Dive compressor install questions

[Pelagic]

Thanks, that sounds like a better option because of less heat generation.

[MarkusK]

Originally Posted by Thuid

There used to be "Soft Start" units available for compressors and pumps that were a smaller form factor than a VFD. But with the prices of small VFDs falling they may have disappeared. They typically were simpler to install and had a little more robustness as require no to little programming.

If going with VFD just make sure the motor is rated for VFD operation (cheap motors tend to pit their internals over time if not) and that you may need line filtering on the incoming and/or outgoing cables depending on length of runs and harmonics being generated.

Are you referring to bearing failure? If so, you need a shaft grounding ring on the motor.

Here is an informative article: http://www.est-aegis.com/js/AEGIS_HV...toneSupply.pdf

Granted, the HVAC VFD is full-time use and OP dive compressor VFD is part-time use but eventually the hours add up so a shaft grounding ring is a good accessory to install.

[Thuid]

Originally Posted by MarkusK

Are you referring to bearing failure? If so, you need a shaft grounding ring on the motor.

Here is an informative article: http://www.est-aegis.com/js/AEGIS_HV...toneSupply.pdf

Granted, the HVAC VFD is full-time use and OP dive compressor VFD is part-time use but eventually the hours add up so a shaft grounding ring is a good accessory to install.

I am referring to the internal motor construction e.g. windings and rotor. But yes induced currents also come into play. On cheaply manufactured motors (e.g. ebay non-vfd rated), sometimes the varnish/insulation just can't handle the high frequencies and harmonics at elevated temperatures that users attempt to drive them at. And will eventually pit and cause an internal failure. Not so much an issue with newer off the shelf brand motors as they are a bit higher quality insulation usually, but still advisable to spend the few extra $$ and get a VFD rated over a non rated. Especially if it is going to be driven to it's limits at times under harsh environments. I would also recommend a sealed motor as you definitely don't want salt air being drawn through an open frame motor for cooling.

[Jammer]

Originally Posted by Tornadosailing

I'm not 100% sure I do, but the 3 phase motor definitely reduces the running current. Can't do 3 phase on a single phase genset without some sort of phase converter.

This is illusory. The power consumed is roughly the same. If you use a VFD with a single phase input and a 3 phase output the input current will be roughly the same as for a single phase motor of the same size and with the same load.

The math is complicated, but a 3-phase circuit delivers 1.732 times as much power as a single phase circuit with the same current and voltage. (square root of 3).

[Jammer]

Originally Posted by Tornadosailing

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

Talk to Jim Sheldon at Shelden Sporting Goods Inc. - High Pressure Air Compressors if you want to do this. He has a number of smaller lighter weight compressors that work well for that.

[Jammer]

Originally Posted by Pelagic

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

Actually there are some 28 volt DC compressors still out there that were used in 1950s era military aircraft. 1800 PSI max, but some people use them for diving with LP steel cylinders (2450 PSI) and run the compressor slightly beyond its rated pressure. I believe they are about 1 cfm so it takes about an hour to fill a cylinder. The power draw is substantial. I wouldn't necessarily recommend that approach, but it could work in some situations.

[Jammer]

Originally Posted by Tornadosailing

I'm looking at installing a Bauer Oceanus compressor on my boat and have a few things to work out electrically.

The boat has a 9KW gen set and I was thinking I should install a main switch to switch power between the compressor and the rest of the boat. As in, I can run either the compressor, or anything else on the boat, but not both so I don't overload the generator.

I was also intending to buy the compressor with a 3 phase motor so I can use a VFD to keep the start current down. The 3 phase motor also draws half the amperage of the single phase motor, 15A vs 30A.

What I need help with is the VFD and how to wire it. I've seen a few out there, but some of them look pretty complex programming wise, and I don't see many that are made for the marine environment. I think I should get one capable of handling roughly twice the run current of the compressor motor. Any suggestions?

So some advice.

First of all, size the compressor to what your genset can handle. The Bauer Jr II is available in 2HP or 3HP. If you want an Oceanus, you can put a smaller motor on it with a proportionally smaller pulley. There are other small compressors available. I have a Kidde that is rated 2.4 cfm that runs off a 2HP motor that I am putting together, for example, hard to find now but they are out there if you look.

You are going to want to start the compressor unloaded. Generally this will be a manual process for the small compressors you are looking at although if you are willing to accept the cost, space requirements, and complexity of automatic drains you could get them. Because the compressor starts unloaded, you will be able to accept a greater amount of voltage drop while starting than you would for, say, a centrifugal pump. So there is no need to overthink this, just be sure you're within reasonable hailing distance of what your genset is supposed to be able to start.

Any compressor is going to be loud and is going to produce a considerable amount of heat. Plan accordingly. If you're going to run it below deck then you will need ventilation.

You may find that you're better off with a receiver/cascade of some kind rather than having more than one dive cylinder per diver. There are all kinds of different ways to set things up but the short of it is that with a reasonable sized compressor you can't keep 6 divers happy without having more than 6 cylinders (counting both dive cylinders and cascade). The advantage of a receiver/cascade in this situation is that you don't have to handle it, you can find some place to put it and mount it there permanently, which can reduce clutter on deck.

