| Author |
Message |
Pooh Bear
Guest
|
 Posted:
Wed Feb 09, 2005 8:41 am Post subject:
Re: torroidal transformer vendor |
|
|
John Larkin wrote:
| Quote: | Hi,
Can anybody recommend a good source for a custom torroidal power
transformer? It will be roughly 50 VA; we need prototypes fast, and
maybe 100 per year after that.
There are about 200 suppliers listed in the EEM for torroids, and I
guess we'll spam lots of them with our spec, but I just wondered if
anybody has a vendor they especially like.
|
Toroid International.
http://www.toroid.co.uk/
The MD owns the company and is highly knowledgable and most helpful.
Their prices are good too as they manufacture in asia.
Graham
|
|
| Back to top |
|
 |
John Larkin
Guest
|
| Posted:
Wed Feb 09, 2005 8:41 am Post subject:
Re: torroidal transformer vendor |
|
|
On Wed, 09 Feb 2005 02:18:59 GMT, legg <legg@nospam.magma.ca> wrote:
| Quote: | On Tue, 08 Feb 2005 13:42:03 -0800, John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:
without the thermistor gadgets. But our existing transformer vendor
mucked the design and they saturate at 50 Hz, so we're blowing fuzes
in Europe. These are megabuck systems and our customer is not happy.
Your own spotty behind was covered by the mention of 50Hz, somewhere
in the spec?
|
Sure. At 10% overvoltage.
| Quote: | Don't you test these things?
|
The guy who spec'd and tested the trannies no longer works for me; one
day he walked into my office, said "it's time to move on" and left.
Interestingly, he used to work for Signal Transformer. I guess he
didn't test it for saturation. All you really need to do is
overvoltage it at 60 Hz, find the knee, and multiply by 5/6.
Our customer (it's an OEM product) took our gadget to a major test lab
for the full CE suite, including specific transformer tests. Their
test report *justifies* why it was not necessary to actually test at
50 Hz. There's lots of blame to go around.
John |
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Wed Feb 09, 2005 3:27 pm Post subject:
Re: torroidal transformer vendor |
|
|
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:
| Quote: | 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.
--
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
|
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Wed Feb 09, 2005 3:34 pm Post subject:
Re: torroidal transformer vendor |
|
|
I read in sci.electronics.design that Paul Mathews
<optoeng@pioneernet.net> wrote (in <1107910282.546062.197810@o13g2000cwo
..googlegroups.com>) about 'torroidal transformer vendor', on Tue, 8 Feb
2005:
| Quote: | If you're concerned about turn-on surges, look for an article about new
toroid transformers designed to limit power-on surge:
http://www.powerelectronics.com
|
Do you have the title of the article? I couldn't find it on the site.
--
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 |
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Wed Feb 09, 2005 4:54 pm Post subject:
Re: torroidal transformer vendor |
|
|
John Larkin wrote:
| Quote: | On Wed, 09 Feb 2005 03:39:08 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
John Larkin wrote:
On Tue, 08 Feb 2005 16:25:40 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:
On Tue, 08 Feb 2005 12:31:37 -0800, the renowned John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:
Hi,
Can anybody recommend a good source for a custom torroidal power
transformer? It will be roughly 50 VA; we need prototypes fast, and
maybe 100 per year after that.
There are about 200 suppliers listed in the EEM for torroids, and I
guess we'll spam lots of them with our spec, but I just wondered if
anybody has a vendor they especially like.
Thanks,
John
I've used their standard products in that range:
http://www.plitron.com/
You know this, but toroidal power xfmrs can have a nasty turn-on
current surge.
Thanks; we'll try them. And yeah, we had to go to TT superslow fuzes
for this one. We also used the inrush limiter thingies, the ones that
look like black disc caps. Primary resistance runs about 5 ohms per
120 winding, 2.5 or so in parallel, so it's not all that bad, 50 amps
without the thermistor gadgets. But our existing transformer vendor
mucked the design and they saturate at 50 Hz, so we're blowing fuzes
in Europe. These are megabuck systems and our customer is not happy.
You didn't put 50Hz on the spec ?
Of course we did.
Sounds like a transformer supplier who doesn't understand that there's a
whole world out there.
Oh - and if you're selling in Europe don't forget to use IEC spec fuses
not UL. The blowing characteristics are very different too.
We're using TT fuses.
