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Topic: Powering 12 Electromagnets (Read 213 times) previous topic - next topic

faarmer

Hello,

I have a project where I want to continuously power 6 electromagnets and power 6 more every time they receive feedback from a sensor for an X amount of time.

I bought the 25/20 magnets here http://www.ebay.com/itm/262734443609?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The situation here is that I know absolutely nothing about voltage, current, or electronics, I have only ever uploaded a pre-written code to my arduino and assembled a pre-designed schematic so this whole circuit design is impossible for me (I am willing to bet that my grandma knows more about electronics than me).
A friend told me the arduino itself is not powerful enough to power the magnets, so what is? and how do i wire everything? I have many basic components including diodes and optocouplers (another friend told me these are indispensable).

Any help is greatly appreciated!

MorganS

That ebay listing doesn't show how much current they draw or what duty cycle you can use. They may draw up to 5A each, which means you will need a 60A power supply to power them all, if they're all on at once. That's a lot of power so they will heat up. They may not survive long periods of "on" time.

You will have to wait until they arrive to experiment with them. A meter which can measure up to 20A will be required, along with a suitable power supply, such as a car battery of gel-cell battery to power the one you're testing.

Controlling that amount of power with an Arduino is possible, but you will need extra parts. A logic-level MOSFET is the minimum although relays might work too. You will probably have to buy driver boards which can handle the current. The SparkFun Monster Moto is a good one for this kind of current although it's sold for motors, it will work well for magnets.

If you don't need the full holding power then you can control the driver with the "analog" out pins on the Arduino, which will reduce the overall drive current and heating of the magnets. You can't do that with relays however. A relay can only be fully on or off and can't switch at high speed.

"The problem is in the code you didn't post."

Wawa

#2
May 18, 2017, 02:49 am Last Edit: May 18, 2017, 02:50 am by Wawa
25/20 seems to be the diameter and height.
Current draw (from other listings) should be 1/3Amp (4watt).
12 solenoids draw 4Amp, so a 12volt/5Amp supply makes sense.
Transistors and kickbck diodes are needed to control these solenoids.
Leo..

faarmer

Hi guys,
Thanks for the fast replies, I got caught up with work so could not reply before.
Indeed like Wawa said, they are .33A. A quick google search shows laptop-like chargers, would it be enough to hack one into a supply? If so, how do i plug it in? I don't think i should plug it straight into the arduino right?
I already have transistors and diodes, i just don't know where to place them on the breadboard -.-
Also, would i still need MOSFETS with this setup?

MarkT

The most important thing is the free-wheel diodes - without those the massive inductance of the electromagnets
may easily fry something... 

Yes you have to use a switching device to switch large currents, the Arduino is a microcontroller and outputs
signals, not power.

Only common the grounds of the supplies, low side switching with  NPN BJT or logic-level n-MOSFET and most
importantly that freewheel diode across the electromagnet(s)...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

faarmer

Hmm ok, so after reading all your comments and discussing this at the university i think the most logical way to proceed would be to feed the signal with the arduino to a wall charger which is hooked up to the electromagnets. This way, the charger is activated only when necessary and it would have enough power. But I am wondering, if half the magnets need to be permanently active and half need to be pulsating, how do i wire this? do I plug the arduino in between the charger and magnets like some sort of switch? or would i need two different chargers?

MorganS

But then you have the problem of switching 110-220V AC with the Arduino instead of just switching 12V.

12V DC is much easier to control.
"The problem is in the code you didn't post."

Wawa

I have a project where I want to continuously power 6 electromagnets and power 6 more every time they receive feedback from a sensor for an X amount of time.
One TPIC6A595 chip can switch those six solenoids.
Leo..

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