What's the function and schematics of the power module(?) of an inverter microwave oven

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
Hi,

Can any expert here tell me what the function of the this module is, which I took from a Panasonic inverter microwave oven? I'd also like to have its schematics. Can I make any use of it?

Also got the inverter module. One question - is it safe to handle it as soon as the power is unplugged? I don't see a high capacity capacitor here. And also any use of this board or, otherwise, any component on this board?

Thanks. Max
 

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Tonyr1084

Joined Sep 24, 2015
5,239
You've asked for an expert opinion. I don't qualify. But the first image looks like a power conditioner. The second, and this is more of a guess than anything else, looks like the power supply. It may be (again guessing) the first stage of an inverter PS. It MAY be the whole inverter. I've never come across one of those before. But now I'm wanting to.

You ask what you can do with it - well, once you know for sure what it is you might be able to use it as a 120 VAC fan speed controller, assuming it puts out a frequency the motor can handle. Otherwise, with my level of (lacking) expertise, I don't really know there's much you can do with it. I'm SURE if you're creative you can come up with a use. I just can't. Not now anyway, not without knowing more about exactly what it is. Others here will likely have some better insight.
 

debe

Joined Sep 21, 2010
1,200
PANASONIC INVERT OVEN.3.png That power supply is only part of it, its driven from the timer board. Its not something thats realy usable except for what its designed for.
 

Tonyr1084

Joined Sep 24, 2015
5,239
Now that I've seen @debe's drawing I understand better that the second picture is the high voltage module. Honestly, you don't want to mess with that. It's dangerous, and you could hurt yourself. Or worse. But I'd imagine a pretty good snap from somewhere around 4KV would probably knock you on your butt. Still, don't try. There's still too much possibility you could end up being one of those guys who have experienced a high voltage shocking and are no longer around to tell us about it. Please - stick around. Don't mess with it in its current form. You MIGHT change the transformer, but now we're beginning to discuss things I know even less about. All I know for sure it it's dangerous. Best to leave it alone.

Earlier I said I was wanting to come across one. I'm re-thinking myself on that statement. Should I come across one - I probably would experiment with changing the transformer. That one, the one with the twisted wires creating a low voltage input at some high frequency may better be suited for a more conventional transformer. But like I said, this is all guesswork. I still think it's better left alone.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
View attachment 180598 That power supply is only part of it, its driven from the timer board. Its not something thats realy usable except for what its designed for.
Thanks for this. I'm pretty sure the first one is the "noise filter" module in the schematics you posted. The second one, according to what I learnt from Youtube videos, is the entire inverter module, producing the high voltage needed by the magnetron and controlled by the controller board by 3 signal wires (or 2?) with which the output power of maganetron could be adjusted.

Now my questions are, with the help of your schematics, what is special with the noise filter module? How does it work? Is it needed only by a microwave oven or also many other home electrical appliances? (I guess no) I'm also very keen to know how the inverter works.

Another question haunting me is that, the term inverter is often used for a device converting DC to AC (110V or 220/230V). I don't think inverter of a microwave is doing this or anything like this. If I'm correct, why is this term used for this module and function? What does adjustable power output (of the meganetron) have to do with inverter or inverting?

Thanks. Please bear with me if I asked some stupid questions.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
Now that I've seen @debe's drawing I understand better that the second picture is the high voltage module. Honestly, you don't want to mess with that. It's dangerous, and you could hurt yourself. Or worse. But I'd imagine a pretty good snap from somewhere around 4KV would probably knock you on your butt. Still, don't try. There's still too much possibility you could end up being one of those guys who have experienced a high voltage shocking and are no longer around to tell us about it. Please - stick around. Don't mess with it in its current form. You MIGHT change the transformer, but now we're beginning to discuss things I know even less about. All I know for sure it it's dangerous. Best to leave it alone.

Earlier I said I was wanting to come across one. I'm re-thinking myself on that statement. Should I come across one - I probably would experiment with changing the transformer. That one, the one with the twisted wires creating a low voltage input at some high frequency may better be suited for a more conventional transformer. But like I said, this is all guesswork. I still think it's better left alone.
Thank you very much for your thoughts and especially for your warnings. I had watched some videos online and was aware of many dangerous aspects with microwave before I opened this inverter microwave (but not sure if I know all; and previously I already dissected another 'traditional' microwave). First it's not advisable to disassemble the magnetron (check youtube for more details). Second, the magetron needs extremely high voltage to work, either through a traditional transformer or a 'newer' inverter, so high voltage is another inherent risk to be careful about. One thing I'm not very sure is that since I don't quite understand how high voltage is generated by an inverter I don't know for sure whether I can freely touch the inverter board bare-handed as soon as the power is unplugged (As I asked previsouly).

