Good afternoon/evening to all,
I bought an Amplimo toroid which shows two white wires for the primary. At diagram (below), it shows the dotted mark in one white wire for the "live/hot", but on the actual xmer there is no indication at all. The secondaries are easy to identify by the different colours.
An email was sent to Amplimo, but no answer/reply so far.
How could I identify "which" white wire should be wired to phase?
Thank you.
P.S.: Is it reasonable to put two ~10A fuses after the secondaries?
I bought an Amplimo toroid which shows two white wires for the primary. At diagram (below), it shows the dotted mark in one white wire for the "live/hot", but on the actual xmer there is no indication at all. The secondaries are easy to identify by the different colours.
An email was sent to Amplimo, but no answer/reply so far.
How could I identify "which" white wire should be wired to phase?
Thank you.
P.S.: Is it reasonable to put two ~10A fuses after the secondaries?
An externally hosted image should be here but it was not working when we last tested it.
Hi Karl,
Any of the white can be used as phase and the other white as neutral. It does not matter. Evidently, the phase of the secondary outputs change 180 degrees as well, but as AC voltage is "first one way and then equally much the other way" it has no effect in operation. This is why they made both lead-wires white.
The real information in that figure is how the secondaries are phased with respect to one another. Therefore, they have different colors.
Any of the white can be used as phase and the other white as neutral. It does not matter. Evidently, the phase of the secondary outputs change 180 degrees as well, but as AC voltage is "first one way and then equally much the other way" it has no effect in operation. This is why they made both lead-wires white.
The real information in that figure is how the secondaries are phased with respect to one another. Therefore, they have different colors.
Ok, thanks.
I remember a while ago someone here saying fuses should be around 3x times the secondary values, but 5A may be ok, indeed.
It's a 100W class AB amp, I'm replacing its old 220V transformer, as it gets quite warm after one hour running, has an annoying permanent buzz, also the rect. bridge gets bit warm. I suspect the amp is draining high(er) currents than it should (with old 220V trafo), so I want to put fuses after secondaries.
As cbdb says, choose the fuses above the nominal current rating but not so much above nominal current rating that a short-circuit current is not certain to blow the fuses. I would also choose 5A-6A, slow-blow types.
NB: It is always better to realize that you have chosen fuse values such that they are activated a bit before you expected, than after the damage is done. It is not exact science to choose fuse values and wire-fuses are not very precise themselves.
Secondary fuses protect the downstream circuitry and wiring, the primary fuse will blow if there's a secondary short due to the massive primary current draw that will trigger. Basically size the primary fuse to prevent the transformer catching fire. A hard short will either blow the rectifier or the primary fuse anyway, but secondary fuses are probably cheaper than bridge rectifiers(!) If you omit secondary fuse the downstream wiring should be generously rated (as least as thick as the secondary windings).
If there's an auxiliary secondary of lower power, that could short without pulling enough power to blow the primary fuse - that kind of winding does need a fuse I think, especially if at the surface of the winding stack.
If there's an auxiliary secondary of lower power, that could short without pulling enough power to blow the primary fuse - that kind of winding does need a fuse I think, especially if at the surface of the winding stack.
3.47A is nominal current, thus maximum (nominal) current. It is not like for a power supply with a current limiter where the maximum current may be well defined. For transformers, the temperature inside the transformer is important for deciding its nominal power. You may have higher currents temporarily. This is why a 4A fuse would leave too little margin.
If 5A blows when you start up the power supply, try 6.3A.
You can determine polarity by a "kick" test,you need an analog voltmeter set to D.C. volts to do this.Hook up the voltmeter to one of the secondaries making note of which transformer wire goes to the voltmeter + lead.Then momentarily touch a 1.5 volt battery to the primary leads again making note of which transformer lead touches the battery + terminal.The voltmeter needle will either move up the scale briefely or down scale(peg at zero).If the voltmeter kicks upscale then the primary and secondary wires attatched to the voltmeter + lead and the battery + terminal are "in polarity" ie: dotted. You can then repeat the test moving the voltmeter to the other secondary (don't reverse the battery to the primary leads) and repeat the test. If the voltmeter kicks up then whatever secondary lead is connected to the votmeter + is in polarity.But as others have said it doesn't really matter in your situation.
Watch you don’t zap yourself doing the “kick test”. Yes, even with a AA cell battery any inductor can nail you if you manage to become series connected with it when it turns off. Harmless for the most part, but you could hurt yourself falling out of your chair, slamming your hand into something, or dropping the soldering iron into your lap.
The only time it really matters which phase the primary is in is if you series or parallel secondaries of two identical trafos. Use a dim bulb tester when you do that, until you get it clearly marked.
The only time it really matters which phase the primary is in is if you series or parallel secondaries of two identical trafos. Use a dim bulb tester when you do that, until you get it clearly marked.
Hello all,
The phase identification is solved. But now it has another thing: at primary the (slow) 1.6A fuse blows "every now and then", even with no load (secondary disconnected)...
I've seen people placing a thermistor between the fuse and the primary of the toroid to attenuates the inrush current, but I'm not sure which one (value) to pick for this 300VA xformer.
#help
The phase identification is solved. But now it has another thing: at primary the (slow) 1.6A fuse blows "every now and then", even with no load (secondary disconnected)...
I've seen people placing a thermistor between the fuse and the primary of the toroid to attenuates the inrush current, but I'm not sure which one (value) to pick for this 300VA xformer.
#help
cbdb, thank you very much. You mean a thermistor between the fuse and primary?
I've seen folks using CL60 or CL80 (5A) ones, but these are not rated 10A.
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