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 Post subject: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Sun 19, 2020 9:37 pm 
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Location: Charlotte, NC 28205
Can microwave SMPS power supplies be cobbled together to make a 3KV @ 1 amp PS [minus the smoothing capacitors] ?

Jack; K4LRH


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 1:47 am 
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Not if it is a home type microwave. 3 KV @ 1 A is 3 KW which is more than you can get from a normal 120 V outlet. If it is some type of commercial microwave that runs on 240 V, the question is still open.

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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 1:54 am 
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Jack

It will also be dangerous. One end of secondary is grounded to the frame. In order to increase voltage you would need to remove a ground and connect two in series. Insulation may not hold up wired this way.

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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 4:47 am 
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I'm going to say not only you can't but also you shouldn't experiment with that. As Norm pointed out the safety issues are too great and there is no way I can see that you could get specs for the insulation ratings on those supplies. You definitely couldn't get that voltage and current from a supply running on a regular household circuit.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 12:14 pm 
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I think it is appropriate to ask: WHY do you need 3KV at 1 amp??---maybe there is another solution.

I think the biggest circuit in our panel is 240V/30A---7.2KW.

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"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 2:14 pm 
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Location: Charlotte, NC 28205
pixellany wrote:
I think it is appropriate to ask: WHY do you need 3KV at 1 amp??---maybe there is another solution.

I think the biggest circuit in our panel is 240V/30A---7.2KW.

Just thinking there's got to be an inexpensive alternative for a 65# plate transformer.

Jack


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 2:24 pm 
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Aren't microwave oven transformers pretty non-linear? Somehow, I think the requirements for plate modulation are quite different...

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"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 5:56 pm 
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Location: Santa Rosa, CA
A traditional iron MOT (microwave oven transformer) weighs over 20 lbs. The SMPS version uses a ferrite core and weighs about half that. The SMPS version is designed to work with a known fixed load (the magnetron). Most MOTs have magnetic designs to cope with the different sizes of cooking load. You may also find that adding any significant filter capacitance will stress the MOT. Most MOT power supplies have 1 or 2 uF of "filtering." The magnetron doesn't require smooth DC.

In order to vary the cooking rate, some ovens use a Triac control to pulse the oven ON and OFF, controlling the duty cycle. More modern ones probably use PWM (pulse width modulation) to reduce the output of the SMPS.

I don't think the SMPS is going to like the "tune-up" period when adjusting the tube amplifier to an antenna.

Also, I think that switching over 1 KW at over 50 KHz is going to be enjoyable to a nearby receiver.

Sounds like a risky experiment.

Rich


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 Post subject: Re: HV PS FROM MICROWAVE SMPS
PostPosted: Jan Mon 20, 2020 8:16 pm 
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Location: hillsborough, nc
You can get 2KV at close to an Amp with two.
You have to get the magnetic shunts out from between the windings, which is easier if you remove the filament winding.
Using two, you leave the grounded ends alone and use the cases as the center tap.
They are minimalist designs and will draw several amps no load, at a PF of about 0.1.
The PF gets reasonable when loaded.
There are several articles out there, some in ham literature.
WL


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