HELP on transformator schematic - Page 1
Forum section: electronics / general

author: pelule
author_rank: Frequent Contributor
timestamp: March 06, 2017, 08:17:43 pm
content: I have 2 of same toroidal transformer, primary 2x 115VAC, secundary 21.6V/9A.As far as I understand the lable, it is a (fused?) security transformer, with conformity to CE, Switzerland and VDE 0551The label states the colors of the wires, but I am not complete confident regarding the correct schematic.Anybody out there, able to confirm or correct my understanding.Is there a way to confirm it with a measurement?Thanks for any help in advance./PeLuLe

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 07, 2017, 03:50:37 am
content: I had never seen that transformer symbol until today; evidently it means it's an"isolating transformer" IEC 60417-5221. I think you have a correct understanding of what the transformer says.The only thing that confuses me is the label2x1, 38A. Nothing in this transformer seems to be anywhere near 38A.Anyway, I made acrude, small simulation of this transformer. It appears it should present 21V unloaded, and when loaded it goes down to about 19V.

author: Ian.M
author_rank: Super Contributor
timestamp: March 07, 2017, 04:08:15 am
content: Quote from: technogeeky on March 07, 2017, 03:50:37 amThat's 1.38A fuse rating, for each primary or 5.8% more than the expected primary current for 300VA with 115V RMS on each primary.There's not a lot of margin there and we don't know the fuse characteristic, although it should be some sort of delay fuse, so I strongly recommend you don't push it too close to its VA limit.

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 07, 2017, 04:40:19 am
content: Quote from: Ian.M on March 07, 2017, 04:08:15 amOh, I was so convinced of the 1x2 that I forgot about European style decimals. Doh!In any case, the output of 21.6 * 9 isn't even 200VA, so...

author: Ian.M
author_rank: Super Contributor
timestamp: March 07, 2017, 05:17:01 am
content: Quote from: technogeeky on March 07, 2017, 04:40:19 amNow that I hadn't spotted. As the secondary is only rated for 65% of the primary VA, there isn't much risk of blowing those fuses without a gross overload.I cant imagine its cost-effective to have that much imbalance between the primary and secondary VA ratings - but maybe the manufacturers do short runs of custom transformers by simply changing the secondary turn count.

author: pelule
author_rank: Frequent Contributor
timestamp: March 07, 2017, 07:01:06 pm
content: Many thanks for all helpful comments.I need to connect it to 115VAC (both primaries in parallel) so the correct polarity is important.I am not sure about is the direction/polarity of the coils (the dots in the schematic).I assumed, the first named color (bl & bn) is the dotted one.Is that correct?Is there a way to measure that?

author: Ian.M
author_rank: Super Contributor
timestamp: March 07, 2017, 07:07:41 pm
content: That's how I'd read it, but its better to check:With no load on the secondary, connect ONE primary and one wire of the other primary. Check voltage between the remaining wire and where its supposed to go - if its low, (a few volts), its safe to connect it, but if you get approximately double the supply voltage, you've got the phasing wrong and must have misunderstood the diagram.

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 07, 2017, 09:03:28 pm
content: Also, there are plenty of ways to test everything involved. A simple multimeter can check the 2 ohm values of the primary. One of those transistor tester gadgets ($20) can test the inductance of all of the coils.You can't really test the phase relationship with a cheap gadget, but you can do that with one or twoAC"wall wart" power packs. Any voltage will do, something like 5VAC or 9VAC or 12VAC. You can also open up any unregulated DC "wall wart" and just remove/bypass the bridge rectifier (sometimes it's just 4 diodes on the PCB) and the capacitor.Then, just put the voltage into whatever wire pair you want. You can hook it up to the secondary, and then test both primary components and see if the two primary coils are in-phase or out-of-phase. You could also connect them to the primary, and test the secondary and/or the other primary.I am not yet an expert on transformers, but I suspect this transformer wasnot intendedto be run with the primary coils paralleled. It appears to be setup for either 120 or 240V operation.In any case, you can also use the combination of the above tests to getcorroborateddata. You can use the multimeter to test the ohms ratings, and use the transistor tester to get the inductance ratings. You can estimate the turns ratio by this (with a simple calculation)You can then use a wall wart to power one of the coils, and then estimate the turns ratio by this as well.If the two ratings agree, then all you need to learn is the phase relationship.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: March 12, 2017, 05:54:13 pm
content: For parallel primay, connect the dots together and the un-dotted together.Any

author: pelule
author_rank: Frequent Contributor
timestamp: March 12, 2017, 09:26:53 pm
content: QuoteYes - that's exactly, what I wan't to do - but the question was, how to confirm, which are the dotted wires.QuoteBased on Ian.M tipp I measured and could confirm the schematic I have drawn. Works fine.