Fuse Puzzle: Which is more likely?

[H2Obuffalo]

Hello-

I'm getting a small, old, very basic house in Thailand ready to move into, and an electrical question has come up. Does anyone have a best guess what might be happening in the following situation?

1) A water pump at the mouth of the house's (private) water well normally drives water into the house without problem. But...

2) When I hook up two large water filters to the water system, forcing the pump to push the water through quite a bit of filtering material, the pump gets the water through at a good rate, but soon makes a strained, moaning sound, and.... the master fuse for the whole house's electicity blows.

3) Replacing the fuse (which I originally thought might be old) does not help. The same thing happens again.

Without knowledge of electricity, I'm guessing that one of two things is happening. Can anyone here tell which is more likely from an electical perspective?

Scenerio A: Maybe the pump is too SMALL and too low wattage to do the new job being requested of it. In other words, maybe the filtering material puts up too much resistance and the pump is just not strong enough to push the water as usual, so it strains, quits, and blows the house fuse. In this scenerio I should probably buy a bigger pump.

Scenerio B: Maybe the pump is too BIG and too high wattage to do the job being asked of it. In other words, maybe the pump is used to pumping a LOT of water through the house relatively easily, and when it meets a significant restraint from the filtering media, it just can't push as much water as it is designed to push, so again it strains, quits, and blows the house fuse. In this scenerio I should probably buy a smaller pump.

Unfortunately quite a bit of (my own) money is on the line. I was planning to replace the old pump anyway, but now I don't know if the electical issue is being caused because I need a bigger (higher watt) pump or a smaller (lower watt) pump. If I buy one size and then find out it was the other one I need, I will be be out a lot of extra money.

The filter technician has a recommendation, but based on past experience with him I don't really trust his knowledge about electricity (or filters for that matter), and I don't want to prejudice anyone here's own guess as to what's happening with the fuse, so I won't specify which size (bigger or smaller) pump he recommended.

Is there an obvious answer to this puzzle based on how electicity and fuses work? Is it clear to anyone whether I should buy a large or smaller pump, based on what is happening with the fuse?

Thank you very much for any insight and advice!

-Paul

 

[Diver300]

There may not be anything wrong with the pump size at all. A pump may well take more current when pushing water though more restriction. (However, centrifugal pumps may take less current, and produce less flow). A different pump might be more efficient and use less current to pump the same amount of water.

The fact that the house fuse blows when the pump seems fine would make me think that the house supply is only rated at a small current. There should be a smaller fuse to protect the pump.

If you have water storage, and can afford a lower flow rate, get a pump with a lower flow rate and run it for longer.

It would help your question if you could tell us the pump ratings in pressure, flow, voltage and current, and the fuse ratings. Photos can help as well.

 

[H2Obuffalo]

Hi Diver300-

Thank you for your post. Unfortunately it will be difficult or impossible for me to find out the electronic specifications mentioned. Would it help for me to rephrase the question as follows?

From an electrical perspective, what is the *most likely* cause for the water pump blowing the fuse? Would such an event be more likely to be caused by a motor that was being asked to work HARDER than it was (hypothetically) designed for, or would the blown fuse be more likely to be caused by a motor that was not being allowed to work at the (hypothetically) high capacity for which it was designed.

I understand that a smaller, local fuse just for the water pump would be a good idea, but right now I need to figure out (or make a best guess) what the water pump is doing to the fuse and if I am more likely to fix the problem by replacing the current pump with a more powerful (higher watt) or less powerful (lower watt) pump.

I should probably emphasize that the rest of the house's electricity all works fine and there is no fuse issue unless I specificially ask the pump to force water through the filters. To rephrase for clarity, the water pump works fine getting water to the house if the filters are not hooked up. The fuse issue does not happen if the pump is run alone, without pushing the water through the filters.

Thanks again.

-Paul

 

[Boncuk]

Hi Paul,

I have been living in Thailand since 2004 and I had some issues with water pumps as well.

