Info - What is balanced isolated power

[scotrajode]

Yeah, it can be a little scary how some people read a few articles on electricity, and then think they are a qualifed person. They fail to realize the reason we have a five year apprenticeship (I assume you are union being in NY state, local 26 here) is not because we are slow learners, there is a lot to learn. And in my opinion, there is always more to learn. I certainly don't discourage people from learning about electricity, but they need to realize there is a whole lot to learn. Not saying this applies to you SF.

Scott

[scotrajode]

Now I undertand, crystal clear.

Nice to meet another union member though, too many of our jobs are being outsourced.

You should be the perfect person to ask on the center referencing of the ground on a 120v circuit. Have you ever seen a need for it in audio systems, or anything for that matter?

Scott

BTW, I believe code requires the ground rod to beat least 8 foot long and at least 6 feet deep if driven at an angle, or maybe no more than a 45 degree angle.

[Guest " "]

""BTW, just to clarify, I was talking about wiring for bringing the power to your isolation transformer, the diagram is for after the transformer with a center referenced ground.""

hmm, looks like the diagram was cut off so I posted a better copy which shows the transformers primary side as well.

[Guest " "]

The site is acting up again...won't be surprised if this shows up twice.

Here is the graph. I came across it a while back. The author did a before and after test to try to plot the reduced noise floor. While the reduced noise floor is clearly there, some strange things are happening at the upper frequencies.

[Jim E]

Scott,

I know what you mean. Labor unions in many areas have been forced out over the last 40 years. At my location we are all union with the exception of security and upper management. I work with our electrical department (Local 40 IBEW) often. I can honestly say they are great guys with plenty of experiance. They are of course very conscious of following electrical code.

In the context of this thread on "center referencing of the ground on a 120v circuit" the answer would be no. We do however use isolated three phase transformers for the audio and electronic equipment in each screening room. The audio is all on the same phase and most all of the equipment is balanced line. We have isolated ground bars in each equipment rack along with isolated receptacles and grounds. A star ground is used for outboard projectors and equipment to the racks. The isolated grounds are routed in heavy insulated cable back to the power room separately from the AC panel and is connected to the transformer ground buss and the building steel. There are separate panels for all the other stuff with more conventional wiring.

If you ever get out to the West Coast let me know. Be glad to show you the layout. Nothing fancy, just solid. I might even be persuaded into a demo.

[Duke Spinner]

Hmmmmnnnn .......

the local IBEW "outsourced" me ...many years ago .........[]

[scotrajode]

speakerfritz, if I am reading that graph correctly, that is the worst harmonics I have ever seen in an AC system. But I don't understand, it looks the minimums were lowered, but the peaks remain the same. It just doesn't make sense to me that it would help to keep the worst parts of the harmonics the same, and lower the least significant. Anyway, do you have any progress updates?

Scott

BTW, I wasn't sure about AC cable, so I asked the supply house and they said it is the same as BX, no better. So I was wrong. They also couldn't tell me what the difference was, so why the different name.

[scotrajode]

That sounds like clean power! I have been on projects similar to that, but not to quite that degree of clean and probrably not the same magnitude. I appreciate the offer and I will try to take you up on it if I can ever afford the gas to get there for a vacation! lol!

Scott

[scotrajode]

Duke- Well that sucks, sorry to hear that. Unions aren't always a good thing, but I think we are better off with them than without them.

[Guest " "]

scotrajode

Parts are on the way.

[Guest " "]

Status on my balanced power supply project.

My parts for the 1.5 KVA power supply have been delayed. I should recieve them by saturday.

I did however come across this transformer on ebay. paid .99 cents for it. Since it wieghted 14 pounds, shipping was 20 bucks. So I decided to buy it and play around with it.

The transformer is 900va. It has an 8 amp continuos rating and 25 amp peak rating.

Voltages are a little high on this model. 66-0-66. Basiclly this sends 129 volts into my voltage regulator. The regulator steps this down to 120 volts on the fly.

So I have it connected. And the claims of reduced noise floor are apparent. It gives a sense of greater dynamic range and increased musical detail. The louder you play it, the more impressive it is.

The transformer is absolutely quite, it makes no noise at all.

The model due in on saturaday will provide exactly 60-0-60 which will result in 120.

[ELA]

Hello Speakerfritz,

I was looking for an isolation transformer to fix a noise issue of another type that I am having to deal with. While searching the internet the other day I came across this forum and your post.

I wanted to support your position on balanced power. It is a very good thing and helps a great deal towards eliminating noise and ground loop issues. I am not an audiophile nor do I do studio work. For those reasons I doubt that I could appreciate the reduced noise floor obtained from the system you added (unless there was a lot of 60hz related hum).

I do recognize the value of balanced power however, especially where equipment with EMI filters can cause ground currents and hum on a non balanced system.

I viewed the link on your DIY balanced system and wanted to make a comment about fusing. When building the 1600VA unit I would recommend that you use two separate 8 amp fuses rather than one 15 Amp.

What do you think would happen if you shorted out just one of the transformer banks? Unless I am missing something this could be a dangerous situation. The transformer would supply the max current that it could and that may not be enough primary current to blow the fuse! It certainly does not comply with the NEC.

You might also what to consider using isolation transformers with farady shields for the absolute best noise rejection in addition to creation of balanced power. Are there some vents in the box? Just in case you are using this at any higher load levels.

