Transistor Issue Plagues Me

Discussion in 'The Projects Forum' started by boingaon, May 15, 2012.

  1. boingaon

    Thread Starter Member

    May 15, 2012

    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

    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

    Last edited: May 15, 2012
  2. #12


    Nov 30, 2010
    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.
  3. boingaon

    Thread Starter Member

    May 15, 2012
    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.
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    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.
  5. John P

    AAC Fanatic!

    Oct 14, 2008
    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.
  6. MrChips


    Oct 2, 2009
    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.
  7. boingaon

    Thread Starter Member

    May 15, 2012
    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.
    Last edited: May 16, 2012
  8. Wendy


    Mar 24, 2008
    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.
  9. BSomer


    Dec 28, 2011

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

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

    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.