Problem with Digital Multimeters

[guidoilieff]

Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".

Thanks. I'll try to find how higher frequency can damage a circuit.


I'm pretty sure argentina has 50/60Hz. Why you say its 220?

[guidoilieff]

Where in the world do you live? What type of socket/plug standard is used?
https://en.wikipedia.org/wiki/Mains_electricity_by_country

I'm from argentina

Type I (Australian AS/NZS 3112); Argentinian version has reversed polarity compared to Chinese and Australian versions ( I don't know what they mean by polarity... phasing? idk. The thing is that I don't know any house that has a conductive rod driven into the ground because its expensive.)


My house has these outlets: So-called "universal socket" which meets no standard[5] but accepts a number of different plug types.(criticized as unsafe)

Polarity in this context means which pin is connected to the hot AC, vs. the neutral. See the "polarization" section of the wiki article.

Isn't that called phasing?

[reddesert]

Isn't that called phasing?

That's different, though related. Phase usually refers to single-phase: https://en.wikipedia.org/wiki/Single-phase_electric_power versus 3-phase: https://en.wikipedia.org/wiki/Three-phase_electric_power.

A typical US home installation has split-phase: https://en.wikipedia.org/wiki/Split-phase_electric_power. There will be three wires coming into the house: positive hot, neutral, and negative hot. Neutral should be tied to ground at a central location. This is not 3-phase: the positive and negative are 180 degrees out of phase. That allows attaching a large appliance (usually a clothes dryer) across positive and negative to get 220 VAC. All of the small appliances in the house run off a connection between neutral and one or the other hot wire, receiving 110 VAC (closer to 120 these days).

Appliances like lamps use a polarized plug (one blade wider) to make sure that the outer thread connection of the lightbulb is connected to neutral, not hot, to minimize the risk of accidental shock.  This is also why you hear about people getting shocks from old amps with un-polarized reversible 2-prong plugs; if you plug it the wrong way round and the amp has a fault, hot voltage can leak onto the chassis.

Anyway, long story, if you have a 3-prong plug the plug can't be plugged the wrong way around, but from the website it sounds like Argentina uses an opposite convention for which is the hot/neutral wire, vs China/Australia.

I am sure that the previous poster misread the table and you have 220 V power at 50 Hz, not 220 Hz.

The remaining problem of why you don't measure AC voltage - are you sure you're measuring it off the proper pins?  Need to measure hot vs neutral or ground, not neutral vs ground. Do you have a wallwart that outputs say 9 VAC or 12 VAC that you can try measuring with the DMM? [Never mind, I guess you mentioned trying a 12VAC transformer in the original post.]

[Rob Strand]

That's different, though related.

It does affect safety if you use equipment from other countries:
- equipment with single pole power switches will still pass live wires through the circuit when the switch is off.  The device is obviously switches off as far as the user goes.
- fusing would be on the neutral will is highly undesirable (and usually illegal).

[guidoilieff]

Isn't that called phasing?

That's different, though related. Phase usually refers to single-phase: https://en.wikipedia.org/wiki/Single-phase_electric_power versus 3-phase: https://en.wikipedia.org/wiki/Three-phase_electric_power.

A typical US home installation has split-phase: https://en.wikipedia.org/wiki/Split-phase_electric_power. There will be three wires coming into the house: positive hot, neutral, and negative hot. Neutral should be tied to ground at a central location. This is not 3-phase: the positive and negative are 180 degrees out of phase. That allows attaching a large appliance (usually a clothes dryer) across positive and negative to get 220 VAC. All of the small appliances in the house run off a connection between neutral and one or the other hot wire, receiving 110 VAC (closer to 120 these days).

Appliances like lamps use a polarized plug (one blade wider) to make sure that the outer thread connection of the lightbulb is connected to neutral, not hot, to minimize the risk of accidental shock.  This is also why you hear about people getting shocks from old amps with un-polarized reversible 2-prong plugs; if you plug it the wrong way round and the amp has a fault, hot voltage can leak onto the chassis.

Anyway, long story, if you have a 3-prong plug the plug can't be plugged the wrong way around, but from the website it sounds like Argentina uses an opposite convention for which is the hot/neutral wire, vs China/Australia.

I am sure that the previous poster misread the table and you have 220 V power at 50 Hz, not 220 Hz.

The remaining problem of why you don't measure AC voltage - are you sure you're measuring it off the proper pins?  Need to measure hot vs neutral or ground, not neutral vs ground. Do you have a wallwart that outputs say 9 VAC or 12 VAC that you can try measuring with the DMM? [Never mind, I guess you mentioned trying a 12VAC transformer in the original post.]

Thanks for the explanation! I got it.


In my country it's a roulette witch is the hot and which is neutral. I think that's why there are problems with electricity all the time at gigs or why sometimes you can "feel" electricity  in the chassis of some electric products while you're barefoot.


