Is this StepDown Transformer faulty? - Page 1
Forum section: electronics / general

author: vinlove
author_rank: Frequent Contributor
timestamp: August 28, 2019, 09:14:23 pm
content: Just bought a new stepdown transformer 230V -> 115V.But when tested with main socket tester, it lights all three LEDs at the top of the tester, which means "LIVE / GRD Reverse, Missing GRD"It sounds like the transformer's LIVE and GRD is reverse, and Ground is missing. Is it serious fault? Should it be returned?

author: vinlove
author_rank: Frequent Contributor
timestamp: August 28, 2019, 09:18:15 pm
content: The transformer says "It is not earthed". Could it be problem?

author: vinlove
author_rank: Frequent Contributor
timestamp: August 29, 2019, 02:05:48 pm
content: Any ideas on this? Thanks

author: richard.cs
author_rank: Super Contributor
timestamp: September 01, 2019, 12:06:18 pm
content: That type of transformer has a 110 V centre-tapped secondary with the centre tap earthed, it is not faulty it is just totally confusing the primitive 3-neon tester. The intended purpose of these transformers is to provide a supply for construction equipment used in wet areas where the maximum shock voltage to earth is 55 V and therefore "safe". It's not clear from your photo but I assume you've filled off the plastic key to allow you to plug that blue 240 V plug into the yellow 110 V socket?The question is more if is this the correct type of transformer for whatever it is you are trying to do?

author: bjbb
author_rank: Contributor
timestamp: September 05, 2019, 04:27:58 pm
content: Let us see if this post gets past the Australian Stasi.Again, you people need to be very careful when answering questions and commenting on the physics and chemistry of regulatory safety requirements. And am still requesting/begging that Dave find an engineer from his local Certification Body (see the JAS-ANZ listing) and do a series of interviews where they discuss product evaluation and standards scope.As a technical advisor to the local fire marshal, have seen three house fires (one was a major loss) and two injury incidents during last 16 months where the root cause was a single-fault condition in electrical equipment having construction/materials/performance not meeting code. That is, 'home-engineered' stuff that failed.The label indicates "Class 1 Construction This Transformer Must Be Earthed".It should be marked as 'Class I' because roman and arabic numeric characters have different meanings (yes, this is stupid, but it is how the standards and building codes are written in the western world).The unit must be connected to a protective earth because the level of protection from shock cannot meet either the withstand requirements, or the insulation coordination requirements, or the overload requirements per whatever safety standard is scoped for this type of transformer (typically IEC61558-x or IEC60076-x).

author: richard.cs
author_rank: Super Contributor
timestamp: September 05, 2019, 04:52:45 pm
content: Despite Vinlove's lack of country flag it is pretty clear to me that the transformer in his second photo is one of these:https://www.google.com/search?q=uk+power+tool+transformer.These are connected internally as described here:https://electrical.theiet.org/wiring-matters/issues/62/reduced-low-voltage/and the earth connects to both the centre tap of the secondary winding and the earth pin of the output connector(s), possibly also the transformer core.What's not clear to me is what he's trying to do with the transformer.

author: vinlove
author_rank: Frequent Contributor
timestamp: September 06, 2019, 12:12:43 pm
content: Oh, I thought no one would come and answer this question, but here we areThanks.Well, the transformer was bought to power on Ham Radio, which is vintage from 1960s, all tube construction. Because it is made in USA, and imported, it must be run with AC 110V mains.Here we have AC mains voltage 230V, so needed the step down transformer. Yes, the converter socket had a pin at the wrong way, and it would not line up to the input socket's groove in the transformer. So I Was going to return it, but then I have no time to browse and order another one, and wait for few days, and still am not sure if it will be the right one. So I cut the pin off with a saw of my multi tool, and it is fitted to the transformer. And I was reading the output with mains socket tester.But it seems all working OK, because I connected and tried a few different items running on 110V such as electric shaver, and Laptop power supply etc. They all functioned correctly without any sign of stress or going "Bang~".

author: vinlove
author_rank: Frequent Contributor
timestamp: September 06, 2019, 12:15:21 pm
content: I still have not powered on the ham radio with the transformer, because it is such as vintage, it needs a through clean up and rust removal on the input plug. The input plug pins are covered in some rubbery stuff and is not conducting as is now.

author: richard.cs
author_rank: Super Contributor
timestamp: September 06, 2019, 01:34:14 pm
content: Electronics from the 1960s is often of a "live chassis" design where the chassis "ground" is not isolated from the mains supply and may be connected to Live, Neutral, or a rectifier output. These can be quite unsafe, and more so on some supply types than on others. Do you have schematics or other design information to confirm?

author: vinlove
author_rank: Frequent Contributor
timestamp: September 06, 2019, 01:41:41 pm
content: The radio must have been in use by previous owner for long time in Uk with a stepdown transformer.I see it has usual uk mains plung attached, but marked as 110v only.Also, the power supply must have had been serviced with new smoothing caps, because they are all new.But the radio itself must have been left unused for long time which needs good clean especially the power input connector, tube sockets and pins, which are rusty and grimey.