SCUBA tank to drive a batt charger motor

[Steve Bean]

When my father was studying mechanical engineering at Cornell in the late 1920s there was a big diesel engine that was started with a 10 gauge shotgun blank.

[daddle]

Simply unbolt your electric start motor and bolt on the pneumatic starter:

http://www.psiautomation.com/air-sta...e-starters.htm

[Astrid]

Coffman starters were capable of starting diesel engines, even quite large ones, but that was not a direct explosion into the combustion chamber: these starters were a separate starter motor, which had a separate cylinder and piston, whereby the piston ran down a multistart threaded spindle, causing that spindle to spin and turn the engine over multiple times.

Exactly.

[model 10]

Coffman Starters were used to start 27 cylinder 4360 cubic inch piston engines and some great big turbine engines also, not little bitty 3 or 4 cylinder piston engines. So it seems like you may not need the all the fancy mechinisms you describe.
Let the shot shell charge the scuba tank with air...

[Dennis.G]

I think one big problem with this whole idea:

Unless you have air compressor on boat to refill your SCUBA tank, seems about a 50% chance your tank will be empty instead of full. Would only always be full if you never went diving.

If applying Murphy's law to equation, the tank will ALWAYS be empty in an emergency when you needed to drive an alternator (or for direct engine starting).

[Dennis.G]

Originally Posted by HappyMdRSailor

If you use an impact wrench on your crank bolt 2 things will happen....

1. The rotation of the engine while doing this would be in the neighborhood of 1 rev/min.... Plenty of time to have one or two sips from your cocktail before TDC passes twice... It's called an impact wrench for a reason...

2. You will tighten the crank bolt so much that it will never come off again...

Great reply

In real world, I think result may only be #2 (tightening the bolt) and that you would not turn engine at all with an impact wrench.

Tighten a lug nut on a wheel with an impact wrench. The wheel does not take off spinning - it hardly spins at all! The torque applied is too short in duration to move a large mass (such as a wheel, or engine crank and pistons).

[HappyMdRSailor]

I totally forgot about this!!!!

I used to sail on an old square rigged Danish topsailer ... There was no starter motor for the engine....

It was a 2 cyl diesel that was started with compressed air... UNFORTUNATELY, the compressed air was supplied by good old fashioned pumping...

There was a separate air tank that was pressurized with a hand pump... What you did was:

1. check the air pressure in the tank.... More often than not this step required the famous 10 minutes of hand pump hell...

2. hit a decompression lever...
3. turn the fuel feed off to the cylinders
4. open a valve from the air tank to one of the cylinders (god awful slow hand wheel)
5. once the engine was spinning, crack open the fuel feed to the cylinder that wasn't being pumped by air
6. release the decompression lever on that cylinder
7. PRAY LIKE MAD the engine caught and fired
8. If it did, close the air tank valve
9. Crack the second fuel feed valve and VIOLA!

You were running....

If it didn't catch.... repeat steps 1-9

You got good at being REALLY quick with the steps in short order, as you really only wanted to do it once!

[Autumns Wind]

I think it could be done, with the proper equipment and setup. However the expense and aggregation of all the steps would so not be worth it. Your better off buying a emergency 50watt flex solar panel & use the air tank to get lunch. At least then you had a good dive and possibly a good meal while you waited the battery to charge. Cheers

[ephyraboater]

Hmm. I really appreciate all of the feedback on my question. While I thought applying a pneumatic wrench to my (decompressed) flywheel via 150 psi of SCUBA tank (above "bingo" from me ), I foremost want to do no harm (over-torque my flywheel bolt). I prefer to sail out of a "situation" anyway (but like to have diff backups for strange situations).

As I said recently, the impetus of my original post was to determine if I could make use of the stored energy of a full tank for something useful in "unexpected" situations, like a stupidly-dead battery to charge-up. Or simply crank engine (could also include failed starter motor).

I'm (pretty) convinced that I should just sigh and not plan on using tank(s) for such contingencies. Just seemed like a good use of stored energy in a pinch - if it didn't involve too many convolutions.

Again - thanks. But still open to good ideas!!

[ephyraboater]

Originally Posted by nimblemotors

...
The simplest thing would probably be to remove your engine belt to the alternator and attach a pulley to an air grinder and use it to spin the alternator, and it will charge the battery without anything special. Or maybe skip the belt if you can use a direct coupler, which I guess if you want to build something custom that might do.

...

