DavyS Posted July 1, 2022 Share Posted July 1, 2022 Portable induction hobs control the temperature of the pan by using pulse-width modulation. So they vary the period between when off and fully on. So, for instance, if you have a 4kW induction hob and you turn the power down to 50% then the induction will be on for only 50% of the time - and during those pulses would be fully on at the maximum power rating. So a 4kW (16A) induction hob will use the full 4kW for short periods even when on a low setting and could blow the fuse on a 10A EHU. Unless of course, the pulsing is very rapid and so the fuse does not have time to over heat. So what I am asking is has anyone used a induction hob which is rated above the EHU max without problems when set to lower power? That would be a power exceeding 2.4kW on a 10A EHU. Link to comment Share on other sites More sharing options...
stevec176 Posted July 2, 2022 Share Posted July 2, 2022 Silly question, but why not use one that does not exceed the amperage? Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 2, 2022 Share Posted July 2, 2022 The trip is designed to protect the circuit wiring which, under overload conditions, would heat very rapidly. So to prevent this the trip will respond to the overload almost instantly, a matter of a few fractions of a second. It is therefore extremely unlikely, IMO, that any appliance rated above the trip capacity would fail to trip the circuit breaker. As these trips are designed to fail safe, they will tend to trigger before, and not when, their rated capacity is reached, especially as they age. As you will have no knowledge of the age of a particular trip at a given site, it would be prudent to avoid connecting even a 10A appliance to a 10A rated breaker. So, as already suggested, either use a lower than 10A rated appliance, or an alternative means of heating your pan. Link to comment Share on other sites More sharing options...
DavyS Posted July 2, 2022 Author Share Posted July 2, 2022 As suggested, I could buy a low power induction hob but then would have low power even when connected to a 16A EHU. So my question is can I buy a 3kW induction hob and turn it down to 2.4kW when connected to a 10A EHU? Link to comment Share on other sites More sharing options...
DavyS Posted July 2, 2022 Author Share Posted July 2, 2022 MikeFitz states "The MCB needs 3 to 5 times rated current for an instant trip, 2 times rated current takes around 100 seconds and 1.2 times rated current up to 10,000 seconds, to trip. Thus its quite possible taking a continual 11 or 12 amps will not trip a 10 amp breaker during a cooking session ." Which would indicate to me that a 2.8kW induction hob run at reduced power will not trip a 10A EHU. Brian Kirby, on the other hand, states that the MCB in the EHU will trip in "almost instantly, a matter of a few fractions of a second." Which would indicate that if the pulse-width modulation, when using reduced power, was wider than a few fractions of a second then the EHU would trip. Confusing! Link to comment Share on other sites More sharing options...
weldted Posted July 2, 2022 Share Posted July 2, 2022 We have an portable induction hob, rated at 1800 w. When using it through our inverter it runs at its maximum current till temp is reached whatever setting the control knob is on. So turning it on at its lowest will cause it to draw 1800 w until the set temp is reached then current demand drops until it falls below a set temp the comes back on again at full power. It cycles like that until turned off. The old hotplate one we had before does exactly the same. We can tell through our control panel exactly what current is being used. Link to comment Share on other sites More sharing options...
thebishbus Posted July 2, 2022 Share Posted July 2, 2022 Yes, that is how hotplates ,ect work, they pulse on and off at full power, the time length of the pulses adjusted by the control sets the heat level. Brian B Link to comment Share on other sites More sharing options...
DavyS Posted July 2, 2022 Author Share Posted July 2, 2022 "So turning it on at its lowest will cause it to draw 1800 w until the set temp is reached then current demand drops until it falls below a set temp the comes back on again at full power. " So does it not have a power control setting so that you can limit the max power used? Link to comment Share on other sites More sharing options...
DavyS Posted July 2, 2022 Author Share Posted July 2, 2022 weldted - 2022-07-02 2:02 PM We have an portable induction hob, rated at 1800 w. When using it through our inverter it runs at its maximum current till temp is reached whatever setting the control knob is on. So turning it on at its lowest will cause it to draw 1800 w until the set temp is reached then current demand drops until it falls below a set temp the comes back on again at full power. It cycles like that until turned off. The old hotplate one we had before does exactly the same. We can tell through our control panel exactly what current is being used. So does it not have a power setting so you can limit the max power used? Link to comment Share on other sites More sharing options...
mikefitz Posted July 2, 2022 Share Posted July 2, 2022 A MCB does not trip the instant the current exceeds the rated value. Whilst it's possible a poor quality or faulty unit may trip at lower values, this is unlikely. In the UK all campsite supply boards are tested at regular intervals and the MCBs must meet specification. There are different standards for MCB, and the most sensitive is type B, this the type normally used in domestic appications. The performance curve is attached, showing the time/ current relationship. Mike Link to comment Share on other sites More sharing options...
thebishbus Posted July 2, 2022 Share Posted July 2, 2022 Davy S Non of the control settings between min and max vary the percentage of power that the hob draws. it varies the amount of time that the hob draws full power when on the live side of the switching cycle. Thus varying the heat. Brian B. Link to comment Share on other sites More sharing options...
DavyS Posted July 4, 2022 Author Share Posted July 4, 2022 thebishbus - 2022-07-02 11:05 PM Davy S Non of the control settings between min and max vary the percentage of power that the hob draws. it varies the amount of time that the hob draws full power when on the live side of the switching cycle. Thus varying the heat. Brian B. Brian, yes that's my understanding too. When on an 'on' pulse then the induction hob drawers full power. So my question is how wide are the pulses? If less than a few seconds then the MCB will not trigger. Link to comment Share on other sites More sharing options...
thebishbus Posted July 4, 2022 Share Posted July 4, 2022 Cannot help there, seems to be so many variables, effecting the pulses, res frequency, heat required , temp and size of cooking utensil ect. I see some claim to be constant power non pulsing at low power settings. Needs some tech bod to come along and explain it. Brian B. Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 4, 2022 Share Posted July 4, 2022 DavyS - 2022-07-02 1:56 PM Brian Kirby, on the other hand, states that the MCB in the EHU will trip in "almost instantly, a matter of a few fractions of a second." Apologies Davy, and apologies for the late response (Domestic disaster struck!). I had in mind the response times for RCDs, and hadn't realised that MCBs behaved as Mike describes. As Mike knows far more about electricity than I do, please disregard my comments and follow Mike's advice. Link to comment Share on other sites More sharing options...
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