looking for electric compressor for my boat

[handyman]

I am looking for an ele. scuba compressor for my boat. plenty of room to work with. It is not a charter but when we go out there are 2 to 6 people on board and I keep 12 to 18 tanks on board and a little gas bauer, to small and dont want any more than 12 tanks on board. any recomendations? anyone know of a used one for sale ?

[veriqster]

What do you have for power?

[IyaDiver]

Yes Handy like Verigster asking, look into your generator power first. If you want 2 to 2.5 hours interval between dives for 6 people and less tank to carry, you need Bauer Mariner 200 or Coltri MCH13, these are big power consumption at approx 3.5Kw.

A single 3.5kw motor full locked rotor current amperage for starting can hit 600% of its nomimal amperage rating for a short spike and that is painfull for generator under 12Kw.

[handyman]

I have a 50' symbol 16' beam twin volvo's. Genset is a 20kw westerbek my backup generator is a 6.5 kw westerbek. The 6.5 will run the boat and i can isolate the 20 kw while running the compressor.

[CraigAClark]

Unless your 20 has 3 phase output, the best you can do starting straight-up is 5 hp on 60Hz. That would put you in a 6 scfm unit which will fill a single 80 from 500 to 3000 in about 15 minutes. With a frequency drive, you could probably step up to a 7.5 hp and 8 scfm. Reducing the same fill scenario to 10 minutes per. Bigger than that, I'm not sure.

Craig

[veriqster]

I have a 50' symbol 16' beam twin volvo's. Genset is a 20kw westerbek my backup generator is a 6.5 kw westerbek. The 6.5 will run the boat and i can isolate the 20 kw while running the compressor.

If you currently have only 1 phase 220 have somebody knowledgeable look at the genset head, some of them can be wired either 1 or 3 phase depending on the needs.
according to Westerbeke brochure you should be able to wire it for 3 phase with a .8 power factor (16kw). this should reduce your compressor cost (and weight), especially if you are looking for a used unit.

[IyaDiver]

All pleasure yacht at that size and USA spec will be using USA type 110-0-100 volt.
So its 220V but two live wire. They wire the air cond and washer/dryer to this 220V and no neutral. The rest of the 110V equipment they take and balance it on either one of the 110V leg.
3 phase US type 460V?? is very unlikely until the yacht hits 120 feet up.

If handy were to wire the genset to three phase he has to re-wire all the loads to balance out and I think single phase to 3 phase converter frequency drive can be used as cheaper alternative and softer demand on the generator. The wiring must be connected direct to the panel bus bar with new MCB and new bigger receptacle, 3.5Kw can't use stock receptacle available on the boat.

However one caution. Frequency drive has high noise level ( harmonic ), it does sometime interupt the generator frequency controller. As late as 1995 model of westerbeke, they already use electronic governor controller on the 25Kw model. Make sure to check properly on this issue specific to generator supplied power.

If Handy can source 220V motor, he can use a soft starter typical tyhristor based one.
I am sure Craig has more experience in this set up.

[handyman]

Iyadiver is correct 3 phase is not standered in most marine applications. 3 phase can be ordered and then they are larger than 20kw. i talked with westerbek. phase converter is a good idea but i will have a twenty % drop in output amps after the converter.

let me through this at you guys. startup amps are high because of the load the compressor puts on the motor. startup amps can run 3 to 4 time's the running amps. if you free wheel an electric motor the startup amps are nothing. here is my point. what if we put a dump valve after the frist stage? this way we are free wheeling the compressor on startup and once the motor hits operating rpm's you close the valve. i understand we will get a rise in amp's but this should minumize startup amps. i have about 55 continous amp's on the 220 side of my genset. not sure what kind of spike the genset will handle. i'm guessing a brief 120. i will email westerbek to see what kind of spike the genset will handle unless iyadiver already knows.

has anyone ever done this

sorry for the sloppy terminogly and typing !!!!

[CraigAClark]

Your 3-4 times FLA at start-up is correct for a 3 phase motor. A single phase motor will be 5-7 times FLA. I worked exclusively in the yachting industry for 20 years dealing with power supply requirements for hp compressors. With single phase, 220, 60Hz, here is the straight-up starting requirements, with no load.

2hp-6.5Kw
3hp-8Kw
5hp-20Kw
7.5hp-25Kw (this size genset is usually where 3 phase becomes available.)

Take it or leave it as you will. Just keep in mind, there were no "surprises" for those that took my recommendations, while several folks who listened to their generator suppliers learned the hard way. It sucks having to run a Mariner at Capitano capacity when you discover that your 20Kw wouldn't start that 7.5 hp and you didn't have the money for a frequency drive, so you had a 5 hp motor installed

Craig

[IyaDiver]

Handy,

The electric motor by design ( squirrel cage induction motor ) is a horrrible start-up current sucker, no matter if you free wheel the compressor. You will free wheel anyway for a dive compressor, I mean open the water seperator is like free wheeling already.

It is not about mechanical load of this SCIM design that caused the 600% current rush, its the way it is designed.

If you free wheel, the current rush magnitude is the same but the duration is so short, unless you have a very good fast sampling data logging current meter, you will see only 300% start up current but in fact for a very-very brief period the 600% exist but not recorded. You don't even need to put on the belt, and run the motor "naked", it will need what it will need by design.

By having a load on it, the duration of the current surge will be longer until the motor hit 80% of its design RPM and it will dip down and eventually when its running at 100% designed speed, the nomimal current rating will apply but less than that actually because people usually rig an electric motor to a compressor or whatever mechanical load choosen at 80% motor capacity.

The motor itself usually will not have a 1.0 power factor for 3 phase model. Usually 0.8PF is common but three phase motor does not need starting capacitor, which sometime is the failure point of a single phase motor.

Your 20Kw should be sufficient power wise if you choose the motor wisely like Craig advised.

Have fun.........
IYA