[Lepke]

For me a better solution to filling tanks is a belt or direct drive compressor off the main engine. You can have a bigger compressor for fast tank fills and don't have all the cost of specialty electric equipment that's eventually going to be impacted by the marine environment. You plan on running a generator, thru a VFD, and then an electric motor spins the compressor. Each transition has a loss.
My experience with gas driven compressors is spending my time filling tanks instead of diving. Two of three dives a day instead of five.

[Pelagic]

Hi Lepke.....That is another consideration

I have 2 extra large pulleys off of front of my 6 cylinder Perkins and filling underway would be easy

What approx RPM do small compressors need to run at for 3000 psi fills?

[transmitterdan]

Most engines are not rated for significant HP off crankshaft pulleys. Check with the manufacturer before doing anything with belt drive from a propulsion engine. You can wreck the bearings and seals pretty easily with large HP side loads.

[nwdiver]

Originally Posted by Pelagic

Hi Lepke.....That is another consideration

I have 2 extra large pulleys off of front of my 6 cylinder Perkins and filling underway would be easy

What approx RPM do small compressors need to run at for 3000 psi fills?

Front of engines is fine, drive shaft side loads not so good......

Re: rpm depends on the compressor, some compressors increase filling with increased rpms, some blowup..........also off your main use a 8-10 cfm continuous duty into a 2-3 tank storage system, load up when you use the motor, use the air as needed to fill your tanks......

You have a big boat so this may be doable........

Rpm 1250-1400 or so

[Pelagic]

Originally Posted by nwdiver

Front of engines is fine, drive shaft side loads not so good......

Re: rpm depends on the compressor, some compressors increase filling with increased rpms, some blowup..........also off your main use a 8-10 cfm continuous duty into a 2-3 tank storage system, load up when you use the motor, use the air as needed to fill your tanks......

You have a big boat so this may be doable........

Rpm 1250-1400 or so

Hi nwdiver

I have been looking at this Dive Compressor discussion along with the discussions on AC vs DC Generators as well as the LifePo Batteries for future planning over the next few years, incase I upgrade my batteries and maybe the Gen.

However the compressor installation will be a purchase next year.

Hear you about the side loads, but the Storage and Cascade system with that size Dive Compressor 8-10 CFM is overkill for our uses.

I would be looking at something much smaller like the Junior Bauer 3.9 CFM which uses 2.2Kw for a 3HP 240V electric drive

4 Tanks /2 Divers doing two dives a Day.....
10 pm and Twilight (crepuscular) Dives is what I like to do now where we cruise in the Philippines, Borneo, Indonesia and PNG.

That would be about 1.5 hrs of compressor time a day if in normal diving mode. That time period fits into using my Northern Lights 12kw AC Gen for other optional needs,.
However, I would have preferred the redundancy of using another driver .....
24v DC, Hydraulic or Direct, in case my Generator went down, while we were in those remote dive spots. (Murphy's Law!

Still researching....

[nwdiver]

Originally Posted by Pelagic

Hi nwdiver

I have been looking at this Dive Compressor discussion along with the discussions on AC vs DC Generators as well as the LifePo Batteries for future planning over the next few years, incase I upgrade my batteries and maybe the Gen.

However the compressor installation will be a purchase next year.

Hear you about the side loads, but the Storage and Cascade system with that size Dive Compressor 8-10 CFM is overkill for our uses.

I would be looking at something much smaller like the Junior Bauer 3.9 CFM which uses 2.2Kw for a 3HP 240V electric drive

4 Tanks /2 Divers doing two dives a Day.....
10 pm and Twilight (crepuscular) Dives is what I like to do now where we cruise in the Philippines, Borneo, Indonesia and PNG.

That would be about 1.5 hrs of compressor time a day if in normal diving mode. That time period fits into using my Northern Lights 12kw AC Gen for other optional needs,.
However, I would have preferred the redundancy of using another driver .....
24v DC, Hydraulic or Direct, in case my Generator went down, while we were in those remote dive spots. (Murphy's Law!

Still researching....

I don't believe the little Bauer compressors are continuous duty (maybe they have changed) you might find you are 40 min on (fill 2 tanks), 40 min off to cool down then fill the next 2 tanks. I found that a hassle, I was filling 6?tanks.........just make sure it's a compressor that can handle the job......

[Pelagic]

Originally Posted by nwdiver

I don't believe the little Bauer compressors are continuous duty (maybe they have changed) you might find you are 40 min on (fill 2 tanks), 40 min off to cool down then fill the next 2 tanks. I found that a hassle, I was filling 6?tanks.........just make sure it's a compressor that can handle the job......

I couldn't attach the PDF file on Technical Data, but I have seen them filling one tank at a time...
NOTE: JRII is designed for filling an individual SCUBA or SCBA. It is neither designed nor intended for filling cascade storage systems of any kind.
1) Based on recharging an 80 cubic foot tank from 500 to 3000 PSIG.


https://www.bauercomp.com/en/product...ving/portables

[nwdiver]

Originally Posted by Pelagic

I couldn't attach the PDF file on Technical Data, but I have seen them filling one tank at a time...
NOTE: JRII is designed for filling an individual SCUBA or SCBA. It is neither designed nor intended for filling cascade storage systems of any kind.
1) Based on recharging an 80 cubic foot tank from 500 to 3000 PSIG.


https://www.bauercomp.com/en/product...ving/portables

Yes 1 at a time but after 2 you may have to rest the compressor to cool it down.......