# Calculating peak current of solenoids

I'm a electronics newbie, and I'm making a project with 8 24v solenoids playing percussion quickly. I want to power these all with the same power source, so I'm being careful.

This is similar to power supply unit for Arduino/solenoid project but different in the fact that I am trying to sense-check what the manufacturers say about their products.

Some solenoids are spec'ed as having a draw of around 350mA: http://www.adafruit.com/product/413

And others are spec'ed as having a draw of 2A: http://www.amazon.com/0-7kg-Holding-Force-Solenoid-Electromagnet/dp/B009PMCSFO/ref=sr_1_4?s=industrial&ie=UTF8&qid=1431813437&sr=1-4&keywords=24v+2a+solenoid

Are these two options just different in terms of the power of the solenoid's movement (i.e. the 350mA will be considerably weaker than the 2A)? If I went for 8 x 2A 24V solenoids would a 20A 24V power source be enough to power everything at its peak usage?

Thanks :)

Are these two options just different in terms of the power of the solenoid's movement (i.e. the 350mA will be considerably weaker than the 2A)?

It is (ampere x turns)$^2$ that determines solenoid pull force so if the number of turns on both solenoids is the same, the 2A solenoid will pull nearly 33 times better than the 350mA device (all other things being equal).

If I went for 8 x 2A 24V solenoids would a 20A 24V power source be enough to power everything at its peak usage?

A 20A power source sounds adequate but would all eight solenoids be hitting simultaneously? A drummer has two hands and two feet meaning that maybe 4 solenoids is the maximum?

• Thanks Andy... ok, the 2A sounds like a better option then. Ideally I would like the power supply to be capable of the maximum frequency of hits (around 180bpm) and on all 8 channels. Not because I am going to be making the most insane percussion music ever written, but so that I know it won't blow if I want to go there. – pepsimxm May 17 '15 at 13:00

Well I think this would depend on many factors. If it's for percussion, you're going to want the solenoid to retract quickly and activate quickly also. If one solenoid is used, then a "tough" spring sounds likely. Mechanical advantage? The longer a pulse is required, the more power. If two solenoids are used instead, then each "beat" will require two fast solenoid activations (twice the power)... so there are many variables. The total current draw is also going to vary greatly depending on what type of beats it is performing, the speed of the score, and so many other things. A few large-ish bypass capacitors on the main power rails sound like a good idea also, to smooth out power coming from the supply.

If this were my project, I'd just build a first prototype, power it from some large battery (such as two 12V car batteries in series) then measure the real current draw for a variety of scenarios. That is easy and highly accurate. Then go about building an appropriate power supply.

• Thanks rdtsc, that is a good idea - I can just buy one solenoid of the higher power rating and test that. I hadn't thought I needed a bypass capacitor... do those work on DC current? Or do you mean install one between the AC mains and the power supply? – pepsimxm May 17 '15 at 13:05
• I mean to add some capacitors right after the power supply, DC, to help "smooth out" the large current spikes required by the solenoids. Without these, those large spikes will have to be handled by the power supply itself, and that's a rather demanding task. Filter caps present the power supply with a more constant load, as they charge slowly and can provide large currents to the solenoids very quickly. Something like 50v, 4700uF for each solenoid would help. So split the 24v power into 8 branches, add a cap across each one, then run those power to the solenoids. – rdtsc May 17 '15 at 14:16
• Ok, will go out and get some then - thanks a lot:) – pepsimxm May 17 '15 at 14:17