I've got several unused coils of 14 gauge wire that have ferrite iron cores cut to the length of their spools. They have maximum current power transmission ratings of ~5.9A, and according to a resistance by length calculator on google the overall resistance is less than an ohm for the entire spool. I'm trying to figure out a part that could be used to power the solenoids. I'm hoping to find a simple unit that can plug into a surge protector with 1 cord for each of the three solenoids.

Eventually after the solenoids are each powered correctly, I'll want to be able to control the current going to each with a microcontroller with a reasonable resolution. Is there any simple way to do this without needing to purchase many more components? I've looked into using a voltage-regulator IC + voltage-divider/digital potentiometer setup. The output of the voltage IC would then adjust a power transistor to let current through based on the voltage.

Would a power supply such as this one be able to be controlled by a microcontroller in this way?



1 Answer 1


Yes but it will not be very powerful (10%) compared to an iron core solenoid.

Ferrite cores have low saturation flux density as compared to Iron cores. ... Advantage of ferrite cores lies in their low eddy current losses (due to their higher resistivity) even at high frequencies used in SMPS where iron cores if used result into extremely high losses.

So the power supply will work to maybe 10V or 1 Ohm as long as stored energy is not released back into supply.

One can superimpose a low frequency sine with DC current and measure the attenuation of 10% to define the max DC current at the threshold of saturation. Such as a rectified sine from a transformer, with an active NPN or Nch load and big heatsink to define this max current as long as transformer has much lower DCR output than solenoid.

Then using Ohm’s Law choose Vdc average or RMS from rectified sine or your adequate DC power supply to drive Imax = V/Z(f) where Z(f)= 2pifL + DCR. Current then rises at the rate to Imax after some time, dt with dI=Vdt/L. After time t, the solenoid if current saturates the core, I will accelerate as L drops to 0 then current must be cutoff. For steel this Bmax threshold is smooth, while for ferrite it is lower and sharply reduces L.

Therefor the current must be limited by the DCR (<1Ohm) under Imax where inductance drops 10% or limited by thermal rise and thermal resistance ‘C/W.

  • \$\begingroup\$ I'm sorry, it is an iron core. 98% Iron and 2% something else. I thought that iron core still act as a ferrite magnet. \$\endgroup\$
    – snowg
    Mar 29, 2019 at 8:53
  • 2
    \$\begingroup\$ 2% silicon. This must be cold rolled grain oriented steel laminated in silicate insulation or CRGOS to get high mu. Ferrite is dispersed iron particles in a ceramic binder \$\endgroup\$ Mar 29, 2019 at 15:26

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