Dodgy step down tranny

[Phil Allison]

** 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

 

[Sylvia Else]

** 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 ??

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.

 

[Sylvia Else]

Also note that he has a 3000W transformer on his website. Would be
interesting to see if this had a 15A plug

Perhaps just two 10A plugs

Sylvia.

 

[Phil Allison]

"Stupider than anything Else on Earth"

** Burn the witch !

Well, it would certainly get quite hot at its rated output, but I don't
think I'd expect smoke.

** Do the math - you stupid fucking bitch.

Try using " I squared R " maybe ......

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.

** Wrong in both cases.

A buyer would have a justifiable gripe at the output voltage drop.

** The voltage dropped 7 volts ( from 110V) at 500 watts with the input kept
steady at 240V.

Do the math for 2000 watts.


..... Phil

 

[Sylvia Else]

"Stupider than anything Else on Earth"

** Burn the witch !




** Do the math - you stupid fucking bitch.

Try using " I squared R " maybe ......

Yes, you're right, I had a brain spasm. Just as well you've never made a
mistake.

** Wrong in both cases.



** The voltage dropped 7 volts ( from 110V) at 500 watts with the input kept
steady at 240V.

Do the math for 2000 watts.

I did make a comment about tap switching.

Sylvia.

 

[Phil Allison]

"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

 

[Sylvia Else]

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.

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.

 

[Sylvia Else]

"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.

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.

 

[Trevor Wilson]

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.

**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).

 

[Phil Allison]

"Sylvia Else"

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.

** Funny about the 10amp fuse being fitted ....

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


..... Phil

 

[Sylvia Else]

**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.

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.

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

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.

 

[Phil Allison]

"Stupider than anyone Else on Earth "

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.

** They are two different models.

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.

** FFS - read the OP.

The stepdown I have here is probably several years old.


..... Phil

 

[Sylvia Else]

"Sylvia Else"


** Funny about the 10amp fuse being fitted ....

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.

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

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.

 

[Phil Allison]

"Stupider than Anyone Else Alive or Dead.

** Burn the witch.

That could just be a consequence of the mislabelling,

** Blah, blah blah,

The fuse holder is NOT labelled at all.

It seems clear that this is not a variant of the currently offered 2kW
model,

** The unit is from the same supplier - that is all I ever claimed.

FFS read the OP again and again til you GET IT !!

that it's not being used in an application that requires anything
approaching that,

** So fucking what ??????????

In the future it may have an owner who needs the whole 2kW.

The owner may loan it to another to use with say 2kW of 110 volt lighting.

Smoke will get out in about 1 minute if he does that.

suggesting that the purchaser probably didn't expect it to be a 2kW
transformer either.

** Yawnnnnnnnnnnnnnnnnnnnnn....



..... Phil

 

[Trevor Wilson]

Also, certain products might have to "feel to be a certain weight" in
relation to its physical volume, for the consumer to perceive them to
be a "quality" product.

You would know more about it than I would - being in the industry -
but I think high end audio would fall into this category ?

**Absolutely. In fact, I've worked on a few Class D amps (that use SMPS)
that are quite heavy, where there is absolutely no reason for them to be so.

 

[Trevor Wilson]

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.

**High end audio is a different world to that which most people inhabit.
Perception is more important than performance in most instances.

 

[Phil Allison]

"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

 

[Sylvia Else]

"Stupider than Anyone Else Alive or Dead.

** Burn the witch.



** Blah, blah blah,

The fuse holder is NOT labelled at all.

Did I say fuse holder labelling?

** The unit is from the same supplier - that is all I ever claimed.

FFS read the OP again and again til you GET IT !!



** So fucking what ??????????

In the future it may have an owner who needs the whole 2kW.

The owner may loan it to another to use with say 2kW of 110 volt lighting.

Smoke will get out in about 1 minute if he does that.



** Yawnnnnnnnnnnnnnnnnnnnnn....



.... Phil

I agree there's a concern about this specific transformer. But maybe
that's all it is - one specific transformer that for some obscure reason
has been mischaracterised. You did refer to the supplier's eBay shop,
which implies that you thought that was somehow relevant.

Presumably you'll replace the fuse with something appropriate.

Sylvia.

 

[Phil Allison]

"Trevor Wilson"

**High end audio is a different world to that which most people inhabit.
Perception is more important than performance in most instances.

** That is true nearly everywhere.

Especially politics.


...... Phil

 

[Sylvia Else]

"Stupider than anyone Else on Earth"


** They are two different models.


** FFS - read the OP.

The stepdown I have here is probably several years old.

Your point being? That the seller used to be a ripoff merchant, but is
now selling quality goods?

Sylvia.