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### Topic: Adafruit Solenoid Valve (Read 1 time)previous topic - next topic

#### backer

##### Dec 11, 2012, 10:46 am
Hi.
Need some help figuring out a Solenoid Valve. I bought this http://adafruit.com/products/996

So as I understand when I put power thru the 2 cords it opens, turn power off and it closes. So I took a power supply 12VDC = 2A and connected. The sound it makes is a high click, almost so I think that it opens, but it repeats the whole time with 0.5-1s interval.

Tried to connect one of the cords to a relay (http://www.lawicel-shop.se/prod/Relay-Kit-1_873852/LAWICEL-AB_8758/SWE/EUR) so I an tell Arduino to open/close the valve. The relay works but when ON it acting same way as when connecting power source straight to the solenoid valve.

Would really appreciate some guidance here.
Thanks

#### jackrae

#1
##### Dec 11, 2012, 12:36 pm
The device requires 3amps at 12 volts so if your supply is rated at only 2 amps there is a possibility that the regulator is shutting down on high current.  Once it's shutdown it effectively resets itself then ends up going into on/off oscillation.

#### JimboZA

#2
##### Dec 11, 2012, 03:00 pm
The volt vs current table there doesn't make sense to me.... surely the power consumption should be (more-or-less) the same at each voltage, and the current would drop with higher voltage? Yet it does the opposite....

At 6V it's 1.6A which is 7.8W, at 10V it's 2.5a or 25W, and at 12V it's 3A for 36W.

It would make more sense if the current column was inverted giving 3A at 6V for 18W and 1.6A at 12V for 19.2W....

Or am I missing a trick here?
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### SurferTim

#3
##### Dec 11, 2012, 03:06 pm
If you use the calculations for a 4 ohm resistor instead of the solenoid, it makes sense.

#### Chagrin

#4
##### Dec 11, 2012, 03:07 pm
Or am I missing a trick here?

Ohm's law. The solenoid coil has a fixed resistance. I = V / R.

#### retrolefty

#5
##### Dec 11, 2012, 06:08 pm
Quote
Or am I missing a trick here?

Yes, you are assuming a solenoid coil is a constant power device. It is not, it's a constant resistance device and as such follows simple ohms law from which you can then determine it's power draw at any given driving voltage. That is why relays and solenoids are specified first by their designed coil voltage, and the coil power consumed is just an outcome of that voltage rating.

Lefty

#### JimboZA

#6
##### Dec 12, 2012, 04:39 am
Well we live and learn.... I would have thought it drew current based on the power required to move the physical load and not be of constant resistance.

Thanks....
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### backer

#7
##### Dec 12, 2012, 01:27 pm
You where right 'jackrae'.

Quote
The device requires 3amps at 12 volts so if your supply is rated at only 2 amps there is a possibility that the regulator is shutting down on high current.  Once it's shutdown it effectively resets itself then ends up going into on/off oscillation.

I bought a new power supply today and it sounds like it works as it should. *happy*
Thanks

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