Powering an electric dive compressor

[a64pilot]

Mine was just a 36' fifth wheel with a single 30 amp power cord.
I did have two AC's though.
Hair driers pull an enormous amount of power, I believe a powerful one will pull 15 amps, which maxes out a regular power cord and wiring.
When I ran wire and added outlets in a house, I always went to 20 amps but that is not common

[mr336]

Bauer Junior II with Auto drain wired for 220v. Westerbeke 8.4 genny. I had to shut off most items when starting the Bauer but then was able to turn on an AC unit while filling the tanks. I checked the startup amps and the load went to I think around 49 amps for a brief moment on startup. But she ran.

[john61ct]

Originally Posted by a64pilot

Your not running this compressor off of a battery bank, no conceivable bank could handle it.

Seeing that there are LFP banks out there providing all the boats' power, including propulsion. . .

[a64pilot]

Originally Posted by john61ct

Seeing that there are LFP banks out there providing all the boats' power, including propulsion. . .

Never seen one, however I would pretty much say that they would be inconceivable to me.
Only real boat that actually was / is fully electric propulsion that I know of is a submarine.
I have heard stories of their battery banks, pretty inconceivable to me too.
Maybe I should have said realistic or maybe affordable? Then of course you have to charge said bank, I think a WW II US fleet submarine could put four locomotive Diesels or similar to the task, God only know how many amps that was

[Sawbonz]

Originally Posted by mr336

Bauer Junior II with Auto drain wired for 220v. Westerbeke 8.4 genny. I had to shut off most items when starting the Bauer but then was able to turn on an AC unit while filling the tanks. I checked the startup amps and the load went to I think around 49 amps for a brief moment on startup. But she ran.

Did the gen you always put out 220v, or was it wired for 110v to the house and 220v when it was needed for the compressor?

[Olddan1943]

My Brownies is about 10+ years old and runs on 120vt.
It is set up for 2 divers.
I have no concerns about leaving the boat with the generator running while diving.
I have noticed, Brownies now offers a secondary air supply, for an orderly assent, if the compressor fails.
I see the local bottom cleaners using a dock side air tank with the Brownie hose and regulator. That makes for an interesting concept and application.

[Symphony]

one thing about electricity in your batteries from solar/wind/hydro -- while it is expensive per KwH it's the only way you can be somewhat self-sufficient.

the renewable sources save you from finding, buying moving and filtering gas, propane, or diesel when in dodgy places.

[Rumpi]

Originally Posted by a64pilot

Your not running this compressor off of a battery bank, no conceivable bank could handle it.

On edit, hat may be old school maybe there is a way to do it with solid state components now, no moving part?.

You are pretty out of date to put it mildly. Nowadays a small shoebox that costs 200-300$ converts 1phase to 3phases, allows full variabe speed control up to overspeeding (0 to 90Hz) and provides many other programable options like soft start and stop. Old wood and metalworking machines are converted all the time. Just do a youtube search for VFD and see for yourself. You can even buy them in dust and waterproof cases (wich doubles the price).

As for the battery comment what can I say? Golf carts are 2hp and they do it on flooded lead acid with DC or AC motors. Power tools do it on lithium chemistries and can be still hold in your hands. They even make electric cars that do highway speeds and have usable ranges that don't cost an arm and a leg. Powering a 2hp motor on a lithium equipped boat is a breeze. Runtime is of course limited by battery capacity but that is a function of ones purse. Given that we are talking about a new 45ft cat the cost of batteries is not that much considering the total costs.

Sawbonz I don't really understand your approach to all this. All the energy conversions from one form to another is just sensless. If you do not mind burning fuel to power the compressor then having it powered directly by an engine is best. If you want to power it by an electric motor using battery power is the logical way. Either by a DC or PM motor using the respective controllers.

