Microwave transformer as choke?

[leadbelly]

I have read the excellent threads on rewinding a microwave oven transformer (MOT) to become either a big choke or a high voltage power transformer.

My question is more about the brief references to just using it without rewinding as a choke for low current applications.

The following picture is of an MOT I pulled out of the oldest, heaviest microwave I've ever seen. The primary measures less than 1R, there are a few turns of insulated wire between primary and secondary bobbins that measure as a dead short, and the secondary measures about 58R, however one end is grounded.

So can this be used as a choke for a 100mA PS? TIA.

[Sch3mat1c]

Hell, use it up to 500mA. Gap the core properly, and disconnect the secondaries (BTW, the insulated wire is for the 3.15V 20-50A or so filament in the magnetron).
If you have two, you might remove the windings from both and put the primaries on one (for a 10A isolation transformer ) and secondaries on the other, in series, for your choke.

Say, anyone ever measure the inductance of one of those?

Tim

[rcavictim]

I've never seen a meter that measures R's, so I do not know what you mean when you say the secondary measures 58 of them, or where you got your meter. An ohmmeter will be immensely useful for such a measurement however. The resistance readings will be in ohms though, not R's. Some lazy people here dislike that I insist on calling an ohm an ohm. Tough. To them I'll state my local temperature in degrees T.

That wasn't aimed specifically at you. You might be an innocent bystander that has seen other dummies use this incorrect nomenclature. Assenine practises have no chance of disappearing if no-one says anything.

Now that I got that off my chest, yes the transformer as-is may work quite well as your choke. You can llift the grounded end of the HV winding, or leave it connected to the frame and isolate the frame if needed. The in-between winding is a 3.15 volt filament winding for the magnetron filament. I have employed them successfully as chokes for breadboarded B+ supplies to valve output stages as high as 500 mA. For more L you can series the primary with the secondary, For less you can anti-series (opposing phase) the two windings.

There are many creative uses for salvaged microwave oven transformers, often called MOT's. I must have 50 of them by now. The magnetrons can source two awesome fridge magnets as well.

I seem to recall seeing about 17-20 Henries in the HV winding with no core gap. I have not experimented yet with adding a gap.

[AudioFreak]

Originally posted by rcavictim
I've never seen a meter that measures R's, so I do not know what you mean when you say the secondary measures 58 of them, or where you got your meter.

R = Resistance = Ohms

[rcavictim]

Originally posted by AudioFreak


R = Resistance = Ohms

Pretty cold here tonight Dan. -10T.

T=temperature

[Sch3mat1c]

Originally posted by rcavictim
[B]I've never seen a meter that measures R's, so I do not know what you mean when you say the secondary measures 58 of them[b]

Screw you. If I'm too lazy to type o-h-m I'll use shift-r too.

R is the standard schematic shorthand for European schematics. I suppose you also gripe about people using 0R22 and nanofarads.

That wasn't aimed specifically at you. You might be an innocent bystander that has seen other dummies use this incorrect nomenclature. Assenine practises have no chance of disappearing if no-one says anything.

The only thing that I hate is seeing commas where a period belongs, I don't know wtf that was about but it makes numbers look ugly. Not like I can't figure out what the heck a 0,22 is (0 then 22 of what? oh wait). 2,054,821.345,876,2 ("two million fifty-four thousand eight hundred twenty one point three four..." yada yada) might be a little confusing though. Which reminds me, why are a billion and trillion not?

(Oh, and give me inches, none of that wussy centimeter junk! )

(And....so forth...)

Tim

[Mr Evil]

Originally posted by Sch3mat1c
...The only thing that I hate is seeing commas where a period belongs...

The 'proper' (SI standard) way of doing it is to use a comma as a decimal point, with a period being an acceptable alternative. Neither should be used to separate groups of digits due to the confusion it causes - a space should be used if required for clarity, so instead of 2,054,821.345,876,2 it should be 2 054 821.345 876 2 or 2 054 821,345 876 2

[rcavictim]

Originally posted by Sch3mat1c


....

R is the standard schematic shorthand for European schematics.

Tim

My ancestors and most folk's here came to North America to get away from the Europeans.

R may be used to designate a resistor but it does not replace the term or symbol ohm or omega. Leadbelly was trying to communicate the resistance of a transformer winding, not that his transformer was a resistor. Ohm is the only existing term for such technical declarations.

[leadbelly]

Originally posted by rcavictim
Now that I got that off my chest, yes the transformer as-is may work quite well as your choke. You can llift the grounded end of the HV winding, or leave it connected to the frame and isolate the frame if needed. The in-between winding is a 3.15 volt filament winding for the magnetron filament. I have employed them successfully as chokes for breadboarded B+ supplies to valve output stages as high as 500 mA. For more L you can series the primary with the secondary, For less you can anti-series (opposing phase) the two windings.

Oh, that is both wonderful and disappointing. At 1st look, the secondary appears to be grounded inside the winding, and I don't think isolating and leaving the whole frame at B+ is a good idea! I'll have to take a closer look in case I'm wrong.

Thanks!

[Sch3mat1c]

Originally posted by rcavictim
R may be used to designate a resistor but it does not replace the term or symbol ohm or omega.

Ok. Can you reproduce said symbol in this medium, reliably on all systems viewing it?

Waiting...

Tim