Mitsubishi water pump getting hot

[mran66]

I have about 10yrs old Mitsu WP-305 water pump that has been working good feeding water to my house with fairly limited on-time as pump only runs when water used in te house.

 

Due to reduced city water pressure, I have lately I used water supplied by the pump also for watering plants, and noticed that after a while (5-10min or so) of continuous running, the pump stops. It appears that this is due to motor heat protection stopping it. After waiting a while it just starts on its own, and faster if cool it by spraying water on it. The motor actually gets fairly hot, though not sure what exactly the temp is but feels pretty hot by fingers, thus I would guess the temp sensor that cuts the power works at about right temp

 

In my neighbors garden have similar type of pump, though smaller size, used for watering the garden, sometimes running for hours without cutting. And that has the plastic cover on top, limiting airflow

 

Pump does not have the plastic over on rather is in a ventilated cabinet with decent space for air. The fan at the end of the motor is ok, though the airflow produced by it is fairly weak. Turning it from the fan it rotates without any big force, though has some friction (guess due to sealing) and does not run freely like a standalone motor would.

 

Anyone else experienced the same with similar pump? Any idea why like that and especially anything that could be done to keep it running? 

 

[ravip]

Try to avoid or minimize using it until you find someone to repair it.

Repeatedly heating it up to the maximum threshold might damage it permanently.

[lopburi3]

You are drawing water from a storage tank as required?  Keeping that tank in shade will greatly reduce water temp in pump (which cools by water-not by air).  Is this a time of the year with direct sunlight on storage tank perhaps?  Pump itself is designed for outside use with just the cover for protection.

[MJCM]

45 minutes ago, lopburi3 said:

You are drawing water from a storage tank as required? 

 

+1

 

As I read it he doesn't!

 

@mran66 If you have connected the pump directly to the mains and the mains don't have enough pressure (less water) then your pump is sucking air which would cause it to overheat.

 

Normal working method for a Pump is have the Mains connect (fill) to a Water tank and then the Pump will draw water from that tank (and not directly from the mains)

 

@Crossy has a great diagram for it on how to connect it, but I can't find it right now.

 

 

Edit: Found it

 

Edited December 30, 2023 by MJCM
Removed some wording

[Crossy]

Yeah, pumping direct from the mains is "unwise" (let's not get into the argument of whether it is actually illegal).

 

A buffer tank makes life much more bearable for your pump and prevents you from sucking in the contents of the neighbour's duck pond 

 

[MJCM]

3 minutes ago, Crossy said:

Yeah, pumping direct from the mains is "unwise" (let's not get into the argument of whether it is actually illegal).

 

That said, it's also not good for your wallet, because when the mains is "out of water", you will be paying for sucking air as the Water Meter (AFAIK) will still spin because the Pump is sucking air which cause the water meter to spin.

Edited December 30, 2023 by MJCM

[Crossy]

3 minutes ago, MJCM said:

 

That said, it's also not good for your wallet, because when the mains is "out of water", you will be paying for sucking air as the Water Meter (AFAIK) will still spin because the Pump is sucking air which cause the water meter to spin.

 

No direct experience (we have a 2,400 litre buffer tank), but I believe that the meter spins rather faster (ok a lot faster) on air too

[VocalNeal]

1 hour ago, mran66 said:

I have lately I used water supplied by the pump also for watering plants,

 

Are you spraying or drip-feeding them.🤔

[Muhendis]

58 minutes ago, MJCM said:

paying for sucking air as the Water Meter

Oh come on please lets stop sucking around.

 

Happy New Year

[xtrnuno41]

IS the fan of the motor still really tight attached to the motor?

If the fan is somehow loose, it can turn, but not efficiently, it slips and then not cooling well, the motor.

You mentioned weak airflow.

A pin maybe be broken or the glued connection of the fan is out of order. 

Motor gets heated and has thermal trip at some point.

[mran66]

2 hours ago, MJCM said:

 

+1

 

As I read it he doesn't!

 

@mran66 If you have connected the pump directly to the mains and the mains don't have enough pressure (less water) then your pump is sucking air which would cause it to overheat.

