Hitachi 280W Water Pump Operating At 600W

[bankruatsteve]

So, I recently acquired an ammeter and find that my "280W" water pump is actually pulling about 2.7a (600W @ 220v). It's about 2 years old and have no complaints: it supplies water when needed (pressure) and while it's not gusher strength, it's adequate.

If there is a start-up higher, I can't see it - the constant is about 2.7a.

So, can anybody 'splain that? I opened up the cover and there's a container with 3 screws on the input side that I thought might have a filter. But, when I started unscrewing, it squirted water even after I thought I relieved pressure. Since I didn't really know what I was doing I just re-tightend.

Thought? Suggestions? I konw it ain't broke so maybe I don't want to "fix" it

[Crossy]

Does the pump motor have a rating plate that details running current? or for that matter Wattage? Or are you relying on the pump blurb?

Did you measure the voltage at the pump when you checked the current? If the supply is low then the current will be higher.

There is a relationship between Watts (W) and Volts x Amps (VA) known as Power Factor, for an induction motor it's usually between 0.8 and 0.9.

Your example of a 280 W pump will have a VA rating of 310-350 VA, still nowhere near what you are measuring mind.

The pump run current will increase as the load (tank pressure) increases, have you (or someone else) adjusted the output pressure from standard so it has to work harder and thus pull more current? Taking that to the extreme may result in the start winding remaining in circuit continually, increasing the power consumption.

If it's working, and not getting excessively hot, I would not worry.

By the way. It's the VA rating that you are interested in when sizing your generator so you are measuring the correct parameter

As you say, 'if it's not bust, don't fix it'.

[bankruatsteve]

The plate on the units states 280W.

Just measured voltage - it's 238 at the pump (we typically run a bit high) and tested current draw again with the gf turning on the faucet. This time I briefly saw 9 something and then leveled out at about 4.1 (this is with other stuff using about 1.1)

I thought power factor was adjustment for start up vs continuous run. (?) Anyway, I've never adjusted anything and if it's running hot I don't notice it (ie: no smell or gee that sounds funny).

On the input side, I have 1/2" pvc going to the larger size (I think they call "#6"). Maybe I should try re-plumbing that so it's all the larger size between the storage tank and the pump? Output is only to 1/2" though.

Hmmm - yeah this could be an unexpected kick for my genset (still haven't got roundtoit for testing the replacement unit).

[Crossy]

Power Factor is the ratio between the Apparent Power (VxA) and the Real Power (Watts). In order to measure Real Power you need a specialist Wattmeter, you can't do it with a multimeter.

Try measuring the current when running at 220V (from the genset). Running induction motors at higher than rated voltage typically reduces the power factor, if it approaches 0.6 then you are getting towards your measured values.

Note, even with a poor power factor you are not actually using more energy it's all down to the phase angle between the current and voltage waveforms. A purely inductive load can have a large VA figure but actually consume zero Watts (PF of zero).

[bankruatsteve]

Ah, that actually rings a bell in my damaged memory circuits. I'll give a try.

To the plumbing, I now think it makes sense to make the whole input side the same size (not sure why it didn't in the first place) so will also do that (after the tank is used up).

Thanks Crossy!

[topher]

If the tank - pump line is long then the reduced size can affect how hard the pump has to work. If it's level (not below the pump) then I'd think it isn't really a problem, but if it also has to suck up some meters and contend with a small input pipe, then maybe together the pump is working harder than normal.

This web site has a nifty calculator that lets you see the effect of different pipe sizes on "dynamic" head, which I believe will act likewise on the input side. It's surpising how much more resistance there is in a 1/2" pipe compared to a 1" one. eg. In one situation 1/2" gives 7 meters head vs. 1" giving 0.27 meters head. It can also account for poor pressure.

http://www.aquascien...lculate_tdh.cfm

Edited March 31, 2012 by topher

[bankruatsteve]

If the tank - pump line is long then the reduced size can affect how hard the pump has to work. If it's level (not below the pump) then I'd think it isn't really a problem, but if it also has to suck up some meters and contend with a small input pipe, then maybe together the pump is working harder than normal.

This web site has a nifty calculator that lets you see the effect of different pipe sizes on "dynamic" head, which I believe will act likewise on the input side. It's surpising how much more resistance there is in a 1/2" pipe compared to a 1" one. eg. In one situation 1/2" gives 7 meters head vs. 1" giving 0.27 meters head. It can also account for poor pressure.

http://www.aquascien...lculate_tdh.cfm

In my case the storage tank is adjacent to the pump so like 1 m. I'm not concerned about the "head" (output side, yah?). I do have pvc reduction on the input side so maybe that's a problem. (?)

[topher]

If the tank - pump line is long then the reduced size can affect how hard the pump has to work. If it's level (not below the pump) then I'd think it isn't really a problem, but if it also has to suck up some meters and contend with a small input pipe, then maybe together the pump is working harder than normal.

