DIY balanced power conditioner

[ashok]

Hi everyone,

There have been a number of threads on AK and other places on balanced power conditioners, and the benefits they can bring in reducing the noise floor in an A/V setup. So, I started building one and wanted to share some of the details. It is not complete yet, but I will wire it all up hopefully over the next couple of weeks.

What can balanced power do for you? It can be a little, a lot or nothing at all. It depends on how clean the ac input is to begin with. A good isolation transformer can bring much of the same benefits that a balanced power conditioner can bring – namely, reduction in the common mode noise that might be riding on the power lines. But I suppose a balanced power conditioner can be used to extract the last bit of performance from your system.

In any case, I decided to build one for myself.

Guidelines for balanced or technical power systems have been part of the US National Electric Code for a number of years now. So, if implemented according to code, it can be said that balanced power systems are indeed safe. But there are some important points to note:

1. Balanced power systems are not meant for residential dwellings.
2. A trained technical person must be supervising the installation at all times.
3. Switchboards and outlets supplied by balanced power must be properly identified and marked.

For more on the text of the code, please look here: http://www.equitech.com/support/647.html. The link is from Equi-tech’s website. The code also addresses proper grounding techniques, and proper overload protection.

Here is a schematic of the conditioner I am building:

It is based on the Cheapskate Unit with a few modifications – notably, fuses on both legs of the secondary of the transformer and a double-pole switch. Some things to note are:

• The transformer does not have an electrostatic shield. It is probably preferable to have one.
• The ground on the balanced power side is tied to the incoming safety earth on the primary side. To meet the code, one would need to run a separate ground wire on the balanced power side to the grounding rod for that facility. This was of course infeasible for me.
• Each leg of the balanced power side is fused. This is OK, but I would rather have a double-pole breaker in there, with independent overload sensing on each pole, and common trip. Thus, either pole on the balanced power side can trip on its own, and also open the other pole simultaneously. With separate fuses, we do not get that feature. According to code, such breakers must be used in a technical power installation.

The unit will be built in a 16” x 12” x 3” Par Metal chassis. Here is a picture of the back of the unit with all the drilling and filing completed. Warning: my metal working skills are rudimentary, and even that is being very generous. It took me about 3 hours, with the bulk of the time being taken by the IEC socket cutout. Luckily aluminum is not so hard to file.

I will post more details, and pictures of the completed unit.

Ashok

Disclaimer: I am not an electrician, just a hobbyist. You are dealing with high voltages that can kill, so please be careful. My balanced power conditioner is not UL/CSA approved, nor will it meet any residential electrical codes. If you decide to build it, it is at your own risk.

 

[Grainger49]

NICE WORK ! ! !

Equi=Tech uses current limiting devices on both of the secondary leads as well. But fuses are better over current protection than a breaker... after the breaker trips once. But I understand wanting to clear both sides of the power.

Please post a picture of the inside, that's the good stuff!

 

[ashok]

Please post a picture of the inside, that's the good stuff!

Certainly, I will. I hope to work on it this week and get it wired.

Re: clearing both legs on the secondary side, what about a relay operating at 120VAC? The relay coil will be connected to the right-side of the fuses. Two N/O open contacts of this relay will now be used in place of the double-pole switch. If the fuse on one side, or the other blows, the relay will drop out, and open both of its contacts.

The only issue with this approach is that the contacts of the relay will switch the same voltage that the coil operates on. Is that a problem?

For the moment, I will reduce the value of the fuse on the primary side to less than 8A. That way, an overload will hopefully blow that fuse first.

One thing that my schematic did not show is Vishay X2 rated capacitors across the balanced power outlets. These perform additional filtering.

Also, one of the outlets, as you can see, is not wired through the Schurter filters. I hope to use that outlet for my amplifier. I think the Avel transformer will have enough juice for it - it is rated at 800VA.

My amp is the diytube ST35, with the power transformer rated at 176VA. So, even assuming a 3x draw from the amp, the Avel should still hold up.

 

[Grainger49]

Ok, yes a relay downstream of the fuses could clear both phases simultaneously.