I also don't understand your need for a generator. In a catamaran you have two engines. Just have one of them fitted with a generator head and be done with it. Small separate generators are for boats with lead acid and/or small battery banks. Depending on chemistry and quality lithium can take multiple C's of charging current, charging at fractional C's is just a waste of fuel. On a big battery bank even 1C requires a big generator. For example if you have a 12V 1000A battery, charging it at 1C requires a 13kW generator running flat out. On a 45ft cat with dual 45hp motors the sensible option would be to wire the boat for 24V and have one of the motors fitted with dual 24V 500A brushless alternators with external regulators. That would be a 24kW load on a 33kW motor or a 72% loading. Not unreasonable for a diesel and you can go higher amps if you want to load the motor at the ideal 80%. That way you can charge a big battery bank in a short time and also save space on the boat. For backup power you can have one of the small portable invertor generators like the Honda 2000i that cruisers love and use it for powertools on the beach.
But yes the separate generator, inverters, VFD also work. They are just needless complication.
How big a battery bank are you thinking of installing?

[mr336]

Originally Posted by Sawbonz

Did the gen you always put out 220v, or was it wired for 110v to the house and 220v when it was needed for the compressor?

I did have the genny rewired for 220v from 110. Dropped a 220v Hubbel twist lock in the cabin and filled the tanks in the salon with cool air as we were able to fire up the AC unit after the Bauer was chugging along. I cant remember the size of the AC unit.

[Sawbonz]

Originally Posted by Rumpi

Sawbonz I don't really understand your approach to all this. All the energy conversions from one form to another is just sensless. If you do not mind burning fuel to power the compressor then having it powered directly by an engine is best. If you want to power it by an electric motor using battery power is the logical way. Either by a DC or PM motor using the respective controllers.



I also don't understand your need for a generator. In a catamaran you have two engines. Just have one of them fitted with a generator head and be done with it. Small separate generators are for boats with lead acid and/or small battery banks. Depending on chemistry and quality lithium can take multiple C's of charging current, charging at fractional C's is just a waste of fuel. On a big battery bank even 1C requires a big generator. For example if you have a 12V 1000A battery, charging it at 1C requires a 13kW generator running flat out. On a 45ft cat with dual 45hp motors the sensible option would be to wire the boat for 24V and have one of the motors fitted with dual 24V 500A brushless alternators with external regulators. That would be a 24kW load on a 33kW motor or a 72% loading. Not unreasonable for a diesel and you can go higher amps if you want to load the motor at the ideal 80%. That way you can charge a big battery bank in a short time and also save space on the boat. For backup power you can have one of the small portable invertor generators like the Honda 2000i that cruisers love and use it for powertools on the beach.

But yes the separate generator, inverters, VFD also work. They are just needless complication.

How big a battery bank are you thinking of installing?

My approach is simple, Rumpi. Come up with a way to run an electric compressor on a boat. My original thought was that it should run straight off of the generator but a seller of the compressors tells me that I need a 12kw generator which I don't believe. I mentioned my battery expectations because I believe it to be possible to utilize them to supplement the generator for start-up power. How to do that, if necessary, is a question we are discussing. I would prefer not to have a gas or diesel powered compressor because I not only don't want another motor to maintain but it bothers me in theory to use a compressor attached to something that makes carbon monoxide and does it all in a closed space.

I am not advocating changing energy from one form to another unless that is what's required to make a compressor run. My preference would be a system with as few moving parts as possible. If it will run off of the generator, fine. If it will run from the batteries that is also fine, but I would expect to then run the generator to recharge the batteries anyway.

I don't understand what you mean by "C's". 24 volts is a great idea, but Leopard ain't Burger King. You get it their way or not at all.

Finally, you ask why a generator at all. Because everyone else does. Even if it wouldn't be used to power two air conditioners, a water maker, a water heater or two and a washer/dryer you would still want it to recharge the batteries. And resell without it would suck. Yes, I do intend to try to run as much off of the batteries as possible for as long as possible (expecting around 1000ah) but recharging over solar capabilities will be required and somehow using the engines I require to get me to safety to perform a duty for which they weren't designed concerns me. That said and this idea being interesting, it is still a topic for another thread I think, so as to avoid thread drift on this one.

