1
\$\begingroup\$

i'm very new to electronics and working thru an udemy course on an introduction to electronics.

I'm trying to get this air pump to activate in a simple DC circuit on a breadboard.

https://www.ebay.com/itm/DC-5V-6V-Micro-2-Position-3-Way-Electric-Control-Solenoid-Valve-For-Gas-Air-Pump/392190802553?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The rating appears to be rated at 5-6v at 220mA. Given nothing else in my circuit, I'd assume that I could just use ohms law to figure out the resistance I need for the pump to work. I'm using a 5v power supply so:

R = v / I

Or

R = 5v / 0.22

or 22.72 ohms resistance.

Is this correct? I've tried a 20 ohm resistor but the pump won't activate. Unfortunately, the pump I got was a cheapo from ebay so it doesn't have a downloadable manual or anything. It just clicks once like its stalling when I power on.

enter image description here

enter image description here

enter image description here

\$\endgroup\$
11
  • \$\begingroup\$ Welcome to EE.SE. Please post the photo of the motor and the basic specification into you post so we don't have to follow a link to find essential information. It also means the question will make sense when the eBay link dies. \$\endgroup\$
    – Transistor
    Commented Jan 3, 2020 at 17:13
  • 2
    \$\begingroup\$ It doesn't make any sense to use a resistor with a motor. Also generally you shouldn't use a bread board for a motor either, granted that is a small one. Not everything you find online is well thought out. \$\endgroup\$
    – Chris Stratton
    Commented Jan 3, 2020 at 17:19
  • 4
    \$\begingroup\$ Hi Fregas, are you assuming that the linked item is a pump? It is not... it is a valve for a pump. It "clunks" once when energized, which opens or closes the valve. That's it... this alone will not pump anything. \$\endgroup\$
    – rdtsc
    Commented Jan 3, 2020 at 17:36
  • 1
    \$\begingroup\$ If the pump is rated for operation from 5 V, you should apply 5V to it directly. If you connect a resistor in series, there will be a voltage drop across the resistor so the motor won't get the full 5 V. You may be thinking of the need to use a resistor with a LED - LEDs are different from most components, in that they have a forward voltage determined primarily by their colour, and applying more than their "natural" voltage will result in excessive currents, so a resistor is added to control the current. Almost all other other components don't need a current-limiting resistor. \$\endgroup\$
    – Peter Bennett
    Commented Jan 3, 2020 at 17:48
  • 2
    \$\begingroup\$ The contacts in breadboards are not intended for high currents - the 220 mA your valve wants is more than I'd want to pass through a breadboard contact. I see at least 6 unnecessary wire-to-board contacts in your picture - each contact could introduce a noticable voltage drop. Breadboards are intended for more complex circuits. Your circuit of power supply, switch, and motor can be done just as easily with clip leads, rather than messing with the breadboard. \$\endgroup\$
    – Peter Bennett
    Commented Jan 3, 2020 at 17:57

2 Answers 2

Reset to default
2
\$\begingroup\$

The user "rdtsc" in has identified that this "pump" is actually a valve, in a comment.

You shouldn't use a resistor with it.

The valve is designed to be connected directly to 6V, and at this voltage, it will use about 220mA (assuming those are the correct numbers). The resistance of the valve itself is what you calculated (22.72 ohms).

If you put a 22.72 ohm resistor in series with it, it forms a voltage divider and the valve only gets half the voltage, which is 3V. This could be useful if you were trying to run it on 12V, since then it would get 6V! But you are not.

The valve might be able to activate with 3V, even though it's designed for 6V. Since you hear a click, apparently it does activate. It might be weaker somehow - with 3V, maybe it won't close when it's connected to pressurized air, for example, or maybe it will get stuck sometimes until you give it a tap.

\$\endgroup\$
0
2
\$\begingroup\$

That's a solenoid, not a pump. It basically allows or disallows airflow from an external source of pressure, it's like a mechanical on/off switch. If you hear a 'thunk' it's working correctly.

To address some of your questions in the comments:

  1. People don't use motors with resistors because it's grossly and unnecessarily inefficient. The power you waste increases by a factor of the current squared, so for a high current load like a motor it's an much more wasteful than if you were current limiting, say, a small LED. The better way is to simply change the effective voltage across the motor terminals, commonly achieved through PWM (pulse width modulation).

  2. There really isn't a particular reason why you can't breadboard with such a small motor. It's a good rule of thumb to avoid though, because often motors will be rather high current devices, and breadboards introduce a lot of unwanted resistance.

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.