Dodgy step down tranny

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** Hi all,

a repair job arrived last night accompanied a step-down tranny  -  the
repair is a US made amplifier that requires 120 volts AC at 60Hz  - but
copes with 50 Hz all right.

The step-down tranny was supplied here in NSW by an eBay seller:

See: www.rhinotools.com.au

It is labelled as "2000W' and  240V to 110 V "  plus the words  "Korean
Technology".

The unit I have here is similar to ones on his eBay shop now, but not
identical.

Inside is a toroidal **autotransformer**.

Problems:

The unit cannot possibly deliver 2000 watts -  the max continuous rating
should be no more than 500 watts. The resistance of the 240 volt winding is
5.6 ohms at room temp. Do the math.

The unit does not output 110 volts under load  -  tested with a 500 watt
resistive load, it outputs only 103 volts.

The only protection for the transformer is via a fuse holder on the back
fitted with a glass fuse rated at 10A  - though the holder is not labelled
with any value.

Anyone smell smoke ??


.... Phil












Re: Dodgy step down tranny
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Well, it would certainly get quite hot at its rated output, but I don't
think I'd expect smoke. If it's the same size as the one on the website,
it's reasonably large, and it only has to get rid of 50-60W.

A buyer would have a justifiable gripe at the output voltage drop. You
don't mention any apparent provision for tap switching, so I assume
there's none.

Sylvia.

Re: Dodgy step down tranny
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the

The size of the case is irrelevant, they could shove a very small
transformer inside
you need to see the internal transformer to make such a judgement.

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Re: Dodgy step down tranny

"kreed"

The size of the case is irrelevant, they could shove a very small
transformer inside
you need to see the internal transformer to make such a judgement.


** Err -  the weight might be a good guide.

The unit I have here weighs just under 3.8 kg including the attached lead.


... Phil





Re: Dodgy step down tranny
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Then it's not the same as the 2kW version on the website, which weighs
12.5 kg. Indeed, it has a similar weight to the 500W version.

Perhaps there's a QA problem with labelling.

Sylvia.

Re: Dodgy step down tranny

"Sylvia Else"
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** Funny about the 10amp fuse being fitted  ....

  Plus a 2kW version of the tranny would not fit in the box.


....  Phil





Re: Dodgy step down tranny
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That could just be a consequence of the mislabelling, or perhaps it's
not the original fuse. Some people can be quite casual about ratings
when replacing fuses - at least it's better than just covering the blown
fuse with metal foil.

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It seems clear that this is not a variant of the currently offered 2kW
model, and that it's not being used in an application that requires
anything approaching that, suggesting that the purchaser probably didn't
expect it to be a 2kW transformer either.

Any chance of your posting a (link to a) picture of the offending item's
front panel?

Sylvia.

Re: Dodgy step down tranny
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Interesting too how the 3kw version seems to have (hard to read) a
32amp breaker on the front panel.
Unless they are fusing the secondary  with it.


Re: Dodgy step down tranny

"kreed"

Interesting too how the 3kw version seems to have (hard to read) a
32amp breaker on the front panel.
Unless they are fusing the secondary with it.

**Bound to be in the secondary.

The unit I have here has the fuse fitted in the primary cos at 18 amps
nominal -  the secondary side would need a fuse and fuse holder bigger than
is cheaply available.

The toroidal auto-tranny inside looks roughly made and carries no labelling
at al.

Dimensions are 120mm dia and 75mm high.

There are just three light gauge, flexible wires coming out.


.... Phil





Re: Dodgy step down tranny

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Three wires indeed makes it an autotransformer. In my copy of AS3000,
section 4.28.4 (Autotransformers) clause 2 states: "Prohibited use.
Autotransformers shall not be used for reducing or controlling the voltage
to equipment which is liable to be handled in normal use."

Seems like the amp you are trying to repair is part of  an all too common
illegal setup; be careful Phil.
--
Regards,

Chas.

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Re: Dodgy step down tranny

"Chas"
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 ** Yep -  I know that section of AS3000 very well  !!!!

 But AS3000 is the "electrical wiring rules"  - ie the electrician's bible.

 4.28.4 prohibits the * INSTALLATION *  of a step down, auto-transformer for
use with portable appliances.

(IIRC, ones that convert 240v to 220v are excepted from the prohibition )

AS3000  is NOT  relevant to plug-in appliances sold to the public.


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** Nothing illegal about it in Australia, at present.

