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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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18th Jul 2019, 11:27 am | #41 |
Nonode
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,062
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Re: Isolation/isolating transformers
I can see that by using an isolation transformer you will bypass any existing RCD so you might consider it more dangerous. For sure, there are some scenarios where that would be true but conversely in some scenarios it might be safer with a energy limited / floating supply. If you ground some part of the circuit (for measurement or it happens accidentally) then this floating advantage is defeated.
An alternative would be putting an RCD on the secondary side of and isolating transformer but also ground the secondary BEFORE the RCD. This would give you a virtual live / neutral set up, with RCD protection, but with a lot less energy available. It would be possible to do earth referenced measurement (on ac side) as long as very little current flows into the earthed point, since it bypasses the RCD. Moving the earth point to a centre tap would half the voltage available for a shock. dc |
18th Jul 2019, 11:34 am | #42 | ||
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Isolation/isolating transformers
Quote:
Quote:
Cheers, GJ
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18th Jul 2019, 12:22 pm | #43 |
Triode
Join Date: Jul 2017
Location: Fairfield, Melbourne, Australia
Posts: 48
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Re: Isolation/isolating transformers
Further more, it is useful to remember (from a DIY & bodging perspective) at any pair of identical transformers can be back-to-backed to make a 1:1 isolation unit. It doesn't matter what the secondary voltage is really.
A second useful tip is that small low voltage transformers can be used in this sort of situation to tweak the output voltage up or down a small amount. This is done by putting the secondary in series with the main transformer's primary (and the little transformer's primary across the mains). Depending on the phase of the small transformer's secondary with respect to the main transformer's primary there is either an additive or subtractive effect. Important to ensure that the small transformer's secondary current rating is at or above the main transformer's primary current. Example: Main transformer is 500 VA so primary current will be a bit over 2 Amps, so a 6.3 V, 3 Amp transformer will do the job and will give +/- (6.3 / 230) which is about 2.7%. A 12 V transformer gives about 5%. See https://www.youtube.com/watch?v=ZEFVNFyG9po http://electricalacademia.com/transf...ing-principle/ https://www.mig-welding.co.uk/forum/...p-mains.38115/ http://www.dms-audio.com/bucking-transformer-diy https://cdn.instructables.com/F12/9C...=webp&crop=3:2 |
18th Jul 2019, 4:13 pm | #44 |
Heptode
Join Date: Feb 2010
Location: Heysham, Lancashire, UK.
Posts: 669
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Re: Isolation/isolating transformers
For the thirst class of circumstances you need the isolating transformer, otherwise the RCD will trip as soon as you connect you test gear earth anywhere in the live chassis circuit.
Stuart |
18th Jul 2019, 5:29 pm | #45 | |||
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
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Re: Isolation/isolating transformers
Quote:
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Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW. |
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18th Jul 2019, 5:49 pm | #46 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: Isolation/isolating transformers
Quote:
In the US, they're very reasonably priced, of course it doesn't eliminate the need of an isolation transformer. I use both! I float all my test equipment from earth by using a 3 to 2 prong adaptor, as I feel using an isolation transformer plus an RCD eliminates a great deal of hazard. In the US, our RCD is known as a GFCI. Ground Fault Current Interrupter. You can install as many as you want or need. |
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18th Jul 2019, 7:25 pm | #47 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Isolation/isolating transformers
Quote:
VB
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http://www.ampregen.com |
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24th Jul 2019, 4:29 pm | #48 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: Isolation/isolating transformers
Quote:
Dave, US radcoll1 . |
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24th Jul 2019, 11:12 pm | #49 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,349
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Re: Isolation/isolating transformers
Interesting use of a train controller. I suppose it would have been for something like the Lionel O gauge system and would have been capable of delivering a couple of amps at up to 20V.
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5th Aug 2019, 7:05 pm | #50 |
Pentode
Join Date: Nov 2009
Location: Welshpool, Powys, UK.
Posts: 121
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Re: Isolation/isolating transformers
This may cause a few raised eybrows but I went down the route of two 110V equipment transformers back to back to give 240 and 110 both isolated from the grid and each other. Tons of power with no sag and about £100 spend.
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