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The circuit below drivers a pump and a valve, the pump works fine, the valve consumes much more current than I'd expect.

Valve (and pump driver)

The valve is rated 2W at 12V (600mA) i'm more like 15W. The PUMP_DRIVE signal isn't PWM, interestingly using a PWM signal with D = 0.5 doesn't even turn it on.

What am I doing wrong? Do I need to add current limiting?

Solenoid Valve

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  • \$\begingroup\$ Where/how are the valve and pump connected? \$\endgroup\$ – Peter Bennett Nov 24 '19 at 20:23
  • \$\begingroup\$ Like motors and other inductive loads, solenoids require a large "surge" of current in order to turn on. Once it has fully switched, you may be able to reduce your duty cycle to 50%. \$\endgroup\$ – Caleb Reister Nov 25 '19 at 5:12
  • \$\begingroup\$ The surge current I can understand, but this should be quite transient, either way it seems I need an inrush current limiter (and probably a less beefy solenoid) \$\endgroup\$ – Andrew Davis Nov 26 '19 at 20:25
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The product description is simply wrong regarding power rating, as You can read on the comments from another user:

"The consideration is the fact that they draw 1.5A continuous while open so you need an appropriate power source and they are dissipating 18W or so of heat. They might overheat with no cool liquid passing through them but can't say for certain"

You can easily measure the solenoid resistance and calculate total power.

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    \$\begingroup\$ I don't know much about what's normal for a solenoid, but 18 watts sounds unacceptable for a simple valve. \$\endgroup\$ – Hearth Nov 24 '19 at 21:08
  • \$\begingroup\$ Here's one with the same designation 2W-025-08, rated at 12V 1.4A = 16.8W amazon.com/creatorele-2W-025-08-Electric-Solenoid-Diesel/dp/… \$\endgroup\$ – Bruce Abbott Nov 24 '19 at 21:41
  • \$\begingroup\$ Thanks for noticing this! I'm going to change to a less 'beefy' Solenoid either way \$\endgroup\$ – Andrew Davis Nov 26 '19 at 20:26

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