 

Normal working method for a Pump is have the Mains connect (fill) to a Water tank and then the Pump will draw water from that tank (and not directly from the mains)

 

@Crossy has a great diagram for it on how to connect it, but I can't find it right now.

 

 

Edit: Found it

 

 

Pump is being supplied from tank, without any direct connection to city water. Tank is filled from city water. No air in system. Connection is properly done, that is not the issue. 

Edited December 30, 2023 by mran66

[mran66]

1 hour ago, VocalNeal said:

 

Are you spraying or drip-feeding them.🤔

 

Usually using the rotation-adjustable sprayer. Pressure probably remains close to the 3bar cut limit as flow is relatively small. But I recall the heating also happened without the sprayer, just using 1/2 inch garden house with open end

[mran66]

39 minutes ago, xtrnuno41 said:

IS the fan of the motor still really tight attached to the motor?

If the fan is somehow loose, it can turn, but not efficiently, it slips and then not cooling well, the motor.

You mentioned weak airflow.

A pin maybe be broken or the glued connection of the fan is out of order. 

Motor gets heated and has thermal trip at some point.

 

Good point, need to check that. That could explain. 

[mran66]

2 hours ago, lopburi3 said:

You are drawing water from a storage tank as required?  Keeping that tank in shade will greatly reduce water temp in pump (which cools by water-not by air).  Is this a time of the year with direct sunlight on storage tank perhaps?  Pump itself is designed for outside use with just the cover for protection.

 

Underground tank. The pump actually is cool even when the thermal will trip and stop the motor, only motor is hot. Pump has only weak thermal connection to the motor and thus dont cool the motor much. 

[Muhendis]

14 hours ago, mran66 said:

I have about 10yrs old Mitsu WP-305 water pump that has been working good feeding water to my house with fairly limited on-time as pump only runs when water used in te house.

 

Due to reduced city water pressure, I have lately I used water supplied by the pump also for watering plants, and noticed that after a while (5-10min or so) of continuous running, the pump stops. It appears that this is due to motor heat protection stopping it. After waiting a while it just starts on its own, and faster if cool it by spraying water on it. The motor actually gets fairly hot, though not sure what exactly the temp is but feels pretty hot by fingers, thus I would guess the temp sensor that cuts the power works at about right temp

 

In my neighbors garden have similar type of pump, though smaller size, used for watering the garden, sometimes running for hours without cutting. And that has the plastic cover on top, limiting airflow

 

Pump does not have the plastic over on rather is in a ventilated cabinet with decent space for air. The fan at the end of the motor is ok, though the airflow produced by it is fairly weak. Turning it from the fan it rotates without any big force, though has some friction (guess due to sealing) and does not run freely like a standalone motor would.

 

Anyone else experienced the same with similar pump? Any idea why like that and especially anything that could be done to keep it running? 

 

Sounds to me like a motor problem.

If you can check the running current (electric that is) and compare it with the rating plate power this will give a good indication of state of the motor. It is quite possible that a 10 year old pump will suffer from stiff bearings and so will be working harder. 

 

Another test for this is to turn the pump motor by hand. It should turn easily. To do this there is usually a screwdriver slot in the accessible end of the shaft. 

 

If the motor does turn easily then it is quite likely to be an electrical problem in the motor windings. As above you should be able to confirm by checking the motor current. You will need to calculate what it should be from the simple formula of Watts/Volts = Amps so, for example, a 300 Watt motor in a 220 Volt supply would be 300/220 = 1.36 Amps under normal running conditions.

 

Measuring this current is best done with an AC current clamp meter around the live wire where it is accessible in the consumer unit. Just make sure there is nothing else running from that particular mcb at the time. 

[mran66]

17 hours ago, xtrnuno41 said:

IS the fan of the motor still really tight attached to the motor?

 

Took off the cowling and fan to check  - it is good, no damage and solid in place.  Also, pump/motor rotates easily, only minor friction from seal, no bearing sound/feeling, no issues there.

 

4 hours ago, Muhendis said:

Sounds to me like a motor problem.

