perik wrote: ↑
Wed Aug 21, 2019 9:37 am
I'm not sure about how to calculate the maximim current and the inductance on the coil. Sorry ...
Calculating the inductance of electromagnets you've wound yourself ... could be difficult!
But having wound them, you may be able to measure it.
The same goes for the maximum current.
But the maximum current is merely the maximum voltage divided by the resistance of the wire you used. Ohm's Law.
When first switched on, current is zero, and rises at the rate given by the volts and the inductance.
As the current rises, more voltage is dropped by the resistance of the coil, and less by the inductance, so the rate of rise tails off, until the current reaches maximum.
When it's switched off, the current tries to drop but the inductance tries to keep it going.
The flyback diode provides a path for the current, so only the resistance of the coil causes the fall in current.
The shape of the current/time curve is exactly the same, just inverted.
And per electromagnet:
1 led 12 v
There's no such thing as a 12v LED - just an ordinary one with built-in resistor.
Also, you've got it connected across the gate-source, so you want to design it for the drive circuit, not the load.
Another concern is the heating with the electromagnet so I might go down in power and drive it with 5v instead. I guess everything would stay the same except for exchanging the 12 v led to a 5 v led instead? Is that correct?
With the same coil, 5v instead of 12v will reduce the heating by the square of (5/12)
But the magnetic field will also drop
To keep the same magnetic field, you'll have to increase the current by using thicker wire.
Which will bring the heating back up to where it was!