Hmm - again.... Though I have indicated a couple of times that I'm done with crazy thoughts regarding SCUBA tank use, I've come up with a follow-up question to nimblemotors and others. I can get a decent variable speed, 4 CFM pneumatic drill for a reasonable (<$50) price (Northern Industrial Air Drill — 3/8in. Chuck, 1800 RPM, 4 CFM, Reversible, Keyless | Air Drills| Northern Tool + Equipment). Supposedly runs at 4 CFM at full-1,800 rpm speed at 90 psi input (lower than input 150psi I will deliver). Hook it either directly to alternator bolt or belt. Spin it at over 1,000 rpm for maybe 20 minutes if I'm lucky. Maybe charge a battery enough. (Maybe buy another used $80 tank for other divers etc).

Assuming I can get 4cfm when delivered at 150 psi, maybe running at just 1,000 rpm. And assuming the friction-load from alternator isn't too great to spin at 1,000 rpm, and enough charge could be gained... As I've said, I have no pneumatic tool experience, so not so sure what a contant 3,000psi tank, regulated to a standard SCUBA 1st stage 150psi, can do w/ such a tool. I tried looking up some of the physics, but there are unknowns on my part. (Likewise unsure of exactly what my Delco Remy 10si 80 amp alternator can do - boat is new to me, and I haven't done lots of research).

Aside from above application, I think a pneumatic drill may come in handy for little (maybe important?) jobs when my battery-powered drill is dead, and my inverter can't power my corded drill cause of my battery status....

Maybe I'm again barking up a hopelessly unworkable tree? Please don't be too rough on me . I am sometimes incorrigible regarding making unusual things work (I've done silly/useful creations in past; my dad invented some strange/cool things, including a "cylindropter" that flies with articulating, forward-rotating foils - I'm nowhere near that clever, but maybe inherited something)....

[model 10]

Cheap drill use more air, You could spend 3x that and use less air.

[Andrew Troup]

Hmm

In my admittedly limited experience, claimed CFM figures for low-budget air tools and air compressors are figments of marketers imaginations, at best; by the time you combine them, you're often an order of magnitude adrift.

This is partly because there's plenty of room for fudging because it's never specified at what pressure that volume of gas is measured: it's not necessarily the same as the pressure delivered or required.

The only way around this AFAIK is to go for highly reputable brands, the likes of Atlas Copco or Ingersoll Rand, which cost five to ten times as much, but use a lot less air, and tell you honestly how much air that is. (I would go second hand eBay to help bring the cost back)

The other untutored observation is that when you're delivering what's more likely to be 10 to 20 CFM through the regulator, assuming it can pass that volume, I'm guessing it will freeze very quickly from the expansion.

I don't know if it's a good idea to submerge it in a bucket of warm water; I guess if it's a SCUBA regulator it won't mind getting wet... but there may be other ramifications, and the water may cool rather quickly...

[ephyraboater]

Originally Posted by Andrew Troup

Hmm

The other untutored observation is that when you're delivering what's more likely to be 10 to 20 CFM through the regulator, assuming it can pass that volume, I'm guessing it will freeze very quickly from the expansion.

Thanks. If a tool really will need 10 CFM, that probably kills my potential application - I have no experience w/ air tools and so don't really know how to properly interpret the (sustained 4 CFM) claims by vendors etc. Don't want to create rapid-draining issues with my tank - condensation etc. (I want to "do no harm" in this whole process - such rapid drain would lead me to, at least, later bring the tank into dive shop for a VIP (visual inspection); the 1st stage (150psi) regulator I have for these purposes is old "junk" that works, but no longer used for diving.

I'd have to have really good knowlege that I could adequately charge a partially-dead battery before abusing my SCUBA tank w/ 10 CFM discharge (if it could even deliver that, as you wondered).

[nimblemotors]

If you want to persist on the idea, the alternator isn't ideal as it takes power for the coils to generate/regulate the output. So the best thing is to turn a small permanent magnet generator that you can control the speed to just 14volts to charge the battery.
The problem is that a dead battery probably needs a lot more juice to bring it back to life than just the energy needed to power the starter. This is why I suggest charging up a supercapacitor then have it power the starter, it takes up all the charge and can spit it all back out in a big burst of energy. Or back to the A123 battery, almost as good as the caps. I think a little brushless dc computer fan will generate nicely by just blowing air on it, build a duct around it to improve its efficiency.

[Ofer]

Originally Posted by Guy

Wrap a bit of line around your prop and shaft like pull rope then hop in your dinghy with the rope and take off, in the correct direction

this gets my vote!!

how about using the scuba tank to blow air onto the sails on windless days.