Submersible Well Pump Amps Draw

[MarkF48]

I've got a 1/2hp submersible that's down about 230'. The static water level I believe varies to some degree with the amount of rainfall we get. September in the Northeast has been a dry month and the time it takes to cycle the tank pressure has been taking longer, which has been the norm in the past when I believe the static level drops. A few months ago, mid summer, the pump was pulled for a bad wire and at that time the static water level was about 130'. At the time the pump was put back down I seem to recall the amps drawn was about 5.4-5.5 amps and at the time we had had a fair amount of rain previously and cycle time of the pump was relatively short. With the dry month we've been having the pump is taking longer to cycle, but I've also noticed the amps drawn had been down to about 4 amps, which is less than when there appears to be more water available. The rating on the pump at 230v is 5.9 amps max. I would tend to think the amps drawn relates to how hard the pump has to work, but what is throwing me is that at lower static water levels the amps drawn is less than when I believe the static level is higher. I would think the the amps would increase when the static level drops because it has to push the water further up, but it seems to be doing the opposite. It could be I have something else going on that's affecting the current draw, but that's why I'm posting this is to get some other thoughts..

 

[buickanddeere]

If the water level dropped 100ft. The pump would have to develop an extra 45psi plus the power already used to push 30-80lbs of water per minute up the pipe and pressurize the tank.

 

[kc5dlo]

The pump will pull the most amps at full flow with no restrictions. When you start closing valves on the discharge or increasing lift, the amp draw goes down.

 

[SirReal63]

The pump will pull the most amps at full flow with no restrictions. When you start closing valves on the discharge or increasing lift, the amp draw goes down.

+1
This is because the increased head on the pump means it is actually doing less work, work being the amount of water pumped. More work (water being pumped) means more electrical usage.

 

[buickanddeere]

+1
This is because the increased head on the pump means it is actually doing less work, work being the amount of water pumped. More work (water being pumped) means more electrical usage.

Throttling the inlet will reduce motor loading.
Work is force and distance. Power demand for low flow and high pressure is similar to high flow and low pressure.

 

[camshawn]

The lower the well level, the less water is forced into the impeller of the pump, the less water is moved which means lower amp draw providing the head stays the same. We are talking about the efficiency of the impeller. All of this information is described on the pump curve. Pumps designed for the wrong volume or head will quite often either not move enough water or burn the motor out. Cam

 

[SirReal63]

Cam, the head isn't the same when the water level is lower, the head pressure increases as the water level drops in the well, and as the water level in the well rises, head pressure is reduced.

Buick, it is improper to throttle the inlet of a submersible pump, it can cause cavitation, throttling the output is always the right way (not that it is relevant here, you don't throttle well pumps), and serves the same as adding head pressure. Yes the work is force and distance, in this case the distance has increased because of the drop in water level, so the amount of water pumped is decreased as well as the electrical consumption, the pump is doing less work. Head pressure is not the total length of pipe, it is the length of pipe above the water level (in this case, the amount of water in the well), change the water level and the head changes with it.

 

[buickanddeere]

I should have specified that throttling of a axial or centrifugal pump/compressor is only really practical when the working media is a gas.
Of course throttling a deep well pump would be counter productive .
Using a VFD to control shaft rpm is a better way to tweak a one size fits all pump into a better curve to suit a particular application.