Dive compressor install questions

[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?

[transmitterdan]

You can get VFDs that convert single phase into 3 phase. Each one will have its own installation and setup instructions as there is no standard setup amongst the various brands. If you don't feel comfortable any good industrial electrician can install it. There are no significant differences between installing it on a boat or in a factory. Almost all VFDs can "soft start" a three phase motor via their programmable functions. Try to find a VFD with internal circuits conformal coated. Also, good paint or aluminum construction helps. That's about all you need for the marine environment.

Alternatively, you may have an inverter charger in your plans. If so, consider one that can "assist" the generator with starting loads. This often can provide the needed starting current for single phase motors (like air conditioners and compressors) thus the generator can be sized a bit smaller for the typical running load and not the starting loads.

If you use either approach then you probably do not need the isolation switch. But it is not a "bad" idea if you have the room.

[Tornadosailing]

Originally Posted by transmitterdan

You can get VFDs that convert single phase into 3 phase. Each one will have its own installation and setup instructions as there is no standard setup amongst the various brands. If you don't feel comfortable any good industrial electrician can install it. There are no significant differences between installing it on a boat or in a factory. Almost all VFDs can "soft start" a three phase motor via their programmable functions. Try to find a VFD with internal circuits conformal coated. Also, good paint or aluminum construction helps. That's about all you need for the marine environment.

Alternatively, you may have an inverter charger in your plans. If so, consider one that can "assist" the generator with starting loads. This often can provide the needed starting current for single phase motors (like air conditioners and compressors) thus the generator can be sized a bit smaller for the typical running load and not the starting loads.

If you use either approach then you probably do not need the isolation switch. But it is not a "bad" idea if you have the room.

Thanks. I had been looking at ones that will convert single phase to 3 phase.

The boat already has an inverter and a charger as separate units, and the 9KW generator is already there as well. I was thinking the isolation switch would prevent one of my guests from turning on the AC chillers while I'm filling tanks.

[a64pilot]

Conformal coating is very easy to add as well. I hav ever to have it mess anything up, although out of ignorance I don’t conformal cost chip sockets and a few other things

[svninkasi]

I was running a compressor off a 6.5 kw genset along with my 220v 1.5 hp water maker (55 gph) ish no issue just open up the air bleed valve. Don’t start eiter under load and you’ll never have an issue with 9kw

[captmikem]

I had a bauer Utlis 10 compressor running off a 5KW genset with no problem at all as long as it was wired for 220. it would not run wired for 110. It would load down a bit on start up but a big cap installed on it softened it a lot and ran fine. Since I had it in the laz I put a six inch muffin fan on the motor to keep it cool as there was little circulation.

M

[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.

[Tornadosailing]

According to Bauer, the 5hp single phase motor draws 28 amps at full load. Start current is often 5 or more times full load current. My 9KW gen set should have an output of 39 amps. This doesn't give me room for even a 2x start current. Of course my math could be wrong as I'm no expert on this.

If I go with a VFD, I can also do phase conversion which will allow a 3 phase motor which draws roughly half the amperage of single phase.

I just got off the phone with the guys at Precision Electric who gave me some great info. They told me I need to go with a water tight VFD because of the humid environment, which adds significantly to the price but the "drip proof" model won't take it. The VFD can also be wired to detect the high pressure shutdown switch and soft start the compressor when it wants to restart. If I go with this setup they'll also walk me through the setup and programming.

https://www.precision-elec.com/shop/esv752n02txd-dr/

They also have VFD training videos.

https://www.youtube.com/channel/UCLZ...7fhdlr93XBbNQ/

[Ivansgarage]

I wind motors for electric vehicles A/C motors, and for the life of me
can't figure out why you would want or need a VFD (variable frequency drive)
for a motor, thats suppose to run at a constant speed your compressor.
A VFD A/C motor is expensive plus the vfd. A 220V 5HP motor with a start
cap won't pull much over 40 amps on start and that's about 2 seconds.

I would think about a gas engine for the compressor instead of spending
an extra 2 grand on motor and vfd.

Ivan's Garage, Electric Vehicles, AC Electric Motors - Index

[Tornadosailing]

Originally Posted by Ivansgarage

I wind motors for electric vehicles A/C motors, and for the life of me
can't figure out why you would want or need a VFD (variable frequency drive)
for a motor, thats suppose to run at a constant speed your compressor.
A VFD A/C motor is expensive.

Ivan's Garage, Electric Vehicles, AC Electric Motors - Index

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.

The main concern is the start current, especially with the compressor configured for a more automatic operation where I wouldn't be opening valves to dump head pressure.

Brownies for instance has a VFD included on all tank fill compressors. I can't imagine they would make it standard vs having you buy one separately unless there was a good reason.

Coltri also includes a VFD on their "Marine Pak" compressors.

https://www.browniedive.com/high-pre...mpressors.html

Coltri Sub MCH6 MarinePak Air Compressor from RCS

[Ivansgarage]

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

[transmitterdan]

Originally Posted by Ivansgarage

I wind motors for electric vehicles A/C motors, and for the life of me
can't figure out why you would want or need a VFD (variable frequency drive)
for a motor, thats suppose to run at a constant speed your compressor.
A VFD A/C motor is expensive plus the vfd. A 220V 5HP motor with a start
cap won't pull much over 40 amps on start and that's about 2 seconds.

I would think about a gas engine for the compressor instead of spending
an extra 2 grand on motor and vfd.

Ivan's Garage, Electric Vehicles, AC Electric Motors - Index

A VFD solves the high starting current problem so will not require a bigger generator. Plus he can use a more efficient 3-phase motor so less heat generated. It's a good solution.

[Ivansgarage]

Originally Posted by transmitterdan

A VFD solves the high starting current problem so will not require a bigger generator. Plus he can use a more efficient 3-phase motor so less heat generated. It's a good solution.

To be honest the part I don't like is the VFD, if and when it takes a ****
how long does it take to get a new one? Not like ya can just run too town.

[transmitterdan]

A soft start is basically a VFD. And we are not talking about life support equipment. No one will die if he can't fill a scuba tank.

The alternative is a much larger generator which has its own set of bad features. The VFD nicely solves a lot of problems.

[Tornadosailing]

Originally Posted by Ivansgarage

I would think about a gas engine for the compressor instead of spending
an extra 2 grand on motor and vfd.

I already own one of those. The problems are many.

First, the new to me boat has limited places to store a compressor that can be pulled out on deck when I want to use it vs having it installed in the port transom and can run it in place. I'm not willing to give up a huge chunk of my locker space.

Second, the gas compressor costs $900 more than the electric version. About the same cost as a VFD.

Third, the compressor I have is a Jr II and isn't continuous duty rated. I'm supposed to shut it down and let it cool off between tanks. I usually just let it run and it's not good on the compressor.

Fourth, and the biggest problem, if I put 6 divers on the boat and dive two tanks each, which I usually do, I have to listen to that loud as hell gas motor run for at least 3 hours twice a day. I'm so done with that. An electric will be in the port transom behind the rudder, and will have a muffled intake. Should be no louder than the genset.