isolation transformer needed
in [Repair]
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From: GregS on 2 Dec 2009 14:05 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 I just put that there. it was not there this morning. >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. Thats probably true, and correct. its up to the contractor to use it in the right way. greg
From: PlainBill47 on 2 Dec 2009 14:06 On Tue, 01 Dec 2009 22:41:38 -0500, 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. Spending too little isn't cost effective either if you manage to fry a scope probe or other piece of test gear. Still, the 30 KVa three phase is serious overkill for your needs. Give a little thought as to how you are going to be using this. If you want to isolate the input side of the power supply from the line so you can look at the control ICs a relatively low capacity isolation transformer will suffice. If you want to isolate 1000 watt power supplies while testing at full load, you'd better have an isolation transformer rated at something over 1000VA. I would say something rated at 250 VA is the minimum you want. The medical isolation transformers or the BK Precision TR110 would be better. PlainBill
From: GregS on 2 Dec 2009 14:15 In article <hf6di4$97m$1(a)usenet01.srv.cis.pitt.edu>, zekfrivo(a)zekfrivolous.com (GregS) wrote: >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. I think to a technician, ground isolation is whats important or really needed. In some cases it may also include line isolation, but I have to think about that for a long time. greg >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&txtMod >elID=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
From: Adrian C on 2 Dec 2009 14:35 PlainBill47(a)yahoo.com wrote: > > Give a little thought as to how you are going to be using this. If > you want to isolate the input side of the power supply from the line > so you can look at the control ICs a relatively low capacity isolation > transformer will suffice. If you want to isolate 1000 watt power > supplies while testing at full load, you'd better have an isolation > transformer rated at something over 1000VA. > > I would say something rated at 250 VA is the minimum you want. The > medical isolation transformers or the BK Precision TR110 would be > better. > > PlainBill Could perhaps the figure of 1000W be taken from what might be repaired as a hobby interest - surround sound home theater amplifiers, where the actual power draw from the mains is considerably less than that hyped 1000W - and if it's that item, ye wouldn't really (if you value your ears) be testing at full load/volume anyway after fixing something that perhaps failed after moderate use. -- Adrian C
From: Baron on 2 Dec 2009 17:51
Dave Plowman (News) 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? > My bench Isolation transformer, 2KW rating, has a 240v primary with a centre tapped secondary that has provision to tie the centre tap to the case which is also earthed. FWIW it weighs about 100 LB its also marked as (Noise Suppressing) ! -- Best Regards: Baron. |