There is no problem with the relay contacts having the same voltage on them that the coil does, as long as both the coil and contacts are rated for the proper voltage and current.

I'll bet you are fine as long as you start your sources, wait 5 seconds and then power up your amp. Tube equipment has higher inrush current but it settles out very quickly.

Sounds like a good plan.

 

[MudPuppy176]

I don't understand why the secondary is fused at all. If the primary is fused at a size to protect the transformer, that's all you need. If an overcurrent condition occurs from excessive secondary load or a fault, the fuse blows and all is protected. I've installed a lot of transformers in my day and have never protected the secondary. Fuses are "better" than breakers in such cases because they generally open much faster. They are 'worse" because they have to be replaced rather than simply being reset.

 

[ashok]

I don't understand why the secondary is fused at all. If the primary is fused at a size to protect the transformer, that's all you need. If an overcurrent condition occurs from excessive secondary load or a fault, the fuse blows and all is protected. I've installed a lot of transformers in my day and have never protected the secondary. Fuses are "better" than breakers in such cases because they generally open much faster. They are 'worse" because they have to be replaced rather than simply being reset.

I agree. If the primary fuse is sized so that it blows for any secondary overload, then there is probably no need for any protection on the secondary. But I was going by the text of the code (copied from Equitech's website):


647.4 Wiring Methods

(A) Panelboards and Overcurrent Protection. Use of standard single-phase panelboards and distribution equipment with a higher voltage rating shall be permitted. The system shall be clearly marked on the face of the panel or on the inside of the panel doors. Common-trip two-pole circuit breakers that are identified for operation at the system voltage shall be provided for both ungrounded conductors in all feeders and branch circuits.

The key phrase, as I interpreted it, is "both ungrounded conductors".

 

[Grainger49]

I don't understand why the secondary is fused at all. . . . .

The rest of that doesn't matter.

NEC states that all "Ungrounded current carrying conductors must be protected from an over current condition." And the transformer does that, lifts ground from both conductors [they are both hot, there is no neutral])

There is a rule that exempts feeders of 3' or 6'. I forget, I have slept since reading the NEC. But the balanced power setup is a "separately derived power source" that requires over current protection for both conductors!

The NEC (from the National Fire Protection Association, who is trying to keep your house from burning down) is adopted by most municipalities.

If you live in the country feel free to ignore that and smoke! (Not really!)

Ashok needs to read further. (I did this for a living for 20 years, the "separately derived source," and "all ungrounded conductors" are in there.)

 

[ashok]

Grainger,

Please be assured, I am not going to do any such thing as remove the fuses on the secondary legs. They will be there for sure. The reason I put in those fuses in my schematic was because of what I read in the code, as I said in my previous post.

Further, even if it were not a technical power set up and simply an isolation transformer, I suppose one would not want to depend on the primary side fuse alone. The feeders on the secondary side must be protected individually, right?

Thanks,

Ashok

 

[MudPuppy176]

Incorrect. There is no need to protect the secondaries of a separately derived system. You're reading the wrong section of the code. Its not too user friendly.

 

[MudPuppy176]

The rest of that doesn't matter.

NEC states that all "Ungrounded current carrying conductors must be protected from an over current condition." And the transformer does that, lifts ground from both conductors [they are both hot, there is no neutral])

There is a rule that exempts feeders of 3' or 6'. I forget, I have slept since reading the NEC. But the balanced power setup is a "separately derived power source" that requires over current protection for both conductors!

The NEC (from the National Fire Protection Association, who is trying to keep your house from burning down) is adopted by most municipalities.

If you live in the country feel free to ignore that and smoke! (Not really!)

Ashok needs to read further. (I did this for a living for 20 years, the "separately derived source," and "all ungrounded conductors" are in there.)

You've both slept and dreamed. I do this for a living today and know better.

 

[Grainger49]

Sorry Ashok, I forgot that it was your thread, and that you had said you would protect the secondary.

For MudPuppy, what about protecting all ungrounded conductors? Just how long have you been doing this for a living? How many fatalities have you see?

 

[ashok]

Sorry Ashok, I forgot that it was your thread, and that you had said you would protect the secondary.

