Electronics > Beginners
Calculating value of resistors in parallel
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soldar:
It seems these hot plates often have the problem that the selector switch burns out and is difficult or expensive or impossible to replace.

I have replaced it with four switches, as shown. Now I think I could replace the four switches with four relays, solid state or electro-mechanical, and control the relays with a very low current single pole, eight position switch. A bunch of diodes would select which relays would be activated in each position.
HackedFridgeMagnet:

--- Quote from: soldar on January 04, 2019, 11:14:45 pm ---It seems these hot plates often have the problem that the selector switch burns out and is difficult or expensive or impossible to replace.

I have replaced it with four switches, as shown. Now I think I could replace the four switches with four relays, solid state or electro-mechanical, and control the relays with a very low current single pole, eight position switch. A bunch of diodes would select which relays would be activated in each position.

--- End quote ---

Selector switch burning out, yes. Mine oven has done it twice. It's selector switch is about 10 pole, single throw , with cams turning it off and on for about 8 positions. Both times I have reorganised and simplified the wiring to adapt to the burnt out positions. With a corresponding loss of features.
From memory it switches Neutral as well as Active to give different control outcomes. 

Because I like my oven I might do something similar to your relay idea, it is a double oven and it was a bit of trouble to adjust the cabinet to fit, so a new control solution would probably be simpler.
ps. You have to be sure the over temp cutout and high temp cooling fan are fail safe though.
soldar:

--- Quote from: HackedFridgeMagnet on January 05, 2019, 03:29:13 am --- Selector switch burning out, yes. Mine oven has done it twice. It's selector switch is about 10 pole, single throw , with cams turning it off and on for about 8 positions. Both times I have reorganised and simplified the wiring to adapt to the burnt out positions. With a corresponding loss of features.
From memory it switches Neutral as well as Active to give different control outcomes. 

Because I like my oven I might do something similar to your relay idea, it is a double oven and it was a bit of trouble to adjust the cabinet to fit, so a new control solution would probably be simpler.
ps. You have to be sure the over temp cutout and high temp cooling fan are fail safe though.

--- End quote ---
The switches carry big currents and will fail sooner or later because the contacts burn out.  Electro-mechanical relays might have the same problem and it is probably best to install solid state relays well oversized and they should last forever. Just make sure they have good heat sinking.

There are quite cheap rotary single circuit switches on ebay but they are plastic and need to be mounted where they will not get too hot.

If you install the relays in the same (electrical) place as the switches are then there should be no problem with protections, fans, etc.

My original switch had one more position that would require one more relay, 5 instead of 4, but I figure it is not worth it as I have enough choice with the four relays.

Of course, another alternative option for power control is to just set it to the max power and use a Triac power control but I prefer not to do that because of the poor power factor and the noise it introduces in the line but you can ameliorate that with a good filter.
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