High Voltage Forum

General electronics => Electronic Circuits => Topic started by: klugesmith on December 05, 2019, 07:25:20 AM

Title: Cost reduction in consumer electrics
Post by: klugesmith on December 05, 2019, 07:25:20 AM
This toaster oven was being thrown away at work, and I took it apart for recycling.  Had been unable to remove the heating rods from inside the oven.

Each plastic end came off with just one screw. 
That revealed internal wiring mostly done without insulation, tab terminals, or even crimp connections.  Assembly by spot welding stiff bare wire from point to point.  Here we see at least five "neutral" and three "hot" connections made that way.

I didn't look at what voltages are present on the circuit board, which I think is an electronic (!) timer for the toaster function. When you push the "start toast" button, an electromagnet holds the switch On until de-energized. Perhaps that's a safety feature.

Only six more screws had to come out to free all sheet metal parts, hinged front door, hinged crumb tray in the floor, etc.  The left ends of heating rods were jumpered together with more welded bare wire.  No expensive sockets to fail. :-)

Seems like a reliable, low-cost way to make an appliance, if nobody wants to fix them when they break.

[edit] the circuit board is, indeed, the toast timer.  Connected to an actual rotary potentiometer on front panel!  It has no connectors, and came out of soldered assembly with wire pigtails that were then welded at final assembly.

Low voltage DC comes from a familiar "hobby" circuit that I'd never before seen in a commercial product.
120 V hot goes through a minimum-width etched trace, as a fuse, then a 1.5 uF series capacitor to be an AC current source, then bridge rectifier.
Title: Re: Cost reduction in consumer electrics
Post by: sjsimmo on December 05, 2019, 11:09:20 AM
Interesting teardown, klugesmith.

I pulled apart a fairly normal pop-up toaster a few weeks back. It was constructed in a very similar manner. had welded wires to connect the heating element, and an electromagnet which held the toast down, whilst also acting as a relay for the 240V. Rather than a capacitor based dropper for the power-supply though, it simply took a tap off the main heating element, and used it as a voltage divider to provide ~12VAC to the control board.
Title: Re: Cost reduction in consumer electrics
Post by: Mads Barnkob on December 05, 2019, 07:33:01 PM
It is quite interesting what you can get away with and still slap a CE (if it was in Europe, I assume you must have similar rules in US?) sticker on a appliance.

For this to be legal there would have to requirements of only using this on a properly fused, ground fault detector (RCD) installation because it does not look like its double insulated, which can lessen some demands for CE mark.

There is another explanation, you can almost get away with anything, there is no check of a product before entering the European market, requirement is only you have a CE mark on, to testify that you obey the rules/laws/standards, but in reality there is little to none reimbursement against those who break it with a intended bad product. It might get removed from a country by local authorities, but a widespread ban of a manufacturer is not viable as there is no juristiction outside of Europe. So the company in Szenchen changes name, rebrands the product and off it goes again :(
Title: Re: Cost reduction in consumer electrics
Post by: the_anomaly on December 06, 2019, 03:35:39 AM
For medical products, IEC standards have creepage and clearance requirements for exposed conductors.  They denote line of sight and surface length from conductor to case.  This is intended for non insulated connection points like flag terminals.  I would expect consumer products have similar standards. 

My current toaster oven's manual requested the unit be run for some time until the elements stopped emitting smoke.  Burning off some manufacturing lubricant I assume. 
Title: Re: Cost reduction in consumer electrics
Post by: davekni on December 06, 2019, 03:48:34 AM
Still safer than early days of residential electrification.  When my great grandparents first got electricity, bath water heating went like this:  Fill tub with cold water.  Take heater from hook on wall and place in tub.  Heater is bare resistance wire wound around a slab of wood, with a cord going to an exposed (no box) knife-switch on the ceiling above the tub.  Close the exposed knife switch and wait for water to warm.  Open the switch and hang the heater board back on the wall hook.  Bathe.

Not that I'm suggesting relaxing standards.  It's just fun to think about where we've come from.
Title: Re: Cost reduction in consumer electrics
Post by: MRMILSTAR on December 06, 2019, 08:35:29 PM
Here is possibly the most dangerous consumer electronic item that I have seen that is available today. There is a Youtube video on the Electroboom channel that shows something very similar to what Dave is referring to except that it is available today on E-Bay and Amazon. Its basically a 240 volt heating element exposed to the water stream housed in a shower head. Apparently they are popular in less-developed countries as a way to get a hot shower. I wonder how many people have been electrocuted by this device?

Title: Re: Cost reduction in consumer electrics
Post by: station240 on January 03, 2020, 09:57:56 AM
I've seen toaster ovens with short lengths of solid wire welded between adjacent elements.
But never that extensive, or over longer distances.

Also seen spade terminals welded to heating elements, at right angles so you can't just slide the element out.
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