Transformer resistance?

[JOEPRO]

On testing my Launch 2 post lift control board tonight I note the transformer seems to be giving continuity on my multimeter between the L & N mains input.







I don't really have anything to compare readings with so does this seem normal enough?

Background is it worked before taken down. And has sat wrapped up for 4 years and now I'm checking it over for reinstalling my used lift.

The isolator switch had missing parts so I was fitting a new one. And when doing this I noted continuity on my multimeter between L & N which I thought was odd and traced it back to the 230v in side on the transformer.

Again maybe this is perfectly normal for a transformer? Beeps on continuity test. 7ohm resistance between terminals.

 

[Blobber]

Yep normal, it's just a continuous length of wire wound around the laminated core, what you shouldn't get is a reading to earth or to the secondary windings

 

[ajlelectronics]

Perfectly normal. It is a coil of enamelled wire, wound onto an iron core (simplified description)

 

[daleyd]

As soon as it’s energised the actual impedance increase rapidly, but when no current flows through it then the resistance is minimal. The low resistance is the reason why sometimes a transformer will trip a breaker when you first power it up, once it has some magnetism they are ok, my oil filled welder used to do this all the time.

 

[JOEPRO]

Thanks all for advice its normal to read like this then which is good news

 

[sako243]

As soon as it’s energised the actual impedance increase rapidly, but when no current flows through it then the resistance is minimal. The low resistance is the reason why sometimes a transformer will trip a breaker when you first power it up, once it has some magnetism they are ok, my oil filled welder used to do this all the time.

Just to be pernickety / clarify it only does that on a change in current so if you applied DC to it then it'll just act as an inductive wire (inductance is essentially resistance to change in current). So a dead short to begin with, followed by a brief period as a resistor as the inductance resists the change in current and then once overcome then it'll be a dead short again.

Transformers need AC to function, that way the coil is effectively acting as a "resistor" all the time to the current.

 

[daleyd]

Just to be pernickety / clarify it only does that on a change in current so if you applied DC to it then it'll just act as an inductive wire (inductance is essentially resistance to change in current). So a dead short to begin with, followed by a brief period as a resistor as the inductance resists the change in current and then once overcome then it'll be a dead short again.

Transformers need AC to function, that way the coil is effectively acting as a "resistor" all the time to the current.

It’s kind of implied that no one would connect a transformer to DC

 

[MattF]

It’s kind of implied that no one would connect a transformer to DC

You overly trust folk.

 

[daleyd]

You overly trust folk.

No, but anyone who connects one to dc is obviously too stupid to understand resistance or impedance so it’s a moot point

 

[voipio]

Unless they want an electromagnet, or a choke.

The resistance of the primary (and secondary windings) gives rise to the resistive losses that occur in a transformer (there are other losses, due to eddy currents and magnetisation of the core).

Under a full secondary load of ~135W, the primary will be drawing 0.68A from the mains (allowing for ~10% loss) which results in 4.7V developed across this 7 Ohm resistance, leading to a resistive loss in the primary of 3.2Watts, which heats the transformer.