I made like 5 or 6 of these http://www.generalguitargadgets.com/effects-projects/power-supplies/ultra-clean-power-supply/ with transformers I alredy meassured and labeled. Now I'm trying to rewire this amp I made a long time ago http://www.generalguitargadgets.com/effects-projects/amps/tda2030-amp/ but I dont know wich cable is negative and wich is positive of a similar transformer like this http://www.electronicagimeno.com/sites/default/files/007581_0.jpg, or does th circuit doesnt know wich is wich?

(I blew a tda7294 because I thought the heatsink was connected to ground instead of negative and now I'm scared to blow another one)

[guidoilieff]

That's different, though related.

It does affect safety if you use equipment from other countries:
- equipment with single pole power switches will still pass live wires through the circuit when the switch is off.  The device is obviously switches off as far as the user goes.
- fusing would be on the neutral will is highly undesirable (and usually illegal).

Never thought of that. I think I'm doing both things in the amp I'm making.


Since in this country there is no polarization in the connectors how do I avoid this?

[PRR]

> Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".

1) It is highly UN-likely he gets 220Hz power. It is not suitable for even urban power distribution. (The stray capacitance means higher losses, which are already problematic at 50/60Hz.) That's gotta be some typo or mis-read.

2) I would not expect large error reading some 220Hz source with a "40Hz-200Hz" meter. The filtering is gentle. It might not meet a 1% spec but should be within 5%. Errors will climb so when you poke your 400Hz large airplane system it may read 20%-30% down.

[GGBB]

Your mains is 220Hz - that meter's rated range for AC voltage is: "Frequency Response: 40Hz - 200Hz".

!!! I need to avoid posting after midnight - can't even keep Volts and Hertz straight. Now that is hilarious!   

[PRR]

"Live" and "Neutral" *should NOT* matter inside your appliance (power unit). The transformer is amply insulated from ground/chassis on both sides. (Over 10KV is different, but none of our business.)

The fact that switch or fuse may be on the "wrong" side does not matter because you should NOT be sticking your hand inside unless the power cord is UN-plugged. (Yes, we sometimes flirt this rule when trouble-shooting, but *very carefully*!!)

The fact that 3-phase power can be delivered at least 6 ways (wYe, Delta, grounded, high-leg) normally does not matter in small audio because we only use one pair of current-carrying conductors.

> I dont know wich cable is negative and wich is positive of a similar transformer

Both legs of an AC transformer swing both + and - of each other.

The polarity which matters when blowing-up chips and cap is determined by the *rectifier*.

[Rob Strand]

"Live" and "Neutral" *should NOT* matter inside your appliance (power unit). The transformer is amply insulated from ground/chassis on both sides. (Over 10KV is different, but none of our business.)

The fact that switch or fuse may be on the "wrong" side does not matter because you should NOT be sticking your hand inside unless the power cord is UN-plugged. (Yes, we sometimes flirt this rule when trouble-shooting, but *very carefully*!!)

I'm pretty sure if you submitted a product for safety testing that (only) switched neutral and/or (only) fused neutral it would not pass.

I believe if the assignment of active and neutral is ambiguous there are cases in the safety standard where you need to fuse both lines.    There's also some statements in the standard with a wider net regarding not creating unnecessary safety risks.    Medical device standards actually enforce fusing both lines as a means of reducing risk.

What is interesting is integrated power inlet modules (IEC inlet + fuse + maybe switch) will have the fuse on a specific line.  I've never looked for or come across modules with fuses on the other line.

[Rob Strand]

For what is is worth, the IEC cable should correctly translate the wall socket pins assignments to the IEC pin assignments.  At the IEC connector the Active and Neutral orientation should be standardized.

As far as Active being on the left or right (say when looking into the power socket on the wall) there's also the issue of the earth pin being up or down.. In AU the earth pin is normally considered to be down.

Here's some cables,  the L and N lines are looking into the faces of the cable ends, on the IEC cable.
http://www.yunhuanelectric.com/Clkj_Images/upfile/Brazil-14136-to-IEC-C13-Power-Cord.jpg
http://www.yunhuanelectric.com/Clkj_Images/upfile/AS-NZ-3112-to-IEC-60320-C13-Mains-Cable.jpg

[thermionix]

"Back in the day"...for US equipment at least...it didn't matter which line you fused because the power cords had non-polarized 2-prong plugs, and could be inserted either way.  For power switches, Fender usually switched one line only with a SPST toggle, while Marshalls tended to have DP power switches.  Might have been a British requirement, but not a bad idea anyway.

[Rob Strand]

"Back in the day"...for US equipment at least...it didn't matter which line you fused because the power cords had non-polarized 2-prong plugs, and could be inserted either way.

There's a few countries where you can still do that.  Basically those with US style plugs or the two round prongs.

Over time the rules for importing products weeds-out the bad practices.

These days the products either break or go obsolete before two versions of the safety standard go by so we don't have to worry about the old stuff not complying to the new rules  .