| Author |
Message |
John Larkin
Guest
|
 Posted:
Thu Feb 10, 2005 7:27 am Post subject:
Re: torroidal transformer vendor |
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On Wed, 9 Feb 2005 21:32:19 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:
| Quote: | I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <92dk015neh8nlivbuecd6si92or91135k6@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
But the transformer smoke test really only forced us to use the TT fuses
and the inrush limiters... it didn't really dominate the transformer
design, which was more of an available-space problem.
Is this transformer driving a motor or something? You should never need
TT fuses for an AC electronic load or a normal rectifier. Unless there
is something very unusual going on, the inrush phase is, for fusing
purposes, over in one cycle of the supply, and T fuses are OK for this
application.
|
It's a pulsed-field gradient amplifier for NMR. The TTs were to allow
us to use the smallest possible fuse rating (to pass the transformer
overload test) and still not blow on high peak pulse loads or
toroid+capacitor powerup surges. I didn't do this personally, but I do
recall that the choice of the relatively hard-to-get TTs wasn't
casual.
John
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John Larkin
Guest
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| Posted:
Thu Feb 10, 2005 8:16 am Post subject:
Re: torroidal transformer vendor |
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On Wed, 9 Feb 2005 09:27:44 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:
| Quote: | I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <mu6j01ds31dgvsq8mfa0br3eft55946dbl@
4ax.com>) about 'torroidal transformer vendor', on Tue, 8 Feb 2005:
The CE test involves loading the transformer secondary to just below the
fuse blow point and then waiting to see how hot the transformer gets;
Which standard are you applying? It sounds to me that you may not be
applying the correct one.
|
Apparently it's IEC/EN 61010 2001 Edition, Clause 4.4.2.6.2
and UL 3101, 1993 Edition, Clause 14.7.2
John |
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Pooh Bear
Guest
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| Posted:
Thu Feb 10, 2005 8:29 am Post subject:
Re: torroidal transformer vendor |
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John Woodgate wrote:
| Quote: | I read in sci.electronics.design that Paul Mathews
optoeng@pioneernet.net> wrote (in <1107968587.578774.44250@o13g2000cwo.
googlegroups.com>) about 'torroidal transformer vendor', on Wed, 9 Feb
2005:
I'm still looking for a better reference, but I've been led to believe
(by a visiting rep) that this toroidal transformer technology, touted
for its EMI filtering benefits, also has improved inrush
characteristics:
http://powerelectronics.com/mag/power_power_transformer_attenuates/
Having just re-read the article, I find no mention there, so apologize
for possibly sending anyone on a goose chase. However, the EMI aspects
are interesting in their own right.
Paul Mathews
I recommend a good deal of caution when considering this paper.
|
The fact that it attemps to encompass the issues of harmonics and EMI in one
overall broad sweep shows the author's basic lack of understanding.
Graham
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Pooh Bear
Guest
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| Posted:
Thu Feb 10, 2005 8:35 am Post subject:
Re: torroidal transformer vendor |
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Paul Mathews wrote:
Bear in mind that the author's 'specially wound transformers' can be
wound by anyone. It looks like they're simply offering transformers with
a lower than usual working flux.
Graham |
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John Woodgate
Guest
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| Posted:
Thu Feb 10, 2005 8:41 am Post subject:
Re: torroidal transformer vendor |
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|
I read in sci.electronics.design that John Larkin <jjlarkin@highSNIPland
THIStechPLEASEnology.com> wrote (in <3sgl01h9kh5dst54uacb30sk2t3eua2dfm@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
| Quote: | On Wed, 9 Feb 2005 09:27:44 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <mu6j01ds31dgvsq8mfa0br3eft55946dbl@
4ax.com>) about 'torroidal transformer vendor', on Tue, 8 Feb 2005:
The CE test involves loading the transformer secondary to just below the
fuse blow point and then waiting to see how hot the transformer gets;
Which standard are you applying? It sounds to me that you may not be
applying the correct one.