I've *never* had to use a TT fuse. Ts normally work just fine for me and
I regularly use toroids.
Fuse only needs to blow when ( typically ) you short out any one of the
secondary side reservoir caps btw.
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; that is a lot nastier than a clean short.
|
This sounds very wrong. IEC regs simply apply component failure simulations
to test such stuff.
| Quote: | And this box has no
fans. So we have to use the smallest possible fuse rating, or we pay
for it in transformer iron. So between the powerup surges (core+caps)
and the fact that this is a pulsed power amp, things get interesting.
I think what happened was that the original transformer design was OK
but a bit too big. Somebody at the transformer company (another
somebody "no longer here") scrunched the design program and wound up
with a transformer that was smaller but had no saturation margin.
|
I think someone's misadvising you re: the CE safety test btw.
I have considerable experience of both safety and EMC CE approvals.
Is it a US lab that thinks you have to test that way ?
Graham |
|
| Back to top |
|
|
Pooh Bear
Guest
|
| Posted:
Wed Feb 09, 2005 4:55 pm Post subject:
Re: torroidal transformer vendor |
|
|
John Woodgate 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.
|
I think you're right John.
Graham |
|
| Back to top |
|
|
Ian
Guest
|
| Posted:
Wed Feb 09, 2005 7:56 pm Post subject:
Re: torroidal transformer vendor |
|
|
"John Larkin" <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote in
message news:e0pi01511lp1m6h3evb488c3jhvp7n6giu@4ax.com...
| Quote: | On 8 Feb 2005 16:51:22 -0800, "Paul Mathews" <optoeng@pioneernet.net
wrote:
As I told Speff, we have NTC surge limiters and TT fuzes, so that
seems to be under control.
John
|
Hi John:
I hit this problem (too) many years ago on a switcher - no toroid, but
serious
issues on inrush current "burning" switch contacts. Even back then the
NTC thermistor was an often used solution, but had a major problem
with time constant - there always seemed to be some timing of the user
"mis-hitting" the power switch that would bypass the protection.
What I did was to put a high voltage power MOSFET inside a bridge
rectifier in series with the input, arranged to always turn on, with a real
simple
R/transistor current sense to turn it off when the instantaneous current
exceeded a set point (together with gate protection). Worked a treat.
No idea if this would now fall foul of CE harmonics legislation, ask
John Woodgate. There may now be easier ways to do this, but it was
pretty cheap even back then.
--
Regards
Ian |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Wed Feb 09, 2005 10:08 pm Post subject:
Re: torroidal transformer vendor |
|
|
On Wed, 09 Feb 2005 10:54:45 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: | John Larkin wrote:
On Wed, 09 Feb 2005 03:39:08 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
John Larkin wrote:
On Tue, 08 Feb 2005 16:25:40 -0500, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:
On Tue, 08 Feb 2005 12:31:37 -0800, the renowned John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:
Hi,
Can anybody recommend a good source for a custom torroidal power
transformer? It will be roughly 50 VA; we need prototypes fast, and
maybe 100 per year after that.
There are about 200 suppliers listed in the EEM for torroids, and I
guess we'll spam lots of them with our spec, but I just wondered if
anybody has a vendor they especially like.
Thanks,
John
I've used their standard products in that range:
http://www.plitron.com/
You know this, but toroidal power xfmrs can have a nasty turn-on
current surge.
Thanks; we'll try them. And yeah, we had to go to TT superslow fuzes
for this one. We also used the inrush limiter thingies, the ones that
look like black disc caps. Primary resistance runs about 5 ohms per
120 winding, 2.5 or so in parallel, so it's not all that bad, 50 amps
without the thermistor gadgets. But our existing transformer vendor
mucked the design and they saturate at 50 Hz, so we're blowing fuzes
in Europe. These are megabuck systems and our customer is not happy.
You didn't put 50Hz on the spec ?
Of course we did.
Sounds like a transformer supplier who doesn't understand that there's a
whole world out there.
Oh - and if you're selling in Europe don't forget to use IEC spec fuses
not UL. The blowing characteristics are very different too.
We're using TT fuses.
I've *never* had to use a TT fuse. Ts normally work just fine for me and
I regularly use toroids.
Fuse only needs to blow when ( typically ) you short out any one of the
secondary side reservoir caps btw.
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; that is a lot nastier than a clean short.
This sounds very wrong. IEC regs simply apply component failure simulations
to test such stuff.