Even (when unplugged) the inverter may be less dangerous than the high capacity high voltage capacitor in the transformer version (but as I said I'm not sure so please don't be misled), I specifically made two insulated sticks with wires in their heads to short circuit any potentially remaining high voltage on the board before I started opening it. I didn't come across high voltage sparks when short circuiting some of of the terminals. I need experts advice on this (how to deal with it and when can I be sure I can freely handle this board). Thanks.
 

Alec_t

Joined Sep 17, 2013
11,744
Another question haunting me is that, the term inverter is often used for a device converting DC to AC (110V or 220/230V). I don't think inverter of a microwave is doing this or anything like this.
Yes it is. It first rectifies the low frequency (50/60 Hz) mains voltage into DC, then inverts the DC into high frequency (umpteen kHz) AC with a controllable duty cycle. The high frequency enables the use of relatively small inductors for smoothing/filtering purposes, rather than clunky great inductors which would be needed at mains frequency.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
Yes it is. It first rectifies the low frequency (50/60 Hz) mains voltage into DC, then inverts the DC into high frequency (umpteen kHz) AC with a controllable duty cycle. The high frequency enables the use of relatively small inductors for smoothing/filtering purposes, rather than clunky great inductors which would be needed at mains frequency.
Thanks for pointing this out. It now makes more sense to me. Also good to know the relationship between frequency and the required inductor capacity.
 

Tonyr1084

Joined Sep 24, 2015
5,239
Please bear with me if I asked some stupid questions.
The only "Stupid" thing you can do is neglect to ask a question when you don't know the answer. It's also equally stupid to assume you know enough about things as that can lead to injury.

None of us know everything. And we all had our first days in this field. We, too, must have asked some pretty dumb questions, the answers to which may have very well saved our lives. Please don't neglect to ask. Those of us here do not judge.

How an inverter works - it has already been explained, but I'll give it a whack too. Sometimes it's not what was said but how it was said. You (like me) know inverters convert battery voltage into usable 120 VAC at 60 cycles. that's been as much as I've known about them until very very recently. It was on the topic of what is meant by inverter. Particularly a microwave oven inverter. I learned that they change AC into DC. It's much cleaner and I suppose easier to control. Then the DC is converted back to AC at a higher frequency; depending on the use. Someone before me said higher frequencies can use smaller coils (if memory serves). So at a higher frequency the oven can be constructed with lighter materials. But one thing remains constant; that you can't get more POWER out of something than you put into it. An 1100 watt microwave (in a perfect world) will draw 1100 watts. Just at a lower voltage. 1200 watts at 120 volts means it's drawing 10 amps. If you were to boost the 120 volts up to 1200 volts, you'd be drawing only one amp. But the final product will still be 1200 watts. That all may sound a little confusing for the moment, but I promise you - it's true. And hopefully my math is correct. I've been known to make dumb mistakes with numbers.

Put it this way: 12 volts and 2 amps is 24 watts. 6 volts at 4 amps is 24 watts. The same "Power" (in watts), just different voltages. That's also the reason why you don't see massive cables carrying household voltages across the countryside. The extreme high voltage means extreme low amperage. With the low amperage you get less heating and less line loss. But the end result is always the same, you can't get more power OUT of it than you put INTO it.

Now, feel free to ask ANY question you have concerning electronics. Someone here will be sure to guide you with their wisdom and experience.
 

MisterBill2

Joined Jan 23, 2018
7,311
"Inverter" is a very broad term, and in power electronics it usually means a device that converts some level of DC power into some level of AC power. Many EVs use inverters to power the drive motors, while some small engine driven power sets use inverters to deliver clean power. And in some microwave ovens an inverter is used in place of a directly line powered transformer to supply the high voltage for the magnetron tube. So the term inverter is quite broad, you see. It is a whole class of circuits.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
"Inverter" is a very broad term, and in power electronics it usually means a device that converts some level of DC power into some level of AC power. Many EVs use inverters to power the drive motors, while some small engine driven power sets use inverters to deliver clean power. And in some microwave ovens an inverter is used in place of a directly line powered transformer to supply the high voltage for the magnetron tube. So the term inverter is quite broad, you see. It is a whole class of circuits.
Yes, indeed. Thanks. With regard to the main feature of inverting DC to AC, an inverter in miceowave is doing the job.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
The remaining questions I am keen to have an answer to are --

1. Why is a noise filter needed?
2. Is it still dangerous to handle an inverter board (from a microwave) when the power is disconnected?
 

