Re: High Voltage Check

Get another meter?

Connect the primary to a 12vac source such as a garden lighting transformer, the secondary should then read about 1/10th it's rated voltage.

Is your insurance paid up? Does your wife know how to cut off the power and do CPR?

N

Agree: Be careful not only of the AC voltage on the secondary of that transformer but the voltage doubling DC circuit which can more than adequately kill you! Not only that; if you operate with the cover off stand clear of possible microwave radiation! After all they are a half kilowatt microwave transmitter in a tin box! I will venture a guess that if the transformer (with the power off and unplugged) tests continuity and doesn't look burnt up, it is not faulty. More likely another component, all operating at very (repeat very) high voltage.

Since you need to ask, you do know enough to undertake this type of repair as it could very quickly lead to your family having to call the Undertaker.

--
John G

Wot's Your Real Problem?

you!

Yep. This is a classic case of stand on dry newspaper, use one hand only, clip the leads to the machine and then cycle AC power at the wall for the test. One flash and you're ash. There aren't many items more hazardous to service - except maybe neon signs.

N

Possibly worse than neon signs. Neon sign transformers tend to have a higher output voltage than microwave oven transformers but are current limited. Whilst microwave oven transformers have magnetic shunts (current limiting through core saturation), they're still capable of chucking out an Amp or so. A couple of kilowatts going through you could ruin your day.

I do it the "sissy" way and feed 'em through a Variac - one fried DMM has shown me that it's not only personal safety that's at stake.

"Toil not thou on energized equipment, for if thou so dost, thy fellow workers will surely buy beers for thy widow and console her otherwise."

M

Neon signs are trivial in comparison.

The different between 20 or 30 mA and 0.5 to 1 AMP.

Neon sign transformers are current limited.

Still near the threshold of lethality but microwave transformers are way over it.

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Stay out of TV transmitters!

--
?

Michael A. Terrell
Central Florida

Can you read ?

only,

the

to

Or tube equipped military transmitters!

N

30 mA will ruin your day hand to hand. N

Very, very, very, very, very, very, very, very, very, very, very, very carefully.

Don't even THINK of touching any part of the multimeter while testing.

N

Build a high voltage probe.

There is a relatively safe way to calculate the secondary voltage - no mains energisation required; it's just not too accurate as it takes no account of losses.

Got a DMM with a decent inductance range? You can get a ballpark value thus:

Zp=sqrt( (Rp^2) + (2 * PI * f * Lp)^2 ); Zs=sqrt( (Rs^2) + (2 * PI * f * Ls)^2 ); np/ns=sqrt(Zp/Zs); Vp/Vs=np/ns;

Where f is your local line frequency.

M

Which are extremely high in a microwave oven transformer.

Yeah, how many have that?

That sounds like the hard way. :)

Just run it with 1/10th the input voltage as has already been suggested.

--- sam | Sci.Electronics.Repair FAQ Mirror:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.