Troubleshooting stove heating elements

[DaveC426913]

TL;DR

Stove elements take an hour to boil water.

Plz forgive. Old man fingers on young whippersnapper phone kb.

This stove takes an hour to boil a pot of water. I'm looking at replacing the burners right now. They look brand new (top) but who knows?

I bought this one (bottom) which is not exactly the same one. The prongs will fit but the new one has that box thing and it has two coils ,not one (apparently for lo and hi settings). Presumably, the box acts as a splitter but might it also act as a thermostat?

Anyway, is it safe to try the new element without blowing up the stove?

 

[Nugatory]

Odds are that the problem is not in the burner, but rather in the controls. Before I replaced the burner I would try digging up the stove manufacturers spec for the resistance of the burner element, check with a VOM.

(And even though this forum is populated by mostly competent people, I wouldn’t trust advice about parts interchangeability that doesn’t come with part and model numbers).

 

[DaveC426913]

I put in this new element and boiled a pot of water in six minutes flat.

I suspect that the box on the original is a thermostat that triggers the second element for cooking on hi. For some reason, it doesn't seem to be kicking in - so on hi I'm only getting half the output.

 

[Averagesupernova]

As far as I know most older cook tops of this style vary the duty cycle depending on how far you turn the knob. While technically it is PWM, it occurs at a fairly slow rate maybe between .25 and several Hertz. I've never seen one with a box underneath like that. I'd be mighty appreciative if you cracked it open to tell us what's inside.

 

[DaveC426913]

PWM?

As soon as I am satisfied the new one works under field conditions, l plan to (get permission to) bust the old one open.

 

[hutchphd]

I used to have a stove that had a "dual" burner where you could select either a six inch diameter center element (for a small pan) or the full eight inch burner. It was not that useful, and I can't remember where the switch was. Could that be what this is?

 

[DaveC426913]

Looks like a thermostat.

Presumably, normally open (circuit) , but closes (electrically ) when sufficently hot.

 

[Averagesupernova]

PWM?

Pulse Width Modulation. Did you think I meant Pretty Weird Mechanism?

 

[Baluncore]

Presumably, normally open (circuit) , but closes (electrically ) when sufficently hot.

There are too many ways to interpret the English language.
"Normally closed" NC, means the second element has power when cold, but the switch contacts open to disconnect the power when hot.

It is a thermostat that regulates temperature by connecting the second element when below temperature. It will switch at the thermal time constant of the controlled element and sensor, probably about a 15 second period. So, yes it is an early PWM or bang-bang controller.

 

[DaveC426913]

There are too many ways to interpret the English language.
"Normally closed" NC, means the second element has power when cold, but the switch contacts open to disconnect the power when hot.

Yeah. As I was writing, I realized that the terms could apply to circuitry or to physical flow. And they have opposite meanings.

An 'open circuit' means nothing passes, whereas an 'open flow' generally means something passes freely.

And I realized I wasn't actually sure which, exactly, this device was doing. Electricity? Or heat? Where exactly does the electricity in an element get converted into heat? Before or after this switch?

It is a thermostat that regulates temperature by connecting the second element when below temperature. It will switch at the thermal time constant of the controlled element and sensor, probably about a 15 second period. So, yes it is an early PWM or bang-bang controller.

I don't follow. I assumed this was a heat thermostat that turned 'on' the second element when the first one got hot enough - to provide a "high" heat setting.

 

[Baluncore]

Where exactly does the electricity in an element get converted into heat? Before or after this switch?

The heat appears along the internal resistance wire of the element. The heat passes radially through the mineral insulation to the outer heated radiating envelope, that is earthed through the stove chassis.

I don't follow. I assumed this was a heat thermostat that turned 'on' the second element when the first one got hot enough - to provide a "high" heat setting.

Either is possible, but I assume it was designed for a fast start, then lower power to simmer. It might be designed as you suggest for more heat, but with reduced cold start current.
When it is cold, measure the resistance across the external element terminals. Then measure the resistance across the internal switched element terminals. If they are the same it is my fast start scenario, if they differ it is your initial surge current reduction scenario, or a faulty thermostat.

 

[DaveC426913]

Pulse Width Modulation. Did you think I meant Pretty Weird Mechanism?

I was working on "Powerful Wave Motion" Gun.

 

[DaveC426913]

The heat appears along the internal resistance wire of the element. The heat passes radially through the mineral insulation to the outer heated radiating envelope, that is earthed through the stove chassis.

:slaps forehead:

It didn't occur to me that the element wasn't homogenous.
(My dumb brain was trying to reconcile either:
- heat being conducted from the terminal all the way through the coil's length,
or
- a coil that is, itself, electrically conductive.)

Of course there's a conductive wire running through the its core, electrically insulated from the ceramic sheath, so as not to zonk every hapless user.

When it is cold, measure the resistance across the external element terminals. Then measure the resistance across the internal switched element terminals.

Er. Ya lost me. external/internal switched?

 

[Baluncore]

Er. Ya lost me. external/internal switched?

I can't see in the picture which spiral is which, but the thermal switch controls one element of a two element assembly, I think it is the inner turns that are switched.

The assembly has two external terminals. Follow one element from a terminal, through the thermal switch, and around and around to the other terminal. That is the controlled element.

Then follow the other element from one terminal to the other terminal, I think that element is the outer turns.

When the thermal switch conducts, the two elements are in parallel.