Transformer help
 

I have a transformer from a dead microwave. Its schematic diagram shows
a primary coil, a secondary coil, and a third one named F. The primary
(115 volts) appears to be two or three turns around the core, insulated
all the way, with both ends sticking out. This primary winding is
sandwiched between the other two coils, both of which have many
windings. One of these coils has two connectors sticking out of the
windings. The other, with very fine wire, has one connector on the
windings, and the other connector is attached to the frame(why?), with
the other end of the fine wire attached to it.

How can I measure the voltage of the outputs? I have a multitester, but
if I connect it across the outputs won't I just trip a breaker with no
load on the output?

There is a series of numbers on the transformer's sticker but I have no
idea how to translate those into something meaningful. (YEC DPC OBJY2
YN-685)

Thanks for any help.

Ted

--
Ted Bennett
Portland, OR

Ted,
I think you are wrong about which coil is the primary. I am
assuming that your transformer is from a microwave that does not have a
inverter in it .

For a conventional micrewave over transformer, the coil that only has a
few windings is for the filament of the magnetron ( F for filament ).
The coil with the very fine wire is the high voltage and the other
winding with maybe one or two hundred turns is the primary.

Since microwave oven transformers produce high voltages with the
ability to supply relatively lots of current, they are dangerous to
test with the full 115 volts on the primary. I would use a much lower
voltage on the primary( maybe 5 volts AC ) and then measure the
secondary voltage. And figure what the secondary voltage is. If you
put 115 volts on the primary, you are likely to fry your multimeter.

If you put 5 volts on the primary, that is about 1/23 of 115 volts. So
if you measure 50 volts on the secondary, the transformer will have
1150 volts on the secondary when connected to 115 volts on the primary.

Be careful.
Dan

On 23 Jan 2005 16:09:27 -0800, wrote:

Ted,
I think you are wrong about which coil is the primary. I am
assuming that your transformer is from a microwave that does not have a
inverter in it .

For a conventional micrewave over transformer, the coil that only has a
few windings is for the filament of the magnetron ( F for filament ).
The coil with the very fine wire is the high voltage and the other
winding with maybe one or two hundred turns is the primary.

Since microwave oven transformers produce high voltages with the
ability to supply relatively lots of current, they are dangerous to
test with the full 115 volts on the primary. I would use a much lower
voltage on the primary( maybe 5 volts AC ) and then measure the
secondary voltage. And figure what the secondary voltage is. If you
put 115 volts on the primary, you are likely to fry your multimeter.

If you put 5 volts on the primary, that is about 1/23 of 115 volts. So
if you measure 50 volts on the secondary, the transformer will have
1150 volts on the secondary when connected to 115 volts on the primary.

Be careful.
Dan


Get 2 MOTs. Measure the voltage of the F winding and connect it to the
primary of the second MOT.It should be less than 5 volts under load,
IIRC.Then measure the output of the second MOT HV winding using a
meter capable of measuring up to 10KV. Just to be safe.

Since you need to ask this question you do not know enough about
electricity to be playing with LETHAL transformers.
DO NOT RISK YOUR LIFE.
--
John G

Wot's Your Real Problem?

"Ted" wrote in message
...
I have a transformer from a dead microwave. Its schematic diagram
shows
a primary coil, a secondary coil, and a third one named F. The
primary
(115 volts) appears to be two or three turns around the core,
insulated
all the way, with both ends sticking out. This primary winding is
sandwiched between the other two coils, both of which have many
windings. One of these coils has two connectors sticking out of the
windings. The other, with very fine wire, has one connector on the
windings, and the other connector is attached to the frame(why?), with
the other end of the fine wire attached to it.

How can I measure the voltage of the outputs? I have a multitester,
but
if I connect it across the outputs won't I just trip a breaker with no
load on the output?

There is a series of numbers on the transformer's sticker but I have
no
idea how to translate those into something meaningful. (YEC DPC OBJY2
YN-685)

Thanks for any help.

