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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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18th Nov 2017, 3:59 pm | #1 |
Octode
Join Date: Jan 2014
Location: Oban, Scotland, UK.
Posts: 1,129
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Gardiner Transformer Ratings
Why does a Gardiner transformer show the secondary as 250-0-250 and 60mA 'DC' ??
Wouldn't the DC mA rating depend on the method used for rectification? i.e. capacitive input (1 x Iac) versus choke input (1.54 x Iac)? So what, exactly, would be the rating for this transformer? |
18th Nov 2017, 5:12 pm | #2 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Gardiner Transformer Ratings
If a DC rating is given for an HT transformer then you can assume this is for a capacitive input PSU - possibly with a valve rectifier. It is good that they specify DC, as some HT transformers uses a DC rating but don't say it is DC. Most other transformers (and any heater secondaries on an HT transformer) use RMS AC for current rating.
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18th Nov 2017, 6:17 pm | #3 | |
Octode
Join Date: Jan 2014
Location: Oban, Scotland, UK.
Posts: 1,129
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Re: Gardiner Transformer Ratings
Quote:
Is there an assumption towards a capacitive input filer in all circumstances? |
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18th Nov 2017, 10:30 pm | #4 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Gardiner Transformer Ratings
I can't remember what the actual factors are for a centre-tapped secondary, but I seem to recall that for a single secondary with bridge rectifier and capacitor input the DC current is around half the AC RMS. Choke input would be a lot nearer 1.
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18th Nov 2017, 10:38 pm | #5 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Gardiner Transformer Ratings
The 250-0-250 format strongly suggests what format of rectifier it is assumed to be used with. The capacitor input filter is by far the most common type, and it's harder on current ratings than a choke input type. So 60mA DC from either type would be fine. It's the output voltage that will be lower with a choke input filter AND you'll need to keep an eye on the minimum current consumption if you don't want the voltage to shoot up to the peak rectification mode voltage.
David
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18th Nov 2017, 11:13 pm | #6 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: Gardiner Transformer Ratings
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18th Nov 2017, 11:27 pm | #7 |
Hexode
Join Date: Sep 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 475
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Re: Gardiner Transformer Ratings
The centre tapped transformer suggests use of a full wave valve rectifier with capacitive input filter. In this case Iac = Idc = 60mA. Vdc = 0.707 x Vac = 0.707 x 500 = 354v
Attached is a useful picture which shows this arrangement at top-right of the diagrams, albeit with solid state rectifiers. |