SCUBA air fills

[Jammer]

You might be surprised. Here's a nameplate from a motor for sale on eBay today for a few hundred dollars. It's a 4hp motor, 24vdc, 3360 watts, would drive most small dive compressors that are designed for a 3-5 hp motor with proper choice of pulleys.


A DC motor could be used on boats that do not have an AC generator or inverter that is large enough to run a dive compressor. It would be possible to make air while motoring with a high output alternator. Even if the alternator could not fully keep up with the load it would carry some of it. In the same light, a small AC generator like yours, through a charger, could make up a good deal of the power and again eliminate the sizing problems inherent in starting a 3hp or 5hp induction motor.

[nwdiver]

The deck box lifts off when the compressor is used.....

As to battery powered.....ha ha ha......maybe top up a tank and kill a battery bank....as pointed out above you might fill a tank with a fully charged 1000 ah battery system...if gas/diesel gen set powered.... A 3.5cfm needs a solid 7 kW generator, to push 5 cfm 12 kW works, 7 cfm take a 17 kW or more, many use a 20.... If you beat the laws of physics let use know......

So the easiest, least expensive for someone who dives and does just talk about it is gas, besides the dingy needs gas also and pull starting a Honda gas engine is very easy....

[Jammer]

Originally Posted by nwdiver

If you beat the laws of physics let use know......

Those aren't the laws of physics. Those are the laws of engineering, and they are negotiable, because they can be overcome with better engineering.


The thing about DC motors is that the starting surge is different. Now, an AC capacitor start induction motor, in order to start, the voltage has to be at least 80% or so of nameplate if there's any kind of load on the shaft at all. For compressors, unloaders on all stages help, but the motor still has to see 80%, and it's still going to draw more than the nameplate amps by a factor of 3x-4x.


DC motors aren't like that. Most of the big ones are shunt wound and they'll start on a fraction of the nameplate voltage, like 25% or 50%. Then they'll run merrily along and make air on 11 or 12 volts and as long as none of the rest of your power system melts everything's fine.



There used to be a widely available AC motor type called a repulsion-induction motor. Starting characteristics like DC, but ran on AC. They had brushes and were maintenance intensive (like DC motors), and big and heavy. They don't meet the federally imposed efficiency requirements so they are no longer made. But they'd be ideal for running a dive compressor off a generator. ::shrug::

So the easiest, least expensive for someone who dives and does just talk about it is gas, besides the dingy needs gas also and pull starting a Honda gas engine is very easy....

I do see your point. Like most divers, I don't like compressors driven by gas engines because of the potential for contamination. At least we have CO detectors for scuba use now.

[a64pilot]

I believe the most common cause of CO in dive compressor air is from the use of incorrect oil, the compressor compresses to such a high pressure that any small amount of flammable oil that leaks past the rings is ignited and burns, creating CO of course.
The way Bauer does it with the cheap PVC pipe snorkel, it would be next to impossible to get exhaust gasses into the compressor, unless maybe you had the whole thing in a small room or something, which the instructions specifically forbid for the reason of possible ingestion of CO.
Or you left the snorkel off or didn’t know about the snorkel, leaving it off

[nwdiver]

Originally Posted by a64pilot

I believe the most common cause of CO in dive compressor air is from the use of incorrect oil, the compressor compresses to such a high pressure that any small amount of flammable oil that leaks past the rings is ignited and burns, creating CO of course.
The way Bauer does it with the cheap PVC pipe snorkel, it would be next to impossible to get exhaust gasses into the compressor, unless maybe you had the whole thidng in a small room or something, which the instructions specifically forbid for the reason of possible ingestion of CO.
Or you left the snorkel off or didn’t know about the snorkel, leaving it off

Yeh, exhaust aft at deck level air intake hose 4m foreword well above the deck......what CO?

[Steve_C]

Originally Posted by a64pilot

AC or DC, it’s still the same load.
Assume 5KW at 120 VAC, 6000W.
That is 500 amps at 12VDC.
Do you have a battery bank that can sustain that kind of load continuously say for an hour? One hour is 500 AH of course.

If you do then your going to have to recharge it anyway, so your going to have to push about 550 AH bank into the bank, likely 600 cause you drew it down in one hour.

