What does the variable resistor on the PCB of an induction cooktop do?

Thread Starter

LMF5000

Joined Oct 25, 2017
108
As per the title, I have a brand new portable induction cooktop that isn't running right (it ignores the temperature setting, and the real power consumption is far lower than the power number indicated on the display), and on disassembly I found a variable resistor on the main circuit board.

I've indicated it on the attached image, which I took from an aliexpress listing of a circuit board that looks similar to mine (original link here).

I tried turning it and going counterclockwise didn't seem to do anything. Going full clockwise reduced the power consumption on turn-on from 1060W down to about 850W and made the high-pitched noise of the coil whine a little louder - both times with the display indicating the default setting of "1600W".

FWIW the induction cooktop is a Royalty Line EIP 2000. It claims 2000W of power but my inline power meter never measured more than 1500W (with the display indicating "2000W"). After adjusting all the way clockwise it draws 1200W with the display indicating 2000W.
 

Attachments

Papabravo

Joined Feb 24, 2006
18,094
The net result of all this detective work is....you paid for something you apparently didn't get. Just get your money back and next time buy from a reputable source. Alternatively do the detective work before you buy.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
108
The net result of all this detective work is....you paid for something you apparently didn't get. Just get your money back and next time buy from a reputable source. Alternatively do the detective work before you buy.
Believe me, I did all the detective work I could. There's no useful information about this nor the other hobs I was considering. The other one available to me in my country is the beper 2000W model, and there doesn't exist a single video of it on the internet nor a single photo of the underside of the unit. At some point I had to take the leap and chose this one, and I guess I leapt wrong. I didn't expect the manufacturer to blatantly lie about the specs. Hindsight is 20/20!
 

jayanthd

Joined Jul 4, 2015
945
Believe me, I did all the detective work I could. There's no useful information about this nor the other hobs I was considering. The other one available to me in my country is the beper 2000W model, and there doesn't exist a single video of it on the internet nor a single photo of the underside of the unit. At some point I had to take the leap and chose this one, and I guess I leapt wrong. I didn't expect the manufacturer to blatantly lie about the specs. Hindsight is 20/20!
If ADC is printed near the VR then it is for the ADC input calibration or VREF setting.

The ViPer chip is the SMPS chip. The Ferrite trf is the SMPS transformer. The other DIP IC is the uC. There is 25 or 35A bridge rectifier and power IGBT fixed to the heatsink.

Zoom the VR portion and show a new image of it.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
108
Is that with a proper induction type pan on the burner?
Yes, with multiple types of pots and pans, all officially induction rated. The PCB inside is exactly like the AliExpress link for the 1500W controller board. Therefore I conclude the 2000W advertised everywhere was probably just fancy marketing.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
108
If ADC is printed near the VR then it is for the ADC input calibration or VREF setting.

The ViPer chip is the SMPS chip. The Ferrite trf is the SMPS transformer. The other DIP IC is the uC. There is 25 or 35A bridge rectifier and power IGBT fixed to the heatsink.

Zoom the VR portion and show a new image of it.
Here you go (not sure which is the VR portion so I'm attaching all the pics I have)-
 

Attachments

Thread Starter

LMF5000

Joined Oct 25, 2017
108
Yes.
The same as when they advertise 100W output from an audio amp which is powered from a 36W supply (which I recently had experience with).
Well, that's slightly understandable in audio if they mean peak sound power (which is basically a meaningless number because it's an impulse measurement; however they should give RMS and PMPO outputs - the PMPO can be many times bigger than the RMS). Same as how every inverter has a "max" rating of double what it can actually maintain continuously or every generator whose number is always something like 25% more than its continuous running watts - but at least they're upfront in the documentation. In this case they sold a 1500W hob as a 2000W one, complete with a display that lies to you.
 
Last edited:

MrSalts

Joined Apr 2, 2020
1,541
Believe me, I did all the detective work I could. There's no useful information about this nor the other hobs I was considering.
Now, you've learned the lesson in detective work...
Finding "no useful information" shouldn't be considered an endorsement.
 

Thread Starter

LMF5000

Joined Oct 25, 2017
108
Now, you've learned the lesson in detective work...
Finding "no useful information" shouldn't be considered an endorsement.
I know, but I needed a hob for the kitchen. Amazon wasn't much help, just dozens of similar-looking hobs with funny-sounding made-up brand names. I'd wager under the hood they're all the same Chinese circuit board. They certainly seem to have the same general layout and same loud fan.

What would you have done?
 

MrSalts

Joined Apr 2, 2020
1,541
I know, but I needed a hob for the kitchen. Amazon wasn't much help, just dozens of similar-looking hobs with funny-sounding made-up brand names. I'd wager under the hood they're all the same Chinese circuit board. They certainly seem to have the same general layout and same loud fan.

What would you have done?
Amazon is an outlet for people that resell crap off of Aliexpress with no expectations of meeting UL or CE safety standards.

I would have checked my local applicants or electronics store and bought one stamped with a brand name that had some risk to their reputation if the product did not function. I'd also look for a .UL or CE rating to with some hope thst the product really meets CE or UL standards and won't burin my house down.

if I'd take an appliance home and it didn't work to my expectation, I'd bring it back to the store and get my money back.

a single burner portable cook top is as low as $35. I don't really know how much saving from AliExpress I would expect on such a basic item with so much risk (performance, durability, safety, odor when hot, ...).
 

Thread Starter

LMF5000

Joined Oct 25, 2017
108
Amazon is an outlet for people that resell crap off of Aliexpress with no expectations of meeting UL or CE safety standards.

I would have checked my local applicants or electronics store and bought one stamped with a brand name that had some risk to their reputation if the product did not function. I'd also look for a .UL or CE rating to with some hope thst the product really meets CE or UL standards and won't burin my house down.

if I'd take an appliance home and it didn't work to my expectation, I'd bring it back to the store and get my money back.

a single burner portable cook top is as low as $35. I don't really know how much saving from AliExpress I would expect on such a basic item with so much risk (performance, durability, safety, odor when hot, ...).
I bought mine from the local shop, not amazon. Sadly the best they can do is a credit note - and that only after the technical department confirms that it well and truly doesn't live up to expectations. Customer service sucks in my country :/
 
Top