Transformer question - Page 1
Forum section: electronics / projects

author: synth-dude
author_rank: Contributor
timestamp: February 22, 2016, 11:03:28 am
content: Hi all,I got a transformer today, a big beefy 2 mm copper winding that weighs a tonne - the best kind.It has 4 wires coming out, and I assumed 2 primary and 2 secondary. Tested with my DMM to confirm, turns out the 4 windings are connected to each other, so its basically got one primary with 4 taps and no secondary.A bit of googling doesn't really turn up much except that APC use these in UPSs, which is where I got my one, but no one really knows what its used for.Someone pointed out the UL database says its a:Class 130 (B) electrical insulation systemshttp://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?name=OBJY2.E154515&ccnshorttitle=Systems,+Electrical+Insulation+-+Component&objid=1073768056&cfgid=1073741824&version=versionless&parent_id=1073767046&sequence=1I've attached a photo of the transformer and also my DC resistance measuremnents on each winding, and the key numbers are:060-00718-01CLASS B(130c) Z150HLEI-4 E154515 0644In the resistance picture, windings B, C, D are attached to a 3-way plug, and winding A is by itself, also winding A has the 5 ohm resistance to all the other windings.Can anyone shed any light on this mystery?If it is indeed an isolation transformer of sorts, how would one use it without a secondary winding?

author: Phoenix
author_rank: Frequent Contributor
timestamp: February 22, 2016, 11:15:23 am
content: Could be an autotransformer to provide a level of step-up or step-down as input voltage varies.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: February 22, 2016, 11:16:06 am
content: Probably some kind of auto-transformer.Uses tap-changing to change the mains voltage (like a variac).

author: Connoiseur
author_rank: Regular Contributor
timestamp: February 22, 2016, 11:20:49 am
content: If there is a continuity between ALL the windings, then certainly this is NOT an isolation transformer. This is an autotransformer.I don't know about other parameters in the label but class B 130(degree)C, is the insulation class of the transformer. Insulation class is a standard way of describing the maximum temperature that the transformer windings can handle before bad things start to happen.Winding resistance is not a great way to determine the turns ratio of a transformer. I suggest you use another step down isolated transformer to get about 12V AC . Feed it into this transformer and observe the voltage.

author: bktemp
author_rank: Super Contributor
timestamp: February 22, 2016, 11:23:07 am
content: Most APC UPSs are line interactive: They can change the output voltage slightly without using the battery. The seperate cable for the beginning of the winding makes sense. The other 3 connections are beeing selected by relais, so they are grouped together.But does it really have no secondary/low voltage winding? It should have thick cables for 12/24V.

author: synth-dude
author_rank: Contributor
timestamp: February 22, 2016, 11:32:50 am
content: OK, wow, that makes sense and is quite amazing, a poor mans variac.Connoiseur, that idea is great for testing it, but I dont quite understand how to. Using the 4 windings denoted by A,B,C,D which 2 wires would go to the 12v AC secondary of the isolated transformer? So for example would I connect A and D, and then measure the voltages from A -> B, then A -> C, etc?I'll go research autotransformers before commenting further, mind = blown.bktemp, yes only has primaries, no secondaries at all.

author: bktemp
author_rank: Super Contributor
timestamp: February 22, 2016, 12:20:33 pm
content: After a bit of searching I found some other transformers from an UPS without a seperate secondary, for example here:http://laird.vectorstar.com/music/amps/ups-transformersI could not find any further info, but it looks like they are using the tapped primary both for line interactive and for stepup operation. So no isolation between mains and all the electronics, but it saves some copper.That makes this transformer not very useful for other uses unless it is ok to have a non isolated output voltage.

author: Connoiseur
author_rank: Regular Contributor
timestamp: February 22, 2016, 12:30:51 pm
content: For the sake of clarity letT1 = transformer with 12V secondaryT2= transformer under testIt doesn't really matter which pair you choose (unless that pair has ridiculously small number of turns <30 or so for this transformer).Just keep a track of applied voltage (measure it when T2 is connected) AND output between terminal A and some other terminal (like A - B; A-C etc.).Turns ratio between energized terminal and other terminal=applied voltage/voltage between terminals in question

author: GamerAndds
author_rank: Regular Contributor
timestamp: February 23, 2016, 07:03:39 pm
content: it probally runs on C and switches between B,D for power demands...