# What is the difference beteeen a solenoid's make current and inrush current?

Sorry if I'm just being noobish, but as I understand it, the make current is the maximum current that the solenoid can handle when switched on, but the inrush current is the maximum current it can handle when...switched on? What am I missing?

• There is no inrush current. The solenoid is an inductor, the current will rise from zero based on R an L values. Solenoids have pull in current and hold current. The highest current is the current defined by the winding resistance alone. Commented Jan 10, 2018 at 5:39
• As @JackCreasey rightly says, the inductor will do the opposite of allow inrush current - it will oppose the current flow then allow it to increase exponentially as it charges. It's the opposite effect to capacitance, which does draw an inrush current from an applied supply. Commented Jan 10, 2018 at 7:07
• Solenoid make current? Commented Jan 10, 2018 at 15:22

A solenoid designed for AC supplies will have an inrush current that can be significantly greater than the steady state current it takes when it has activated. It all depends on how the solenoid is initially supplied voltage and the part of the AC cycle that the voltage is applied. If you apply AC voltage to the solenoid at the peak of the waveform then there is little or no inrush current whereas if the solenoid is connected to an AC source as it passes through zero volts then the current waveform in the solenoid can reach an excessive value that causes magnetic saturation of the solenoid core and make the problem of inrush even worse.

Here's a table of numbers taken from the internet that can give some insight into the level of the problem: -

And here's what AC inrush current can look like when the applied AC voltage occurs at a zero crossing and at full peak: -

The top half of the picture above shows the problematic inrush current taking time to settle down. Solenoids, transformers, inductors and AC motors can all produce this effect because when lightly loaded, they are basically an inductor and the inductor current is proportional to the integral of applied voltage.

• +1 I have spent too long in the low voltage DC world. Essentially the increase in inductance at pull in causes a drop in AC current. That makes sense.
– RoyC
Commented Jan 10, 2018 at 9:47
• @RoyC Sure, there will be a change in inductance when the core moves but I'm genuinely referring to AC solenoids because they do exhibit inrush currents and can saturate causing bigger currents (for a few cycles of AC). Commented Jan 10, 2018 at 10:02
• Very pretty diagrams would you mind attributing them so we can decide on their applicability. Current through an inductor is 1/L integral V dt plus initial current, initial current is zero. Can you please tell us where this inrush current is coming from, nothing in this equation explains that. Saturation is a function of field strength which is proportional to current, if the current is not increasing unreasonably you will not get saturation.
– RoyC
Commented Jan 10, 2018 at 14:59
• @RoyC the table was taken from here: olino.org/us/articles/2013/10/22/… and the waveform one was a modified one taken from here: electronics.stackexchange.com/questions/135601/…. Unfortunately I can't remember where the 2nd one came from. However, that 2nd link is to an answer I gave on SE relating to inrush current in transformers. Commented Jan 10, 2018 at 15:06
• @RoyC think about the steady state case as V rises through zero volts - the current begins at a negative value (-I). As integration proceeds during the first half cycle of the voltage the current rises from -I to +I. That's the steady state case. Now, if current is zero at t = 0 then current will peak at 2I at the end of the first half cycle of voltage. Do you think I deserved the down vote? Commented Jan 10, 2018 at 16:58

As @Jack Creasey said the solenoid is basically an inductor so it does not have an inrush current. Solenoids are specified with the pull in current, enough current to pull in the solenoid; hold current, enough current to hold the solenoid pulled in and the DC resistance which allows you to calculate the maximum current for any applied voltage.

The amount of current a solenoid takes as it pulls in is a little more complex than a simple inductor. The inductance varies as the core is pulled into the solenoid giving a current profile like this.

Diagram credit:- http://www.ti.com/lit/wp/ssiy001/ssiy001.pdf

• An inductor can certainly have an inrush current when fed from an AC supply. When fed from a DC supply no, there is no inrush current. I think you need to think about this. Commented Jan 10, 2018 at 17:02

Assuming a relay, rather than a solenoid, 'make current' refers to the switching capacity of the contacts, not the coil current.

• @Armadillo 2001 are we talking about a solenoid or a relay?
– RoyC
Commented Jan 10, 2018 at 9:39