Grainger,

No problem at all. I appreciate the fact that you share freely of your knowledge.

Just to confirm, from NEC 2005, as per Equitech website:

Article 647 of the NEC covers "Sensitive Electronic Equipment".

647.1 Scope. This article covers the installation and wiring of separately derived systems operating at 120 volts line-to-line and 60 volts to ground for sensitive electronic equipment.

647.3 General. Use of a separately derived 120-volt single-phase 3-wire system with 60 volts on each of two ungrounded conductors to a grounded neutral conductor shall be permitted for the purpose of reducing objectionable noise in sensitive electronic equipment locations provided that the following conditions apply.
(1) The system is installed only in commercial or industrial occupancies.
(2) The system's use is restricted to areas under close supervision by qualified personnel.
(3) All of the requirements in 647.4 through 647.8 are met.

647.4 Wiring Methods

(A) Panelboards and Overcurrent Protection. Use of standard single-phase panelboards and distribution equipment with a higher voltage rating shall be permitted. The system shall be clearly marked on the face of the panel or on the inside of the panel doors. Common-trip two-pole circuit breakers that are identified for operation at the system voltage shall be provided for both ungrounded conductors (emphasis mine) in all feeders and branch circuits.

etc.

I think I am satisfied with that. The local Borders has a copy of the code in their shelves. I will be there tomorrow to read section 647 for myself.

 

[MudPuppy176]

My newest code book is 1999 and has no section 647, but thats a moot point. You're improperly applying the code. There is no panelboard, no 3 wire system in this case. A single phase panelboard has two hot legs and a neutral hence a 3 wire system. This is used when say a 480V primary/120V secondary transformer feeds a panel. There is no overcurrent protection between the transformer and the panel. The branch circuits out of the panel have protection.
Article 240-3(f)states quite clearly:Transformer secondary conductors. Single phase (other than 2 wire) and multiphase (other than delta-delta, 3 wire) transformer secondary conductors shall not be considered to be protected by thr primary overcurrent protective device. Conductors supplied by the secondary side of a single-phase transformer having a 2 wire (single voltage) secondary, or a three phase, delta-delta connected transformer having a three wire (single voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with Section 450-3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary to primary transformer voltage ratio.
etc.
The qualified personnel part, that would be me.

 

[avionic]

Hi everyone,

There have been a number of threads on AK and other places on balanced power conditioners, and the benefits they can bring in reducing the noise floor in an A/V setup. So, I started building one and wanted to share some of the details. It is not complete yet, but I will wire it all up hopefully over the next couple of weeks.

What can balanced power do for you? It can be a little, a lot or nothing at all. It depends on how clean the ac input is to begin with. A good isolation transformer can bring much of the same benefits that a balanced power conditioner can bring – namely, reduction in the common mode noise that might be riding on the power lines. But I suppose a balanced power conditioner can be used to extract the last bit of performance from your system.

In any case, I decided to build one for myself.

Guidelines for balanced or technical power systems have been part of the US National Electric Code for a number of years now. So, if implemented according to code, it can be said that balanced power systems are indeed safe. But there are some important points to note:

1. Balanced power systems are not meant for residential dwellings.
2. A trained technical person must be supervising the installation at all times.
3. Switchboards and outlets supplied by balanced power must be properly identified and marked.

For more on the text of the code, please look here: http://www.equitech.com/support/647.html. The link is from Equi-tech’s website. The code also addresses proper grounding techniques, and proper overload protection.

Here is a schematic of the conditioner I am building:

It is based on the Cheapskate Unit with a few modifications – notably, fuses on both legs of the secondary of the transformer and a double-pole switch. Some things to note are:

• The transformer does not have an electrostatic shield. It is probably preferable to have one.
• The ground on the balanced power side is tied to the incoming safety earth on the primary side. To meet the code, one would need to run a separate ground wire on the balanced power side to the grounding rod for that facility. This was of course infeasible for me.
• Each leg of the balanced power side is fused. This is OK, but I would rather have a double-pole breaker in there, with independent overload sensing on each pole, and common trip. Thus, either pole on the balanced power side can trip on its own, and also open the other pole simultaneously. With separate fuses, we do not get that feature. According to code, such breakers must be used in a technical power installation.

