Transformer coil resistance query?

[Lightning]

Hello,

I am experimenting with magnetism and I am trying to provide a high current through a wire, to do this I am going to build a step down transformer.

I will use a high voltage source but I want a low current drawn by the primary coil to preserve battery charge (assume I am using a switch mode to provide AC).

What I was taught was that transformers transfer power with ratios of coils/voltage/current and that in an idea system, power in = power out; so I was thinking that I could have a high resistance in the primary coil so high power was being transferred while keeping currents low.

But I have recently confused myself as magnetic systems seem to rely heavily on how much current there is and voltage seems to be arbitrary, so my understanding is contradicting itself.

Is it possible for me to use a high resistance primary coil to transfer power while keeping my current low?

 

[(*steve*)]

You want the resistance of the primary and secondary to be as low as possible.

It is the inductance of the winding which limits the current for an AC signal (or at least which does so in a way that doesn't waste power).

So, many turns for the primary and fewer for the secondary will convert a higher voltage and lower current to a lower voltage and higher current. Efficiency issues aside, the power out = power in as you observed.

Yes, the magnetic field is proportional to current, but you can get the same magnetic field with a lower current if you have more turns. Essentially this is exactly what is happening inside the transformer.

 

[Arouse1973]

I am pretty sure this is how a Mig welder works. It has a large primary winding and small secondary winding. It will give you only a few volts on the output but with 100s of amps. But of course this runs on mains.
Thanks Adam

 

[Lightning]

Thanks guys, that clears things up immensely.

 

[JimW]

Maybe I am the only one confused by the original posters description. It is the mention of conserving battery, followed by a switch mode power supply to create the AC for the step down transformer that is the general problem that I see.

If the plan is to make a battery powered magnetic field, then just drive the coil with the battery. Generating a high voltage AC signal that can be converted to a 60 Hz high voltage that can then be stepped down is still still limited to what the battery can supply, minus all the losses from the intermediate circuitry.

Maybe I am misunderstanding the posters plan...

JimW

 

[Arouse1973]

Maybe I am the only one confused by the original posters description. It is the mention of conserving battery, followed by a switch mode power supply to create the AC for the step down transformer that is the general problem that I see.

If the plan is to make a battery powered magnetic field, then just drive the coil with the battery. Generating a high voltage AC signal that can be converted to a 60 Hz high voltage that can then be stepped down is still still limited to what the battery can supply, minus all the losses from the intermediate circuitry.

Maybe I am misunderstanding the posters plan...

JimW

Yep mig welder tranny is indeed step down. You wouldn't have to run this on mains actually to get a large current. We are not talking about running this on a PP3 he will need an old car battery or somthing like that. Don't know what smps he is planning on using he doesn't say.
Adam