[Syrah]

Hi All,

I have a power question.  I own a Signal Transformer DU-2, which is a dual core iso trannie that I rigged up following Jon Risch instructions.

As it stands, it is wired for 120v unbalanced primaries in and 60-0-60 balanced secondaries out.

I have been thinking about wiring it instead as a step down from my home's 240v balanced.  I can't help but think (perhaps wrongly??) that two 120v balanced lines are better than one.

I read that to do this I need to wire up the primaries in series with the 120-0-120 in and in parallel on the secondaries.  Agree?  Disagree?

Will this then give me 60-0-60 on the secondaries or will it give me 120v unbalanced? 

If 60-0-60, is there any way I can wire it to give me 120v unbalanced?  I'm asking because my PS Audio PPP is designed to take unbalanced 120v.  In a truly perfect world, I could tap the secondaries twice - once to give me 60-0-60 and a second line with 120 unbalanced for my PPP.

I was going to use this handy chart which sets out "in parallel" vs. "in series" wiring - http://hammondmfg.com/5CHook.htm .  Oh yeah, before the (much appreciated and much warranted) safety warnings start, my plan was to wire it up then take it in to my local electrician to have it "inspected" before plugging it in.  I don't trust myself enough.

Thanks in advance.

[Speedskater]

For the best way to wire the isolation transformer go to:

http://www.exactpower.com/wpapers.aspx

Download the "Truth" paper.

Read the whole thing, but the important part is pages 26 &27.
A 240 Volt input and two paralleled 120 Volt unbalanced secondary's is way better than a balanced system. By the way NEC 2008 does not permit unbalanced systems in residencies.

[Syrah]

Thanks for this.  Does the Exact Power chart contemplate 240v in and 120v out?

My question is, if I wire it as below (primary in series, secondary in parallel) do I get 120-0 or 60-0-60 on the output?


120           120
 |     ___     |
 |     |   |    |
 1     2  3    4
 ____   ____  Primaries

 ____   ____  Secondaries

 8   7   6    5
      _ ____
 |   |        |
 _____
 |       |
 |            |

 0          120?

       OR

 60        60?

 Thanks.

[BPT]

Syrah:
On the DU, with primaries in series and secondaries in parallel you will have an unbalanced 0-120 output. Make sure you use the correct taps.

Speedskater:
NEC does not recommend in-wall balanced 120VAC. Stand alone external units like BPT or Equitech are fine. In the 2010 NEC code there very well may be a recommendation for in-wall balanced 120VAC.

Chris H.

[Syrah]

Excellent!  Thanks for this Chris.  I've inserted the corresponding numbers below for the DU taps (which is a 1:1 transformer as you seem to know).  Is this still correct?

Also, looking at the Exact Power chart (and using the numbers 1 to 8 for the taps below) which ones should get connected to ground?  2 & 3 only?

I have grounded the shield and the box it's in, and obviously connected a ground wire to the "out" wire, to ground the components.

I'm happy about this, it also seems to increase the max output amps to 18 from 9 when wired in parallel on the secondaries.


120                120
 |       _____      |
 |       |     |      |
 1       2    3      4
(120) (0)(120) (0)
 ______   ______  Primaries

 ______   ______  Secondaries

 8      7     6      5
(120) (0)(120) (0)
         _________
 |      |             |
 _________        |
 |                     |
 |                     |

 120                 0

[BPT]

Syrah:
What are you trying to do? I think you may be confusing an external box isolator with a mains AC panel set-up. The information at Exact Power refers to a mains AC panel set-up (neutral to earth ground) and must be installed only by a qualified electrician--it is not for DIY. An external DIY box type isolator would maintain the existing household earth ground from input through output (neutral not connected to earth ground).
Chris H.

[Syrah]

It's an external box. 

So I take it the ground just connects to the shield and flows through to the output and I should ignore the Exact Power diagram and leave 2 and 3 alone.

Otherwise, is my wiring diagram right?

Thanks again for your help.  Much appreciated!

[BPT]

Syrah:
You didn't say if this is in the US, where we have have balanced 240VAC or somehwere else that might have single ended 240VAC.
Chris H.

[Syrah]

Thanks Chris.  It's in the Caribbean - same wiring as in the U.S.  My current setup on the DU-2 is per Jon Risch's formula, so it's single ended 120v in, 60-0-60 out.  But I think it might sound better and give me more juice with 120-0-120 in, 120-0 out.

It sounds like I'm almost there.

If I connect the 240v using a standard 3 or 4 prong dryer plug, black and red go to 1 and 4 on the primaries.  Green is ground and (as discussed) just flows through to output ground.  This leaves me with white (neutral).  Should that go to 2/3 on the primaries or should it just float?

Once again, I'm taking the whole rig to my local sparky before plugging it in.

