Need help to make Solenoid valve work with Arduino and TIP120 transistor

I am trying to turn off an on 12 solenoid valves using Arduino and TIP120 TO-220 Darlington Transistors NPN. I connected everything as I show in the diagram but my solenoid valve wont work since when its connected and I checked the voltage, it only shows 10.8 Volts, but when I check the voltage without the solenoid valve, it shows 11.98 volts.

|500x262

I am not an Electrical Engineer and have minimal knowledge in the field so sorry if this is a stupid question. I was wondering what causes this voltage drop that prevents solenoid valve from working. Also what is the role of the resistor here and am I using the correct one if its needed ?

I will provide the links for all the parts in case if it is needed.

TIP120 Transistor

Solenoid Valve

Thank you.

I think 2.2K is too high a resistance. The resistor is just there to protect the Arduino. Try 220 Ohms which will limit the current to under 23 mA, well below the 40 mA absolute maximum..

With the 2.2K resistor your Base current is limited to about 2.3 mA. With a current gain of 1000 that would limit the current through the transistor to 2.3A and not the full 5A the transistor is rated for.

Saikedo: I am trying to turn off an on 12 solenoid valves using Arduino and TIP120 TO-220 Darlington Transistors NPN. I connected everything as I show in the diagram but my solenoid valve wont work since when its connected and I checked the voltage, it only shows 10.8 Volts, but when I check the voltage without the solenoid valve, it shows 11.98 volts.

|500x262

I am not an Electrical Engineer and have minimal knowledge in the field so sorry if this is a stupid question. I was wondering what causes this voltage drop that prevents solenoid valve from working. Also what is the role of the resistor here and am I using the correct one if its needed ?

I will provide the links for all the parts in case if it is needed.

TIP120 Transistor

Solenoid Valve

Thank you.

A couple of questions:

  • Can you manually (without transistor) drive value? Just connect the black wire from the solenoid to the PS ground. This should operate the valve. Many of these valves only work if they have water pressure applied at their input.
  • When you say you measure the 12V supply at 10.8V when you connect the Arduino/Transistor, it tells me that he power supply is NOT providing enough power. If the PS is actually 150W there is no way that a 4.8W load should pull the PS output down to 10.8V. Something is fishy. Either there is a direct short somewhere in your wiring, or your PS is configured to limit current. The Valve specifications states is "The coil uses direct current and energizes at 12 volts DC; voltage range + or - 10%. 4.8 Watt power rating. ". +- 10% is 10.8V to 13.2V so your voltage is right on the edge.
  • Try increasing the PS output voltage to 13.2V, see if that does not allow it to work

Chuck.

chucktodd: A couple of questions:

  • Can you manually (without transistor) drive value? Just connect the black wire from the solenoid to the PS ground. This should operate the valve. Many of these valves only work if they have water pressure applied at their input.
  • When you say you measure the 12V supply at 10.8V when you connect the Arduino/Transistor, it tells me that he power supply is NOT providing enough power. If the PS is actually 150W there is no way that a 4.8W load should pull the PS output down to 10.8V. Something is fishy. Either there is a direct short somewhere in your wiring, or your PS is configured to limit current. The Valve specifications states is "The coil uses direct current and energizes at 12 volts DC; voltage range + or - 10%. 4.8 Watt power rating. ". +- 10% is 10.8V to 13.2V so your voltage is right on the edge.
  • Try increasing the PS output voltage to 13.2V, see if that does not allow it to work

Chuck.

If I directly connect the solenoid valve it works just fine. I was using Solid State Relay DC-DC to drive the valve before but they are relatively expensive and that is why I am trying to use the TIP120, hoping it will work.

I am not sure what causes the voltage drop. I am using the following transformer to transform AC current to 12 VDC

Transformer

johnwasser Thank you for your comment as well. I will try to use it with 220 ohm resistor and will reply here with the result.

A TIP120 darlington is normally driven into saturation with a collector/base current ratio of 1:250.
2k2 should be ok for a 400mA (12volt, 4.8watt) solenoid. Use 1k to be sure.

You MUST use a back-EMF diode (e.g. 1N4004) across the solenoid, otherwise the voltage spike will damage the transistor when the relay turns off.

The transformer (12volt, ~12Amp) seems ok, even for up to 30 solenoids.

A darlington transistor has a relatively high saturation voltage.
You won’t see 12volt across the solenoid with a 12volt supply.
More like the 10.8volt you mentioned.
I don’t see that as a problem for a solenoid.

If you want (almost) full voltage on the solenoid, use logic level mosfets instead of darlingtons.
Or increase the supply by ~1.5volt.
Leo…

Wawa: A TIP120 darlington is normally driven into saturation with a collector/base current ratio of 1:250. 2k2 should be ok for a 400mA (12volt, 4.8watt) solenoid. Use 1k to be sure.

You MUST use a back-EMF diode (e.g. 1N4004) across the solenoid, otherwise the voltage spike will damage the transistor when the relay turns off.

The transformer (12volt, ~12Amp) seems ok, even for up to 30 solenoids.

A darlington transistor has a relatively high saturation voltage. You won't see 12volt across the solenoid with a 12volt supply. More like the 10.8volt you mentioned. I don't see that as a problem for a solenoid.

If you want (almost) full voltage on the solenoid, use logic level mosfets instead of darlingtons. Or increase the supply by ~1.5volt. Leo..

Wawa so I decided to go with the logic level mosfets instead of increasing the supply. My question is do I still need a diode for logic level mosfet? Also are these mosfet and diode good for my purposes ?

MOSFET

1 Amp Diode

A diode across a solenoid is always needed. The 1N4007 is ok.

You linked to a triac, not a mosfet.

I doubt you see a difference in performance between 12volt and 10.8volt on the solenoid. Leo..

Wawa:
A diode across a solenoid is always needed.
The 1N4007 is ok.

You linked to a triac, not a mosfet.

I doubt you see a difference in performance between 12volt and 10.8volt on the solenoid.
Leo…

Great. So do I need N-Channel mosfet ? Something like this ?
N-Channel Mosfet

Or this, AOI514 http://www.digikey.com/product-search/en?keywords=aoi514

Ebay item location: Item location: Minneapolis, Minnesota, United States

http://www.digikey.com/product-search/en?keywords=IRLB8743PBF

Digikey Location: Thief River Falls, MN 56701 USA