PSU / pump not working to spec. - Page 1
Forum section: electronics / beginners

author: the_ether
author_rank: Newbie
timestamp: July 18, 2014, 09:06:42 pm
content: I'm experimenting with a water pump. Its specs say that it can pump water up a 3m height but I only get around 0.5m.The pump's specs are: 12V, 1.8AThe PSU's specs are: 12V, 2.5A, 60VAThe PSU is a standard brick of the type that is used for laptops.This is the pump:https://www.sparkfun.com/products/10455I measured the voltage at 12.3V but the current was only 0.33AI measured the pump's resistance to be 2 Ohms but presumably as soon as it starts spinning the inductance will cause the motor to have a higher resistance.Even though the PSU is rated for up to 2.5A, why do I only see 0.33A?Should I simply buy a new PSU but with 6x the current rating?

author: corrado33
author_rank: Frequent Contributor
timestamp: July 18, 2014, 09:57:52 pm
content: It could be that the laptop power brick has circuitry that prevents it from working if it doesn't detect the correct thing on the other end.Try it with a real power source (or a simple car battery) and report back.

author: the_ether
author_rank: Newbie
timestamp: July 18, 2014, 10:33:08 pm
content: It's not a laptop PSU. It is simply similar to one. There is nothing in the specs to suggest that it is designed for a specific device:http://cpc.farnell.com/ideal-power/25hk-ab-120a250-d5-fr/psu-desktop-12v-2-5a-3-pin-iec/dp/PW03344?Ntt=PW03344And it is working, it is simply only outputting 0.33A. My guess is that it's something to do with the inductance of the load.I have no other power source to verify whether it is the pump or not.

author: Psi
author_rank: Super Contributor
timestamp: July 18, 2014, 10:57:55 pm
content: Could also be that they shipped a 24v version by accident.Or installed 24v motor in 12v model etc..If it doesnt draw the current its supposed to, and pump the water quantity, when using a proper power source then i might suspect thatA car batt ,with engine not running, is a easy source of 12v.Just dont slip and short it, they have crazy current available

author: rob77
author_rank: Super Contributor
timestamp: July 18, 2014, 11:13:10 pm
content: Quote from: the_ether on July 18, 2014, 10:33:08 pmif you measured that 0.33A , with the pump, then it's the pump drawing only 0.33A , not the supply outputting only 0.33Ago ahead testing with a 12V battery as suggested above. furthermore you could test the supply by attaching a 10R power resistor to it's output (without the pump connected)- you should measure approx 1.2A.

author: Circuitous
author_rank: Unknown
timestamp: July 18, 2014, 11:26:58 pm
content: By 0.5m is that the lift height you're getting? Lifting is the intake side of the pump. I would think that it should be able to pump water to a few meters high, but the lift height wouldn't be anything like that.

author: the_ether
author_rank: Newbie
timestamp: July 18, 2014, 11:38:20 pm
content: Quote from: Circuitous on July 18, 2014, 11:26:58 pmI don't see why the lift should be different from the head. The two together should be the max capability of the pump. The pump is rated for a head of 3m ie the lift plus head should be < 3m.At any rate, the lift was zero. This is a bilge pump. the intake is through its base and I tested it resting on the bottom of my bathtub.And to answer the others, as I said, I have no other power source. This also means a 12V battery.And testing the PSU with a passive resistor won't tell me much. The motor is inductive.Thanks anyway. I think that I'll just buy a PSU with a higher power rating.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: July 18, 2014, 11:39:58 pm
content: Where does it list the 3m height? I might be slow (its cold today!) but I can't see it?

author: rob77
author_rank: Super Contributor
timestamp: July 18, 2014, 11:46:57 pm
content: read the comments on the page you posted - it's explained there in the very first commentit's a centrifugal pump - high flow rate with minimal pressure

author: tautech
author_rank: Super Contributor
timestamp: July 19, 2014, 12:12:33 am
content: QuoteSorry you are quite wrong, it is not that simple.The suction lift of a pump has the greatest affect on it's capabilities.The only way to expect rated specs is with a "flooded" suction lift.That is with the pump below the point of suction.

author: SeanB
author_rank: Super Contributor
timestamp: July 19, 2014, 04:43:39 am
content: 3m head means at ZERO flow the pump can generate 3m of static pressure on the outlet water column. With flow ( even just pointing the outlet up and seeing how far it goes up) you will have a loss of head, so 0.5m sounds about right.If you want higher head go get a larger mains operated pond pump, as there you can get a 15m head one designed to operate fountains, which will easily operate a 3m high fountain at full flow.

author: PE1RKI
author_rank: Regular Contributor
timestamp: July 19, 2014, 08:38:57 am
content: did you reverse the power leads ?