isolation transformer needed
in [Repair]
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From: PlainBill47 on 3 Dec 2009 16:02 On Wed, 02 Dec 2009 19:35:30 +0000, Adrian C <email(a)here.invalid> wrote: >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. Well, the OP said 'Power supplies'. I have a bad habit of taking people at their word. The last time I worked on an amplifier I noted the power supply was an classic 'heavy iron' design, with the AC line feeding a transformer. Still, I wouldn't be surprised to find a SMPS in something rated at a pretend 1000 watts. IMHO, it's a fool who repairs a power supply, then does not test it with a dummy load BEFORE hooking it up to it's intended load. And again, the OP has to decide if he wants an isolation transformer capable of handling the full rated load. Personally, that is always my recommendation. It avoids nasty surprises when one is in a hurry to test and forgets to switch the power cord to an isolated source. PlainBill
From: whit3rd on 3 Dec 2009 16:57 On Dec 2, 8:55 pm, mm <NOPSAMmm2...(a)bigfoot.com> wrote: > On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd <whit...(a)gmail.com> > wrote: > > >Yes, they are. In terms of shock hazard, you can use a GFI to > >the 1000W unit, and a small isolation transformer to run your > >oscilloscope, > > Do they make plug-in GFI's? Yes, of course; more important, one can get a GFI socket and wire it into a handy box (or a string of boxes with multiple plugs) and make a power distribution panel. There are (expensive, alas) sockets that offer 'isolated ground' so that the metal case(s) of the distribution panel can be grounded while the special sockets can be floated. Thus, you can wire sockets with ground-optional to the isolation transformer and have only the distribution panel on the workbench (the transformer can live on the floor or wherever).
From: whit3rd on 3 Dec 2009 17:14 On Dec 3, 6:20 am, Adrian C <em...(a)here.invalid> wrote: > whit3rd wrote: > ... In terms of shock hazard, you can use a GFI to > > the 1000W unit, and a small isolation transformer to run your > > oscilloscope, > This must probably again be a voltage US/UK thing - or maybe me - but if > I was working on 240V live equipment I'd rather it was ALL floating > through an isolation transformer than rely on the complexities and > effectiveness of a GFI/RCD to prevent shocks at the bench. Working on live 120V or 240V, you can always touch two points and get a shock. Either an isolation transformer, or a GFI interrupter, prevents the shock if one of those points is GROUND. I'm not sure why you would distrust a GFI, but they have a test button. Use it, and be reassured. The main plan, always, is not to touch the live wires.
From: Dave Plowman (News) on 3 Dec 2009 18:25 In article <8122d63d-b1ef-41f7-bf49-24e4d16c165c(a)g12g2000yqa.googlegroups.com>, whit3rd <whit3rd(a)gmail.com> wrote: > > This must probably again be a voltage US/UK thing - or maybe me - but if > > I was working on 240V live equipment I'd rather it was ALL floating > > through an isolation transformer than rely on the complexities and > > effectiveness of a GFI/RCD to prevent shocks at the bench. > Working on live 120V or 240V, you can always touch two points > and get a shock. Either an isolation transformer, or a GFI > interrupter, prevents the shock if one of those points is GROUND. If one of those points is ground touching the other gives you a shock. If neither is ground you can touch either one without a shock. The whole principle of using an isolating transformer for safety. Makes for better odds. > I'm not sure why you would distrust a GFI, but they have a test > button. Use it, and be reassured. > The main plan, always, is not to touch the live wires. That is the best safety advice. But have a backup plan for if you do. -- *A snooze button is a poor substitute for no alarm clock at all * Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: mm on 3 Dec 2009 20:53
On Thu, 3 Dec 2009 13:57:06 -0800 (PST), whit3rd <whit3rd(a)gmail.com> wrote: >On Dec 2, 8:55�pm, mm <NOPSAMmm2...(a)bigfoot.com> wrote: >> On Wed, 2 Dec 2009 17:13:20 -0800 (PST), whit3rd <whit...(a)gmail.com> >> wrote: >> >> >Yes, they are. �In terms of shock hazard, you can use a GFI to >> >the 1000W unit, and a small isolation transformer to run your >> >oscilloscope, >> >> Do they make plug-in GFI's? > >Yes, of course; more important, one can get a GFI socket and >wire it into a handy box (or a string of boxes with multiple >plugs) and make a power distribution panel. There are >(expensive, alas) sockets that offer 'isolated ground' so that >the metal case(s) of the distribution panel can be grounded >while the special sockets can be floated. Thus, you can >wire sockets with ground-optional to the isolation transformer >and have only the distribution panel on the workbench (the >transformer can live on the floor or wherever). Very good. Thanks to you and bz. |