Regards,

[Guest " "]

You rasie an intresting point, one best answered by the manufacture of the transformer, who usally provide data sheets with specific recomendations. Any safety concerns can usally be resolved by reviewing this data.

It is concieveable that one can argue that transformers with multiple primary windings have independent circut breakers for each of the windings if the windings are wired in parallel. Obviously, if the primary windings are wired in series, only one would be needed. But the fact of the matter is that most appliances that have multiple primary windings to serve as multi-voltage compatable (windings in series for 220 or windings in parallel for 110) only use one circut breaker. This is because the breaker is targeting the continuos rating of the transformer rather then the max surge rating of the transformer. More on that below.

However, I did try your senerio. I took 2 800VA transformers, wired the primaries in parallel, shorted the secondaries of each individually, and immedately popped the 15A breaker. In researching this further....the particular transformers I used for testing your senerio were rated at 8 amps continuous and 25 amps surge. So even if I shorted one, and tripped the 15amp breaker, still quite not near the 25amp max surge rating of the transformer. The combined max surge rating of the 2 transformers I used in my test is actually 50 amps. The combined continuous rating of the 2 transformers is 16 amps.

As far as the faraday sheild....I'm currently using a piltron 5000VA medical transform that has a faraday sheild. I connected the sheild per the recomendations. Electrically, I can't prove the sheild is doing anything.

Ventilated cases would be needed if the application that the transformer is being used for approaches the thermal limit of the transformer as specified in the manufactures data sheets.

If you use a soft start circut, I see no reason why you could not use two 8 amp breakers. However, if you do not use a soft start circut, 8 amp breakers may trip well in advance of the individual transformers 25 amp max surge rating , with unsuccessful turn on attempts, depending on the transformer and any load of it's primary windings.

[ELA]

Very cool that you actually tried it!

Did your test take into account the added impedances of the EMI filters, input and output lead impedances? The better design would use two fuses. At the site you originally referenced the intial unit used one 10 amp fuse so why not two 10 amp fuses on the larger unit?

The transformer data sheet on the ones referenced in the design make no recommendations as to fusing. They do not even list the pimary or secondary impedances and this is why I questioned it. The transfomers are actually rated at 6.7 amps.

Also cool that you are using a shielded transformer. The shield definitely helps as the frequency rises.

As for cooling you may not melt the transformers but are the caps rated to 25C + 55C temp rise due to the transformer at full load? It is well documented that reliability and life of equipment is directly related to how warm they run.

Sorry, I did not chime in to pick on the design. I wanted to support your position on balanced power.

[Guest " "]

I think you have some intresting point one should consider.

The test I did was using two transformers and a breaker, no other devices. I basiclly wanted to just check breaker tripage under a worst case senerio.

I have no issues with any particular size breaker. Only consideration should be if any soft start circut is needed and if not used what impact that has on any inrush current that could trip your breaker.

For the test, I used 2 800VA transformers made by AH Electrical & Industrial Ltd, part number 600-016-00A. It's definitely rated at 8 amps continuous and 25 amps max.

Before I switchted to the 5000VA piltron medical transformer, I actually used the 2 800VA transformers completely in series. The primary of both transformers in series as well as the secondary of both transformers in series. The lead that connected both transformers together on the secondary side was my zero reference ground. Using two transformers in series maintains the 1:1 ratio while allowing 60-0-60 on the series wired secondary of both transformers.

Now, with my HD 34 inch tube monitor, my HT reciever, my sat dish recorder, in my living room running while my computer, 19" LCD monitor, my HTPC computer, my media server, two tube mono block tube amps, and a tube pre-amp in my adjacent home office, the transformers where drawing 9 amps. The transformers were barely warm to the touch.

I think that one 15 amp breaker under this senerio would be fine considering a continuous rating of 16 amps and a max rating of 50 amps. The advantages of series winding if possible is reduced idle current.The two transformers totally series wired idle current consumption drops to 75 ma's whereas parallel wired idel current consumption would be 300 ma's. The series connected approach reduces any softstart issues as well.

I moved to a single bigger transformer from the two medium size ones due to the efectiveness a larger transformer has over smaller ones in dealing with surges....larger transformers absorbs a single phase surge pluse much better.

[Groomlakearea51]

At the risk of "lowering the bar" for some of us "electrical challenged" folks, a very good article is in the November issue of Live Sound International: Denny Van Der Mulm's, "The Real World of Power Quality Problems - Outages and uninterruptible power".

Van Der Mulm's article is, as titled, more focused on UPS systems, but is an excellent primer for those new to the problems of power. For a number of folks who may not be able to "mess with" their power until it leaves the wall socket (renters), or are not technically proficient to build something like SF, a line interactive UPS with an isolation transformer, while pricey, may be a good solution.

[Guest " "]

http://www.etasys.com/Main/MagazineReprints/LiveSound_Mar2006.pdf

I did a google search and came up with the above.

below is a site with common questions and answers about balanced power.

http://www.equitech.com/faq/faq.html

From the same site...here are some articles and technical papers.

http://www.equitech.com/articles/articles.html

common types of electrical problems

http://www.firstenergycorp.com/Get_Help_With/Safety/Electrical_Safety/Common_Types_of_Electrical_Problems.html

[Groomlakearea51]

Thanks Mike!! These are really great articles for those new to the problems that area associated with power problems, solutions and some of the technical "stuff". For those of us getting ready to go down that road of building a "room", HT room, etc., or simply interested in protecting our investments, well worth reading!