If you can check the running current (electric that is) and compare it with the rating plate power this will give a good indication of state of the motor. It is quite possible that a 10 year old pump will suffer from stiff bearings and so will be working harder. 

 

Measured the current of my pump and also measured my neighbor's pump current (same model but newer). I guess I am getting to the tails of the issue.

 

When water flow is low, just below pressure switch cutting off, my pump runs around 2.8-2.9 amps. Same test for my neighbor shows about 2.4-2.5 amps, i.e both about double the 'nominal' level. It appears the nominal value indeed is just nominal, basically pump running without much load, just pumping water out with low pressure and no load for motor to pump against pressure.

 

What is different between my pump as my neighbor's pump though is that I have tuned the pressure switch a bit, basically adjusted the cut-off closer to the max level that the pump can make (to get higher pressure to 3rd floor). I think the std cut-off is 3bar, mine is around 3.5 according to the gauge I have. When tuning it, I recall the pump was able to make close to 4bar, however obviously needed to work hard to get there, so set a bit down from max level.

 

Now, when using my long 1/2 inch garden hose, with or without the sprayer, the pressure remains in 3+ bar range, keeping the pump running at 2+ times current vs the nominal level.  I believe this is the explanation for the heating - the motor is simply not designed to run  extended times at this load level, and the thermal protection just cuts it off if used like that. The pump does it job OK to deliver water at 3+ bar load level for normal household use though, no cutoffs from that use as usage times are normally fairly short.

 

So I guess nothing can do, it is what it is. Would be interesting to hear if someone is actually using this pump model with long run times at low pressure level without the thermal tripping - or alternatively having the same behavior as I have with higher pressure and extended runtime

Edited December 31, 2023 by mran66

[lopburi3]

12 minutes ago, mran66 said:

Now, when using my long 1/2 inch garden hose, with or without the sprayer, the pressure remains in 3+ bar range

Do you have original spec sheet for that pump?  Unless they have greatly changed over the years working pressure was in the 2 bar range as I recall (about 25 psi I believe) - prime reason we changed to Grundfos pumps (decent shower water pressure).  Was using 405 models and pressure was nowhere near 3-4 bar range.  But that was about 20 years ago so things may have changed. 

[mran66]

25 minutes ago, lopburi3 said:

Do you have original spec sheet for that pump?  Unless they have greatly changed over the years working pressure was in the 2 bar range as I recall (about 25 psi I believe) - prime reason we changed to Grundfos pumps (decent shower water pressure).  Was using 405 models and pressure was nowhere near 3-4 bar range.  But that was about 20 years ago so things may have changed. 

 

the pump motor nominal power in label is 300w.

pressure switch  spec for wp-305 is 2.4 start and 3.0 stop, and this is how my neighbor new pump actually works.

 

as said, few years ago I actually tested how much pressure the pump can do, and as result set the cut off to about 3.5. I recall he pump itself can make close to 4 however not obviously with any meaniful flow. With small flow like house tap or shower, it keeps at 3+

 

But it is obvious that the power motor takes within the switch start-stop range is way more than the 'nominal' - I guess the motor nominal power is defined in state when pump just moves water from inlet to outlet without having any (or at least much) pressure. Maybe can test some day out of curiosity

 

Edited December 31, 2023 by mran66

[Muhendis]

44 minutes ago, lopburi3 said:

prime reason we changed to Grundfos pumps

Yeah,

Grondfos is the Rolls Royce of pumps but I swapped mine to Mitsubishi 350W because the Grondfos was 1100W and didn't 'arf use my electric.

The Mitsubishi does the job equally well.

Edited December 31, 2023 by Muhendis

[lopburi3]

1 minute ago, Muhendis said:

Yeah,

Grondfos is the Rolls Royce of pumps but I swapped mine to Mitsubishi 350W because the Grondfos was 1100W and didn't 'arf use my electric.

The Mitsubishi does the job equally well.

That was defiantly not our experience - shower pressure much better using Grundfos.

[mran66]

1 hour ago, Muhendis said:

Yeah,

Grondfos is the Rolls Royce of pumps but I swapped mine to Mitsubishi 350W because the Grondfos was 1100W and didn't 'arf use my electric.