6000W may not be the correct answer, but I know it’s not 4000W

I am looking at doing this with an electric motor and a large LFP bank.

Assuming a 3 HP motor

https://www.engineeringtoolbox.com/e...nt-d_1499.html

34 Amps at 115 Volts = 3910 Watts = 325 Amps at 12 volt.


Assuming a 2 HP motor

24 Amps @ 115V = 2760W = 230 Amps @ 12 V

According to the Bauer attachment in post#4 its listed as 2.2KW (2200 Watts) which is apparently really efficient for a 3 HP motor. It must not be heavily loaded.

I could be wrong but that is VERY doable with the appropriate bank.

For my use it will be a Cat with lots of Solar and an LFP bank of 1400AH or Larger.

[a64pilot]

Originally Posted by nwdiver

Yeh, exhaust aft at deck level air intake hose 4m foreword well above the deck......what CO?

Well, apparently some have put their Bauer into a small closet sized room and filled tanks before, you know they have.
Never thinking of the build up of CO in the small room where the compressor also drew its air from.

[BenBowSirocco]

What type of depths are you guys after?

Or maybe the question would be, what would be your most common/average depth your diving?

I only ask because I have spent quite a bit of time thinking and trouble shooting this same problem and have decided to go with a hookah rig. This is definitely a compromise and not for everyone as it limits usable depth to about 60ft (which is based on the pump/HP)

I took the time to design and trouble shoot my way through a Lithium 24V electric system (works about 3 hours without solar panel assist and 5-7 with solar assist) and then made the decision to go with a gas powered unit and a collapsible compressor intake antenna.

We will also be carrying our BCD's so that we can rent tanks whenever desired. To me the "we can go anytime or all the time" convenience sold me on the surface air supply system.

[Jammer]

Originally Posted by BenBowSirocco

What type of depths are you guys after?

To be sure, much of the best diving is shallow. Some of my best dives have been to 20'.


Then again some of my best dives have been, well, snorkeling, really, with a little bit of freediving to maybe 20' or so.



But I would feel limited by having to stay under the boat. I like to swim around and explore. It is not unusual for me to end up several hundred feet from my entry point.

[Steve_C]

In regards to shallow diving, I agree with Jammer that many times shallow is by far the best. BVI was one place where everything I saw shallow was better. possibly due to clarity of the water.

Cozumel is opposite probably for the same reason.

I intend to keep a regulator with two thirty (or so) foot hoses between the first and second stage(s) to use under the boat or with a tank in the RIB for shallow water when I just don't feel like full blown diving. A Hookah is not the only way to do this. You could also have a much smaller float (with a flag) for the tank just to ease having to tow it along.

[BenBowSirocco]

I have towed tanks before and while convenient for swim speed/spearing, still requires the tank to be refilled, so it leaves you with the same problem- where to get air fills.

If you were to budget the amount of money spent on the tank fill compressor into a surface air system, you could have an all electric, fully sealed lithium ion system capable of 12 hours of diving. It would be VERY low maintenance, just change the filters, and it could charge itself between uses by the sun for free. Rebuild the compressor every 300 hours. No CO risk, no gas/explosion risk. But you have to tow it while you swim and deal with the hose. Still a compromise.

[nwdiver]

Deep shallow, I dive where the beasties are......

[daletournier]

I have a hookah for boat maintenance but tanks to dive. A compressor can not be justified using price. It sits for long periods of time unused BUT when in a good diving spot nothing beats the convenience and freedom that tanks and a compressor gives you, a hookah is non comparable.

[DefinitelyMe]

We carry two full sets of dive gear and two tanks. We’re just completed a circumnavigation and spent a lot of time in remote areas. We don’t have a compressor on board, but if we had more money I would get one.

We had to budget our dives sometimes and usually opted to do two short dives (half an hour or so each) on each fill rather than one long one. I breathe less than my partner so this allowed us to switch in the middle and get the most out of it. Overall, we were surprised at how many opportunities there were to fill tanks. Even in pretty remote areas there is often a dive shop, a local with a compressor or in the busier anchorages we’d do a round of the anchorage and meet people until we found someone with a compressor on board.

I wouldn’t rely on renting tanks unless you plan to visit only mainstream places. Often the times you want to dive are not when you’re in the bay where the dive shop is, if there is one at all.