pump motor overheating, need help.

[KarlJay]

I'm using a Harbor Freight 12V DC 100W (10 amp?) motor with a pump rated at 300GPH @ 50PSI.

It's connected to the bottom bucket so that it doesn't have to pull water up, the water is above it. I'm using it to raise the water thru a 1/2" tube to a point about 6 feet up.

I burned up the 1st motor and just installed a replacement and it's overheating as the 1st one did.

The pump doesn't seem to be protected and I'm testing things using a 12V car battery. I've use the battery a few times, so it might be down a bit.

The pump need to run for about 1/2 hour at a time. Think of a basement water pump that pumps flood water out of the basement to about the height of a wall.

The cost and size of the pump is important and this one seems to be about the right size and cost.

Because of shock hazard, I'm using 12V as it could get flooded. The other pumps I've seen don't have the pressure/flow that I need, this one does. (300GPH / 50PSI)

I was going to use 12V computer power supply, but if AC would be better and could be made safe, that would work as well.

Q1. How do I determine the type of pump or size of motor that I need for this?

Q2. What effect would a heat sink on the motor housing make?

Q3. Can I add a self resetting thermal protection to the outside of the metal motor housing, if there is such a thing?

Here's the pump: https://www.harborfreight.com/12-volt-marine-utility-water-pump-94639.html

I'm running tests now to see if this is because of the pressure as it goes thru the valves. The motor clearly makes more noise when I apply more pressure.


Thanks!

 

[BradtheRad]

The specs for the pump appear ideal for your purposes.

From the manual:

"5. This utility pump is designed for intermittent use only. Do not use the utility pump over excessive lengths of time, as premature wearing will result."

I suppose the manufacturer will say 1/2 hour is excessive.

If you were to consider an AC pump, you might look at specs for sump pumps (although this is likely to be high-capacity, brief-running).

Questions:

* Has the pump ever run dry for more than a few seconds at a time? Dry running will degenerate motor performance.

* Has the pump had grit or debris go through it? This might erode the blades, with the result that the motor runs overly fast and overly long.

* Cavitation is not so likely when the pump pushes water upward, but it could come into play if the blades are sped to the point where cavitation happens.

 

[chuckey]

Make sure that the inlet piping to the pump is as unobstructed as possible. As an aside you don't need 50 PSI, this will be the pressure when the pump is cocked off at its output, i.e. its a test of how tight the pump seals are. Likewise the 300 GPM is with the pumps output open. Your actual pressure is 6 foot plus a bit more for pipe losses, say 10 foot water gauge or .7 Bar or 10 PSI. I suspect that your HF pump is under rated, have you tried putting a fan in some ducting to cool it. A thermal trip would still allow the inside to get too hot, just not for so long!

You could try to run it at a lower voltage, say 10 V, see what the minimum voltage is for adequate performance and see if it over lheats at this voltage.
Frank

 

[KarlJay]

Thanks for the quick reply!

I actually have 2 of these pumps for testing. The pump that pushes water to 6 feet is never started until the water level is above the pump level. Right now, for testing, I have a tap (bulkhead) at the bottom of a bucket so that it has water right there the whole time.

I didn't have a filter and I'm testing with tap water, so I think some stuff would have drawn into the pump.

I didn't know if 10 volts would hurt the motor or not.

I've heard you can damage a car's starter motor by running it below 12V or cranking it with low amperage, so I thought that might be the problem.

I've run both pumps into the same bucket as a test. They both raise the water the height of the bucket (std 5 gallon paint bucket). The only difference is that one is using 1/2" tube vs 3/8" tube.

The one motor got hot, whereas the other remained cool. Both were being tested from the same car battery.

I think I'll swap the pumps with each other and see if that changes things. I know HF is well known for poor quality.

Neither pump has a cooling fan or any protection.

The specs for the pump appear ideal for your purposes.

From the manual:

"5. This utility pump is designed for intermittent use only. Do not use the utility pump over excessive lengths of time, as premature wearing will result."

I suppose the manufacturer will say 1/2 hour is excessive.

If you were to consider an AC pump, you might look at specs for sump pumps (although this is likely to be high-capacity, brief-running).

Questions:

* Has the pump ever run dry for more than a few seconds at a time? Dry running will degenerate motor performance.

* Has the pump had grit or debris go through it? This might erode the blades, with the result that the motor runs overly fast and overly long.

* Cavitation is not so likely when the pump pushes water upward, but it could come into play if the blades are sped to the point where cavitation happens.

- - - Updated - - -

Make sure that the inlet piping to the pump is as unobstructed as possible. As an aside you don't need 50 PSI, this will be the pressure when the pump is cocked off at its output, i.e. its a test of how tight the pump seals are. Likewise the 300 GPM is with the pumps output open. Your actual pressure is 6 foot plus a bit more for pipe losses, say 10 foot water gauge or .7 Bar or 10 PSI. I suspect that your HF pump is under rated, have you tried putting a fan in some ducting to cool it. A thermal trip would still allow the inside to get too hot, just not for so long!

You could try to run it at a lower voltage, say 10 V, see what the minimum voltage is for adequate performance and see if it over lheats at this voltage.
Frank

Thanks for the reply! I'd rather the pump shut off than burn up, although if I can't cool it or keep it running for about 1/2 hour then I need a different pump.

I see bilge pumps used on boats, maybe they'll work better for this. HF has some of the best prices, but I need something that'll hold up better.

I'm going to swap the 2 pumps I have because it's only the one pump that's having a problem.

The only difference in the work they do is that one has to draw the water up to it and the other has the water pushed to it.

Maybe that's the problem. Maybe I need to make both pumps pull water up to themselves.

I thought having the water pushed into the pump would make for less work and better performance from the pump. Maybe it need to pull and push.

 

[chuckey]

" Maybe I need to make both pumps pull water up to themselves.". This is impossible, repeat after me, "you can't tow water". What is happening is the air pressure is pushing down on the water in the tank that is causing it to flow into the pump. Your pump will pull a tiny vacuum, but it will burn out the seals.
The reason car starters can burn out with low voltage is that the solenoid does not engage them, by the way ALL car starter motors will perform at 100% at 10 V, because when they are being used that the voltage they actually get.
Running a typical brushed DC motor at a lower voltage causes them to rotate slower and take less current. Have you taken apart the faulty unit, or better take it back to HF, because its faulty.
Frank

 

[KarlJay]

" Maybe I need to make both pumps pull water up to themselves.". This is impossible, repeat after me, "you can't tow water". What is happening is the air pressure is pushing down on the water in the tank that is causing it to flow into the pump. Your pump will pull a tiny vacuum, but it will burn out the seals.
The reason car starters can burn out with low voltage is that the solenoid does not engage them, by the way ALL car starter motors will perform at 100% at 10 V, because when they are being used that the voltage they actually get.
Running a typical brushed DC motor at a lower voltage causes them to rotate slower and take less current. Have you taken apart the faulty unit, or better take it back to HF, because its faulty.
Frank

I replaced the one pump but now the replacement is getting hot doing the same job. I have two pumps for this project and only one pump is getting hot. They are both the same specs.

I'm going to swap the workload and see if that changes things.

I'll need to find something that can control the voltage so I can find the proper level.

 

[KarlJay]

Update: I swapped the pumps and tested the pump that was getting hot and it didn't heat up as much. It still made some noise and seems to vibrate more than the other. This might be Harbor Freight's quality control (or lack of).