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A useful tip when checking high voltage mains transformers - or for that
matter any mains transformer.
1. Establish the approx VA rating (output volts x current)
2. Calculate the primary current when fully loaded.
3. Connect the transformer primary to the mains (secondary/-ies open
circuit) and measure the quiescent primary current.
4. If the current measured is less than 10% of the calculated full load
current - the transformer is OK. Else it has a higher than normal
magnetising current and investigation needs to be made to ascertain where
the problem lies. (Could be the transformer was wound for 60Hz and you are
using it on 50Hz).
Anyway it is a useful tip I was taught many years ago by a transformer
expert.
John ZS5JF
----------
> From: Will K6NDV <k6ndv@contesting.com>
> To: amps@contesting.com
> Cc: henry@qth.net
> Subject: [AMPS] Fw: Transformer Selection
To: <amps@contesting.com>
> Date: Monday, October 19, 1998 10:53 PM
>
>
> Here some interesting information about transformers.
> I asked Bob's opinion about transformers and this is what he send me.
> Will, K6NDV
> -----Original Message-----
> From: Bob Marston <k1ta@earthlink.net>
> To: Will K6NDV <k6ndv@contesting.com>
To: <amps@contesting.com>
> Date: Sunday, October 18, 1998 9:55 PM
> Subject: Transformer Selection
>
>
> >Here are some hints regarding transformer selection
> >
> >For Secondary Voltage if you want to use a tuned choke filter You will
be
> >limited to 1 of 2 rectfier configurations Full Wave Bridge or Full Wave
> >Center Tapped.
> >
> >First Choice: Full Wave Bridge the Secondary Voltage must be between
3000
> >volts and 3600 Volts The transformer secondary current rating must be 1
amp
> >
> >Second Choice: Full Wave Center Tapped the Secondary Voltage must be
> >between 6000 and 7200 Volts The transformer secondary current rating
only
> >needs to be 500ma. Note: The secondary MUST HAVE A CENTER TAP
> >
> >Third Choice: Voltage Doubler the Secondary must be between 1500 volts
> >and 1800 volts with a 2 amp rating. Note: This circuit will preclude the
> >use of a choke
> >
> >Some hints when selecting a transformer. These same techniques can be
> >applied in the choke selection. The secondary resistance is a factor in
> >regulation. The higher the resistance the poorer the regulation. It's
> >simple ohms law and Kirchoff's voltage law if you are swinging 1 amp
> >between no load and full load conditions the Supply Voltage will drop 1
> >Volt for each ohm of secondary resistance. Bring a VOM with you and
measure
> >the resistance of the secondary.
> >
> >CAUTION!!!!! You are measuring the resistance of a storage device IT
WILL
> >CHARGE UP...Even with a VOM that uses a 9 volt battery. the stored
charge
> >has knocked this author on his ass. It's an experience you'll only do
once
> >if you have to learn the hard way.
> >
> >When you first contact the transformer it will look like a dead short.
If
> >you have an analog meter you will see the needle rise as it charges. The
> >secondary resistance will be the value indicated after the charging is
> >complete.
> >
> >It has been some time since I transformer shopped but as I remember a
> >secondary of
> >100 ohms is an exceptional transformer
> >200 ohms is good
> >250 ohms ehhh
> >300 ohms or more---Look for another transformer
> >
> >For a transformer in the 6000 to 7200 volt range you can double these
> values
> >
> >Also check the primary to make sure its not burned out
> >
> >these same techniques can be used with the plate choke
> >
> >Bob
> >
> >
>
>
> --
> FAQ on WWW: http://www.contesting.com/ampfaq.html
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
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<html><head></head><BODY bgcolor=3D"#FFFFFF"><p><font size=3D2 =
color=3D"#000000" face=3D"Arial">A useful tip when checking high voltage =
mains transformers - or for that matter any mains =
transformer.<br><br>1.	Establish the approx VA rating (output =
volts x current)<br>2.	Calculate the primary current when fully =
loaded.<br>3.	Connect the transformer primary to the mains =
(secondary/-ies open circuit) and measure the 	quiescent primary =
current.<br>4.	If the current measured is less than 10% of the =
calculated full load current - the transformer is 	OK. Else =
it has a higher than normal magnetising current and investigation needs =
to be made to 	ascertain where the problem lies. (Could be =
the transformer was wound for 60Hz and you are 	using it on =