Apparently it's IEC/EN 61010 2001 Edition, Clause 4.4.2.6.2
and UL 3101, 1993 Edition, Clause 14.7.2
Unfortunately, I don't have either of those standards. Maybe someone |
else can comment. You are sure that the product falls within the scope
of IEC/EN 61010?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
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John Larkin
Guest
|
| Posted:
Thu Feb 10, 2005 10:05 pm Post subject:
Re: torroidal transformer vendor |
|
|
On Thu, 10 Feb 2005 07:53:49 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:
| Quote: | I read in sci.electronics.design that John Larkin <jjlarkin@highSNIPland
THIStechPLEASEnology.com> wrote (in <3sgl01h9kh5dst54uacb30sk2t3eua2dfm@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
On Wed, 9 Feb 2005 09:27:44 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <mu6j01ds31dgvsq8mfa0br3eft55946dbl@
4ax.com>) about 'torroidal transformer vendor', on Tue, 8 Feb 2005:
The CE test involves loading the transformer secondary to just below the
fuse blow point and then waiting to see how hot the transformer gets;
Which standard are you applying? It sounds to me that you may not be
applying the correct one.
Apparently it's IEC/EN 61010 2001 Edition, Clause 4.4.2.6.2
and UL 3101, 1993 Edition, Clause 14.7.2
Unfortunately, I don't have either of those standards. Maybe someone
else can comment. You are sure that the product falls within the scope
of IEC/EN 61010?
|
I'm not sure of anything. My customer wanted our boxes tested to CE
and UL, so we told them to test them themselves, and they did. They
told us that the loaded-transformer-smoke-test was required.
But if the only function of a fuse is to clear shorts, why can't I
just slap in 10 amp fuses and be done with it?
And if the transformer overload test isn't required, then I should be
able to use a cheap transformer that will smoke and catch fire if,
say, a fet in the output stage failed.
Right?
John |
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John Woodgate
Guest
|
| Posted:
Thu Feb 10, 2005 10:47 pm Post subject:
Re: torroidal transformer vendor |
|
|
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <ua1n01lg3kh7ms6fgldndt1kg4i2cjf1sp@
4ax.com>) about 'torroidal transformer vendor', on Thu, 10 Feb 2005:
| Quote: | I'm not sure of anything. My customer wanted our boxes tested to CE and
UL, so we told them to test them themselves, and they did. They told us
that the loaded-transformer-smoke-test was required.
But if the only function of a fuse is to clear shorts, why can't I just
slap in 10 amp fuses and be done with it?
|
The 'smoke test' is indeed designed to prevent that.
| Quote: |
And if the transformer overload test isn't required, then I should be
able to use a cheap transformer that will smoke and catch fire if, say,
a fet in the output stage failed.
|
That's not quite the point. IEC/EN 61010-1 is unusual in requiring that
test, which some consider too stringent, insofar as it assumes a fault
with just the critical worst-case resistance. Other safety standards use
a different test.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
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John Larkin
Guest
|
| Posted:
Fri Feb 11, 2005 6:10 am Post subject:
Re: torroidal transformer vendor |
|
|
On Fri, 11 Feb 2005 04:54:46 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
John Larkin wrote:
On Thu, 10 Feb 2005 07:53:49 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjlarkin@highSNIPland
THIStechPLEASEnology.com> wrote (in <3sgl01h9kh5dst54uacb30sk2t3eua2dfm@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
On Wed, 9 Feb 2005 09:27:44 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <mu6j01ds31dgvsq8mfa0br3eft55946dbl@
4ax.com>) about 'torroidal transformer vendor', on Tue, 8 Feb 2005:
The CE test involves loading the transformer secondary to just below the
fuse blow point and then waiting to see how hot the transformer gets;
Which standard are you applying? It sounds to me that you may not be
applying the correct one.
Apparently it's IEC/EN 61010 2001 Edition, Clause 4.4.2.6.2
and UL 3101, 1993 Edition, Clause 14.7.2
Unfortunately, I don't have either of those standards. Maybe someone
else can comment. You are sure that the product falls within the scope
of IEC/EN 61010?
I'm not sure of anything. My customer wanted our boxes tested to CE
and UL, so we told them to test them themselves, and they did. They
told us that the loaded-transformer-smoke-test was required.
But if the only function of a fuse is to clear shorts, why can't I
just slap in 10 amp fuses and be done with it?
A short on the secondary side will happily draw maybe 5A from the a.c. supply
and the fuse will never blow.
