A/C Isolation Transformers

[DonH56]

Im struggling to understand how having a large Transformer within inches of the amplifiers that are fed by it could possibly have more resistance and losses then having the same amplifiers being fed straight from the wall, assuming the transformer is of adequate size to perform task.

If you have a hypothetical bucket full of electricity sitting inches away from the amp power supply how can that be more detrimental to power delivery then having the amp wait for adequate juice to arrive from the breaker panel, thru the house wiring, thru the receptacle to the power cable of the amplifier?

What am I missing?

A transformer does not generate power, it transfers it from one side to the other. Losing a little along the way as Amir said. You don't have a "hypothetical bucket full" -- you just have a another hose to connect the amplifier to the bucket (wall outlet) on the other side. And the transformer also has limited bandwidth and current capability, usually less than what the wall socket itself can provide.

 

[RayDunzl]

I think we need a test to put all this to rest.

I have a 60lb transformer at the end of 80 (or more) feet of 14AWG Romex, Amir has a $300 meter.

"A Mexican standoff is a confrontation between two or more parties in which no participant can proceed or retreat without being exposed to danger. As a result, all participants need to maintain the strategic tension, which remains unresolved until some outside event makes it possible to resolve it."

 

[amirm]

Is that 46 hours with or without bathroom breaks??? I am too old to hold it all the way!

 

[RayDunzl]

There's a $53 Clone:

http://www.ebay.com/itm/MASTECH-MS5...083798?hash=item237e325796:g:3BUAAOSw5dNWnF16

http://www.p-mastech.com/about/detail/20.html

 

[RayDunzl]

Is that 46 hours with or without bathroom breaks??? I am too old to hold it all the way!

Your coach doesn't have Autopilot?

The $3 alternative:

http://www.bettymills.com/male-exte...IfW0igAKVnDXDwqJtXf1vPnYwM9m2zcN7IaArwQ8P8HAQ

 

[amirm]

Mastech stuff can be hit and miss. They are usually great value but safety is an issue and QC not good. See these reviews: https://www.amazon.com/Analyzer-Compared-Industries-Suretest-61-164CN/dp/B008OPW56U

Looks like it is for Chinese market.

 

[RayDunzl]

I'm still thinking the field can dump an instantaneous current higher than what's available on the line, to fill a monentary request...

But I'm susceptible to moments of WrongThink.

I agree that what-goes-in is greater than the-usable-what-comes-out over time for all the reasons listed above.

Blow up a balloon (create the field), you can get the about the same energy and amplitude out of it over time or pop it for an exciting instantaneous bang...

 

[RayDunzl]

Our Hero:

http://www.eevblog.com/forum/testge...rue-mastech-ms8268-digital-acdc-automanual-r/

PS: My VOM is a Fluke, liberated from the ashes of Nortel.

 

[DonH56]

An inductor (transformer) will resist making fast changes in current and will instead allow the voltage to sag (or spike, depending upon the current flow). A capacitor will resist rapid voltage changes in favor of sourcing or sinking more current. The capacitors in your power supply help stabilize the voltage and deliver the current needed. A transformer, unless it is really needed for galvanic isolation or whatever, is going to hurt current delivery unless it is sized to deliver more than the wall outlet, with greater bandwidth, and without saturating the core or any other badness happening. An isolation transformer allows you to break the neutral connection from the ground at the service box, one reason they tend to be against code, and can help isolate your system from that noise, but as far as the actual amount of power that is delivered it is always going to be less than just plugging into the wall. We can use a big honkin' transformer so the loss is minimal and probably insignificant, but it cannot be zero. Entropy and all that jazz.

 

[blackmetalboon]

Out of curiosity, on your side of the pond is the ground conductor the same gauge as the other conductors in a circuit?

I only ask as Shunyata using the ASCC readings seems an odd way to demonstrate their point.

 

[RayDunzl]

Ok, I give up.

Now to think up something else...

 

[RayDunzl]

Out of curiosity, on your side of the pond is the ground conductor the same gauge as the other conductors in a circuit?

I would say, typically, yes, as a minimum, as it must be sized to carry the full fault current.

I just bought some common electrical service wire, Hot, Neutral, Earth, all 10AWG in the sheath. I suppose I'll find out for sure when it arrives...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Wiki:
"Most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed (NM) cable designated type.[7] This type of cable is the least expensive for a given size and is appropriate for dry indoor applications. The designation NM XX-Y indicates, respectively, the type of sheathing (in this case, non-metallic), the size of the main conductors, and the total number of circuit conductors (exclusive of the grounding conductor). For example, NM 14-2 cable contains three conductors (two plus one ground) at 14 gauge, a size typically used for circuits protected at 15 amperes."

 

[blackmetalboon]

Good to know. Generally in the U.K. the earth conductor is smaller than the live and neutral, especially in domestic installations.
Shunyata's measurements wouldn't look so impressive in the UK when using the same test procedure.

 

[amirm]

Out of curiosity, on your side of the pond is the ground conductor the same gauge as the other conductors in a circuit?