[BPT]

3 is all you need, 120V , 120V and ground, 2 & 3 you can float. However, you will not get any more power than your previous set-up and you will still only have one balanced line (this time at the input). What you are basically doing is trading a balanced output for a balanced input. Probably just best to leave it the way you have it.
Chris H.

[Syrah]

Will it not reduce common mode noise by using balanced power on the input?  My simpleton understanding was that if there is noise on one 120v line that is not on the other 120v line, I thought this can be reduced (cancelled out) by using both as balanced power?

Also, I thought the DU-2 needed to be downgraded to 9 amps if used in my current configuration (balanced out), but it will give me the full 18 amp quack if wired the other way.

The other reason I was thinking of doing this is because my PS Audio PPP only conditions the hot line, so it does not respond well to balanced power.  As a result, I have the iso trannie running some of the components and the PPP plugged into the wall running the critical stuff.  But I'd like to try the PPP with isolated power.

Obviously, if you don't think it will improve things I won't waste my time.

Many thanks again!

[BPT]

Yes, balanced AC reduces common mode, whether at the input or output. Sorry, I needed to reread your initial wiring set-up. Doing too many things at once. You will have more power with the secondaries in parallel. Give it a try and let us know, if you get overall improvements. Make sure you test the output with a meter before you plug anything in.
Chris H.

[Syrah]

Thanks again for your help with this Chris.  I wired it up per the above.  It gave me 120 balanced rather than 120 unbalanced.  It was a clear improvement over the former set up with 120 in vs. the new 240 in.  More dynamic sounding.

I did several A/B tests, mostly with my amps.  They still sounded best plugged into my PS Audio PPP.  It sounded best plugged into the wall rather than plugged into the iso trannie (even in its new configuration).

Any way I could get 120 unbalanced out with 240 balanced in?  The PPP is really meant to be fed an unbalanced 120v line.

PS I'm going to ping you off line about an umbilical for my Supratek pre.

[Occam]

Syrah,

Actually, you don't have balanced 120vac (60-0-60) with your wiring. With the DU-2

you cannot derive balanced 120vac when the primaries wired in series for 240vac. What you do have is isolated 120vac, where the voltage is unreferenced to ground.
http://www.csemag.com/article/176827-Isolated_power_systems_for_healthcare.php
When you measure the voltages, unloaded, you might well measure (60-0-60) but it is not balanced, technical power.

In order to get single ended 120vac from the paralleled secondaries, you need to rebond the safety ground, to reestablish the neutral, to one of the paralleled secondary wires. Which one will determine what phase you get.

As you mentioned that you have a 4 wire 240vac outlet, you have an opportunity to avail yourself of additional power conditioning efficacy. Those 4 wires are typically -

1)A black wire which is often known as the "hot" wire, which carries the current in to the fixture. This is 120vac referenced to ground.
 
2)Another "hot" wire which is red, which also carries current in to the fixture. This is another 120 vac referenced to ground but of opposite phase to 1) above.

3)A white wire called the neutral which completes the electrical circuit for the 120 volt accessories only.
 
4)A bare copper wire called the ground, the sole function of which is to enhance user safety.

If you wire the primaries and secondaries as you already have for 240vac input and 120vac output (and reestablish neutral by bonding the safety ground to one side of the paralleled secondaries), you can -
a) connect the center tap of the primary to neutral
b) put a capacitor across the 2 hots (black and red). These caps MUST be either X or Y rated caps or a protected motor run capacitor.(or a combination of them.)

The technique is rather spiffy, and is explored here -
http://www.plitron.com/pdf/nbt.pdf
Look at fig.3. Its equally applicable at the primary as well as the secondary.

FWIW,
Paul

[BPT]

If you wire the primaries and secondaries as you already have for 240vac input and 120vac output (and reestablish neutral by bonding the safety ground to one side of the paralleled secondaries), you can -
a) connect the center tap of the primary to neutral
b) put a capacitor across the 2 hots (black and red). These caps MUST be either X or Y rated caps or a protected motor run capacitor.(or a combination of them.)

Paul:
It would be better to connect the primary center tap to ground and one side of the secondary to the neutral wire. The Plitron fig. 3 can also be applied to a linear power supply for DIY components.
Chris H.

[Occam]

Hi Chris,

I'm not a P.E. so I can't speak to this with any authority. My understanding is that at a at new 'point of service' neutral is reestablished via a bond to safety ground. I've not mentioned this technique previously, specifically because split phase 240 vac In North America is ofttimes only 2 hots and a safety ground. Obviously, you  realize that the net flow at the center tap (like the center tap on the secondary of a technical balanced power output transformer) nominally nets to 0, and is not retuning significant current. Perhaps fusing the 240vac with GFI breaker at the supplying panel or the transformer's input would address this issue. So the answer is, I don't know from a code/liability perspective. I'd think a definitive answer could be obtained from the right tech person at Plitron/Torus/Brystron, as I believe this configuration is exactly what is used on the Torus conditioners when fed by split phase 240vac.[I'd assume they also have a non current supplying control winding on the secondary, but that is covered by Menno Van der Veen's patent] So I'd think they'd have addressed this issue as 4 wire 240vac outlets are typically found only in kitchens and laundry rooms, and elsewhere 3 wire, with no neutral in addition to safety ground.