And this box has no
fans. So we have to use the smallest possible fuse rating, or we pay
for it in transformer iron. So between the powerup surges (core+caps)
and the fact that this is a pulsed power amp, things get interesting.
I think what happened was that the original transformer design was OK
but a bit too big. Somebody at the transformer company (another
somebody "no longer here") scrunched the design program and wound up
with a transformer that was smaller but had no saturation margin.
I think someone's misadvising you re: the CE safety test btw.
I have considerable experience of both safety and EMC CE approvals.
Is it a US lab that thinks you have to test that way ?
Graham
|
My customer wanted it CE tested, so we told them to do it themselves.
They took it to ITS, a big US test lab, and that's what they did. I'll
try to find out which spec they were working to.
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.
John |
|
| Back to top |
|
|
Paul Mathews
Guest
|
| Posted:
Wed Feb 09, 2005 11:03 pm Post subject:
Re: torroidal transformer vendor |
|
|
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 |
|
| Back to top |
|
|
Paul Mathews
Guest
|
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Thu Feb 10, 2005 2:22 am Post subject:
Re: torroidal transformer vendor |
|
|
On Wed, 9 Feb 2005 19:56:58 +0000 (UTC), "Ian"
<ian.buckner@btinternet.com> wrote:
| Quote: |
"John Larkin" <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote in
message news:e0pi01511lp1m6h3evb488c3jhvp7n6giu@4ax.com...
On 8 Feb 2005 16:51:22 -0800, "Paul Mathews" <optoeng@pioneernet.net
wrote:
As I told Speff, we have NTC surge limiters and TT fuzes, so that
seems to be under control.
John
Hi John:
I hit this problem (too) many years ago on a switcher - no toroid, but
serious
issues on inrush current "burning" switch contacts. Even back then the
NTC thermistor was an often used solution, but had a major problem
with time constant - there always seemed to be some timing of the user
"mis-hitting" the power switch that would bypass the protection.
What I did was to put a high voltage power MOSFET inside a bridge
rectifier in series with the input, arranged to always turn on, with a real
simple
R/transistor current sense to turn it off when the instantaneous current
exceeded a set point (together with gate protection). Worked a treat.
No idea if this would now fall foul of CE harmonics legislation, ask
John Woodgate. There may now be easier ways to do this, but it was
pretty cheap even back then.
|
I did a similar thing on one big amp: AC power series resistor to
limit surge, then shorted by a triac later on. We even cheated and
used it to improve transformer regulation, sort of a 1-step AC
switching regulator.
John |
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Thu Feb 10, 2005 3:32 am Post subject:
Re: torroidal transformer vendor |
|
|
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:
| Quote: | 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.
--
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 |
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Thu Feb 10, 2005 3:37 am Post subject:
Re: torroidal transformer vendor |
|
|
I read in sci.electronics.design that Ian <ian.buckner@btinternet.com>
wrote (in <cudpua$a8k$1@sparta.btinternet.com>) about 'torroidal
transformer vendor', on Wed, 9 Feb 2005:
| Quote: | What I did was to put a high voltage power MOSFET inside a bridge
rectifier in series with the input, arranged to always turn on, with a
real simple R/transistor current sense to turn it off when the
instantaneous current exceeded a set point (together with gate
protection). Worked a treat. No idea if this would now fall foul of CE
harmonics legislation, ask John Woodgate.
|
No. First 10 s after switch-on is not measured for harmonics. Clause
6.2.3.2 of IEC/EN 61000-3-2.
| Quote: | There may now be easier ways
to do this, but it was pretty cheap even back then.
|
This is an interesting idea for a high-power toroid, where NTCs and
other fixes are unattractive. You'd have to watch for spikes caused by
leakage reactance when the current is cut off suddenly.
--
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 |
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Thu Feb 10, 2005 3:47 am Post subject:
Re: torroidal transformer vendor |
|
|
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:
| Quote: | 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. |
--
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 |
|
| Back to top |
|
|
John Woodgate
Guest
|
| Posted:
Thu Feb 10, 2005 3:48 am Post subject:
Re: torroidal transformer vendor |
|
|
I read in sci.electronics.design that Paul Mathews
<optoeng@pioneernet.net> wrote (in <1107977208.169814.26130@g14g2000cwa.
googlegroups.com>) about 'torroidal transformer vendor', on Wed, 9 Feb
2005:
--
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 |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in