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 Good Ideas done Badly

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Bad Floor Sweeper  
I while back I bought an electric broom type floor sweeper.  We needed something simple and light weight to pick up dog hair, crumbs and dust from the hard wood floors and the various throw rugs.  The “Swivel Sweeper” seemed like it would be perfect for this light duty application.  After giving the 7.2v battery pack a full over night charge, I turned the thing on and put it to work.  It seemed to do OK in picking up small bits and dog hair and it was easy to use.  But, after just 3 minutes of operation, it turned itself off.

The way the motor slowed then died, suggested that the device contained positive temperature coefficient thermistor as a thermal fuse.  The fuse would turn off the motor if it over headed but this thing was not working hard when it was just sucking up dirt from hard wood floors.  After a few minutes, I was able to turn it on again.  But, just like the first time, the motor cut out after about 3 minutes of operation.  The engineer in me pushed for a quick experiment.  I gave it a full 30 minutes of rest, raised it off the ground, turned it on and timed how long it ran before turning off again.  Sure enough, in only 3 minutes, it turned off again.  Good Grief!  This is not right.  I needed to find that pesky thermal fuse and bypass it if I was ever to get this any use from this broom.

Swivel Sweeper
I would have designed to sweeper to place the fuse inside the 6 NiMH cell battery pack.  There it could protect the pack from excessive high currents both during charging and discharging. But, the pack was housed inside a plastic case glued together.  It only took a few minutes of sawing to cut the housing into two manageable parts. 
Inside, I saw 6 1300ma-hour AA NiMH cells. There was no thermal fuse.  The 1300ma-hour capacity was about half the capacity of the more common 2500ma-hour devices found in a lot of battery packs. 

Also, it looked like the battery housing had room for two more cells, which could have brought the operating voltage up to 9.6v.  Clearly the manufacturer went for the cheapest parts possible in this product. 

Sweeper Battery Pack
Sweeper Battery Pack Sweeper Battery Pack
I wrapped some tape around the battery pack so it could be reused.  I then shift my attention toward the battery pack connector and on/off switch.  Unlike the battery pack, two screws held the pack together.  Once opened, there I saw what I was looking for, a thermal fuse (yellow part in photo).  I cut out the device and soldered the wires directly to the on/off switch.  After I reassembled the switch housing, and turned on the sweeper, it ran for more than 20 minutes without a hitch.

The thermal fuse turned an otherwise useful product, into a worthless piece of trash.  The manufacturer should be ashamed that the selection of an improper thermal fuse made the whole product worthless.  Of course, the Swivel Sweeper was made in China, where quality control is non-existent.

Sweeper On/Off Switch w Thermal Fuse

 

August 2011

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