The unit will be built in a 16” x 12” x 3” Par Metal chassis. Here is a picture of the back of the unit with all the drilling and filing completed. Warning: my metal working skills are rudimentary, and even that is being very generous. It took me about 3 hours, with the bulk of the time being taken by the IEC socket cutout. Luckily aluminum is not so hard to file.

I will post more details, and pictures of the completed unit.

Ashok

Disclaimer: I am not an electrician, just a hobbyist. You are dealing with high voltages that can kill, so please be careful. My balanced power conditioner is not UL/CSA approved, nor will it meet any residential electrical codes. If you decide to build it, it is at your own risk.

What VA rating is the toroid?

 

[MudPuppy176]

Sorry Ashok, I forgot that it was your thread, and that you had said you would protect the secondary.

For MudPuppy, what about protecting all ungrounded conductors? Just how long have you been doing this for a living? How many fatalities have you see?

I have unfortunately seen quite a few fatalities. More than one attributed to people who think they can do an electrician's job. I took the IBEW oath in 1979 if that really matters. The code book is a very poorly written document, IMHO. If you don't deal with it a lot its very easy to be in the wrong section and/or apply the wrong section.

 

[ashok]

What VA rating is the toroid?

It is 800VA.

 

[Grainger49]

I have unfortunately seen quite a few fatalities. More than one attributed to people who think they can do an electrician's job. I took the IBEW oath in 1979 if that really matters. The code book is a very poorly written document, IMHO. If you don't deal with it a lot its very easy to be in the wrong section and/or apply the wrong section.

And again, you don't say anything about protecting ungrounded conductors.

As I see now, you should know that!

 

[ashok]

My newest code book is 1999 and has no section 647, but thats a moot point. You're improperly applying the code. There is no panelboard, no 3 wire system in this case. A single phase panelboard has two hot legs and a neutral hence a 3 wire system. This is used when say a 480V primary/120V secondary transformer feeds a panel. There is no overcurrent protection between the transformer and the panel. The branch circuits out of the panel have protection.
Article 240-3(f)states quite clearly:Transformer secondary conductors. Single phase (other than 2 wire) and multiphase (other than delta-delta, 3 wire) transformer secondary conductors shall not be considered to be protected by thr primary overcurrent protective device. Conductors supplied by the secondary side of a single-phase transformer having a 2 wire (single voltage) secondary, or a three phase, delta-delta connected transformer having a three wire (single voltage) secondary, shall be permitted to be protected by overcurrent protection provided on the primary (supply) side of the transformer, provided this protection is in accordance with Section 450-3 and does not exceed the value determined by multiplying the secondary conductor ampacity by the secondary to primary transformer voltage ratio.
etc.

Wow, my project seems to have set off quite the firestorm. But no matter, if I learn something at the end, it would be worth it.

Article 647 was introduced in 2002, if I am not mistaken. Prior to 2002, the contents of 647 used to be in article 530-G.

The way I see it, the primary of the transformer is two-wire, but the secondary is no longer a 2-wire system. There are two hot legs, each at 60V with respect to neutral. I would consider this a three-wire system. Certainly, the loads are connected across the hot legs, but the system is three-wire.

According to 240-3(f) as you have quoted, if the secondary is single-phase (other than 2-wire), transformer secondary conductors shall not be considered to be protected by the primary-side overcurrent device.

I would submit that you need to protect each secondary leg. Further, clearing should occur on both poles, irrespective of which pole the protection operated.

Regards,

Ashok

 

[cfranz]

It occures to me in situations like this that an old professor of mine used to say: The average human body can make a practical 100 watt, 47K ohm resister.

This, of course, was back when a 47K ohm 100 watt resister was big bucks, and students were a dime a dozen.

Be careful.

 

[Grainger49]

All in all, it is good to protect more than is required, if you are of the opinion that protection is not required.

Can't hurt, can help.

I'm unsubscribing.