50Hz).<br><br>Anyway it is a useful tip I was taught many years ago by a =
transformer expert.<br><br>John	ZS5JF<br><br>----------<br>> =
From: Will K6NDV <<font =
color=3D"#0000FF"><u>k6ndv@contesting.com</u><font =
color=3D"#000000">><br>> To: <font =
color=3D"#0000FF"><u>amps@contesting.com</u><font =
color=3D"#000000"><br>> Cc: <font =
color=3D"#0000FF"><u>henry@qth.net</u><font color=3D"#000000"><br>> =
To: <amps@contesting.com>
Subject: [AMPS] Fw: Transformer Selection<br>> Date: Monday, October =
19, 1998 10:53 PM<br>> <br>> <br>> Here some interesting =
information about transformers.<br>> I asked Bob's opinion about =
transformers and this is what he send me.<br>> Will, =
K6NDV<br>> -----Original Message-----<br>> From: Bob Marston =
<<font color=3D"#0000FF"><u>k1ta@earthlink.net</u><font =
color=3D"#000000">><br>> To: Will K6NDV <<font =
color=3D"#0000FF"><u>k6ndv@contesting.com</u><font =
To: <amps@contesting.com>
color=3D"#000000">><br>> Date: Sunday, October 18, 1998 9:55 =
PM<br>> Subject: Transformer Selection<br>> <br>> <br>> =
>Here are some hints regarding transformer selection<br>> =
><br>> >For Secondary Voltage if you want to use a tuned choke =
filter You will be<br>> >limited to 1 of 2 rectfier configurations =
Full Wave Bridge or Full Wave<br>> >Center Tapped.<br>> =
><br>> >First Choice: Full Wave Bridge the =
Secondary Voltage must be between 3000<br>> >volts and 3600 Volts =
The transformer secondary current rating must be 1 amp<br>> =
><br>> >Second Choice: Full Wave Center Tapped the =
Secondary Voltage must be<br>> >between 6000 and 7200 Volts The =
transformer secondary current rating only<br>> >needs to be 500ma. =
Note: The secondary MUST HAVE A CENTER TAP<br>> ><br>> =
>Third Choice: Voltage Doubler the Secondary must be =
between 1500 volts<br>> >and 1800 volts with a 2 amp rating. Note: =
This circuit will preclude the<br>> >use of a choke<br>> =
><br>> >Some hints when selecting a transformer. These same =
techniques can be<br>> >applied in the choke selection. The =
secondary resistance is a factor in<br>> >regulation. The higher =
the resistance the poorer the regulation. It's<br>> >simple ohms =
law and Kirchoff's voltage law if you are swinging 1 amp<br>> =
>between no load and full load conditions the Supply Voltage will =
drop 1<br>> >Volt for each ohm of secondary resistance. Bring a =
VOM with you and measure<br>> >the resistance of the =
secondary.<br>> ><br>> >CAUTION!!!!! You are measuring =
the resistance of a storage device IT WILL<br>> >CHARGE UP...Even =
with a VOM that uses a 9 volt battery. the stored charge<br>> >has =
knocked this author on his ass. It's an experience you'll only do =
once<br>> >if you have to learn the hard way.<br>> ><br>> =
>When you first contact the transformer it will look like a dead =
short. If<br>> >you have an analog meter you will see the needle =
rise as it charges. The<br>> >secondary resistance will be the =
value indicated after the charging is<br>> >complete.<br>> =
><br>> >It has been some time since I transformer shopped but =
as I remember a<br>> >secondary of<br>> >100 ohms is an =
exceptional transformer<br>> >200 ohms is good<br>> >250 =
ohms ehhh<br>> >300 ohms or more---Look for another =
transformer<br>> ><br>> >For a transformer in the 6000 to =
7200 volt range you can double these<br>> values<br>> ><br>> =
>Also check the primary to make sure its not burned out<br>> =
><br>> >these same techniques can be used with the plate =
choke<br>> ><br>> >Bob<br>> ><br>> ><br>> =
<br>> <br>> --<br>> FAQ on WWW: =
&=
nbsp; <font =
color=3D"#0000FF"><u>http://www.contesting.com/ampfaq.html</u><font =
color=3D"#000000"><br>> Submissions: =
&=
nbsp;<font color=3D"#0000FF"><u>amps@contesting.com</u><font =
color=3D"#000000"><br>> Administrative requests: <font =
color=3D"#0000FF"><u>amps-REQUEST@contesting.com</u><font =
color=3D"#000000"><br>> Problems: =
&=
nbsp; <font =
color=3D"#0000FF"><u>owner-amps@contesting.com</u><font =
color=3D"#000000"><br>> Search: =
&=
nbsp; <font =
color=3D"#0000FF"><u>http://www.contesting.com/km9p/search.htm</u><font =
color=3D"#000000"></p>
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ont></font></font></font></font></font></font></font></font></font></font=
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FAQ on WWW: http://www.contesting.com/ampfaq.html
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Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
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