Big AC motors

geem said:
The 277 and 247 Cat pumps can both use a 1.5kw motor. They can be used with a couple of 21" membranes all the way up to 3x40". From about 70l/hr to 200l/hr range of output.
If you run them from a belt drive, I am sure you could slow the pump down to use less hp on a smaller motor for low output. For me, we want the maximum output for the system to give is a high litre/Watt. It uses less power and we have less run time on the system
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@geem
unless I'm mistaken, it's not a good idea (ie filmtek/dow don't recommend it!) to run the membrane at less pressure to achieve less output as the membranes tend to gum up with deposits and eventually are rendered useless.
@Kelpie
I'd definitely NOT buy anything like a motor before I would get the rest on my hands! You may end up buying things that wont fit either on existing frame, or with incompatible mounting, or, or...

PS. study a bit the motor frame sizes, front plate options re sizes and clearances, keys for mounting pulleys.
 
vas said:
@Kelpie
I'd definitely NOT buy anything like a motor before I would get the rest on my hands! You may end up buying things that wont fit either on existing frame, or with incompatible mounting, or, or...

PS. study a bit the motor frame sizes, front plate options re sizes and clearances, keys for mounting pulleys.
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Oh absolutely!
I've already got the membrane block but that was given to me by a friend.
Not spending any money until I have a viable plan.
 
Squinting at the dessalator website the 100l unit has a 4 pole 1.1kw motor with a 80 or 90 frame size, most makers use a 90 frame for 1.1kw. I speculate that the AC motor is over-rated to provide enough starting torque.
 
penfold said:
Squinting at the dessalator website the 100l unit has a 4 pole 1.1kw motor with a 80 or 90 frame size, most makers use a 90 frame for 1.1kw. I speculate that the AC motor is over-rated to provide enough starting torque.
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If a larger motor is fitted, will it not actually use as much power as rated, because it's not having to work so hard? Or does it not work like that?
I'm curious as to why the DC version can apparently generate 100l/hr on just 700w.
 
Just to reiterate AC motors come in 2 forms. One is the brush type motor as found in vacuum cleaners electric drills, sewing machines and small appliances. They work just like a DC motor. Speed is dependent on load. As speed increases back EMF opposes in volts to limit max speed. (usually quite high) They are not as reliable as induction motor.
Here the AC forms a rotating filed which pulls the rotating element around. 3 phase has 3 rotating fields giving better start torque. Single phase is a bit like bicycle pedals pushing down and not necessarily around until you start rotation. Hence single phase motors must have a phase shift capacitor or coil switched out after start.
The speed of the motor is dependent on the rotational speed of the field and will be 1500 RPM for dual p[ole or 3000RPM single pole. Now because that is the speed of the rotating field actual motor speed must lag behind to get torque so typically 2750 RPM or 1450 RPM depending to some degree on load.
As said an induction motor has only bearings and possibly a centrifugal switch which might fail. So are very reliable. Found in old washing machines refrigerators water pumps and heavier machinery. I would expect you would use an induction motor in a water maker. NB induction motors require pure AC and will over heat on square wave inverter. While brush motors are happy on any wave form including DC. ol'will
 
What you want is something such as shown in the link. Assuming your inverter is pure sine wave, as noted by WH. You then have to decide how to couple it to the pump!

1.1kW (1.5hp) Single Phase Motor 4 Pole (1500RPM) 90S Frame

Just to be utterly pedantic. They are small motors a big one would sink your boat ;)

PS. The difference between the quoted DC and AC power is all to do with Power Factor in AC circuits. don't worry about it. Gets all complicated. ;)
 
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If you drive a syndromes motor with a variable frequent inverter you can adjust the speed by adjusting the frequency output of the inverter
 
andsarkit said:
It has been a while since I worked with AC motors but I remember the following.
The vacuum motor will be a lightweight universal motor with brushes and is not really suited to continuous use. I have had a Dyson go up in flames and my little strimmer has just given up with a lot of smoke.
The better motors are induction motors which have no brushes and little to wear out except the bearings. They are designed to work on 3 phase and so need a capacitor to create a phase shift in one of the windings and start the rotation. The capacitor can be switched out after starting with a centrifugal switch or left in circuit if it has a continuous rating. These motors tend to have a cast frame and will be much heavier.
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Sorry, I don't mean to "nit pick" but that is confusing. 3 phase motors are just that, 3 phase. Single (1) phase motors are also just that, single phase. Totally different animals. The single phase is the one that needs the phase shift capacitor for start or start and run. I won't further confuse the issue with all the variants of both types, not applicable in this thread! The OP needs simple answers not theoretical confusion!
 
vas said:
@geem
unless I'm mistaken, it's not a good idea (ie filmtek/dow don't recommend it!) to run the membrane at less pressure to achieve less output as the membranes tend to gum up with deposits and eventually are rendered useless.
@Kelpie
I'd definitely NOT buy anything like a motor before I would get the rest on my hands! You may end up buying things that wont fit either on existing frame, or with incompatible mounting, or, or...

PS. study a bit the motor frame sizes, front plate options re sizes and clearances, keys for mounting pulleys.
Click to expand...
The 247 and 277 pumps will operate in the range of 600GPD to 2100GPD. This causes no problems of flow rate, although the 3x40" membranes is on the limit of scavenging velocity on the third membrane with a 1.5kw motor at 1450rpm. The third membrane will see some salt build up towards the end of thr membrane. I used to run 2x40" membranes and then a single 21" membrane as the third in the row. This didn't suffer from salt build up. With that set up, we made 175/180 litres per hour. When the 21" housing developed a leak ( very old), I replaced it with a 40" as they were the same price for housing and membrane as the 21". A friend has been running the same pump, motor and membrane set up for 20 years without problem.
Our pump is direct drive, not belt driven. There are opportunities to vary the pump speed and the membranes are quite tolerant of varying flow/velocity
 
geem said:
The 247 and 277 pumps will operate in the range of 600GPD to 2100GPD. This causes no problems of flow rate, although the 3x40" membranes is on the limit of scavenging velocity on the third membrane with a 1.5kw motor at 1450rpm. The third membrane will see some salt build up towards the end of thr membrane. I used to run 2x40" membranes and then a single 21" membrane as the third in the row. This didn't suffer from salt build up. With that set up, we made 175/180 litres per hour. When the 21" housing developed a leak ( very old), I replaced it with a 40" as they were the same price for housing and membrane as the 21". A friend has been running the same pump, motor and membrane set up for 20 years without problem.
Our pump is direct drive, not belt driven. There are opportunities to vary the pump speed and the membranes are quite tolerant of varying flow/velocity
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good to know, was going by what I was told...
 
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