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I'm looking to purchase a power supply/wall-wart for a small pump. The pump is listed to operate at 12VDC input upto 3A. I'd like a 12VDC/4A power supply so that I may power a second low-current device (mA order) from the supply, but then I noticed the nominal voltage rating of the pump: 9-14VDC.

The nominal voltage rating is confusing me and I'm no longer certain if the 12VDC supply will be sufficient for the general operation of the pump. I think the nominal rating means that depending on the load, the voltage may fluctuate during operation. In this case, a higher voltage demand may draw more current, which the power supply should provide. Maybe -- I'm not sure anymore.

Is my concern warranted, or am I just thinking about this too hard?

Here is a picture of the "style" of the supply. I'm not sure if it is regulated, but it looks like a typical supply that powers household electronics such as printers, speakers, and small form-factor computers.

enter image description here

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    \$\begingroup\$ More likely in means the pump will work at 9V, (maybe slow) work at 14V (maybe get warm) and work just fine at 12V \$\endgroup\$ – Brian Drummond Oct 9 '16 at 16:29
  • \$\begingroup\$ @BrianDrummond: That makes perfect sense -- thank you for the clear and simple answer! \$\endgroup\$ – Steve Guidi Oct 9 '16 at 16:40
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    \$\begingroup\$ What Brian said. One other note. Sometimes items designed for "12 V" are intended for cars or boats that use a 12V lead acid battery. When the engine is running, such systems are usually more like 14V. When the engine is off, they can be quite a bit lower. So if your pump is designed for a 12V car or boat it would be expected that it would have a wide voltage input Voltage range. \$\endgroup\$ – mkeith Oct 9 '16 at 16:42
  • \$\begingroup\$ On the other hand (which is not the case here), some devices contain microcontrollers and other logical components that use a specific voltage level for their digital signals. (e.g. 5V is popular). In those cases the requirement may specify 4V-6V, because the hardware is built to withstand some fluctuations. Still, in those cases it's obviously best to use a 5V power supply. \$\endgroup\$ – bvdb Oct 9 '16 at 16:54
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Assuming you are talking about a air pump, which often have a simple dc motor and often designed to accept car "12V" unregulated input, then you have a wide latitude of voltage you could supply. As mentioned in the comments, a typical auto supply is from 11 to 14.5V depending on the age and state of the battery, alternator, etc.

The pump itself should not vary much in current or voltage draw, until it hits a point where it is stalling out. Like you stick a finger in the blower motor, or leave it running when the bag is full. Even then, the current draw will increase but your voltage source will stay the same and try to compensate by delivering more current until a safety feature kicks in. Current overload protection most likely, or a fuse if wired to a car outlet.

In short, go with the 12V supply, as directed.

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From the looks at the label it looks like a regulated supply. At least it is not a simple transformer with diodes. This because the imput voltage can vary between 100 and 240V 50/60 Hz. This supply can easely handle the requirements you indicate.

I have seen this type of powersupply being sold for 12V led strings. This underlines the assumption that it must be regulated.

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  • \$\begingroup\$ There is a downvote on this item. Would appreciate to know why? \$\endgroup\$ – Decapod Oct 9 '16 at 17:37

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