Peak current into water pump?

[Tony Stewart]

Why not write to OEM service dept and ask them how much current and duration can be expected after 10yrs with rusty bearings to be overcome by a SMPS? In the meantime plan a test by running in a tank of water and design in a safety factor for sludge restricting the pipes or excessive long pipes of inertial water to move from existing installations.

Do the math or make it resilient. A slow start from 6V may work but with how much margin for failure? Perhaps a controlled CC start is better for you if you are sure that voltage is rising, meaning that water is flowing. But then fuses may blow. Do the math.

Or do the virtual poop test.

Either way it appears the motors runs around a planetary gear cycle of 1 Hz with a 2 Hz current peak duration depending on load length and pressure. So the current limit in the core of the supply must be much be several times greater than the average max current or fuse rating.

 

[alec_t]

we are just wondering what voltage is too low and will result in too much incidence of stalling?

A: As long as a piece of string . Why not just try it and see?

 

[Flyback]

we can just try it and see, but with a new motor, maybe the voltage will be lower than with an old one, we want to be sure of not stalling......we can get new motors, but don't have access to older ones.
Tony Stewart: Thanks, that is very interesting the video. The whale gulper is , at least I think, supplied by a mains transformer, which as we know can handle big overloads no problem. I am wondering what would be the difference in current for when just pure water is being pumped.

I can see an SMPS potentially tripping out on overload unless it was designed for the maximum load (16 sheets of toilet roll)....but goodness knows what the current draw has to be to allow 16 sheet "mulch" of toilet tissue to be pumped.

 

[Tony Stewart]

I might suggest a load test to see how much excess torque there is, or assume 50%V
With excess loading, stall voltage will be rated voltage.
Next define a load test.

Use recirculating hoses with a shutoff ball valve and measure pressure, if you like.
If 2.5 A fuse blows before SMPS shuts down. Supply = OK
Thus stall voltage is defined by recommended fuse limit .
Vmin= ESR total * Fuse rating.

So 6Vmin is OK.
( in general for thermal heat rise ) but still may occasionally stall under great transient pressure. )

But I wouldn't want to be the tester of a live waste pump test and find it fails and then the flex-pipes leak or burst from over-pressure. Then the current limit should be correlated with pump pressure limit with a safety factor and possible damage to the plastic planetary gear.