Switched Mode Power Supply's & Microwave Ovens - Page 1
Forum section: electronics / beginners

author: jonovid
author_rank: Super Contributor
timestamp: February 25, 2018, 02:58:18 am
content: why are switch mode power supplys not used in microwave ovens?just the other day, I was moving a microwave oven from the kitchen, and noted the weight of the transformer.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2018, 02:59:50 am
content: Because you aren't lifting the ones that say "Inverter" on the front.Tim

author: eblc1388
author_rank: Frequent Contributor
timestamp: February 25, 2018, 03:12:53 am
content: Because a switch mode power supply does not produce the lovely humming noise that a conventional transformer does. I prefer the oven to "hum" while it is busy working rather than to look to make sure it is not operating.

author: jonovid
author_rank: Super Contributor
timestamp: February 25, 2018, 03:46:33 am
content: Inverter have not encountered that type ? most microwave ovens are the heavy type. oldit Ok new I get it! has one of this ..... people do not throwing out new Inverter types yet.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2018, 06:11:23 am
content: And yes, they're useful for high voltage experiments, as I understand it. Not really suitable for making a general purpose SMPS, AFAIK -- wrong kind of topology and controller, but good for parts if you want to go to the trouble of making your own.If you can't find any in the junk* yet, the boards are pretty cheap (and a lot less in shipping than an MOT).*Not that junk may be all that useful, since several parts are probably toast when they go. Might find it more economical to buy replacement parts/boards and fix, rather than scrap them.Tim

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2018, 10:25:56 am
content: I would guess the cost cutting of the older parts is pretty well down the line now, to the point that there really is not a lot of valuable materials in making it. Steel core, aluminium windings, cheap high voltage diode, low cost high voltage capacitor containnig thin foil and polypropylene with palm oil dielectric is pretty much as low cost as you can go. Doing an inverter costs more, as the core has to be specific types of ferrite, you have to use copper wire, more expensive electronics and such along with it not being any smaller. Freight wise the transformer mass difference is not relevant, the unit is shipped as volumetric mass in almost all cases, as it overall is so light when packed for shipping, being mostly air in the cavity ad the protective box.The transformer is worth around $2 as scrap value, while the copper in the small transformers of the inverters will be around $3. Add to that that the lines set up to manufacture them are well established, have gotten to large volumes and thus material cost reductions, and are all paid for, no real machinery depreciation to pay off, and also the labour cost is low as most of the work is either heavily automated or is low skill labour.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2018, 10:45:59 am
content: Inverters are still very cheap, and well optimized, of course, but they mostly sell based on improved specs and actual controllability, AFAIK. Which goes along with the above claim.Tim

author: jonovid
author_rank: Super Contributor
timestamp: February 25, 2018, 01:00:52 pm
content: now I know what microwave oven Inverter is ,the next question is ...can Isafelyre-use or rewindan Inverter's secondary for a 50 amp DC power supply or do I just look it up on YouTube.

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2018, 04:44:06 pm
content: You can, just remember that the control circuit is going to be optimised for a high voltage output, and the feedback will be as well. However you can try, but the winding of the 50A winding onto the limited space in the core, along with the 50A rectifier required will be hard to do easily.With the older magnetic ones you can rewind them easily as a high current source, but need to remember that the core generally is run right at near full saturation, and needs forced air cooling for any operating time over a minute as otherwise it will overheat.

author: paulca
author_rank: Super Contributor
timestamp: February 25, 2018, 04:53:51 pm
content: Having watched this... I look at my microwave with different eyes these days. Probably worth a watch before you consider playing with them.