The Mitsubishi does the job equally well.

 

51 minutes ago, lopburi3 said:

That was defiantly not our experience - shower pressure much better using Grundfos.

 

Both statements probably equally true...sure the 15-20k baht multi-stage Grundfos pumps can move more water at higher pressure than the usual wp-305-405 single stage small-household Mitsus - however makes hardly any difference if you set the pressure switch to 3bar on both, and only use water for ordinary household purpose for 1-2 persons for shower, bathroom sink, kitchen and laundry etc.

 

But if you need more supply (e.g for family of 6 with all taking shower/bath simultaneously, with washing machine, dishwasher and garden watering running at same time) - esp so if you want water to come with higher pressure and set the switch to 4 or 5 bar, you can get that from multi-stage pumps (regardless of brand) by just adjusting the pressure switch as long as you have picked a pump that has enough (and large enough) stages, driven by large enough motor. Limit at the end is your breaker amp size... Alternatively if you install 2 or more of those Mitsus in parallel to cope with the higher usage moments, you are fine as long as you dont need much more than 3bar at pump when tap/shower is open, going higher than that wont work with Mitsus (unless you put two of them in series)

 

But for people like me, with one person household with a random visitor, rarely having more than one tap/valve open simultaneously, such higher capacity pump or multiple single stage ones would be simply waste of money, kind of like installing a 20kw water heater for my shower for which 4.5kw (out of the 6kw adjustable heater) is enough to have nice warm shower...

 

In my home country is usual to have 100-150m deep well, into which you drop a long multi-stage (often Grundfos) pump - in such application the Thai Mitsus would only generate heat, no water!

 

The real learning for me out of this was that the nominal 300w actually does not mean much as in reality the motor uses more than the nominal almost always when it runs, and that if you use the pump in normal use case (shower, bathroom sink, garden watering), the real power is about double.  Have not given any thought to the whole issue before actually, but that's how it seems to be

 

Edited December 31, 2023 by mran66

[lopburi3]

41 minutes ago, mran66 said:

Grundfos pumps can move more water at higher pressure than the usual wp-305-405 single stage small-household Mitsus - however makes hardly any difference if you set the pressure switch to 3bar on both

There was no bar reference on pumps from Japan 20 years ago and as recall PSI was max at about 30psi (not even close to 3 bar).  Our bath was second floor so that may have made the issue more extreme but shower pressure was nothing like even 3 star hotel.  Grundfos made a huge difference - even when only one tap in use.

At any rate fear I have taken topic off point - just was not sure 305 pump of 10 years ago was designed to operate at such a pressure setting and offered as a possible overheating reason.

[mran66]

20 minutes ago, lopburi3 said:

There was no bar reference on pumps from Japan 20 years ago and as recall PSI was max at about 30psi (not even close to 3 bar).  Our bath was second floor so that may have made the issue more extreme but shower pressure was nothing like even 3 star hotel.  Grundfos made a huge difference - even when only one tap in use.

At any rate fear I have taken topic off point - just was not sure 305 pump of 10 years ago was designed to operate at such a pressure setting and offered as a possible overheating reason.

 

Yes understand. 

 

Re 305 pump, seems my 10yrs old works about same as neighbors new one what comes to power use at a certain pressure/volume level.  Your 20yrs ago pump may have had different spec esp the pressure switch setting, maybe switch set so that pump can not heat too much even if it could supply water at 3+ bars if swich adjusted so

 

Even today's pumps have default different settings dependent on model (guess smaller ones have lower as they simply can not go higher with any meaningful supply). And as I have done, you can tune up a bit as long as you don't need the pump to run for extended periods.

 

 

Edited December 31, 2023 by mran66

[Fruit Trader]

3 hours ago, mran66 said:

What is different between my pump as my neighbor's pump though is that I have tuned the pressure switch a bit, basically adjusted the cut-off closer to the max level that the pump can make (to get higher pressure to 3rd floor). I think the std cut-off is 3bar, mine is around 3.5 according to the gauge I have. When tuning it, I recall the pump was able to make close to 4bar, however obviously needed to work hard to get there, so set a bit down from max level.

