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# Maximum current in a 24v supplier circuit

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#### crazy-igzp

##### Member level 1
hello
I'm trying to build a power supply 24v, and I need to make sure to have a maximum current.
I need it to create a magnetic field using an electric coil that I made myself (0.8mm, 60 of turns).
so, what's the maximum current that I can get out of a sector (220 v).
Because I need the magnetic field to hit at least 1 tesla.

crazy-igzp said:
I need to make sure to have a maximum current.
You should be specific about how much current.

I made an electromagnet from a steel handle and many loops of wire. I powered it from a 12 volt car battery. It drew several amps and became hot after 10 seconds.

My aim was to strengthen a magnet inside an old meter movement. I think I made it worse the first couple tries. Then I managed to restore its strength, partially. I think the end result was slightly less than its original strength.

I cannot be sure whether my electromagnet simply needed more turns, or whether the meter had reached its maximum limit of its strength no matter how strong a field I applied.

There is a formula for the strength of a magnetic field, based on number of turns, Amperes going through it, etc.

I already have 100m of copper wire of 0.8mm, and I know the formula (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html#c3 ) and I need the maximum current that I can get out of a sector of 220v, I'm okay with the fact that the wire might overheat, I just need to know what's the maximum amperage I can get if I try to use a transformer directly linked to the sector, so I can then see the limitations the sector has in amperage intensity.

Temperature rise will be what limits the maximum current.
Time, and the safe maximum temperature rise of whatever insulation is on that wire.
What type of insulation does this wire have ?

Does this coil have to run constantly at one Tesla, or is it only on for for brief intervals with long cool down periods ?

Don't know for sure about your circuit breakers, but suppose they trip at 10A, 220VAC.

So you step it down to 24 VAC. The ratio of primary to secondary is 9:1.

Therefore you can expect 90 A from the secondary. Is that what your question is about?

Your primary must be designed to admit 14A. In simulation I've seen a default value of 4H for power transformers, so I suppose that is a suitable value.

Your secondary must have a tiny ohmic resistance, if you hope to get full power from it. Its wiring must be a large enough diameter, or else you can make a doubled-up cable from the wire you have.

As the magnetic field will be established very rapidly, you only need to run the current for 10mS or so. If you have a "fuse" of thinner copper wire in series with your coil, you then know which bit is going to melt. So build a 24V 2A (or less)PSU. Have a current limiting resistor then a huge capacitor wired via your fuse to the coil with thick wire. 10t of .8mm = length? = resistance = ? . I guess its .5 Ohms, so the current will be 24/.5A = 50 A. Let the capacitor charge then connect the coil. There will be a flash and a bang and the fuse should melt and the pole piece should be magnetised..
Frank.

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