Don't forget the joker g1's Avatar
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    Doubt that the ptc is the issue, more likely the caps as were mentioned.
    But where are you measuring the 3.6mA ? I don't see how that kind of draw would make the transformer get hot. That's like one of the LED's turned on.

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    Old Timer tedmich's Avatar
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    Good luck on keeping them going! Yours is a noble pursuit!
    Actually "nurse maiding" their charging with a CC/CV power supply is sometimes required; the chargers can have too many protection sub routines to allow you the flexibility to do this. Many call it quits at too low a voltage, or if the charging is off schedule.

    Part of this is to avoid fires; I might do the alchemy in an unattached out building!

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    Quote Originally Posted by tedmich View Post
    NiCd??

    Those bats are OBSOLETE!
    From the manufacturer , last I knew you could still get NICD/NIMH packs rebuilt at Batt +/Interstate centers. A little pricey but cheaper than buying new interchangeable Li ion + charger.

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    Last edited by shortcircuit; 08-14-2019 at 02:08 AM.

  16. #16
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    "You could test it with a hair dryer if you like- PTC, so resistance should increase with temperature. Does it locate near the heat sink as I conjectured?"

    It is about 1/2" from the heat sink, but I still don't see how this would make the transformer heat up like this.

    "But where are you measuring the 3.6mA ? I don't see how that kind of draw would make the transformer get hot. That's like one of the LED's turned on."

    Measured across the open fuse at the secondary of the PT. No LEDs are on.

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    It's weird, because it WAS working fine.....

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    Measured across the open fuse at the secondary of the PT. No LEDs are on.
    What matters regarding transformer heating is primary current.

    Please measure with and without secondary load.

    Do you have a "Kill a Watt" meter that reads real input power?

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    Last edited by Helmholtz; 08-13-2019 at 06:21 PM.
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  18. #18
    Supporting Member Randall's Avatar
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    Current measured by placing ammeter in AC line is 0.093A loaded and unloaded, that is with secondary fuse in/out, but not charging a battery. 11.6 watts.

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    Last edited by Randall; 08-13-2019 at 11:41 PM.
    It's weird, because it WAS working fine.....

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    Quote Originally Posted by Randall View Post
    Current measured by placing ammeter in AC line is 0.093A loaded and unloaded, that is with secondary fuse in/out, but not charging a battery.
    At 120V that means an apparent input power of 11.2W, which is quite a lot for a small transformer (what are the core dimensions?). Unfortunately without a "Kill a Watt" we don't know the percentage of real power (heating up the transformer) and reactive power.

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by Randall View Post
    The BR and the X0405 thyristor are the components mounted to the heat one sink. They are not real close together. I don't see a thermistor.

    "Those bats are OBSOLETE!"

    Tell that to the 40 -50 year old satellites that are still running on NiCads. They can be rejuvenated, I just did it to a "dead" Ryobi 18v battery. Totally dead, wouldn't even turn my drill after 1 hour on charger. Put the battery in the charger with red light on, unplug/replug the charger several times, surging the cells until the grren light comes on. Now a dead battery charges up to 20v, and holds a charge for days. How's that for obsolete?

    Now if I can just get this charger to cool down, I'm good for another few years.
    I have a pair of NiCd batteries in a vintage General Radio 1564A Sound & Vibration Analyzer (1/3 Oct, 1/10 Oct, All Pass) that I bought used in Aug 1992 for $40 at a Radio Amateur's Technical Swap Meet TRW in Redondo Beach, CA, and those NiCd batteries are STILL going strong. I don't know who GenRad found as a battery supplier, but they picked a great one! (Gould 9.6V x 2)

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  21. #21
    Supporting Member Randall's Avatar
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    I have 125v here, puts it at 11.6W. Laminate dims are 2.5" x 2.25" x 1.15".

    I just ordered a Kill A Watt meter.

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    Last edited by Randall; 08-14-2019 at 12:20 AM.
    It's weird, because it WAS working fine.....

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Randall View Post
    I just ordered a Kill A Watt meter.
    You're bound to have some fun with that! Excellent piece of kit to have around the workshop & house.

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by Randall View Post

    Measured across the open fuse at the secondary of the PT. No LEDs are on.
    My thinking was that during normal operation, when a LED was on, drawing that kind of current, the supply should not overheat. 3.6mA at the secondary should not pull approx. 100mA from the primary, in any case.
    I think we may be seeing a limitation of the neon bulb test for transformers, as you said it passed.

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    Supporting Member Randall's Avatar
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    "I think we may be seeing a limitation of the neon bulb test for transformers, as you said it passed. "

    I was thinking the same thing.

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    It's weird, because it WAS working fine.....

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    Shorted turns should show in the neon bulb test and would most probably cause way higher input current.

    I think it's just a poor transformer design with relatively high magnetizing current. This is caused by low primary inductance. I also assume relatively high primary DCR.
    DCR times input/magnetizing current squared heats up the winding. (Any chance that the core laminations loosened allowing Es and Is to separate?)

    I just measured a smaller transformer having a core size of 2.15"x1.79"x0.8". Apparent input power at idle is 8.4W, real (heating) power 2.1W. Gets barely warm.

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  26. #26
    Supporting Member Randall's Avatar
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    So what is the bottom line here? I don't remember it always getting hot like this. Is the transformer malfunctioning? I have included a couple of shots of it, but it doesn't look to me like there is anything amiss with the laminates or anything else. I looked it up, it is used in microwave ovens as well as Ryobi chargers, and they are available used for a price.

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    edit: after being plugged in for over an hour out of the case and with secondary fuse out, the laminates measure 128*F at the top of the transformer, somewhat less at the bottom.

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    Last edited by Randall; 08-14-2019 at 10:12 PM.
    It's weird, because it WAS working fine.....

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    Bottom line is that a PT that gets too hot even without a load should be replaced because it is a potential safety risk. Even more alarming if it ran cooler before, as that means that something inside the PT must have changed and might continue changing.

    The neon bulb test shows that there is no problem with the windings. I rather assume that for some reason (temperature, vibration, mechanical shock, corrosion) the effective airgap of the core has increased. This would explain increased input current and transformer dissipation/heating.

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    Last edited by Helmholtz; 08-15-2019 at 10:05 PM.
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  28. #28
    Supporting Member Randall's Avatar
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    "I rather assume that for some reason (temperature, vibration, mechanical shock, corrosion) the effective airgap of the core has increased. This would explain increased input current and transformer dissipation/heating. "

    Well it does live in my garage always plugged in, in SW Florida where it is often hot and humid. Time for a new one I guess.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Randall View Post
    "I rather assume that for some reason (temperature, vibration, mechanical shock, corrosion) the effective airgap of the core has increased. This would explain increased input current and transformer dissipation/heating. "

    Well it does live in my garage always plugged in, in SW Florida where it is often hot and humid. Time for a new one I guess.
    Man if it's been heat indices of 105 to 113 down there like it's been here they need a new word for hot n humid maybe F'ing hot!

    nosaj

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