Handheld vacuum cleaner kills power adapters (With schematic)
Good day folks. A friend of mine asked me to take a look at this handheld/upright vacuum cleaner which supposedly has power adapter issues and would no longer charge. Upon first inspection, its original 14v/400mA adapter was dead - the thermal fuse in the transformer's primary windings was open. I went out of my way to replace it and indeed brought the adapter back to life. I gave it back, it worked fine for a few days, then the chap calls me again and tells me the vac no longer charges again......
Ok, so this time I asked him to bring in the motor part as well since I thought something must be drawing excess current or is shorted and that causes the adapter to overheat and blow the thermal fuse, which was open again, by the way. I opened up the vac today and here's what it's inside....pretty basic, not that I expected more, but nothing looks out of the ordinary either. The battery pack was replaced at one point after it would no longer hold a charge, as it happens with NiMhs, and indeed it works now, but it doesn't charge back for some reason.
I doodled a schematic myself just out of curiosity and to better understand how it works and how it's supposed to charge: when you close the power switch on the handle, current from the battery goes straight to the motor - easy enough. When the charger is plugged in, current starts flowing through R2 and D1 to the battery. When discharged, the battery's resistance to GND will be low, so LED1 also comes on...I THINK. Not sure what happens with Q1 and those zenners on the right there...looks like some sort of regulator, but I can't understand how it works....
Another thing I don't get is SW2+ and SW2- points: there's a set of 4 metal contacts on the bottom of the motor part - these mate up with a set of contacts on the floor adapter/dock. Two send power to the roller brushes and two connect the second power switch on the top of the handle, though this last part I'm only speculating, since I don't have the dock part too, so I don't know if there's additional components in it too, though I doubt it. I imagine when the base of Q2 is pulled low, Q2 conducts (since it's PNP A1270) and closes the relay. To do this, I was expecting the switch on the top handle to simply close a path to GND across those two metal plates, but SW2+ goes to the adapter input...what gives ? :|
What I'll try is to drain the battery and charge it up with my bench supply in place of the power adapter to see what the current draw is. Could've just been a bad adapter, BUT here's the catch: the owner also tried it with a 12v SMPS adapter while I was fixing the original one, which although didn't match the voltage precisely, was good enough for a test and I think what happened was the vac didn't charge and also shut down that one too at some point, pointing to overcurrent. It only worked after I patched up the original one for a little while, until it died again....
Any help with this issue is appreciated, as always. Cheers guys. Thanks
Ok, so this time I asked him to bring in the motor part as well since I thought something must be drawing excess current or is shorted and that causes the adapter to overheat and blow the thermal fuse, which was open again, by the way. I opened up the vac today and here's what it's inside....pretty basic, not that I expected more, but nothing looks out of the ordinary either. The battery pack was replaced at one point after it would no longer hold a charge, as it happens with NiMhs, and indeed it works now, but it doesn't charge back for some reason.
I doodled a schematic myself just out of curiosity and to better understand how it works and how it's supposed to charge: when you close the power switch on the handle, current from the battery goes straight to the motor - easy enough. When the charger is plugged in, current starts flowing through R2 and D1 to the battery. When discharged, the battery's resistance to GND will be low, so LED1 also comes on...I THINK. Not sure what happens with Q1 and those zenners on the right there...looks like some sort of regulator, but I can't understand how it works....
Another thing I don't get is SW2+ and SW2- points: there's a set of 4 metal contacts on the bottom of the motor part - these mate up with a set of contacts on the floor adapter/dock. Two send power to the roller brushes and two connect the second power switch on the top of the handle, though this last part I'm only speculating, since I don't have the dock part too, so I don't know if there's additional components in it too, though I doubt it. I imagine when the base of Q2 is pulled low, Q2 conducts (since it's PNP A1270) and closes the relay. To do this, I was expecting the switch on the top handle to simply close a path to GND across those two metal plates, but SW2+ goes to the adapter input...what gives ? :|
What I'll try is to drain the battery and charge it up with my bench supply in place of the power adapter to see what the current draw is. Could've just been a bad adapter, BUT here's the catch: the owner also tried it with a 12v SMPS adapter while I was fixing the original one, which although didn't match the voltage precisely, was good enough for a test and I think what happened was the vac didn't charge and also shut down that one too at some point, pointing to overcurrent. It only worked after I patched up the original one for a little while, until it died again....
Any help with this issue is appreciated, as always. Cheers guys. Thanks
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