[transmitterdan]

You are over thinking this I believe. An 8kW generator will run a single phase 1.5HP compressor. Even if you find there are problems getting the compressor to start there are after market solutions. You can try a hard start kit for <$25. Or you can get a small single phase variable frequency drive (VFD) that can soft start the compressor. These cost about $100-$150 and are quite small. Going to 3 phase will not be efficient. I think the advice you are getting from dive shop isn't very good, I recommend visiting a different shop or looking online for a shop that has more experience with pleasure boaters. There are plenty of dive shops that cater to your specific needs.

[Sawbonz]

Originally Posted by transmitterdan

You are over thinking this I believe. An 8kW generator will run a single phase 1.5HP compressor. Even if you find there are problems getting the compressor to start there are after market solutions. You can try a hard start kit for <$25. Or you can get a small single phase variable frequency drive (VFD) that can soft start the compressor. These cost about $100-$150 and are quite small. Going to 3 phase will not be efficient. I think the advice you are getting from dive shop isn't very good, I recommend visiting a different shop or looking online for a shop that has more experience with pleasure boaters. There are plenty of dive shops that cater to your specific needs.

I agree. In Annapolis I will be searching out some purveyors of compressors to do a face to face. I can probably find a generator salesman there too and get them together if there is a lack of understanding. I have also written the manufacturer an email after the distributor declined to answer a question.

Perhaps the thread will die, or perhaps not.

[dwedeking2]

Sawbonz, thanks for starting this thread. It's helped me a lot as I plan on adding a dive compressor next year.

[Sawbonz]

Originally Posted by dwedeking2

Sawbonz, thanks for starting this thread. It's helped me a lot as I plan on adding a dive compressor next year.

Thank YOU for the thank you! I did work hard on it and I am glad it turned out so well.

[Rumpi]

Okay, on topic:
1. What is the running power of the intended compressor in kW?
2. What type of motor is fitted to the compressor? 1 phase/3 phase /Volts
3. Is the intended compressor fitted with a unload valve or clutch or does it always has to start against full load?
4. Do you intend to run other loads while running the compressor or not?
5. Is the compressor the biggest load or do you have bigger loads that you have to size the generator to?

Without this parameters nobody can answer your question. Your dive shop is right by the way, if you inquired about a 2.5hp compressor. Conventional rule for direct starting under load is 6 times the nominal power, that is 750Wx2.5x6=11250W. For a 2000W compressor that is 12kW of generator. Solid state soft start devices or VFD's would cut that figure by half, starting with little or no load plus soft start would cut that figure again by some. So for a 2000W compressor with unloader and softstart you would need around 3-5kW of generator depending on the components fitted. If you want to use a smaller generator and supplement the rest with battery power you need to wire the motor (plus soft start) to the inverter and use an inverter capable of combining separate power sources in the required power range.

So basicly my advice: select a compressor you like. Take the specs to the chosen generator manufacturer and ask for a recomandation for direct staring/solid state soft start/VFD use (no it's not the same as a dedicated soft start device). Please mention at this time any other significant loads like dryer or AC's and what other loads you would like to run at the same time as the compressor or combined without it. Then ask Leopard if the recomended genset can be mounted in the available space.

Off topic:
C rate is the current batteries can deliver or accept. Nominal rating is at 1C or what current can be sustained over 1 hour. Example: a 12V 100Ah battery has a theoretical capacity of 1200Wh. You can extract this watts all in 1 hour at a rate of 100A (1C rating) or you can do it over 20 hours at a rate of 5A (C/20 rating) or you can do it in 30 minutes at 200A (2C rating). Depending on chemistry and build form batteries can dump or accept different C rates.
This means that a 12V 1000A battery can be charged at C/2 with 500A in two hours or at 2000A in 30min. Since lithiums are especially good at C rates and have a very flat and long curve of constant current charging it means that charging at fractions of C is wastefull.

On topic again:
Given the lithiums charging curve any generator (or alternator) is going for a workout whenever you are charging. The only limiter is the charging circuit. The batteries will basicly suck rated power out of the charger every time. Make sure you can disconnect the charger from the generator when starting heavy loads like AC, dryer or compressor. Especially important if you plan on a high power charger (C/2 would be a 500A for a 1000Ah battery) but even a common 60A one loads the generator with about 1000W.
As for alternators go for the biggest you can find. Electrodyne with external regulators for example.