I have personally campaigned against the open sale of auto-transformer 240V
/120 V step-downs for many years. There was a Forum column about the topic
in EA magazine in the mid 1990s that was due to my efforts.

I pointed out some of the dangers inherent in the use of such transformers
with old, US made appliances like valve radios and guitar amplifiers -
which are now pouring into this country, courtesy mostly of eBay sales.

I believe I was largely responsible for getting Jaycar to drop all but one
of the units they were selling, getting Arlec to stop importing them and
getting Farnell to drop the Arlec brand one they were selling. Unfortunately
eBay sellers appear to be a law unto themselves  - even the ones operating
in this country.

It will probably take at least a couple of fatal accidents before Government
authorities step in and ban them completely.

Even that will be far too late -  as there are currently many thousands in
circulation.


.....  Phil



Re: Dodgy step down tranny

"kreed"
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** At 12.5 kg including box and assuming there is a toroidal tranny inside,
the unit must be an isolation type.



.....   Phil








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However, I noted that their 1kW version weighs quite a lot less than the
1kW isolating step-down transformer from Jaycar.

On the eBay web site the supplier has two 500W step down transformers.
On is an isolating transformer, the other is not. The isolating
transformer weighs 12kg, the non-isolating version only 3.4kg. Since
they've expressly identified one transformer as isolating, but none of
their other transformers that way, it seems reasonably safe to assume
that the others are autotransformers.

Sylvia.

Re: Dodgy step down tranny

"Stupider than Anyone Else Alive"

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** The Jaycar one is obviously an E-Core type  -  see the pic ??

An E-core will be up to double the weight of a comparable toroidal type.

An auto-transformer will be around half the weight of a comparable isolation
type.



....  Phil



Re: Dodgy step down tranny

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Even at 12.5kg I doubt the 2kW rating is genuine. I have a 1kW rated
isolation transformer which weighs in at over 16kg - and that isn't in a
case. Admittedly, mine is not a toroidal but the variation in weight for a
supposed 2kW toroidal versus a 1kw E-I tranny is still an indication of lack
of truthfulness in the rating for this tranny.



Re: Dodgy step down tranny

"Ross Herbert"

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** A 2kVA toroidal *auto-transformer * uses the same core size as a 1300 VA
isolation type.

Makes the weight around 11kg plus box.

The stupid thing is the 110 volt rating - which suits neither the US or
Japan.

And if they deliver only 100 volts or so ON LOAD -  like the one I have
ere  - they are suitable for Japanese local market gear only.

The valve amplifier that came with that " dodgy step down " loses 40% of its
normal output power when used this way.


.....  Phil










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You are correct.  There is a specified weight in the listing.

This is a pretty good guide as to what to expect in VA rating.

Re: Dodgy step down tranny
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I'm assuming the case is as small as they can make it, simply because
that reduces the cost, and increases the potential profit.

Also, it weighs 12 kg, so it either contains a metal brick, or has a
hefty transformer.

Anyway, Phil has correctly pointed out that I've made a mistake in
calculating the heat to be dissipated given the resistance he measured.

Yet I can't help thinking that something that heavy should be able to
achieve more than 500W. Perhaps Phil could post its exterior dimensions
- it may simply have been mislabelled.

Sylvia.

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**The mass SHOULD be a giveaway. However, I've worked on more equipment than
I care to think about, where the manufacturer (usually Chinese) has
incorporated large pieces of non-structural steel to increase the mass of
the product. I've even seen all-aluminum chassis devices, where steel has
been used to increase mass. The first time I saw this done, was with an
Onkyo (Japanese) CD player, back in the 1990s. The CD player weighed in at a
hefty 25-odd kg. More than half that mass was the result of a large piece of
steel bolted to the base plate. Without opening the player, an owner would
never realise that it was the reason for all that mass.

Mild steel plate is still less expensive than copper and laminated iron (in
the shape of a transformer).


--
Trevor Wilson
www.rageaudio.com.au



Re: Dodgy step down tranny
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Seems an odd thing to do with a CD player, given that I wouldn't have
thought a consumer would expect it to be particularly heavy - and
certainly not 25kg heavy.

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Yes.

In this particular case it's become apparent that there's a disparity
between the mass of the example Phil has, and the mass of the 2kW model
on the website. I suppose the website could just be mis-stating the
mass, but anyone who paid attention to it on the website would notice
the difference as soon as the transformer was delivered.

Sylvia.


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