Ted

--
Ted Bennett
Portland, OR

Ted wrote:

I have a transformer from a dead microwave. Its schematic diagram shows
a primary coil, a secondary coil, and a third one named F. The primary
(115 volts) appears to be two or three turns around the core, insulated
all the way, with both ends sticking out. This primary winding is
sandwiched between the other two coils, both of which have many
windings. One of these coils has two connectors sticking out of the
windings. The other, with very fine wire, has one connector on the
windings, and the other connector is attached to the frame(why?), with
the other end of the fine wire attached to it.

How can I measure the voltage of the outputs? I have a multitester, but
if I connect it across the outputs won't I just trip a breaker with no
load on the output?

There is a series of numbers on the transformer's sticker but I have no
idea how to translate those into something meaningful. (YEC DPC OBJY2
YN-685)

Thanks for any help.

Ted

This would be a good question for sci.electronics.design or
sci.electronics.basic. I would warn you about the off-topic political
posts on etc.design, but they're only the _second_ worst newsgroup in
that regard that I subscribe to.

The HV secondary has one connector attached to the frame because the
frame is grounded and the microwave is either operating on a
single-phase rectifier circuit, or with a voltage-doubling rectifier
circuit (probably single-phase, they're incredibly cheap).

Get a copy of the ARRL handbook, it'll have some good pointers on HV safety.

What are you trying to do that you need 1200 volts?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Tim Wescott wrote:

Ted wrote:
I have a transformer from a dead microwave.
[snip]

This would be a good question for sci.electronics.design or
sci.electronics.basic. I would warn you about the off-topic political
posts on etc.design, but they're only the _second_ worst newsgroup in
that regard that I subscribe to.

The HV secondary has one connector attached to the frame because the
frame is grounded and the microwave is either operating on a
single-phase rectifier circuit, or with a voltage-doubling rectifier
circuit (probably single-phase, they're incredibly cheap).

Get a copy of the ARRL handbook, it'll have some good pointers on HV safety.

What are you trying to do that you need 1200 volts?

Nothing really. Your comments, and others', made me decide to be not
such a packrat and toss the thing.

Thanks for you input.

Ted

--
Ted Bennett
Portland, OR

"Ted" wrote:
Tim Wescott wrote:

Ted wrote:
I have a transformer from a dead microwave.
[snip]

This would be a good question for sci.electronics.design or
sci.electronics.basic. I would warn you about the off-topic political
posts on etc.design, but they're only the _second_ worst newsgroup in
that regard that I subscribe to.

The HV secondary has one connector attached to the frame because the
frame is grounded and the microwave is either operating on a
single-phase rectifier circuit, or with a voltage-doubling rectifier
circuit (probably single-phase, they're incredibly cheap).

Get a copy of the ARRL handbook, it'll have some good pointers on HV
safety.

What are you trying to do that you need 1200 volts?

Nothing really. Your comments, and others', made me decide to be not
such a packrat and toss the thing.

Thanks for you input.

It's a small world; I just pulled that *exact* same model tranny out of a
microwave this morning (ISTR it coming out of the Kenmore I dismantled),
down here in Eugene.

Jon

Whoa! DON"T PANIC !!

Microwave oven transformers are kind of neat things. The primary and
secondary are loosely coupled because they are not wound one on top of
the other. That makes it easy to take off just the high voltage
secondary.( the one with many turns of fine wire ). Once you do that
most of the danger is gone.
Not that 115 volt house power is danger free, but it is not the same as
about 1200 volts at close to an amp. While you are at it take off that
filament winding.

Now you can wind a few turns of heavy wire and have a source of low
voltage.


Dan

What a coincidence. I just pulled your transformer out of the trash
can ! JUst what I needed
Thanks


Ted wrote:
I have a transformer from a dead microwave.
[snip]


Nothing really. Your comments, and others', made me decide to be not
such a packrat and toss the thing.

Thanks for you input.



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"John G" wrote in news:cwZId.30$IT2.2317
@nnrp1.ozemail.com.au:

Since you need to ask this question you do not know enough about
electricity to be playing with LETHAL transformers.
DO NOT RISK YOUR LIFE.

It's his life, let him risk it!

The ultimate result of shielding men from the effects of folly is to
fill the world with fools. – Herbert Spencer (1891)