Transformer questions - Taps on the primary? - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: November 14, 2014, 08:16:29 pm
content: Hello,So I've got this big E core transformer that I belive is 220V Primary to 24V Secondary. I'm not really sure since it is "burned out". When I connect primary and secondary, I get 5V on secondary and smoke on the primary.Now, on the primary side, there are 4 connection points, a 220V (Live), a -5%, a -10% and a Neutral.I get the 220V and the Neutral, but what are the -5% and the -10% taps?What about power rating? What is that dependent on? The wire gauge? Core size? Can I use this site for calculations?http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/tracir2.htmlThe size of the transformer is 42mm wide by 125mm tall by 150mm long, but I've yet to take it apart to measure the E core size.Thanks

author: German_EE
author_rank: Super Contributor
timestamp: November 14, 2014, 08:26:21 pm
content: A guess, the primary is 240V. 240-5% is 228V, just about right for 230V mains. 240-10% is 216V, close enough to 220V. Some units have a close specification on input voltage, for example RF power amplifiers need you to set the taps exactly right or the filaments on the tubes may fail.Back in the old days Continental Europe ran on 220V and the UK ran on 240V (+/- the fiddle factor in each case). When the EU got involved they arranged for everyone to meet in the middle and now we all use a nominal 230V.

author: made2hack
author_rank: Frequent Contributor
timestamp: November 14, 2014, 08:29:05 pm
content: Ok,But mine starts at 220V (live), so does it mean that if you have 209V (-5%) or 198V (-10%), you would use those connectors? Who uses 209V or 198V?What I mean by starts at 220V, that is the label on that connector.

author: IanB
author_rank: Super Contributor
timestamp: November 14, 2014, 09:24:47 pm
content: Quote from: trs80 on November 14, 2014, 08:16:29 pmExcept all the installed hardware is the same as it was before. Nothing really changed.

author: wazzokk
author_rank: Contributor
timestamp: November 14, 2014, 10:20:14 pm
content: EU voltage alignment. Nothing changed.Yes! Certainly in this part of the UK the 230v supply still normally reads 242v on my meters.Cheers Dave P

author: GEuser
author_rank: Frequent Contributor
timestamp: November 15, 2014, 06:25:32 am
content: Quote from: wazzokk on November 14, 2014, 10:20:14 pmhttp://en.wikipedia.org/wiki/Mains_electricity_by_countryEven out here its listed in the above as 230 , its supposed to be 240 my meter right now says 239 , a good day its 243+ a bad day its 235 out rural I is .That EU thing I suppose wants the whole world to conform to their idea ? lets say 200 ....in the middle of everyone , DuH ...edit>> I forgot to post for the OP , no mention of what voltage your on/using , one cannot assume 220 as one has not categorically typed so ...

author: made2hack
author_rank: Frequent Contributor
timestamp: November 15, 2014, 10:17:14 am
content: Well, Essentially I would be using 220V.The reason I mentioned 220V, was because the transformer had a label with 220 on it, and then -5% and -10%.So I assume that the transformer was "designed" originally for 220V use, without taking into consideration the EU 230V directive.

author: Psi
author_rank: Super Contributor
timestamp: November 15, 2014, 10:40:16 am
content: Quote from: trs80 on November 14, 2014, 08:29:05 pmThe transformer is 220V, but if you happen to use it in a 230V or 240V country then you're going to end up with extra volts on the secondary.The -5 and -10% primary feeds are to correct this.220, -5% ,-10% could just as well be labeled 220 230 240