Dive compressor install questions

[Tornadosailing]

Originally Posted by Ivansgarage

The automatic operation refers to, it shuts off at desired tank fill 2800 or...
never needs to restart under head pressure.

You assume that I'm going to fill one tank and go diving by myself. If I plumb a fill manifold and fill two tanks at a time, then disconnect from those tanks and connect two more tanks, the compressor does in fact need to restart.

[Thuid]

I haven't done much research on dive compressors, but just for giggles; Is there such a beast as a higher output electrically clutched compressor that could be added to the main or an auxiliary diesel engine?

Sounds like you need a higher output compressor anyway with your typical refill use of six divers at a time. Higher output should draw some horses on the engine so it is loaded.

[Thuid]

The other thing to think about is if you are going to be a bit more than casual filling. It may be more benefit to have a cascade system like fire fighting, with a large cascade bottle that is filled by compressor but allows you to fill a bunch of bottles before/while using the compressor (or be refilled on shore power or air supply maybe).

All depends on your desired usage though.

[Tornadosailing]

For the next couple of years the intended use is to put myself and girlfriend, plus four more diver friends on the boat for a week at a time and do 10-12 tanks each over the course of a week. Repeat 4-6 times a year. After that I should be able to drop the dock lines and go cruise so the usage would end up being much fewer tanks but more often. Something along the lines of maybe 4 tank fills a week average. Maybe less depending on where we are.

Not really wanting the added cost and weight of a cascade system that would only be really useful for a couple of years. Plus I believe they have a similar visual inspection/hydro/lifespan schedule as a dive tank.

I've seen pics of engine driven compressors. They seem big and clunky, not to mention right in the way of servicing the engine.

[AHoy]

I work for a VFD manufacture now and was a service tech for years, I think I and can provide some insight here.

As others mentioned a VFD will eliminate the inrush current of the motor.

A VFD and a soft start are NOT the same thing, a soft start (reduced voltage starter) will reduce the inrush but on a 3 phase induction motor you will still see around 3x inrush.

A wash down enclosure VFD would most definitely work here but I think it is overkill and as long as the boards are conformal coated a normal (NEMA 1) enclosure unit should work for many years and be much less expensive.

Most VFDs are very easy to program especially for this application. I can say my inverter / charger is more difficult to program than any 230/460V VFD I have worked on.

You do want to make sure the motor is "Inverter Rated" most are these days but if it isn't your motor can fail prematurely.

I would not recommend having any sensitive equipment connected to the generator while running the VFD. It will create a very large amount of harmonic distortion that can damage electronics.

There are VFDs that are marketed as single phase input that will work. Also for many manufactures you can use an oversized (5Hp motor with 7.5HP or 10HP VFD) 230V 3ph unit on single phase as long as the programming allows you to turn off the input phase failure detection. If you are not sure call the manufacture and they will tell you.

[Tornadosailing]

Originally Posted by AHoy

I work for a VFD manufacture now and was a service tech for years, I think I and can provide some insight here.

As others mentioned a VFD will eliminate the inrush current of the motor.

A VFD and a soft start are NOT the same thing, a soft start (reduced voltage starter) will reduce the inrush but on a 3 phase induction motor you will still see around 3x inrush.

A wash down enclosure VFD would most definitely work here but I think it is overkill and as long as the boards are conformal coated a normal (NEMA 1) enclosure unit should work for many years and be much less expensive.

Most VFDs are very easy to program especially for this application. I can say my inverter / charger is more difficult to program than any 230/460V VFD I have worked on.

You do want to make sure the motor is "Inverter Rated" most are these days but if it isn't your motor can fail prematurely.

I would not recommend having any sensitive equipment connected to the generator while running the VFD. It will create a very large amount of harmonic distortion that can damage electronics.

There are VFDs that are marketed as single phase input that will work. Also for many manufactures you can use an oversized (5Hp motor with 7.5HP or 10HP VFD) 230V 3ph unit on single phase as long as the programming allows you to turn off the input phase failure detection. If you are not sure call the manufacture and they will tell you.

Thank you. I'll make sure the motor is rated correctly.

I was intending to install an isolation switch so the only load would be the compressor simply to make sure no one accidentally turned on AC chillers etc. Isolating harmonic distortion is one more good reason to make sure it's fully isolated.

[svJasmine]

are you sure changing the phase will reduce the current? Maybe the amps are lower, but you are raising the voltage. Current is current. There are no magic bullets here.

[Tornadosailing]

Originally Posted by svJasmine

are you sure changing the phase will reduce the current? Maybe the amps are lower, but you are raising the voltage. Current is current. There are no magic bullets here.

5hp 230V single phase pulls 28 amps. 5hp 230V 3 phase pulls 15.2 amps. It's just more efficient.

Bauer Air Compressors -- Power Usage

[Pelagic]

What is the feasibility of powering a small dive compressor with 24vDC motor?

[Brewgyver]

Pelagic,
The short answer is your boat would sink.

Seriously, it would take literally TONS of batteries, and you’d need the genset anyway to charge them.

Or was that a joke, and I’m just being dense?

[Pelagic]

Originally Posted by Brewgyver

Pelagic,
The short answer is your boat would sink.

Seriously, it would take literally TONS of batteries, and you’d need the genset anyway to charge them.

Or was that a joke, and I’m just being dense?

Lol....probably just me being dense

I have been following the thread on Best Generator and the evolution towards LFP batteries and DC Generators.

I just started this thread

http://www.cruisersforum.com/forums/...d.php?t=193694
to review my own 65 ft boat's evolution.
If the dive compressor was mounted to minimize cable runs and in concert with a DC generator.....

My non technical thinking is that we use DC for high load starts....Main Engine, Bow thruster....

..... So.....Is a DC powered dive compressor still a dumb idea?

I really don't know??

[AHoy]

If you need a 5hp motor for the dive compressor and convert that to watts your load is 3729 watts. If no losses are taken into account the compressor will require 311 amps at 12v continuously. To fill a few tanks the dive compressor would need to run for an hour or more. It just requires too much power for almost any 12V DC system to provide.

[Pelagic]

Thanks Ahoy....but to clarify....my system is 24v and I would be running a sizeable diesel DC generator at same time to feed compressor load and replenish battery and other DC loads

So assuming 160amps at 24v needed to continuously run dive compressor and say a diesel DC generator that could provide about 400amps @24v of charging power

Does DC handle the initial high cranking load better than AC?

[Tornadosailing]

You'd have to get a continuous duty cycle motor with lots of ability to cool itself. You'll have to dissipate over 3000 watts of heat for an hour straight. I think in terms of the starter on a car. You're basically cranking the engine on your car for an hour straight. Granted, it's fewer amps because it's higher voltage, but the heat output doesn't change.

[nwdiver]

Another option hydraulic PTO on your gen set or main and use that for power, Bauer makes in install that uses hydraulic