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Posted By Topic: LED flickering when cook top turns on

Apr 25 2018 18:21

I was wiring my friends new kitchen and the last thing they had to order was the cook top.

We were using the existing 32A supply to the old free standing stove.

They ended up ignoring what I said about the maximum size and got a 7.5kW induction cook top.

I wired it up and said they will probably get some nuisance trips but when you turn it on it causes the LEDs in the kitchen to flick on and off.

It doesn\'t effect any other LED light that are installed in the house (they are a different type though)

The lights and cook top are different circuits and after it is on every runs fine.

Has any one encountered something like this before? Is it just the transformers in the LEDs not liking the dip in power as the cook top starts?

I told them to see if they can take the cook top back because it\'s too big for the circuit anyway.

Apr 25 2018 19:23

its the led\'s fault, you could try fitting a clipsal CAP31, otherwise your changing the drivers or lights.

Apr 25 2018 20:10

Yes, I agree, the LEDs would usually be the problem, have you sighted the SDoCs? Induction cooktops may be rated at 7.5kW but I have never tested a single hob that draws that sort of current, the load sharing function switches in well ahead of that rating.

Apr 25 2018 23:51

What about induction? Does the oven circuit run parallel to the switched wire, or strap wire if there is a 2 way? If there is a 2 way is it wired in a way to reduce induction?

Apr 26 2018 06:46

The cables would definitely be running side by side for a short time where they leave the switch board. But they would run beside all the cables that go to that end of the house.

Apr 26 2018 07:50

Hoiho why are you saying 7.5kW is too big for the circuit? It works out to exactly 32A - and besides that, the circuit breaker is there to protect the cable and doesn\'t have to be sized for the full load of the cooktop.


Apr 26 2018 08:45

There is also a wall oven on the circuit. They replaced a free standing range for. Oven and cook top. So both combined is over the 32A. That would only be with both units going full noise though.

Apr 26 2018 18:35

\"The cables would definitely be running side by side for a short time where they leave the switch board. But they would run beside all the cables that go to that end of the house.\"
It\'s the switched wires under inductance that cause the flickering. Other light circuits may have more load on them meaning they are not affected the same. 2 Way strap wires cause this also if they are not wired with the common wire in between the other two conductors.

Apr 27 2018 08:42

voltage on 2-way straps etc is not inductance, it\'s capacitance.
It can cause CFLs & LEDs to flicker when switched \"off\", but unlikely to be related to flickering when switched on,
The timing indicates that the load of the hob may be dropping the voltage, with the LED drivers taking a moment to compensate.

Apr 27 2018 11:00

There is no 2-way switching, It is only a single switch controlling the kitchen lights. I will try and replace them with other LEDs in the house and see if this changes how they operate.

Apr 27 2018 12:54

One thing that you could do is a series of efli tests to rule out a bad connection either on the supply phase or neutral or any point in between.

Just test at the hob and work your way back to the main switch. If the efli is higher than expected there could be a bad connection in the supply pillar / pole fuses.

Apr 27 2018 13:17

Does the voltage dip at the terminals on the light when you turn on the hob?

May 15 2018 13:32

Sorry for the late reply,

The voltage does not dip when the cook top turns on. and I have done efli tests on the surrounding power points but not on the actual cook top circuit.

The lights stopped doing it for a while and now hardly do it at all.

May 16 2018 08:14

Funnily enough I had this happen the other day. A customer mentioned that his kitchen lights \'dimmed\' when the induction hob was turned on. My first thought was small mains up a long driveway however I checked voltage & both circuits seemed fine.

May 16 2018 08:41

Those of you who are witnessing this phenomena; next time you\'re on the troubleshoot and it happens by the cooktop but not to LEDs further away \"but they are of a different type\": Could I ask you to swap the lamps over to see if the fault follows the lamp, or the location please.

I have a (fairly wild) theory on what is happening here, but I\'d like a bit more evidence before I suggest it. This has occurred to me because of problems these induction cooktops things cause in TV studio settings.

I don\'t think this is related to the installation, or to the supply, or to voltage drop issues.


May 16 2018 10:37

A harmonic?

May 16 2018 14:10

Wilder than that :)

May 16 2018 17:53

In my experience the hob & oven combined on a 32A supply is not the nightmare your trying to turn it into.

Usually at most people will only use a max of 2 elements at the same time (occasionally 3) but not for very long.

So pretty much you’d have to have all four elements & the oven going full tit to blow the fuse - will hardly ever happen - maybe once at Xmas at the very worst.

No need to create drama where there isn’t any.

May 17 2018 22:37

dbuckley are you pointing towards the possibility that the induction the hob creates is enough to generate a current in the light fittings or associated wiring?

I Linked a site below that mentions that the EMF from induction hobs may be magnified if; an incorrectly sized pan is used (too small for the hob), a pan with a bottom that is warped or a pan made of non ferromagnetic material is used. Watch out if you have a pacemaker!

May 21 2018 15:24

Satobsat enquires:

> dbuckley are you pointing towards the possibility that the induction the hob
> creates is enough to generate a current in the light fittings or associated wiring?

You are getting warm there with the induction word.

Most induction hobs appear to be a coil driven at about 24KHz with 2.something KW of power behind them. Which is a nasty thing with oodles of power. And the metalwork is also rattling round at 24KHz, but you can\'t hear it, obviously because it is above our hearing range.

However, it is extremely unlikely that this magnetic field could interfere with ordinary installation wiring, because although TPS isn\'t twisted pair, it is two cores parallel and close to each other with current flowing in opposite directions, so any magnetic field impinging on the TPS that would induce current would induce almost identically in both cores, so the sum effect would be nowt.

Not all LED lamps are equal some are very low tech and others are quite sophisticated with interesting electronics in them.

My crazy notion is that this field might be large enough to magnetically couple to something like a PCB trace or an inductor in a sophisticated LED lamp, and disturb the operation of the electronics. It\'s a damned long shot, I grant ye, which is why I\'m curious to know if the effect is related to a particular type of LED lamp.

The other (perhaps more likely!) possibility is that there actually is a significant voltage disturbance present but of such short duration that the test equipment is not noticing it, one would need a disturbance meter and/or a scope to discover the events.


May 22 2018 20:47

dbuckley what about induction from the hob generating current in an inductor in the LED driver?

May 30 2018 09:36

Once again sorry for the late reply. I forget to check this and don\'t get a notification when a reply is made.

The installation has been working fine the last few weeks with no interference with the LEDs.

Still not sure what was causing it to happen but what ever it was has stopped doing it now.