This web site has a nifty calculator that lets you see the effect of different pipe sizes on "dynamic" head, which I believe will act likewise on the input side. It's surpising how much more resistance there is in a 1/2" pipe compared to a 1" one. eg. In one situation 1/2" gives 7 meters head vs. 1" giving 0.27 meters head. It can also account for poor pressure.

http://www.aquascien...lculate_tdh.cfm

In my case the storage tank is adjacent to the pump so like 1 m. I'm not concerned about the "head" (output side, yah?). I do have pvc reduction on the input side so maybe that's a problem. (?)

I think with only 1m between the effect would be minimal, but also the cost to replace it with a 1" pipe would be small as well.

"Head" does usually refer to the output side but the "pipe resistance" (friction) would be the same either side so the calculator helps to estimate the effect.

[Pib]

For comparison I'll do some amp/voltage readings on my Mitsubishi 255W water pump tomorrow and post some feedback....I've got a clamp-on amp meter and voltmeter to make the measurements. I'm interested in seeing what the start-up current, current under normal load (pumping water) and current under no load (running but pumping no water...no water input) are. I just wonder if the wattage rating the water pump manufacturers give are under no load conditions. Can't do the tests right now because it's dark and raining...hopefully it won't be raining tomorrow and the sun will come up....but right now I'm going to continue to concenrtrate on my cold Chang beer...and if the sun don't come up tomorrow I guess this will be my last beer.

[Pib]

OK, I did the tests on my Mitsubishi WP255Q water pump this morning (the sun did come up) which is one of those pumps which consists of the motor/manifold assembly setting on top of a small booster/pressure tank. Used a clamp-on amp and a voltemeter to take measurements. The pump is about 5 years old but in very good shape...I have changed the electrical pressure switch and air-volume-control valve (this valve maintains proper air volume in the water booster tank) over the years. The pump is rated at 250 watts; when looking at how Mitsubishi issues its model number on this series they appear to add 5 to the wattage rating to develop the model number. Examples: 250W is desginated a WP255, a 350W is designated a WP355, etc. See images below for a picture of my pump and the WP series specs.

Results under load and no load (load means pumping water; no load means water input and output turned off...pump basically dry...the pump is just spinning air vs pumping water).

Under Load: 225 volts (voltage at the pump), 2.4 to 2.6 amps...when pumps kicks on it draws 2.4A and then over the 5 seconds or so the pump is running it climbs to 2.6A...let's say a 2.5A average). This kind of pump kicks-on for approx 5 seconds and then cuts-off for approx 5 seconds...during those 5 seconds of off time pressure water continues to flow from the pressurized booster tank. For the kind of pump I have an approx 50% on-off cycle say with one or two water taps fully open is normal. Other kinds of pumps such as constant pressure pumps may run 100% of the time in order to maintain pressure. Now if you have a pump which utilizes a pressure/booster tank and your pump is running the great majority of the time then you probably have a water-logged tank, but that's a whole different technical subject in itself.

Under No Load: 225 volts, steady 2.0 amps. Motor of course continues to run because there is no water being pumped into the booster tank, the pressure can't build-up to cause the pressure switch to tell the motor to cut off.

So, using the formula of Power= Current (I) * Voltage (E) or PIE as I like ot remember it, the Under Load wattage usage was 225V * 2.5A = 563W. Under No load 225V * 2A = 450W. Obviously, neither of the wattage amounts comes close to the 250W rating.

What I'm thinking is the manufacturer may provide a wattage rating "not" based on the wattage used while the pump is running but instead provides a wattage rating based usage over a certain time frame, with the pump running/pumping at a certain capacity, and the on-off cycle calculated in. So if we take that Under Load wattage I mentioned above of 563W, say we based the wattage usuage over a 60 second period while remembering the pump only ran approx half the time (5 seconds on, 5 seconds off), then half of 563W is approx 283W which comes pretty close to the 250W rating of my pump. And let's say the on-off time is really a ratio of 55% of the time off and 45% on, then 45% of 563W is 253W....and what if it's a 60%/40% off/on time (6 seconds off, 4 seconds on), then 40% of 563W is 225W.

Without knowing exactly how manufacturers spec their pumps and knowing my pump runs today like the day it was brand new, I feel an under load amp draw of around 2.5A for my 250W pump is normal....and the OP's amp draw of 2.7A for his 280W pump is also normal.

[bankruatsteve]

Pib - thanks for the research! So maybe this is normal. (Anybody else want to weigh in?)

I think I'll go ahead with the 1" on the incomer anyway. Both the tank and the pump use the same size fitting so I don't know what I was thinking to reduce it in the first place (unless I ran out of 1" PVC). But, that will take a few days for the water to use up. Anybody know if there are filters that should be cleaned on these things?

Cheers

[Kwasaki]

I know if it ain't broke so maybe I don't want to "fix" it.

That's me, our Hitachi is a 275w. 50 Hz. 220v. 1 phase it does not say anything about amps.

Just a thought is what you call your ammeter the same as a multimeter and does it work OK when testing other things.

Mine is just a multitester meter and does ohmns, AC & DC. with different voltage levels.

