uln burning out on connecting a solenoid valve

hai,

This is my first project with motors so i'm not well much familiar with its operations and feedbacks

i'm designing pcb to control the flow from a solenoid valve. I used a microcontroller, a relay and other related components. Everything works fine without solenoid valve.

But on connecting the solenoid valve, the uln gets heated up.
I connected the diode across the solenoid valve but it was in vain..
should i go for an relay...is there any other option to exclude relay

I have few doubts.........
what all precuations should be taken on connecting a solenoid valve with microcontroller?
what are the other methods to drive a solenoid valve with microcontroller?
Should a pwm signal should be used to drive solenoid valve?

What is the supply voltage of the solenoid?
What is the coil resistance of the solenoid?
How much current is drawn by the solenoid when it is turned on?
Can the device driving the solenoid switch such current and not be overloaded?

How large is the current running through that ULN? ULN meaning ULN2008 or something? You should ofcourse stay within the max ratings of the IC. You can parallel these things for more current. You can use a heatsink. And you can always ditch the ULN and use a MOSFET instead.

But first thing to measure would be current through the solenoid, and voltage across the ULN. That should give you an idea of how much heat it's going to be dissipating. And the datasheet should give you information what is within acceptable limits...

hai,
iam using uln2003a. The solenoid drives about 1.5A. I know the uln supports only 500mA. But one of my friend says on connecting the three output directly to the solenoid the problem can be solved

can i go for that?.
Is there any other option to drive the solenoid directly by uln or should i go for the relay.

You can parallel more outputs to get more current but the max current is highly dependent of the duty ratio of the output.
You can't get 3x500mA with 100% duty from three outputs.



Please reads my post https://www.edaboard.com/threads/231528/#post987570

The graph above is from ULB2803, the following graph for ULN2003 seems to be even worse (allows lower currents)



www.datasheetcatalog.org/datasheets/120/489337_DS.pdf

It would appear that the ULN2003 is not up to the job!

It might be better to use a protected Fet to drive the solenoid, such as a VNN3NV04 or similar.

avirajose said:

hai,
iam using uln2003a. The solenoid drives about 1.5A. I know the uln supports only 500mA. But one of my friend says on connecting the three output directly to the solenoid the problem can be solved

can i go for that?.

Click to expand...

You can go for that, but the ULN2003 is going to die horribly at 1.5 Amp. As has been suggested, you're better of using a MOSFET for this.

uln2003 can do nothing for solenoid.

As i early mentioned, i go for the shorting the 3 outputs of uln. But it just heated up even without solenoid. can anyone explain it why it happans so?
can transistor help me or is there any uln that drives 1.5a or more.

MOSFET? MOSFET. Also, try a MOSFET as has been suggested by several people.

The entire package of that uln2003 is not going to be able to handle 1.5 Amps of current. So, despite the fact that numerically 3*500 = 1500, it still will not handle that current.

Also, MOSFET? As btbass suggested: VNN3NV04 for example.

As far as I'm concerned, those ULN200x things are nice enough for a few hundred mA when you want a quick fix. But 1 Amp and above is far easier to manage with a FET.

You can also use a standard logic level MOSFET to drive the solenoid and connect a diode across the solenoid, like how you would drive a relay.