isolation transformer needed
in [Repair]
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From: Dave Plowman (News) on 2 Dec 2009 11:50 In article <hf5svh$5gg$2(a)usenet01.srv.cis.pitt.edu>, GregS <zekfrivo(a)zekfrivolous.com> wrote: > In article <%llRm.94141$gg6.27160(a)newsfe25.iad>, sbnjhfty <fgsdfgrr(a)asfffwer.com> wrote: > >I'm looking for an isolation transformer for repairing small (less > >than 1000W) power supplies. I see loads of them on ebay and some are > >medical grade and inexpensive. Are these usable for what I want? > >Other than that, any tips on where to get a good deal on one? I > >don't want to spend a load as this is hobby work only. > Just an 'isolation transformer" means NOTHING for what you want. Most > all isolation transformers sold have the secondary tied to ground. You > need a service isolation transformer. You can usually get inside and > remove a secondary "neutral" connection. That's interesting. I've never seen any transformer with the secondary tied to ground - unless as part of an installation. The word 'isolation' means just that. Sure you're not thinking of an auto transformer? -- *I'm already visualizing the duct tape over your mouth Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: Adrian C on 2 Dec 2009 12:03 Dave Plowman (News) wrote: > GregS <zekfrivo(a)zekfrivolous.com> wrote: >> Just an 'isolation transformer" means NOTHING for what you want. Most >> all isolation transformers sold have the secondary tied to ground. You >> need a service isolation transformer. You can usually get inside and >> remove a secondary "neutral" connection. > > That's interesting. I've never seen any transformer with the secondary > tied to ground - unless as part of an installation. The word 'isolation' > means just that. Sure you're not thinking of an auto transformer? > Seems to be a US safety requirement to ground one leg. http://en.wikipedia.org/wiki/Isolation_transformer I've got here a Farnell 500W 240V/240V isolating transformer that looks and weighs similar to a typical building site transformer, the outputs are floating. -- Adrian C
From: GregS on 2 Dec 2009 12:09 In article <hf5svh$5gg$2(a)usenet01.srv.cis.pitt.edu>, zekfrivo(a)zekfrivolous.com (GregS) wrote: >In article <%llRm.94141$gg6.27160(a)newsfe25.iad>, sbnjhfty > <fgsdfgrr(a)asfffwer.com> wrote: >>I'm looking for an isolation transformer for repairing small (less >>than 1000W) power supplies. I see loads of them on ebay and some are >>medical grade and inexpensive. Are these usable for what I want? >>Other than that, any tips on where to get a good deal on one? I >>don't want to spend a load as this is hobby work only. > >Just an 'isolation transformer" means NOTHING for what >you want. Most all isolation transformers sold have the secondary tied to > ground. >You need a service isolation transformer. You can usually get inside and remove > a >secondary "neutral" connection. Futher explanation, if the transformer is raw unmounted, its output is not tied to anything. A company who sells a transformer mounted in a box with outlets to consumers, MUST ground one leg of the isolation transformer. This also makes for what the transformer is mostly used, to help cut down on noise, especially noise not in common with ground. I think you can buy service transformers ungrounded, but I never had one. greg
From: Dave Plowman (News) on 2 Dec 2009 13:47 In article <7nnkudF3n27mkU1(a)mid.individual.net>, Adrian C <email(a)here.invalid> wrote: > Dave Plowman (News) wrote: > > GregS <zekfrivo(a)zekfrivolous.com> wrote: > >> Just an 'isolation transformer" means NOTHING for what you want. Most > >> all isolation transformers sold have the secondary tied to ground. You > >> need a service isolation transformer. You can usually get inside and > >> remove a secondary "neutral" connection. > > > > That's interesting. I've never seen any transformer with the secondary > > tied to ground - unless as part of an installation. The word > > 'isolation' means just that. Sure you're not thinking of an auto > > transformer? > > > Seems to be a US safety requirement to ground one leg. > http://en.wikipedia.org/wiki/Isolation_transformer Interesting. > I've got here a Farnell 500W 240V/240V isolating transformer that looks > and weighs similar to a typical building site transformer, the outputs > are floating. Indeed. They used to be very common for feeding things like electric guitars in a TV studio, etc. And grounding one leg of the secondary would negate the whole purpose of them. These days it's more usual to do a quick PAT (test) and supply the mains via an RCD. -- *It's this dirty because I washed it with your wife's knickers* Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: GregS on 2 Dec 2009 14:03
In article <50c36de762dave(a)davenoise.co.uk>, "Dave Plowman (News)" <dave(a)davenoise.co.uk> wrote: >In article <hf5svh$5gg$2(a)usenet01.srv.cis.pitt.edu>, > GregS <zekfrivo(a)zekfrivolous.com> wrote: >> In article <%llRm.94141$gg6.27160(a)newsfe25.iad>, sbnjhfty > <fgsdfgrr(a)asfffwer.com> wrote: >> >I'm looking for an isolation transformer for repairing small (less >> >than 1000W) power supplies. I see loads of them on ebay and some are >> >medical grade and inexpensive. Are these usable for what I want? >> >Other than that, any tips on where to get a good deal on one? I >> >don't want to spend a load as this is hobby work only. > >> Just an 'isolation transformer" means NOTHING for what you want. Most >> all isolation transformers sold have the secondary tied to ground. You >> need a service isolation transformer. You can usually get inside and >> remove a secondary "neutral" connection. > >That's interesting. I've never seen any transformer with the secondary >tied to ground - unless as part of an installation. The word 'isolation' >means just that. Sure you're not thinking of an auto transformer? I have been thinking about it. The MAIN purpose of an isolation transformer is to make it non isolated by making a NEW neutral close to the device being powered. The main purpose of an isolation transformer is noise control. Now we have us tecks who all our lives have learned isolation and that stuff. I taliked to the people at Tripplite and verified ALL their isolation transformers ARE grounded. Read the paragraph, and yet it says above, "Complete line Isolation" http://www.tripplite.com/en/products/model.cfm?txtSeriesID=325&EID=13703&txtModelID=230 Also look through http://www.tripplite.com/en/keyword-search.cfm?q=isolation%20transformer The isolator you buy from MCM is very unlikely to have the secondary grounded, but I really can't verify that. In reading PC Power Protection by Mark Waller, he pointed out their is a NEC requirment for this grounding. I have not found an exact description in the code. There is about 75 references in that book, but no index marks. Man, I should sell that book !!!! Big Bucks. greg |