Hello,

I'm controlling 35 solenoids using an Arduino board and some transistors. When I activate more than one solenoid at a time, the system shorts out, and the DC power adapter shuts off momentarily as a safeguard. I believe that this is happening because the solenoids do not offer enough resistance, thus shorting out the circuit. Here's my data:

Power Supply: 19V, 1.9A DC
Transistors: TIP120 60V, 5A (NPN)

Solenoids: 12V DC, 12 Ohm Impedance
http://www.goldmine-elec-products.com/prodinfo.asp?number=G18567

I understand that I am overdriving the solenoids, but I need to get more power out of them. I will be giving them a rest period between uses to cool down.

My question: how can I prevent the system from shorting? Thank you

Preston

 

It's not the transistors you need to get more power out of, it's the power supply.

Solenoids: 1 amp + 1 amp = 2 amps
Power supply: 1.9 amps.

Either get a better power supply or solenoids that use less current.

 

I meant to say that I need the solenoids to be more powerful, which I have successfully achieved with the given voltage/amperage. The power supply has no problem actuating multiple solenoids at a time.

It's still unclear to me why the system is shorting out.

 

Your initial request was answered.

You are not acknowledging what was told to you and you change your request instead. Why?

Be kind and solve the first thing. Then, move to the next.

It seems quite evident that 2 (or MORE!) solenoids should mean an overload to your supply as per the specs you provided.

 

It is worse than
Solenoids: 1 amp + 1 amp = 2 amps

If the solenoids are overdriven by using them on a 19V supply, the current draw will be 1.58 amps each. Two solenoids will pull >3 amps from a 1.9 amp supply. Problems? Of course there are problems.

 

The system is not shorting out.
You have a couple of problems.
The first is the power supply is not powerful enough.
Fix that first and then we can tackle the other problem.

 

So, the power supply is too weak- understood.

Bare with me here-

1) If I increase the amperage of the power supply, however, wouldn't the solenoids draw even more current? (bad).

2) Lets say that each of the 35 solenoids draw 1A, and I use a power supply that can provide 35A. If all 35 solenoids are actuating at the same time, I can see how this would be okay. But what if only 1 or 2 solenoids are actuating? Wouldn't they receive far too much current?

3) Does the current draw for the solenoids change depending on how many solenoids are drawing current from the power supply at a given time?

I didn't realize I was changing the subject earlier- sorry to enrage you sir.

 

Components draw what they are meant to draw, what they are specified to draw. You must meet their specs to use them. You are currently not doing this, but are dismissing it as minor issue. It is not.

 

So, the power supply is too weak- understood.

Bare with me here-

1) If I increase the amperage of the power supply, however, wouldn't the solenoids draw even more current? (bad).

No. They will only draw what they need to operate.

2) Lets say that each of the 35 solenoids draw 1A, and I use a power supply that can provide 35A. If all 35 solenoids are actuating at the same time, I can see how this would be okay. But what if only 1 or 2 solenoids are actuating? Wouldn't they receive far too much current?

Read through the sticky that is linked below. It is simple math and understanding Ohm's Law.

3) Does the current draw for the solenoids change depending on how many solenoids are drawing current from the power supply at a given time?

Kind of depends on a few variables, but typically no. #12 wrote a fine sticky about some of the things you seem to be getting hung up on. It is all about Ohm's Law which is how current, voltage, and resistance relate to each other.

http://forum.allaboutcircuits.com/showthread.php?t=69757