Big AC motors

[Kelpie]

I'm looking at putting together a watermaker and will need a motor to drive it. Seeing as I already have a large AC system onboard, it probably makes sense to go AC rather than DC.

The hard bit will be sourcing a decent industrial type motor out here in the Caribbean. Needs to be around 700w/1hp. I could get something easily enough in the UK but at around 10kg I may have reached the limit of what SWMBO is willing to cart around on her upcoming trip home.

So my question- does it actually have to be a big industrial motor? Surely watts are watts?? I have a vacuum rated at 1kw, couldn't I just use a motor like that, and adjust the pulley sizes?? I'm guessing a smaller motor will be faster and with less torque. But if the power is there, is there any reason it won't work?
Another option I have is my Bison outboard which is defunct these days, it's rated at 686w and is 12v.

 

[Daverw]

you need to check the motor name plate

 

[andsarkit]

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.

 

[Kelpie]

you need to check the motor name plate

What am I checking for?

 

[Kelpie]

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.

Thanks! I think I understand now.
Quite a few people have built watermakers using a pressure washer motor/pump assembly. I presume they're running the risk of burnout, not something you'd want in a boat

 

[Stingo]

Speak to https://www.cruiserowaterandpower.com/ who were exceptionally helpful when my watermaker died. They shipped the parts to SXM very reasonably.

 

[rogerthebodger]

1 hp is not big for an industrial AC motor.

I have several AC motors on my boat driving my water maker , a dive compressor (200 bar) and a low pressure compressor 100 psi

Go fro one wht an aluminium finned frame for lightness some are case iron .

What voltage do you need and do you only have single phase of do you have 3 phase availabel (3 phase tend to be more efficient and possible smaller

You also need to look at the mounting style, My water maker motor is a foot and flange mounting as the HP pump is flange monted and the motor and pump is then foot mounted

My dive compressor is a foot mounting driving the compressor using Vee belts and pullies where as my water is direct drive.

The pump will also dedicate the speed of the motor 1500 rpm or 3000 rpm

There are also 3 phase inverted that can be used with 12VDC to convert to 3 phase.

Lots of options and decisions to make

https://flic.kr/p/WYNt2v

Just right of my battery charger is my water maker pump

https://flic.kr/p/WYNKPt

My dive compressor before I converted it to electric so I could run it onboard from a generator or shore power

I made it so I could replace the electric motor with the Honda engine for use on the beach

TEC Single Phase Electric Motor, 0.75KW, (1HP), Foot & Flange Mounted(B35), 3000rpm(2 pole), IE1 efficiency, 80 Frame, Aluminium Body

 

[Kelpie]

My two options are 12v DC or 240v single phase from the 3kva Victron inverter.

Looking at the specs for the watermaker, the DC version needs 700w and the AC version needs 1100w. Both to produce 100l/he. What's the explanation for that? It's a huge difference.

 

[rogerthebodger]

My two options are 12v DC or 240v single phase from the 3kva Victron inverter.

Looking at the specs for the watermaker, the DC version needs 700w and the AC version needs 1100w. Both to produce 100l/he. What's the explanation for that? It's a huge difference.

Motor speed and efficiency

Give us the specs for the pump and the membrane

 

[Bilgediver]

What am I checking for?

The motor rating for starters.

Is it Intermittent rating or Continuous. what is rotational speed and how does it relate to the speed at which the load requires to operate to meet its rating. can thie difference be handled with just different sized pulleys?

 

[Kelpie]

The motor rating for starters.

Is it Intermittent rating or Continuous. what is rotational speed and how does it relate to the speed at which the load requires to operate to meet its rating. can thie difference be handled with just different sized pulleys?

Unfortunately the original motor is missing, and whilst the manufacturer of the watermaker can supply a replacement (at great cost!) they don't say what specification it is.
I've been doing some digging and I know of three different motors that can be used to run this pump.
Must admit I'm feeling a bit out of my depth, it's not an inconsiderable amount of money. Although still far cheaper than an off the shelf unit.

 

[penfold]

What's the make and model of the watermaker? What are the physical constraints of the motor; how big a space does it have, what are the mountings and shaft coupling?

 

[geem]

What speed does your pump turn at? Is it direct driven or belt? My cat 247 pump is running a 1.5kw 220v motor at 1450rpm. Standard motor off the shelf. We produce 200 litres per hour.

 

[vas]

just summing up some of the previously mentioned info and adding a bit more (I hope)
1kw is not going to be enough to run a decent pump. 1.5kw would
At a guess and from looking around at all sorts of cat and wm (iirc) pumps, they run at 1400-1500rpm, so a 4pole motor (iirc again, been some time I was playing with all that) with 1:1 pulleys
Kelpie, no way a decent motor is going to be 10kg! 25+ I recon. At least my HRO motor was around that.

Assuming original setup had pulleys (usually they are direct coupled!) you'll need to get that into consideration and figure out pulley sizes, find the right one for the motor shaft, mounting on hopefully existing frame, silent blocks to reduce noise when running, etc etc...

if you want to keep it cheap and accept that you're going to be around when running the thing (avoid fire...) I'd go for the karcher motor option tbh
Mind it's noisy, whenever I get it running I take a half hour swim

 

[Kelpie]

It's a Dessalator 100l unit, I'm trying to find out what sort of pump it uses- possibly a CAT 277. I've seen different figures for how much power of will need. Dessalator themselves say 700w for the DC version but 1100w for the AC, which I don't really understand.

 

[Kelpie]

just summing up some of the previously mentioned info and adding a bit more (I hope)
1kw is not going to be enough to run a decent pump. 1.5kw would
At a guess and from looking around at all sorts of cat and wm (iirc) pumps, they run at 1400-1500rpm, so a 4pole motor (iirc again, been some time I was playing with all that) with 1:1 pulleys
Kelpie, no way a decent motor is going to be 10kg! 25+ I recon. At least my HRO motor was around that.

Assuming original setup had pulleys (usually they are direct coupled!) you'll need to get that into consideration and figure out pulley sizes, find the right one for the motor shaft, mounting on hopefully existing frame, silent blocks to reduce noise when running, etc etc...

if you want to keep it cheap and accept that you're going to be around when running the thing (avoid fire...) I'd go for the karcher motor option tbh
Mind it's noisy, whenever I get it running I take a half hour swim

I'm just working off the information I can find about the unit at originally built.
It was designed to use a belt drive and the total weight, including a three chamber membrane block, was 45kg.

It is tempting to simply pick up a Karcher but a couple of friends have tried this... very very noisy, low output for the power use, and they don't seem to last very long.

 

[vas]

so you haven't actually bought it yet, so cannot read labels and see what's what?

V.

 

[Kelpie]

so you haven't actually bought it yet, so cannot read labels and see what's what?

V.

It's a bit complicated tbh. But yes I don't have the old motor... or the pump, right now. Looking in to it.

 

[geem]

It's a Dessalator 100l unit, I'm trying to find out what sort of pump it uses- possibly a CAT 277. I've seen different figures for how much power of will need. Dessalator themselves say 700w for the DC version but 1100w for the AC, which I don't really understand.

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

 

[geem]

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

This might help