Just try it and see.
|
No need; I can do the math. More like 50 amps.
| Quote: | A colleague of mine was once convinced that he could protect a toroidal
transformer of around 30VA with a 1A fuse on the primary. I warned him but he
insisted. We put a short on the secondary and we rapidly had one transformer
with nicely melted insulation after a few secs ! Didn't wait to see the final
outcome.
And if the transformer overload test isn't required, then I should be
able to use a cheap transformer that will smoke and catch fire if,
say, a fet in the output stage failed.
Nope - nothing is allowed to smoke and catch fire.
|
Which is why, presumably, they did the test.
John |
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| Back to top |
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John Larkin
Guest
|
| Posted:
Fri Feb 11, 2005 6:10 am Post subject:
Re: torroidal transformer vendor |
|
|
On Fri, 11 Feb 2005 04:48:22 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
John Larkin wrote:
On Wed, 9 Feb 2005 21:32:19 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <92dk015neh8nlivbuecd6si92or91135k6@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
But the transformer smoke test really only forced us to use the TT fuses
and the inrush limiters... it didn't really dominate the transformer
design, which was more of an available-space problem.
Is this transformer driving a motor or something? You should never need
TT fuses for an AC electronic load or a normal rectifier. Unless there
is something very unusual going on, the inrush phase is, for fusing
purposes, over in one cycle of the supply, and T fuses are OK for this
application.
It's a pulsed-field gradient amplifier for NMR. The TTs were to allow
us to use the smallest possible fuse rating (to pass the transformer
overload test) and still not blow on high peak pulse loads or
toroid+capacitor powerup surges. I didn't do this personally, but I do
recall that the choice of the relatively hard-to-get TTs wasn't
casual.
I'm not familiar with the specific EN you mentioned. Seems to be rather more
application specific than the ones I'm used to.
Can you explain the 'transformer overload test ' ? Sounds most unusual to me.
|
I explained it in my post of 2/8/05.
John |
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Pooh Bear
Guest
|
| Posted:
Fri Feb 11, 2005 6:10 am Post subject:
Re: torroidal transformer vendor |
|
|
John Larkin wrote:
| Quote: | On Wed, 9 Feb 2005 21:32:19 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <92dk015neh8nlivbuecd6si92or91135k6@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
But the transformer smoke test really only forced us to use the TT fuses
and the inrush limiters... it didn't really dominate the transformer
design, which was more of an available-space problem.
Is this transformer driving a motor or something? You should never need
TT fuses for an AC electronic load or a normal rectifier. Unless there
is something very unusual going on, the inrush phase is, for fusing
purposes, over in one cycle of the supply, and T fuses are OK for this
application.
It's a pulsed-field gradient amplifier for NMR. The TTs were to allow
us to use the smallest possible fuse rating (to pass the transformer
overload test) and still not blow on high peak pulse loads or
toroid+capacitor powerup surges. I didn't do this personally, but I do
recall that the choice of the relatively hard-to-get TTs wasn't
casual.
|
I'm not familiar with the specific EN you mentioned. Seems to be rather more
application specific than the ones I'm used to.
Can you explain the 'transformer overload test ' ? Sounds most unusual to me.
Graham |
|
| Back to top |
|
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Pooh Bear
Guest
|
| Posted:
Fri Feb 11, 2005 6:10 am Post subject:
Re: torroidal transformer vendor |
|
|
John Larkin wrote:
| Quote: | On Thu, 10 Feb 2005 07:53:49 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjlarkin@highSNIPland
THIStechPLEASEnology.com> wrote (in <3sgl01h9kh5dst54uacb30sk2t3eua2dfm@
4ax.com>) about 'torroidal transformer vendor', on Wed, 9 Feb 2005:
On Wed, 9 Feb 2005 09:27:44 +0000, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:
I read in sci.electronics.design that John Larkin <jjSNIPlarkin@highTHIS
landPLEASEtechnology.XXX> wrote (in <mu6j01ds31dgvsq8mfa0br3eft55946dbl@
4ax.com>) about 'torroidal transformer vendor', on Tue, 8 Feb 2005:
The CE test involves loading the transformer secondary to just below the
fuse blow point and then waiting to see how hot the transformer gets;
Which standard are you applying? It sounds to me that you may not be
applying the correct one.
