12V and 50 Amps using them

Other Hardware General Electronics
1

I want to use Arduino Uno with my own DIY pinball machine.
I use 3 x solenoids 12V - 8 amps (each) for the flippers. I am thinking of buying a power supply 12v 50 amp.
I think it will be too strong for the Arduino board, soo I have decided to use the power supply directly to the solenoids.
Questions:

  1. Is the power supply to strong (amps) for the solenoids?
  2. The cables lenght will be about 60cm long. Which thickness (gauge wire type) should I use?
  3. I want to connect a 12v single led to 12v relay module, and the relay module to the arduino, so I can control the led from the arduino. The module will be used with the power supply to energize the led. The used module says it can use 230Vac - 10A / 30Vdc - 10A. Will this be posible?

Please help :slight_smile:

2

What do you mean by too strong ?

3

No, you can run Arduino Uno from 12V. You could connect 12V to the barrel socket or the Vin pin. The amps of the power supply is irrelevant. The Uno will draw what it needs, no more, no less.

But there are two dangers to avoid.

  1. Don't connect the power supply so that all that current passes through the Uno. It can only handle maybe an amp or two. So if you want to power the Uno like this, take wires from the power supply to the solenoids and a second set of wires from the power supply to the Uno.

  2. The Uno has a regulator built in to make 5V from the 12V input, to run its chips and maybe a few other low power components. But if you attach too many other components to the 5V pin or components that need a lot of current, like 5V relays, the Uno's regulator will overheat and fail. So if you plan to use more than a very small power for 5V components, you need a separate 5V power supply. The easiest way is to buy a 12V to 5V DC-DC converter module. Connect this to your 12V power supply and then run 5V to the Uno's 5V pin and the other components that need 5V.

4

If they are 12V solenoids, then no, they will draw the amps they need. No more, no less.

Google for "wire gauge maximum current" and you will find tables where you can look up what AWG or mm² you need for a number of amps. Copper cable is better, but more expensive. Other types like aluminium are cheaper but cannot carry as many amps before they begin to get hot and reduce the voltage.

5

A 12V single led? Please post a link to the specifications of that. If it draws only a few milliamps, a relay would be overkill. A simple small transistor will probably be ok, for example bc337. But we need to see the specs of this led to be sure.

I would also recommend transistors to control your solenoids also. Because of the amps drawn by the solenoids, these transistors should be high current MOSFETs and they should have "logic-level gates" so that the Uno can control them directly with its output pins. An example would be stp16nf06l. You must also fit "flyback" diodes to your solenoids to protect the rest of the circuit from the reverse voltage/current that is generated when a solenoid is switched off.

6

A device will ONLY consume the power they need (as long as the voltage is correct). You can connect an Arduino Uno through the barrel connector to a car battery which can provide 350 amps or more.

7

FYI, there is no problem for an uno being powered on Vin or the External DC Barrel jack with 12V, although as is frequently pointed out, this may cause the 5V regulator
to run hot. The MAIN and MOST IMPORTANT thing to remember is that if there is
a miswire or a short inside an IC (ie:LM555 pin-4 (GND) shorted to pin-3 (output) by
a DMM probe slipping off pin-3 and shorting 3 to 4, the internal output transistor
will short creating a path to ground from the + power pin (8) to the GND pin-4
THROUGH the IC. I can tell what happens when the power supply is only a 10A
supply: the LM555 IC bursts into flames and begins to glow red, melting the solderless breadboard it is plugged into. NOW IMAGINE what would happen if
the power supply was a 50A supply instead of 10A. Trust me , you don't want to
go there. You can of course use fuses for arduino support circuitry (I didn't have
one when that happened. I thought "What could go wrong ?" This means each
subcircuit powered by the 50A supply would need it's own fuse, including the
arduino. Any support circuitry should be fused for it's maximum rating.
If this protocol is followed, it doesn't prevent IC damage if mistakes are made,
but it prevents a fire since the current for each leg cannot exceed the fuse rating.
Consider yourself warned.

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