Amps for 2HP AC watermaker

[willyritch]

I’m going to install a large AC powered watermaker and I’m trying to figure out how much current it will use. I can spec a 1.0, 1.5 or 2.0 HP motor. We have a 10KW generator so plenty of power to run the biggest one and the additional cost is marginal. So that’s an easy choice. But as a backup, we would run the watermaker with an inverter and I can’t find any good information on what the startup and running current consumption of those motors would be.

Everything is 230vac and our inverter can maintain 3kw at 230vac and handle inrush loads up to something like 6kw.

I think we would always want to run our engine when using the watermaker-inverter combo—and the alternator puts out 95 amps at 24vdc so there should be sufficient power there

If anyone has a larger AC watermaker and has experience with current consumption insure would like to hear it.

Thanks

[SailingHarmonie]

At full load, a 2hp 230v motor will draw 12 Amps. Which will likely require about 120 Amps at 24V into your inverter. A 1hp motor, about 8 Amps. No, it’s not totally linear. Start up load is hard to predict accurately, since it depends on the load, but 3 to 5 times the full load current is a good guess.

It’s not clear to me it you are selecting between different watermakers or just different motors? If you can generate the pressure and flow rate you need with a 1hp motor, why would you install a 2hp? There would be no benefit.

On the other hand, if you need a 2hp motor to feed the water flow and pressure, a 1hp motor will not work.

[willyritch]

Thanks for that info.

The watermakers (Sun Pure) are offered in several different configurations with different sized motors and different outputs.

[jamhass]

A good rule of thumb is 1 hp equals 750 watts (748 if you want to be picky.) This is independent of voltage, etc, but also ignores inevitable losses. Generally, add about 10% should cover most losses (motor loss, inverter loss, line losses, and so on.)

Also, starting current can be considerably higher, and if you are pushing the limits of your power source (gen set, inverter etc) you may need a soft-start kit.

[Orin]

Originally Posted by willyritch

Thanks for that info.

The watermakers (Sun Pure) are offered in several different configurations with different sized motors and different outputs.

Need more info here to give you a conclusive answer. What you’ll want to look at is the locked rotor amps of the motor. Seems like with a normal motor and installation the most I would want to do is about a 1hp motor on that inverter. You’ll want locked rotor amps to be below around 25A if the inverter is powering nothing else.

What model of water maker are you looking at?
Edit: I read that wrong. Let me look up the sun pure water makers and get back to you.

[Orin]

So it says on their webpage that these units come with a soft start. Depending on the soft start it will reduce inrush by 35-70% with the likely case being closer to 35%.

This isn’t enough that I would feel confident running anything other than the 1hp without contacting the manufacturer and asking for the nameplate data for the motor.

[Jammer]

Originally Posted by willyritch

Everything is 230vac and our inverter can maintain 3kw at 230vac and handle inrush loads up to something like 6kw.

Here is the nameplate from a fairly typical 2hp motor of the type used on watermakers.





The KVA code is D. Here's what the codes mean:


(see attachment)



Since this is a 2 hp motor, we multiply 4.3 (from the table) times 2 (horsepower), to get a starting KVA of about 8.6. That exceeds the 6 kw surge capacity of your inverter, so the motor may not start. If the watermaker has a bypass for the pump (most that I've seen don't) then your chances would be better.


But for the analysis to work you really need to look at the nameplate of the motor actually used on your particular watermaker. A fact to consider is that smaller motors tend to have higher code letters so the benefit (from a surge management standpoint) of switching to a smaller motor is reduced by that somewhat.


24v DC motors are available up to 2 hp and are a drop-in replacement mechanically for AC motors in many cases. That would be my choice:



https://www.electricmotorwholesale.com/LEESON-109106