Electromagnet basic question (Resolved)

I've been searching the web for an hour and cannot find an answer- I would really appreciate some help with a more simple issue.
I'm currently working on a project that involves multiple (88) 24v 350ma electromagnets (https://www.amazon.com/Uxcell-a13060500ux0006-Frame-Solenoid-Electromagnet/dp/B00DN7BFDS/)
controlled independently by Arduino boards and a few relays. No more than 10 will ever be on at once.
I'm trying to figure out how to use one hot 24v ~5a wire across the whole relay setup without the electromagnets sucking up too much current and frying. I thought they would only take as much current as they need, but it seems that's not the case with electromagnets? Getting pretty terrifyingly loud as I move beyond the rated current on my variable power supply. Thank you so much in advance for your time.

In steady state, the electromagnet will draw current = 24V/(winding resistance in Ohms).

That may be what the "350 mA" specification means, but you should measure the resistance to be sure. If so, 10 of those will draw 3.5 Amperes in steady state.

Use 16 AWG (or lower) stranded wire for the "hot 24v ~5a wire".

What does this mean? Your power supply MUST be rated to handle more current than the project could ever require. A 2X safety margin is usually recommended.

as I move beyond the rated current on my variable power supply

Thank you! So sometimes just a single electromagnet will be on. In this case, will 3.5a of current not be sent through and fry it? What I meant by that sentence was that while I was testing my electromagnet I changed the current on my adjustable power supply to a higher value (1a instead of 350ma) and this caused an alarming increase in strength that I assume is the result of the electromagnet accepting more current than rated. This confuses me as I thought the magnet would only draw 350ma.

In steady state, the electromagnet will never draw more current than 24V/(coil resistance).

The instantaneous current draw during turn on will depend on the inductance, which depends on the plunger position, and will be less than the steady state current draw.

Please use your multimeter to measure the coil resistance and post that value, and post a link to your power supply, or at least, its current rating.

If the power supply is limiting the current, it is impossible for us to guess how. Some power supplies have a "crowbar" reaction, which shuts it off instantly if current draw exceeds the maximum setting.

Those things WILL be loud! Each solenoid draws 8 W, so 10 of them will draw 80 W, and a lot of that energy goes into sound when the plunger bangs into the end stop. The number 88 suggests a very noisy piano.

It's reading 40.3 ohms. The power supply is a generic variable supply with V at 24 and A at .350
Side question, would it cause any concerns if I slipped an o-ring in to prevent it from slamming?

Not a useful specification. Can it provide at least 120 W (24V at 5 A)?

24V/(40 Ohms)= 595 mA, WAY more than the specification.

this is it! SRA Soldering Products KD3005D - Precision Variable Adjustable 30v 5a DC Linear Power Supply Digital Regulated Lab Grade - Micro Center

Yeah I had a feeling the specs were bad, considering the origin of the product. Thanks. Half of them aren't even consistent with their resistance, fluctuating by up to 30%.

Most people use a rubber pad. But consider getting better quality solenoids, since that one is inaccurately marketed.

The "duty cycle" is an important consideration. Most solenoids are not intended to be powered for more than some fraction of the operating cycle, and will quickly overheat if left fully powered for a significant length of time.

Thanks for the enlightenment, made my day. Will upgrade once I find something comparable that doesn't turn a $300 project into a $5000 one.

It might still be possible to use those solenoids, if the mechanical stroke is appropriate.

A series resistor will limit the solenoid steady state current, and you might be able to get the action you like with much less current. For example, a 100 Ohm series resistor will limit the current to about 170 mA (assuming 40 Ohm coil resistance).

The resistor will dissipate a lot of heat, in this case 100*(0.17)^2 = 3 W, so use a 5W or higher wattage rating.

Unfortunately I need to beat a dead horse here. I just audibly measured the force against my piano keys as I raised my amperage well beyond the measured max draw of approx .5 amps.. all the way up to 3.5 amps the force of my electromagnet is increasing in a seemingly linear growth. This doesn't make sense as the volts/ohms should mean a max draw of around .6 amps, but it's blatantly drawing as much as it's fed. Is something being overlooked?

It is not possible for the electromagnet to draw more current than dictated by the power supply voltage and the winding resistance.

Use your multimeter to measure the actual current draw -- don't trust the power supply.

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Not wishing to barge in on the excellent advice @jremington is giving you but from reading your answers @theblt69 you seem to be assuming that because you have set your power supply to 24V then it must be supplying 24V. If it is limiting the current, which appears to be the case, then the only way it can do so is to lower the voltage. The result being that when you turn up the current limit the voltage increases. You really need to start taking measurements so we know what is really happening, you need to measure the voltage actually applied to the electromagnet and the actual current it draws.

I also think you don't know Ohm's law, which is fundamantal to all electrical circuits and would help you understand what is happening.

Please read:
Ohm's Law

While you are at it also read:
Kirchhoff's circuit laws

If you don't understand those laws you will not understand why circuits behave the way they do.

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You can't adjust voltage & current independently. Usually if the power supply has a current control knob it's intended as a current limit (so you don't fry something) and then if you connect a load that takes more current, the voltage drops. But it can be used as a variable current control if enough voltage is available.

...With nothing connected you won't get any current. And it takes1000V to get 1A through a 1K resistor so you could never get 1A through 1K with a 24V power supply.

Ohm's Law is a law of nature... Current is proportional to voltage (with a constant resistance.) If you double the voltage you double the current and that's the only way to double the current (with constant resistance). Adding a 2nd solenoid in parallel will cut the total resistance in half which will also double the current,

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Thanks all for the replies. The actual issue was an actuator shipped broken from the factory. How it's broken is beyond my limited understanding, but the resistance is constantly changing from 10 ohms to 100+, and it is drawing as many amps as I send to it. This was blowing my mind, but after performing these same tests on another identical actuator I have, the resistance never changed and the draw remained the same (approx .6 amps at 24v) regardless of how much current I offered.
Nothing makes learning more difficult than faulty parts. I appreciate everyone's time.

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Still way out of specification. But then, it is not clear what that specification actually means.

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Well done for getting to the bottom of the problem.

This:

and

Are both nonsense. You do not 'send' or 'offer' current, you apply voltage and the load takes current in accordance with Ohm's law. Please re-read the help given and if this point is still not clear then ask a question about what has been explained.

This is like a case of "Déjà vu all over again" to quote Yogi Berra. My read in another forum not long ago was you wanted to push the 88 keys on a piano keyboard using servo motors. It was suggested rather than servo motors you may wish to consider using solenoids (push pull type) to push the keys. Apparently you took that advice. I am not sure where relays figure into this?

A solenoid coil or relay coil will only draw its rated current at its rated voltage. The only way it will draw more current is if more voltage is applied across it. That assumes a known good working coil.

Your project reminded me of the old pneumatic operated "Player Piano" of years ago. A link to exactly what part(s) you have would help considerably.

Ron

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