Converting a 110v watermaker to 12v DC?

[Privilege]

I've been given a complete Prowatermaker (21 gph) system which includes all filters etc...the pump is a 1.5hp 110v A/C but needs replacing. Although I have a genet, I also have a large solar panel array which recharges my batteries by mid-morning and then has nothing to do with the excess power. It therefore makes sense for me to have a 12v DC watermaker system.
As the pump is the only part of the system that needs power, can I just replace it with a 12v version? I realize that I won't be able to match the gph output but that's OK. Does the pump need to be matched to the membrane filter?
Thanks.

[Cheechako]

I have done this. The problem is you cant find a 12v motor that is 1.5 HP and if you could it would draw a zillion amps. I took the motor off mine and mounted the HP Pump on the engine with a fabricated bracket and a new 12V clutch. I also got rid of all the fancy water sensing controls which never did work right on the 120V unit.
1.5 hp is approximately 1200 watts right? That would be a 100 amp draw at 12 Volts!

[Privilege]

Yeah, I worked out that I couldn't match the 1.5hp in a DC pump so don't expect to get anywhere near the 21gph...but I'd settle for a third of that. Will a DC pump work with the membrane filter though?

[Cheechako]

There are some more knowledgeable than me on this forum, but you need a High Pressure pump. The pump needs to run a minimum 600++ PSI and pumps only come so small, so you will need a certain amount of HP just for it to make water. That's what I think I know anyway....

[skipmac]

Originally Posted by Cheechako

There are some more knowledgeable than me on this forum, but you need a High Pressure pump. The pump needs to run a minimum 600++ PSI and pumps only come so small, so you will need a certain amount of HP just for it to make water. That's what I think I know anyway....

This is also my understanding. If you can't reach a certain minimum psi the water will not pass through the membrane and it will not be reduced capacity but essentially no output at all

[a64pilot]

You don't need a DC pump, just a DC motor, your pump is still good?
It can be done, but I'm gonna guess the load will be around 130 amps, how many hours can you pull that from your batteries?

If you could run a high output watermaker off batteries, you could run a a decent sized Airconditioner too, most can't.

I think if the pump didn't have enough volume to go along with the pressure, you will ruin your membrane as your not flushing enough water past the membrane to carry away the waste.

You have a genset, stay with AC. If you want DC, sell it and buy a Spectra.

[nimblemotors]

1.5hp is about 1200 watts, 12v at 100amps.
Solar isn't going to keep up with that, how long you want to run it?
Can the batteries delivery 100amps without killing them?

[accomplice]

My 4x4d house batteries are regularly called on to supply 1200w at a time without a problem. They power a 4000w inverter!
(Although I rarely use 4000w)

Your point about power is a good one though. Even if one only ran the water maker for an hour, consuming 100ah, how long will it take to generate that much excess power? And one hour with a 1.5hp motor will only produce 21 gallons.




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[Privilege]

Thanks guys. Maybe I didn't explain myself properly but although I understand the concept and electrics, I'm new to watermarking. I know I can't match the performance of the AC model, pumping out 100+ DC amps is not practical. But you can buy DC watermaker systems using anywhere between 10-20amps and obviously creating high pressure water for the membrane and producing 5-10 gph. So, seeing as I already have the rest of the system, can I buy a DC motor (Thanks a64pilot) to match my system or is the membrane going to need the full performance of the AC pump to work properly?

[SV THIRD DAY]

Originally Posted by Privilege

Thanks guys. Maybe I didn't explain myself properly but although I understand the concept and electrics, I'm new to watermarking. I know I can't match the performance of the AC model, pumping out 100+ DC amps is not practical. But you can buy DC watermaker systems using anywhere between 10-20amps and obviously creating high pressure water for the membrane and producing 5-10 gph. So, seeing as I already have the rest of the system, can I buy a DC motor (Thanks a64pilot) to match my system or is the membrane going to need the full performance of the AC pump to work properly?

The difference in those low and reasonable 12v power usage water makers is that they are using an energy recovery pump, the one you have with Prowatermaker is a nonengery recovery power HOG, so there is no real way to make it efficient...it's all about the pump and HOW it gets the water up to 800PSI.

The Big question you didn't tell us yet is the volume of your Hp pump?
Based on the 1.5Hp motor I'm guessing 2.3GPM??? You can't just do a motor swap out to lower the pump's volume because on a positive displacement pump, you have to match the motor-Pump-Membrane surface area up. So a 1/2 Hp motor would stall out on your larger 2.3GPM Hp pump. If you want to change motors, you either have to STAY at the same Hp OR change both the pump and motor as a set.

We do 7-10 of these "I have pieces and want to do X with it" projects per month, so I'm happy to help balance out your Hp Motor/Pump/Membrane combination based on what you want to do. I'll also scream STOP...that won't work...if I see you running off the rails. So just shoot me an email at Rich@cruiserowater.com and I'll be happy to help.

[Tellie]

I think you're trying to reverse engineer this thing when the easiest way is to just replace/repair the bad pump and bolt it back on to the 110 motor. You already have a capable genset. Let the solar array take care of your other electrical charging needs. Trying to convert this to a 12Volt system with any real end satisfaction to dollars spent won't make a lot of sense. A 21gph PRO watermaker is probably the PRO500 series. A better bet would be to increase your existing system to a higher capacity watermaker 900-1200gpd by adding a second/third membrane. Check with PRO on this but I believe they've always claimed this can be done with your existing motor and pump. The amp draw will increase some on the genset so knowing your gensets kw rating is important. But in the long run making more product water faster with 110V makes far more sense than reducing capacity with 12V at what would be, I would guess, about the same cost investment.

[SV THIRD DAY]

Originally Posted by Tellie

But in the long run making more product water faster with 110V makes far more sense than reducing capacity with 12V at what would be, I would guess, about the same cost investment.

Tellie just nailed it!
Once you make the decision to go 120v/AC then you want to make as much water as possible to minimize the generator run time. With your current 21GPH output and pump/motor set-up you can add a second pressure vessel/membrane for about $750 and turn it into a 30GPH unit for about the same power.

[OneTwoSail]

If you have a 4000w inverter why not just let that feed the watermaker 110v from the batteries instead of the generator?

[skipmac]

Originally Posted by patrickza

If you have a 4000w inverter why not just let that feed the watermaker 110v from the batteries instead of the generator?

Because you will still be drawing 100 amps or more from the batteries to run inverter to run the pump motor. It's all a matter of the total power you need or Watts at then final load. Doesn't matter whether you get it from inverter or generator or batteries.

If the pump is using about 1200 Watts in 120V AC that is only 10 amps but to get 10 amps at 120 V from an inverter you have to feed 100 amps at 12V DC. Not many boats have batteries that can do this for long enough to make water without running the engine or generator to charge the batteries. Even then a lot of boats don't a have an alternator or battery charger than can put out a solid 100 amps continuous.

[diver61]

All of the above posts have good points. I am a marine engineer with deep knowledge of water hydraulics and such.First of all you need to match a motor to the pump that will run at the same speed as the ac motor(1750 rpms) in order to match the gpm requirement for the hi pressure pump. Water in equals supply and the demand for the pump. Not enough water = low pressure. All other concerns (amp draw and hp ) don't matter if you cant feed the pump. If you put a smaller pump you still have the problem of water in and water out. It takes about 8 gals of salt water to make one gal of fresh water, the membranes are sized to fit the output of the hi pressure pump so you could get smaller membranes or take one out ,if it has more that one.All of this being said keep what you got and use as is or get a 12 lt system. Hope this helped some.GARY