Edited April 1, 2012 by Kwasaki

[Pib]

Pib - thanks for the research! So maybe this is normal. (Anybody else want to weigh in?)

I think I'll go ahead with the 1" on the incomer anyway. Both the tank and the pump use the same size fitting so I don't know what I was thinking to reduce it in the first place (unless I ran out of 1" PVC). But, that will take a few days for the water to use up. Anybody know if there are filters that should be cleaned on these things?

Cheers

On my setup the storage tank is only about a meter away with a 1" outlet and the pump's inlet and outlet are 1". However the pipe from the tank-to-pump and from the pump outlet-to-the-piping system is 3/4" (1" to 3/4" adapters used). It was already installed when we bought the house...I expect they used 3/4" connectors/adapters since the pipe from the soi to the tank is 3/4" and the house piping is mix of 1/2" and 3/4" piping; therefore, since they had plenty of 3/4" and 1/2" stuff that is what they used versus buying more of the 1" stuff just to hook the tank to the pump and then on the pump outlet just have to reduce it anyway from 1" to go to the 1/2" or 3/4" piping. I have good pressure throughout my two story house, yard outlets, etc.,...no complaints.

[bankruatsteve]

I know if it ain't broke so maybe I don't want to "fix" it.

That's me, our Hitachi is a 275w. 50 Hz. 220v. 1 phase it does not say anything about amps.

Just a thought is what you call your ammeter the same as a multimeter and does it work OK when testing other things.

Mine is just a multitester meter and does ohmns, AC & DC. with different voltage levels.

Most multimeters have an ammeter but you have to break the circuit to hook it up (and not advised unless you know what you're doing). What I just got is called a "clamp on" (is that right?) ammeter which measures the electriic field created when current passes through a wire (so it has tongs that surround just one of the wires). It is also a multimeter (V, ohms, capacitance, temp, Hz). BTW: I got this one at Amorn's top of the Fortune in Bangkok for B1300.

[Kwasaki]

I know if it ain't broke so maybe I don't want to "fix" it.

That's me, our Hitachi is a 275w. 50 Hz. 220v. 1 phase it does not say anything about amps.

Just a thought is what you call your ammeter the same as a multimeter and does it work OK when testing other things.

Mine is just a multitester meter and does ohmns, AC & DC. with different voltage levels.

Most multimeters have an ammeter but you have to break the circuit to hook it up (and not advised unless you know what you're doing). What I just got is called a "clamp on" (is that right?) ammeter which measures the electriic field created when current passes through a wire (so it has tongs that surround just one of the wires). It is also a multimeter (V, ohms, capacitance, temp, Hz). BTW: I got this one at Amorn's top of the Fortune in Bangkok for B1300.

OK Stevie boy. sorry one of my sons is Steven and I always call him that.

" (is that right?) " Wouldn't know, I guess the saying is " If it 's not broke don't try and fix it ", is the way to go.

Wait until something goes wrong instead of testing things.

[bankruatsteve]

Just to follow up...

I replaced the incoming pipe (which had been reduced to 1/2") to full 1" from the tank to the pump. The only noticeable difference is that the pipes used to jerk a bit when the pump started/stopped and now they don't. And, the water delivery seems slightly smoother.

Otherwise, it still draws 2.7-3 amps running whether it's 240v from the PEA or 220v from the genset.

So, I guess that's the way it is.

[Pib]

Yea, without knowing exactly how different pump manafacturers develop their wattage ratings we are all guessing. But my guess is they develop the rating over a certain time period of use which averages out the on and off pump cycles. Say over a 60 second period the pump ran for 30 seconds (or minutes, hours, or days) drawing 500 watts and then for the next 30 seconds it was off not drawing any power....average power usage over those 60 seconds would be 250 watts. Then again, my guessing right percentage ain't that great.

[T_Dog]

Yea, without knowing exactly how different pump manafacturers develop their wattage ratings we are all guessing. But my guess is they develop the rating over a certain time period of use which averages out the on and off pump cycles. Say over a 60 second period the pump ran for 30 seconds (or minutes, hours, or days) drawing 500 watts and then for the next 30 seconds it was off not drawing any power....average power usage over those 60 seconds would be 250 watts. Then again, my guessing right percentage ain't that great.

Spec'g a pump like that would not make any sense. I just measured my Hitachi 300gx. The current draw nudges up to 3.4 amp before it shuts off. 3.4 amps times 242 volts is over 800 watts and not anywhere near 300. So now I know why this little pump acts like a 1 HP unit back in the west!

[electau]

Your pump may be rated at 280 watts output mechanical power, you are measuring input power in amps.

Efficiency % = output /input x 100.

[Pib]

Your pump may be rated at 280 watts output mechanical power, you are measuring input power in amps.

Efficiency % = output /input x 100.

That's probably the answer...we were too hung up on "electrical" power.

[bankruatsteve]

Yeah, I suppose that could be the reason for rating that way and perhaps related to the head. But when almost all (?) appliances are rated on consumption, I remain a bit skeptical. In any case, I am only interested in the actual electric demand and that is what it is. Cheers.