It depends on the situation. If the main (hot+neutral) conductors are oversized for lower voltage drop, then the ground conductor need not be oversized just the same. It only needs to carry enough current to trip the breaker.

As a normal course though, the main lines are not oversized so the ground conductor is the same as main lines.

I only ask as Shunyata using the ASCC readings seems an odd way to demonstrate their point.

Agreed. This is a quick check for electricians and is not meant to be a precise way to determine current capability.

 

[Fitzcaraldo215]

I would say, typically, yes, as a minimum, as it must be sized to carry the full fault current.

I just bought some common electrical service wire, Hot, Neutral, Earth, all 10AWG in the sheath. I suppose I'll find out for sure when it arrives...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

Wiki:
"Most circuits in the modern North American home and light commercial construction are wired with non-metallic sheathed (NM) cable designated type.[7] This type of cable is the least expensive for a given size and is appropriate for dry indoor applications. The designation NM XX-Y indicates, respectively, the type of sheathing (in this case, non-metallic), the size of the main conductors, and the total number of circuit conductors (exclusive of the grounding conductor). For example, NM 14-2 cable contains three conductors (two plus one ground) at 14 gauge, a size typically used for circuits protected at 15 amperes."

I don't know what typical local codes now say, but I have lived in houses several decades ago where the 14 gauge Romex was bundled with an obviously smaller, more flexible safety ground wire, which was solid like the hot and neutral. I am guessing it might have been 16 ga. Note that the quote does not exactly say that the ground must be the same gauge, only that 14 gauge is typically used for the hot/neutral for a 15A circuit.

My house previous to my current (ha ha) one was built around 1990. It had 14 or 12 ga. 2 conductor copper in a flexible steel shield. The steel shield was the safety ground. I never liked that system, though. I had ground loop hum problems using three separate 2 wire, 20A audio circuits to the music room. Fortunately, all three of those circuits terminated in the same 3-gang wall outlet. I just tied the three metal shield safety grounds together inside that wall box and all was well. Code? Who knows or cares. There was an audio issue here that needed fixin'.

All is fine in my new house as of 2013. All circuits appear to use copper safety grounds at the same gauge as hot/neutral. I added four 20A, copper grounded circuits to to music room, about 35 ft. from the breaker box. My system, which is all XLR interconnected, is absolutely dead silent in all 7.1 channels with a host of different amp and component plugins to different circuits.

I live in a very densely populated part of Philadelphia. I have not taken measurements, but I am not thinking I need an isolation transformer.

 

[DonH56]

Nor is it meant to serve as an indication of the actual current draw (requirement) of a component such as an audio amplifier on the line. I'd be pretty surprised if a real amplifier actually draws several hundred amperes even for a short time; over the long haul that would probably trip a breaker. Once the amp is up and running the line must supply enough power to keep the amplifier happy and recharge the filter capacitors twice per cycle (assuming full-wave rectification) which should be the power output plus loss, say 1.5 ~ 2 x the output power per channel. If the amp were putting out 1 kW that is 2 kW with 2x for losses and thus 4 kW for a stereo amp. Now 4000 W/ 120 Vrms = 33 1/3 Arms = 94.28 App which is a far cry from 500 or 1000 A and this is assuming a pretty big amplifier. Even more margin if the ASCC uses RMS current as I suspect.

 

[cjf]

And the transformer also has limited bandwidth and current capability, usually less than what the wall socket itself can provide.

Speaking about the one I use in particular (Torus RM20) its claimed to be 95% efficient and is rated for 2400w which is the same as the 20A circuit I have it plugged into. So if it is indeed 95% efficient then it appears I'm down 5% from what the wall can provide. Doesn't seem like a bad compromise given the surge protection it offers that the wall does not.

The mention of these devices having "Limited Bandwidth" doesn't necessarily seem like a bad thing. Actually that seems like more of a good thing. If an amplifier or speaker or whatever you have plugged into the transformer has no usefulness above say 200kHz then why wouldn't we want to filter out noise above that which would otherwise be riding on the line unfiltered without a transformer in place?

My main purpose for using one of these devices is to offer some form of protection to the expensive equipment plugged into it without causing too much of a bottleneck in the process.

 

[DonH56]

An isolation transformer alone may not provide surge protection -- depends on how it is connected and what else is in the box (my guess is they included some sort of surge protection with the transformer).

Was not referring to noise bandwidth, but limited current bandwidth could reduce its ability to handle the shorter current spikes needed to charge the power capacitors. Which may or may not matter given the load and slew rate (time) needed to charge them. Too many unknowns.

 

[blackmetalboon]

I'd be pretty surprised if a real amplifier actually draws several hundred amperes even for a short time; over the long haul that would probably trip a breaker.

I would agree, even if it was only drawing that periodically I'm sure over time the thermal effects on the breaker would eventually cause it to trip (and I wouldn't want to turn it back on straight away without burning my fingers!).

 

[RayDunzl]

How about another $10,000 Challenge?

It sure riles some people up enough to make it interesting regardless of the outcome.