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Balanced vs standard power

Searching for an Isolation Transformer 10 or 15kva. I have the budget for Equitech but I'm sold only on the benefits of isolation and not "yet" on the benefits of balanced power unless one is recording live musicians. My rationale is that most if not all audio components are not designed with balanced power so they may be optimal performers with standard power and lesser performers with balanced power. Until someone does a side by side comparing isolated balanced to isolated standard power we may never know.

I have read the various threads regarding isolation transformers from Equitech 10wq, MGE Topaz etc, and the Euqitech stereophile review. For larger non-balanced options there is Ultra K 600 with K factor correction and triple shielding from the Controlled Power Company. They range from 5 to 25 kva.

I think supersizing Isolation transformers for audio is not well recognized yet because no one has done the necessary review/ comparisons to determine the performance curve of Isolation Transformer size to Audio Performance. Although Isoclean advocates the use of two of their Isolation Transformers for each piece of equipment. Maybe they're trying to tell us something or just sell more transformers. 10 KVA is "plenty" for my system according to Martin at Equitech, but "plenty" is not quantified enough to convince me, so I 'm leaning toward the 15kva on the Ultra K 600 from Controlled Power about $4000 vs Equitech 15 kVA at upwards of $14000.
natan6355
almarg's avatar
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almarg
9,670 posts
 
03-11-12: Jea48
Norm has the transformer configured for balanced power. That cuts the KVA rating of the xfmr in half. The xfmr maximum continuous FLA rating is 5 KVA.
Good point, Jim. Agreed.
03-11-12: Jea48
Just wonder if the poor PF, caused by too much capacitance on the AC line, is doing anything to the power xfmrs and switching power supplies of his audio equipment. You are the EE here.... What say you?
Good question, which I had been wondering myself. I don't know the answer.
03-11-12: Norm
Would you please elaborate how increasing the capacitance to the secondary side of the transformer may cause voltage to "lag"?
The voltage across a capacitor cannot change instantly. It changes in response to the accumulation or depletion of the charge it is storing, which in turn is proportional to the integral of current, over time. As a consequence of that, for a sinusoidal AC waveform of a given frequency, and assuming an idealized capacitor model, and since the integral of a sine wave is an inverted cosine wave, the voltage across a capacitor will lag the current by 90 degrees, or 1/4 cycle.
03-11-12: Norm
Also, how much additional current is the transformer "pulling" by adding 220uf.
10 amps, based on the assumption that 120 volts is placed across the 12 ohm impedance which the capacitor has at 60 Hz.
03-11-12: Norm
Jim, are you saying that by adding 220uf to the circuit I have effectively lowered my 10kVA xfmr rating to 5kVA?
No, the capacitor has nothing to do with that, although the capacitor significantly increases the amount of current the transformer has to supply, and significantly increases how much of the 5 kVA capability is being utilized. Referring to the data sheet for the transformer, each of the two secondary windings is rated to handle 41 amps. Presumably you have them connected in series, with nominally 60 volts appearing across each winding, and 120 volts across the series combination. 120 x 41 = 4920 VA, or a little under 5 kVA.

Also, to make sure I'm envisioning your setup correctly, I'm assuming that the two primary windings are connected in series, and are fed by a single-phase 120V line and breaker rated at 40 amps or more. Is that correct?

Best regards,
-- Al
jea48
4,268 posts
 
Are you saying that by adding 220uf to the circuit I have effectively lowered my 10kVA xfmr rating to 5kVA?
03-11-12: Norm
Norm,

I agree with Al's explanation.

Not sure why the manufacture shows 41 amps FLA for each winding instead of 41.67A.... 5000 Va / 120V = 41.67A.
Could be the size of wire he used for each winding. Or maybe he just rounded the number down.
I am just guessing he used # 8 copper wire.

One thing for sure the specs given are for the nominal input and output voltages shown on the data sheet.
Without actual load testing the power the xfmr could deliver under full load, configured for 60/120V, is unknown. Remember you are halving the voltage fed to the primary of the xfmr. 60V across each winding.

JMHO,....
I would have configured the xfmr primary for 240V and the secondary for single phase 120V out.
The full 10KVA rating of the xfmr could then be utilized.
FLA rating would be 82 amps instead of 41 amps. Your power amplifier will appreciate it.

Ditch the 220uf capacitor and the added cost of the wasted electrical power it is consuming.

Also, to make sure I'm envisioning your setup correctly, I'm assuming that the primary windings are connected in series, and are fed by a single-phase 120V line and breaker rated at 40 amps or more. Is that correct?
03-11-12: Almarg


Al,

Per NEC code the minimum would be 125% of the xfmr name plate FLA rating. 41 x 125% = 51.25 amps, roll up to a 60 amp breaker.

If the secondary of the xfmr has overcurrent protection the primary overcurrent protection can be as high as 250% of FLA rating.
Jim
norm's avatar
norm
52 posts
 
Hi Al,

Thx for your thorough explanation.

A 2 x 20 amp breaker tied together a single=phase 120v line is feeding the Primary windings of the xfmr. The Secondary side of xfmr is also connected in series. Thus, -60V/+60V.

Would you care to take a guess what is happening to the electronics(tube gear) with voltage and amperage being 1/4 cycle out? The overall results with the additional capacitance is a big improvement, especially LF.
Am I doing any damage to my xfer and/or electronics by the additional capacitance?

Best regards,
Norm
norm's avatar
norm
52 posts
 
Thx Jea. You are correct. By adding capacitance to the secondary side this did raise the output voltage to approx. 1v. However, input voltage is still 2V higher than output voltage.

Hi Al,

Would you please elaborate how increasing the capacitance to the secondary side of the transformer may cause voltage to "lag"? Also, how much additional current is the transformer "pulling" by adding 220uf.

Best reagrds,

Norm
norm's avatar
norm
52 posts
 
Hi Jim,
Currently the xfmr is configured for Balanced powered, -60V/+60V, to reduce unwanted noise by CMR (by 10-12 db?). If I were to, configured the primary for 240V and the secondary 120V out, as you suggested, would I not be using the DU-10 as an isolation transformer as opposed to BP? If this is the case, what are the pro/cons, besides doubling the amperage capacity from my present set-up?

Best,
Norm
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