Connect Two 100A SSRs Arduino Uno Power

The set up: 12V DC adapter to Arduino to 2 separate 100A SSR modules.

Are you trying to switch 12volt DC electromagnets with these SSRs?
The SSRs are for AC only.

If you ever have a project that uses the SSR at 100 amps, you very definitely need heat sinks for them. There are SSRs for DC, but only pretty low current.


If you ever have a project that uses the SSR at 100 amps, you very definitely need heat sinks for them. There are SSRs for DC, but only pretty low current.


I have found (and have one) for 25A. Caveat, its from China and haven't used it yet. I'll report back later. :smiley:

If the application is DC could you not just use MosFet's.

I know you stated the SSR's are capable of 100A but what does your application require?

Hope you're not expecting 100 A out of that wall wart. :slight_smile:
Tell us about those E-magnets, how many Amps?
BTW: The ' ~ ' symbol by the terminals means AC, not "adjustable strength".

BTW If you use the AC SSR on a DC circuit, you will be able to turn your load on but you will NOT be able to turn it off. You will have to disconnect the coil power to turn it off.

Perhaps Barry's web site would be of interest"Barry Hanson


To energize a DC coil the Arduino is not the limitation. The switch and powersupply are typically the limitation. You should choose a MosFet that can deliver the current you want. DigiKey has an excellent webpage for selecting MosFets.

I'll guess, unless you are using a car battery, your powersupply is likely the limit

Question, will you be controlling the coil current using PWM?

If NO then I would drive the MosFet with an optoisolator (like a 4N25), this will keep the high current isolated from the Arduino, this will reduce your headaches in the long run as coils tend to generate voltage spikes that would otherwise be hard to suppress at the Arduino.


I AM BUILDING an induction launcher that can vary the strength and frequency of what is launched, a few times per second.

I am using two electromagnets, one to launch and the other to be launched. The strength needs vary from enough to be repelled to enough to lift 3lbs 1 foot high.

For the electromagnets I don't know the gauge of wire to be used or how many turns so don't know the area. I want to focus on how many Amps I can even get and will use that for finding out the wire gauge and turns.

FOR NOW I need to focus on the relay, mosfets? were suggested - and yes I do believe I need DC amps for the electromagnets.

Since Amps mean current and current is good I need to find out just how many amps I can work with the Arduino Uno and how to connect everything correctly.

I would appreciate some suggestions as for components.

The inductance of the coils, which you don't know, will severely limit how fast you can build up the current in the coils. The way everyone else does this is to charge very large capacitors to a high voltage and then discharge the capacitors through the coil. The high voltage forces the current while the inductance tries to limit it. It all comes down to time constants.


So if I use mosfets how would I connect them to the Arduino, wall outlet for power and to each electromagnet? Can I get an electrical diagram.

And how many amps do I even need to lift/launch 3lbs 25cm?

Is everyone afraid to tell the OP he is designing this thing completely backwards?

You need to compute the energy needed per second to begin to lift his 3lb weight and to move it some distance, against gravity, in some unknown time.

Once you have the energy required for your project, then you can compute the magnetic force needed to begin to move the object. Then realize as soon as it is a bit away from the electromagnet, the magnetic force is now reduced and more force will be needed to move another increment, and continue this process until 25 cm is reached.

Knowing the force required for each step, now you can compute the ampere turns required to generate this force. Knowing that, you can decide on the size of the wire that will handle the current and the insulation of the wires to withstand the heat generated.

Once that is all designed, you can begin to design the current supply for the coils.

Are you going to use some magnetic material for the wire turns to be wrapped around? If so, that will need to be considered in making the electromagnet.


As Paul_KD7HB said, I think your approach is orders of magnitude away from what you need.

The repeated reference to "wall warts" tells me you don't have a feeling for the amount of power you need.

I suggest you look through a catalog of DC solenoids and see the amount of power needed to create force under optimum physical conditions. Now consider that an electric field is reduced by the cube of the distance from the actual coils to the object you are attempting to move.

Now you said you wish to move 3 lbs 1 foot. Look at the solenoids for force and stroke length. You will find the typical stroke (i.e. movement) is far less than your desired 1 foot.

Next pickup up your wall wart (or any wall wart) look at the amps it is capable of........ compare it to the current the solenoids you might find......see if you are close.


wall plug, 2 EM set ups; mosfet and secondary unit that can handle 10amps

I’m not sure how you differentiate the “wall plug” and the “secondary unit”

You will need a 120VAC to 10 or 12V that can supply nearly 30 amps and be protected from short circuits.

Quick calculation:
If your coil diameter is 6" and you have 100T of #14. Then DC resistance is approx = 0.42 ohms

Then at 12V the current will be 12 / 0.42 = 28 amps

When you are learning like this it is best to take thing is small sections.

I suggest you get some #14 AWG wire and make a coil. Ideally you would like "enameled" wire like one would use in a transformer but to start I would go to my local Home Depot or similar and purchase some #14 wire. How much wire to purchase? see below


Do you know the shape of the coil? (i.e. tall and thin or all bunched together etc)
Do you have an estimate of the diameter you need?

Once you get these then calculate the length and buy 25% more.

Wind your coil and connect it with a heavy switch or simply by hand. But be careful when you de-energize the coil the collapsing magnetic field will create a high voltage on the coil wires that will shock you if you are holding the copper part of the wires.

How will you know if you are getting close to your 1T goal?

There are several magnetic circuit calculators on the internet you might try one of them to get a starting point for the coil design.