NiCad charger getting hot

[Randall]

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?

[The Dude]

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.

[Randall]

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.

[The Dude]

Those Samxon caps aren't the best quality (mildly put). It wouldn't surprise me if one was leaky.

[Randall]

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

[eschertron]

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.

[The Dude]

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.

[tedmich]

NiCd??

Those bats are OBSOLETE!

Eventually they will take no charge and charger will die trying. Sadly Ryobi makes no adapters like these

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

[Randall]

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.

[The Dude]

Thermistor is the yellow device marked PTC on the circuit board.

[Randall]

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?

[The Dude]

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?

[g1]

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.

[tedmich]

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!

[shortcircuit]

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.