How to test a heating element

[amateur_24]

Hi
We have a ninja air fryer which has blown it's internal fuse. It's a mains rated 3.15a fuse.

Afaik a heating element is just basically a giant resistor. So I measured it's resistance which worked out to be 31 ohms.

Now am I correct in saying at 230v, it will draw over 7Amps. If so then I believe I have found the problem

 

[rjenkinsgb]

Yes, that sounds right.

Heating elements, lamp filaments etc. are normally "positive temperature coefficient", which means the resistance increases as they get hotter, and the current reduces somewhat - but it's still got to be able to warm up in the first place!

 

[Nigel Goodwin]

Yes, is an element was faulty it will either be open-circuit, or short ed to earth - check for a reading from the element to the earth connection or metal body work.

31 ohms sounds perfectly normal.

 

[alec_t]

It is common for the resistance wire in a heating element to short to the casing. This should blow a fuse or trip a circuit-breaker.
31 Ohms suggests a 2kW-rated element.

 

[Nigel Goodwin]

It is common for the resistance wire in a heating element to short to the casing. This should blow a fuse or trip a circuit-breaker.
31 Ohms suggests a 2kW-rated element.

So does an air fryer

 

[rjenkinsgb]

Agreed, the 3.15A sounds more like an electronics fuse than main heating element power.

(I was still in somewhat zombie mode at 4am, sorry).

 

[MaxHeadRoom78]

As per the double post, generally the fan stops working or is clogged.
Most counter top kitchen appliances, coffee makers et-al, have these fuses fitted for safety.

 

[Nigel Goodwin]

Agreed, the 3.15A sounds more like an electronics fuse than main heating element power.

(I was still in somewhat zombie mode at 4am, sorry).

In his other thread he shows a thermal fuse, so it's likely there is no 3.15A fuse?, which as you say was a common CRT TV fuse size

 

[ramondo]

The 3.15 fuse appears to be mounted to the circuit board as FS1.. Why not place a 100 watt bulb in series with now missing thermal fuse and see if any other problems show up. (Fan,short,relay,etc).

 

[amateur_24]

I don't have a 100 watt light bulb.

I shorted both thermal fuses. Is it a good idea to have a thermal fuse on both the line and neutral? I thought it was frowned upon.

Anyway, it switches on now and the fan is working when I press start. If it fully works after replacing the thermal fuse, I will be stunned. I would be interested in knowing why all three fuses failed and yet there is no sign of a fault.

Seems coincidental to me.

 

[Nigel Goodwin]

There's a VDR across the mains, a mains spike could cause the 3.15A fuse to blow - but the thermal fuses would take more than that to blow (multiple numbers of seconds - perhaps minutes - for them to get to a high enough temperature). I wonder if perhaps the 3.15A fuse blew, and somehow left the element running with no control and no fan?.