 

Most common house pumps like the Mitsubishi WP-305 are of the regenerative turbine type. When changes are made to pressure control switches it’s important not to exceed the limit of the motor because regenerative turbine pumps act differently to regular centrifugal pumps when the head changes.

 

Running these pumps continuously against a high head will surely cause the motor protection switch to reach its limit.

 

 

This following link explains in more detail how regenerative turbine pumps compare to regular centrifugal types.

https://www.rothpump.com/regenerative-turbine-pump-little-pump-big-head.html?no_redirect=true

[lom]

Motor bearing problem or faulty capacitor (if the pump has one).

[sometimewoodworker]

4 hours ago, mran66 said:

 

Now, when using my long 1/2 inch garden hose, with or without the sprayer, the pressure remains in 3+ bar range, keeping the pump running at 2+ times current vs the nominal level.  I believe this is the explanation for the heating - the motor is simply not designed to run  extended times at this load level, and the thermal protection just cuts it off if used like that. The pump does it job OK to deliver water at 3+ bar load level for normal household use though, no cutoffs from that use as usage times are normally fairly short.

 

So I guess nothing can do, it is what it is. Would be interesting to hear if someone is actually using this pump model with long run times at low pressure level without the thermal tripping - or alternatively having the same behavior as I have with higher pressure and extended runtime

You have run into the problem that is inherent in your pump as you have modified the pressure switch, this is trying to force the water through a far too small pipe that is far too long
 

The answer, though it seems counterintuitive, is to use a bigger garden hose probably at least a 1” or 1½”.

 

SWMBO made the same mistake. She was using a ¾ pipe and complaining that the garden watering took too long. I bought a 1½“ 100 meter hose, she was extremely dubious about using it, within a week she was completely convinced by the results.

 

Your problem is that a ½” is introducing far too much friction so slowing your watering use a 1½ hose and you have almost a 20 fold reduction in friction loss, though it is also dependent on the flow NOTE bigger numbers are worse. 

 

[mran66]

13 minutes ago, sometimewoodworker said:

You have run into the problem that is inherent in your pump as you have modified the pressure switch, this is trying to force the water through a far too small pipe that is far too long

 

Yeah - seems the pressure difference at pump with and without sprayer is fairly small due to size and length of the hose. Actually the problem would be not much less even with the std pressure switch setting as the pressure seems to remain at around 3bar (i.e at cut off level) when using the hose. Might even be worse if the pump would stop and start frequently, causing heat from that start-stop cycle.

 

However, as my watering needs as well as other uses for my garden hose are not too long lasting, I will stick to the 1/2 inch one as the 5/8 is substantially less convenient to handle e.g when washing something etc.

 

But clear, if would need water with extended times, would need to have larger hose to reduce the load to pump/motor

Edited December 31, 2023 by mran66

[sometimewoodworker]

@mran66 if you want to keep using the pump with your small hose then put in a standard pressure switch or even adjust the switch to a lower than standard pressure. This should, though once again it is counterintuitive, allow you to run the pump for far longer before it cuts off.

 

look at the chart I posted the higher the flow you are trying to achieve the far greater the friction loss. 
Reduce the flow 

The friction loss drops drastically for your pipe.

[mran66]

18 minutes ago, sometimewoodworker said:

@mran66 if you want to keep using the pump with your small hose then put in a standard pressure switch or even adjust the switch to a lower than standard pressure. This should, though once again it is counterintuitive, allow you to run the pump for far longer before it cuts off.

 

look at the chart I posted the higher the flow you are trying to achieve the far greater the friction loss. 
Reduce the flow 

The friction loss drops drastically for your pipe.

 

Understand, not counterintuitive to me. My problem is that I want to have high pressure as mostly use the hose to spray or wash something... 

[sometimewoodworker]

15 minutes ago, mran66 said:

 

Understand, not counterintuitive to me. My problem is that I want to have high pressure as mostly use the hose to spray or wash something... 

in that case don’t use the wrong pump for the job. Use one of these

cheap enough that if it grenades, unlikely but possible, jut buy another.

Edited December 31, 2023 by sometimewoodworker