Apparently it's IEC/EN 61010 2001 Edition, Clause 4.4.2.6.2
and UL 3101, 1993 Edition, Clause 14.7.2
Unfortunately, I don't have either of those standards. Maybe someone
else can comment. You are sure that the product falls within the scope
of IEC/EN 61010?
I'm not sure of anything. My customer wanted our boxes tested to CE
and UL, so we told them to test them themselves, and they did. They
told us that the loaded-transformer-smoke-test was required.
But if the only function of a fuse is to clear shorts, why can't I
just slap in 10 amp fuses and be done with it?
|
A short on the secondary side will happily draw maybe 5A from the a.c. supply
and the fuse will never blow.
Just try it and see.
A colleague of mine was once convinced that he could protect a toroidal
transformer of around 30VA with a 1A fuse on the primary. I warned him but he
insisted. We put a short on the secondary and we rapidly had one transformer
with nicely melted insulation after a few secs ! Didn't wait to see the final
outcome.
| Quote: | And if the transformer overload test isn't required, then I should be
able to use a cheap transformer that will smoke and catch fire if,
say, a fet in the output stage failed.
|
Nope - nothing is allowed to smoke and catch fire.
Graham |
|
| Back to top |
|
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Tony Williams
Guest
|
| Posted:
Fri Feb 11, 2005 6:59 am Post subject:
Re: torroidal transformer vendor |
|
|
In article <kogo01hcc2ssonngc9tqj7ls0c4kb7719h@4ax.com>,
John Larkin wrote:
| Quote: | On Fri, 11 Feb 2005 04:54:46 +0000, Pooh Bear wrote:
John Larkin wrote:
And if the transformer overload test isn't required, then I
should be able to use a cheap transformer that will smoke and
catch fire if, say, a fet in the output stage failed.
Nope - nothing is allowed to smoke and catch fire.
Which is why, presumably, they did the test.
|
Some 30VA transformers we buy for a particular application
have a Woods-metal fusible link inside them, in series with
the 240V primary. If the transformer gets too hot the link
opens and the mains is disconnected, permanently.
Standard practice AFAIK on devices with small transformers,
such a swall warts.
--
Tony Williams. |
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Tony Williams
Guest
|
| Posted:
Fri Feb 11, 2005 9:35 am Post subject:
Re: torroidal transformer vendor |
|
|
In article <420C7589.EA92F6AB@hotmail.com>,
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
[Woods-metal links]
| Quote: | Standard practice AFAIK on devices with small transformers,
such a swall warts.
It certainly is - cheap and reliable - no bother about the fusing
characteristics since it monitors the actual transformer temp -
and that's the issue.
I was considering suggesting something similar - but for a
serious piece of kit you'd want an auto-resetting thermal switch.
|
Since this is a last-ditch safety measure it could
be argued that a permanent cutoff is the safest, in
that it forces the equipment to be examined by a
qualified person.
However, I think there is a polyswitch type of device
that opens at a set temperature, but which then only
requires a trickle current to keep it open. Removal
of the supply is required to re-set it.
--
Tony Williams. |
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Pooh Bear
Guest
|
| Posted:
Fri Feb 11, 2005 12:29 pm Post subject:
Re: torroidal transformer vendor |
|
|
John Larkin wrote:
| Quote: | On Fri, 11 Feb 2005 04:54:46 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
John Larkin wrote:
But if the only function of a fuse is to clear shorts, why can't I
just slap in 10 amp fuses and be done with it?
A short on the secondary side will happily draw maybe 5A from the a.c. supply
and the fuse will never blow.
Just try it and see.
No need; I can do the math. More like 50 amps.
|
Not with a 50VA toroidal transformer.
Note - *a short on the secondary side*
Graham |
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John Larkin
Guest
|
| Posted:
Fri Feb 11, 2005 12:56 pm Post subject:
Re: torroidal transformer vendor |
|
|
On Fri, 11 Feb 2005 06:29:53 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
John Larkin wrote:
On Fri, 11 Feb 2005 04:54:46 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
John Larkin wrote:
But if the only function of a fuse is to clear shorts, why can't I
just slap in 10 amp fuses and be done with it?
A short on the secondary side will happily draw maybe 5A from the a.c. supply
and the fuse will never blow.
Just try it and see.
No need; I can do the math. More like 50 amps.
Not with a 50VA toroidal transformer.
Note - *a short on the secondary side*
|
I can *still* do the math!
John |
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