Tonyr1084

Joined Sep 24, 2015
5,239
Line power can fluctuate and create noise and spikes. The filter board conditions the incoming AC and makes it easier for the rest of the electronics to digest the power.

As for danger - if there are no large caps or high voltage charged caps hanging around you should be good. If there ARE caps and you want to be sure they're safe to handle just get a set of jumper wires and a 10KΩ resistor and bridge the caps to make sure they're fully drained. Leave the resistor connected for a few minutes to make sure there are no caps waiting to BITE you.

I messed with photo flash caps a long time ago. I quickly learned how vicious they can bite. Got a good burn on my fingers.

Just use good sense (not common sense, common sense is just the level of sensibility common among your contemporaries - - - if you hang around with idiots - - - ). And when unsure, keep one hand in your pocket. Usually the left hand.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
Line power can fluctuate and create noise and spikes. The filter board conditions the incoming AC and makes it easier for the rest of the electronics to digest the power.

As for danger - if there are no large caps or high voltage charged caps hanging around you should be good. If there ARE caps and you want to be sure they're safe to handle just get a set of jumper wires and a 10KΩ resistor and bridge the caps to make sure they're fully drained. Leave the resistor connected for a few minutes to make sure there are no caps waiting to BITE you.

I messed with photo flash caps a long time ago. I quickly learned how vicious they can bite. Got a good burn on my fingers.

Just use good sense (not common sense, common sense is just the level of sensibility common among your contemporaries - - - if you hang around with idiots - - - ). And when unsure, keep one hand in your pocket. Usually the left hand.
Thanks. Does that mean the noise filter is a useful module to reuse even when the down stream circuitry is somehow noise tolerant? Of course the capacity of the module is a factor to consider.
 

MisterBill2

Joined Jan 23, 2018
7,311
The noise filter in an "inverter powered" microwave oven is to keep the electrical noise generated in the inverter circuit from traveling back out the power connection and interfering with other things. Just like the power line filter in a good computer power supply. Switching power supplies all generate a lot of electrical noise, and the filter is to keep it from going back out the line connection. Some junk-quality switching power supplies do not include adequate filtering, and they radiate interference that bothers many devices for quite a distance .
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
The noise filter in an "inverter powered" microwave oven is to keep the electrical noise generated in the inverter circuit from traveling back out the power connection and interfering with other things. Just like the power line filter in a good computer power supply. Switching power supplies all generate a lot of electrical noise, and the filter is to keep it from going back out the line connection. Some junk-quality switching power supplies do not include adequate filtering, and they radiate interference that bothers many devices for quite a distance .
Thanks for the explanation. In the meantime, I have found some good reference materials --

http://www.vk3hz.net/amps/Microwave_Oven_Inverter_HV_Power_Supply.pdf
http://media.datatail.com/docs/manual/371449_en.pdf

Thought maybe helpful to those who are also interested.
 

MisterBill2

Joined Jan 23, 2018
7,311
Thanks for the explanation. In the meantime, I have found some good reference materials --

http://www.vk3hz.net/amps/Microwave_Oven_Inverter_HV_Power_Supply.pdf
http://media.datatail.com/docs/manual/371449_en.pdf

Thought maybe helpful to those who are also interested.
The first of the links is very interesting and even more educational. and a note about RFI from the oven is that when our panasonic microwave oven is operation it is not possible to use the wi-fi link for internet access. Tghe mechanical design of the panasonic product is so very poor that the plastic door hinges have worn abd the seal is no longer adequate. So whatever engineering budget went into the electronic design was taken from the mechanical design budget for producing a solid product. Thus we step well away while the oven is running.
 

Thread Starter

max.wwwang

Joined Jun 24, 2019
29
The first of the links is very interesting and even more educational. and a note about RFI from the oven is that when our panasonic microwave oven is operation it is not possible to use the wi-fi link for internet access. Tghe mechanical design of the panasonic product is so very poor that the plastic door hinges have worn abd the seal is no longer adequate. So whatever engineering budget went into the electronic design was taken from the mechanical design budget for producing a solid product. Thus we step well away while the oven is running.
True. I also found Panasonic mechanic and structural design very inadequate. I would not buy my next Panasonic microwave.
 
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