I've often put a cap across the secondary of a center tapped transformer (single bridge) on linear supplies. I'm unsure as to the specific benefit, whether as a counterbalance to the inductance of the transformer interacting with the rectifiers, or as an adjunct in minimizing mains noise. But its probably a combination of both. On a typical split rail ps, the current draws are not differentially balanced, so the efficacy of using a current carrying secondary also as a control winding would be somewhat compromised. An exception to this would be a linear supply to a split rail balanced bridged amp where the rail draws are balanced.

FWIW,
Paul

[Syrah]

Hi Occam. Excellent. Thanks again for your advice.

It's actually a 3-wire dryer plug that I'm using for now - just to figure out if the improvements warrant putting in another plug.

Would these be two 120 hots and a neutral or two 120 hots and a ground?  I suspect it's a neutral.

Either way, I have a nearby 120v socket that I can use for the neutral or the ground.  Unlike my old house, it's a proper ground with a big copper rod outside.

So let me make sure I've got the steps right.

1) I pick one secondary hot (pressumably the nominal neutral side so my equipment stays in phase) and hook it up to ground?
This does seem strange to hook a live wire to ground?  This won't trip anything?  My ground will stay quiet?  This will then give me 120 on the other hot?

2) I then wire neutral to the center tap of the primary (these are the 0 and 120 that are connected together)?

3) I have already done the cap trick.  On the primaries I have Auricap 0.1, .01 and .001 on the secondaries I have 0.47, 0.1, .01 and .001 - across the line in both cases.  I take it I can keep these.

Cheers.

[Syrah]

Sorry guys.  I just read the subsequent posts.  I will wait for a consensus before proceding.

[Occam]

It's actually a 3-wire dryer plug that I'm using for now - just to figure out if the improvements warrant putting in another plug.

Would these be two 120 hots and a neutral or two 120 hots and a ground?  I suspect it's a neutral.[

Assuming its a dedicated line with its own service panel breaker, using standard States side plugs the 3rd wire is a safety ground. You'd use this wire to reestablish your neutral on one side of the paralleled secondaries as well as to connect the shield between primary and secondary. This will give you that 240vac in, 120vac single ended ouput.  This would be standard practice in configuring a non-medical step down transformer. (Chris, please chime in as necessary).

Either way, I have a nearby 120v socket that I can use for the neutral or the ground.  Unlike my old house, it's a proper ground with a big copper rod outside.

I wouldn't think your electrician would approve of that. A neutral (a separate grounded conductor) would need to be added to the dedicated line if you needed a neutral. A line from a different circuit shouldn't be re-purposed.

So let me make sure I've got the steps right.

1) I pick one secondary hot (pressumably the nominal neutral side so my equipment stays in phase) and hook it up to ground?
This does seem strange to hook a live wire to ground?  This won't trip anything?  My ground will stay quiet?  This will then give me 120 on the other hot?

Yup. Unless you re-bond one side of the secondary to safety ground, a ground fault inside your components, like the power transformers winding shorting to the chassis, will not trigger the proper ground fault response of tripping your breaker/fuse. While this is great when working on a 'live' (powered) component internally for diagnosis of problems, it doesn't alert you to a potentially fatal condition. No, you are not adding noise to the ground, you are referencing an unreferenced circuit, to ground. (indeed one could have a meaningful epistimological debate on this but serves no purpose, as this re-bonding is a requirement for non-medical isolation transformers.)

2) I then wire neutral to the center tap of the primary (these are the 0 and 120 that are connected together)?

I believe the safety ground would be equally proper, but you should get the opinion of both Chris and your electrician.

3) I have already done the cap trick.  On the primaries I have Auricap 0.1, .01 and .001 on the secondaries I have 0.47, 0.1, .01 and .001 - across the line in both cases.  I take it I can keep these.

Its not a trick, its MAJIK circuit analysis. I'll simply point out that Auricaps are not approved for use across mains lines, and its between you, your family and potentially, your insurance adjuster. I've never heard of a 630 v Auricap failing in 120vac use, or a 1000v with 240vac, but that is anecdotal , and they are not tested and approved (by testing laboratories whose 'seal' is for insurance purposes) for across the line use.

The proper amount of capacitance across the primary would be determined by measuring the transformers leakage inductance, but less than 1 uf  isn't too much.

You could simply wire the safety ground to both the electrostatic shield and one of the secondary winding's leg, and defer deciding about grounding the primary's center tap until you get more consensus from those you trust.

Regards,
Paul