I was given a small, 12-bottle thermoelectric wine fridge from a friend who retrieved it from a metal recycler. It was a nice black countertop unit with a glass door and an LED temperature readout with controls at the top. My friend thought I would probably be interested in the solid-state cooling unit if it were still operational, so I checked it out.
The first thing I tried was to just plug it in and see if anything worked. There were no lights or fan. Maybe the main fuse was open? There wasn't a fuse anywhere on the outside. There were two on the switching power supply board.
I didn't relish digging into someone else's switching power supply if the main fuse was gone, and I decided I would give up if the fuse were missing. However, I found that the fuse had blown on the DC side of the supply. The fuse was soldered into the circuit board cordwood style with heat shrink over it, with one end sticking up in the air.
I dissected the fuse and found that it was a fast blow 3A fuse. I decided it was worth a shot, so I replaced the fuse with a new one. I was careful to not overheat the end of the fuse near the circuit board. The unit worked, but I was still wondering why the fuse blew. Was there was a condition that caused the unit to draw too much current?
I decided to monitor the current drawn by the fridge and discovered that the nominal draw was very close to the current rating of the fuse. Any design engineer knows to use a fuse rated at least 125 percent over the actual current. I installed a four-Amp fuse, and now the unit has worked for quite a while.
I got looking around and noticed that this same model had a lot of failures. I even found an identical broken one on Freecycle -- same problem. My friend and I now both have working wine fridges. All it cost was a bit of time and two new fuses.
This entry was submitted by Jack Gilmore and edited by Rob Spiegel.
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In many ways, fuse ratings is an art form. Inrush current, load current, spikes, motors starting up, and numerous other factors come into play. You have to consider the steady state of the device, but what if all peripheral functions operate at the same time? So rating a fuse can be tricky. I assume the cooler design engineer was looking at the steady state current and not considering inrush from start-up. But then again, running a fuse so close to steady state was foolish, unless he was forced to use wiring or other devices that could not handle much more current. Then. that was just plain stupid, but cost effective. Fused flex on start-up or an increase in current, so they will wear out if they aren't designed properly. But, if there was no warranty, then who cares?
I wish I could find a Ferrari that someone threw away because of blown fuses. I am sure I could find the fix...
Nice catch--both for figuring out the fuse issue and for scoring a working wine fridge. Seems like a pretty basic case of specing the wrong part and overlooking fundamental design principles. You have to wonder if it's a case of oversight or a design choice caused by pressure to reduce costs. Either way, a pretty overavoidable design flaw.
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