With the first one everybody got an electric shock when touching the faucet in the bathroom. So I decided to install protective ground for the pump. When done the main fuse (50A) blew as I started the pump.

The reason was a short between the wiring and the pump case. I had the motor rewound and it worked alright.

Is there a possibility that the pump case gets ground (earth) when connecting the filter? Try to mount the filter isolated from earth and retry.

A centrifugal pump can't be overloaded other than running dry and separating into many parts.

The same applies to a piston type pump, where the rubber piston will start melting when the pump gets hot.

For high output pressure the suction pipe should be as short as possible with the max available cross section. E.g. with pressure pipe 1/2" the intake pipe should be at least 3/4" to 1".

On the other hand 5,000l plastic tanks (select dark blue) are fairly cheap and you might pump the water unfiltered into the tank and use the filter at the outlet (if necessary with a small boost pump with automatic pressure control).

Regards

Boncuk

 

[Mark_R]

Not a problem to be solved by guessing. Some simple tests / fact finding are in order.
How much (current) is the pump drawing?
How big is the motor (so you can tell how much you would expect it to draw)?
How big is the fuse?
Is it the fuse that was originally designed for the circuit (what size wire?)
How much voltage do you have?

The point is, maybe the pumps fine and you have an electrical problem, maybe it's sized wrong, maybe the voltage coming into the house is low for some reason, etc. but throwing new parts at the problem without some more info is a sure way to burn through some cash.

 

[MikeMl]

One minor input: centrifugal pumps draw the most current when the flow is the highest. If you throttle them to reduce flow, the current drops. The lowest current draw occurs when the fluid flow is completely shut off.

 

[kinarfi]

If the pump is positive displacement instead of centrifugal, it will draw more current as you add resistance to flow such as your filter system. If you stop the flow of a positive displacement, the motor will overload for sure, if you stop the flow of a centrifugal pump, the current will be at it's lowest, as MikeMi stated. My first guess is you have positive displacement pump. If you have a storage tank, fill it and use another pump to pump through filters and store or get another pump. I'm not sure if deep well, multi vane pumps are positive displacement or not.

Suggest making sure you have a centrifugal pump.
Kinarfi

 

[H2Obuffalo]

Thanks, All. This question sort of took care of itself for the moment, because the water filter guy now explicitly warned against going higher than 150 watts, since he has seen his filters burst with higher water pressure in this situation. The lowest watt available here for the "constant pressure" type pump that I need was 150, so it became a mute point. I got the 150. There's a picture of the new pump below. The original, old pump that was involved in the original issue was either 125 or 150 watts, but in any case, it was quite old, left unused for I think several years, and more old-fashioned looking, too- with a wheel that turned a band of rubber. I'm going to contact an electrican to put in the new pump, but I'm hoping whatever was happening won't happen again, with the old pump retired. I'll post when I know. It'll be a few weeks.

-Paul

 

[Boncuk]

If the pump is positive displacement instead of centrifugal, it will draw more current as you add resistance to flow such as your filter system. If you stop the flow of a positive displacement, the motor will overload for sure, if you stop the flow of a centrifugal pump, the current will be at it's lowest, as MikeMi stated. My first guess is you have positive displacement pump. If you have a storage tank, fill it and use another pump to pump through filters and store or get another pump. I'm not sure if deep well, multi vane pumps are positive displacement or not.

Suggest making sure you have a centrifugal pump.
Kinarfi

Positive displacement pumps are available on special order only in Thailand.

There are just two main types of water pumps: piston operated and centrifugal.

I'm almost certain the problem is an earthing problem. If the filter is made of metal (supposedly) and it is earthed it will cause a short between motor housing due to faulty motor windings.

My experience was with a brand new pump.

Boncuk

 

[Boncuk]

Hi Paul,

the pump you show is a centrifugal type.

You just happened to buy the most expensive on the Thai market. Mitsubishi pumps are about double as much as "ITC" (made in Korea).

Boncuk

 

[H2Obuffalo]

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