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Old 01-06-2013, 17:12   #1
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SCUBA tank to drive a batt charger motor

I have a (3000 psi) SCUBA tank, primarily for pleasure and/or bottom-work. I wonder if I could use this as an energy source to drive an alternator/charger, for the (hopefully never-occurring) event when I have dead batteries that will not start my diesel engine. I assume (?) that a full/near-full tank could run a small motor (alternator/charger) quite awhile, long enough to adequately charge a engine-starting battery.

There are many pneumatic tools on the market, but I would like to find/build a pneumatic (SCUBA-driven, ~150 psi available) generator/alternator (not sure proper name). Aside from my diving regulator, I have an old "1st stage" regulator that has an output hose that can deliver the 150psi to whatever.

Any of the experts out there have insights into this? I've done a fair amount of googling, but can't come up with anything useful.... Especially if it has not been done by others, this may be cost-prohibitive, but it would be great if there's something simple/useful out there. Thanks.
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Old 01-06-2013, 17:18   #2
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Re: SCUBA tank to drive a batt charger motor

Use the SCUBA tank for diving ONLY. These air tanks were not designed to be used in anything else.
Mauritz <PADI Dive Master>
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Old 01-06-2013, 17:27   #3
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Re: SCUBA tank to drive a batt charger motor

having trouble with the image............

I am sure it could be done but you may have to build something.

great idea.

I cannot for the life of me take a image I find on the net and get it in here.
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Old 01-06-2013, 17:28   #4
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Re: SCUBA tank to drive a batt charger motor

Thanks for expressing your safety concern. However, the tank doesn't care where the air is delivered - absolutely zero impact on the SCUBA tank (unless it's bled too quickly w/ subsequent temperature-induced condensation on outside - but not gonna happen here). If anything, use of a SCUBA tank to drive pneumatic "tools" is an expensive way to go!
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Old 01-06-2013, 17:30   #5
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Re: SCUBA tank to drive a batt charger motor

Air motors don't seem very efficient and I don't think you would get much run time out of 1 fill. Plus when you factor filling the air tank up I think it would be a looser.
An air tank is an air tank so why would it make a difference what it was made for?
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Old 01-06-2013, 17:32   #6
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Re: SCUBA tank to drive a batt charger motor

as there not an Indian car designed to run on compressed air. Try google.
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Old 01-06-2013, 17:35   #7
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Re: SCUBA tank to drive a batt charger motor

Forget Electric Cars, This One Runs on Compressed Air - John Metcalfe - The Atlantic Cities

I want one of them.
Forget Electric Cars, This One Runs on Compressed Air - John Metcalfe - The Atlantic Cities
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Old 01-06-2013, 17:54   #8
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Re: SCUBA tank to drive a batt charger motor

An 80 CuFt scuba tank only lasts me about an hour while taking a breath every few seconds. I would guess that it would be empty in a matter of a few minutes trying to operate some sort of pneumatic generator. My little DA sander needs an amazingly large volume of air to run, I would think at least as much as a generator contraption. I don't think you would get much a charge before you run out of air. Of course I have been known to be wrong once in a while too....
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Old 01-06-2013, 17:59   #9
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Re: SCUBA tank to drive a batt charger motor

A standard full tank has 80 cu ft... if your motor used 10cfm, you have 8 minutes; not much charge there. A more efficient use would be an air starter..... or carry a small Honda genny!!!!
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Old 01-06-2013, 18:35   #10
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Re: SCUBA tank to drive a batt charger motor

I hear you, capngeo and Capt.Alex. My assumption that I could run a small alternator-type motor from one tank is fundamental. There are multiple unknowns (to me), but some sanders (using 90psi input) state that they run on ~2 cfm (I don't use air tools, so not sure of the importance of specs relating to 15-second vs full-load runtime, effect of input pressure, etc).

An 80 cuft tank could supply about 40 minutes of run-time if I assume the alternator/generator consumes about 2 cfm; BUT I have no idea what the friction/load requirements are of an alternator/generator, i.e., whether 2 cfm is anywhere in ballpark. Nor whether that time could charge a dead/near-dead battery enough to just-barely-crank my diesel (& glow-plugs)!

Sounds like the physics may(?) mean that no-one bothers with any consumer-product. Just a crazy-idea of mine I guess.

Nevertheless, I'd love to hear from others regarding the feasibility - I could get a second SCUBA tank ($80 used) if things were marginal - then I would also not be w/o a tank for actual diving.... ;-)
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Old 01-06-2013, 18:58   #11
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Re: SCUBA tank to drive a batt charger motor

You would be further head configuring your engine to start on the compressed air stored in the Scuba tank.
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Old 01-06-2013, 19:00   #12
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Re: SCUBA tank to drive a batt charger motor

As most trucks and heavy equipment start their engines on compressed air starters, is that not a better alternative than trying to charge a battery to do the same thing?

Yes if you wanted to make an air powered battery charger for some other purpose i can understand but it all you want to do is to start your motor, maybe look in a truck wreckers and save yourself some headache.

Plus you would still have most of your scuba tank full for diving.

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Old 01-06-2013, 19:57   #13
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Re: SCUBA tank to drive a batt charger motor

A truck starter would use up a tank of air in just a few minutes. Where would you get the compressed air anyway? Sitting in an anchorage listening to a gas powered scuba compressor run for an hour makes me think this is not a sound idea.
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Old 01-06-2013, 19:58   #14
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Re: SCUBA tank to drive a batt charger motor

I think the best option is to just buy a second battery. Isolate it so that it charges when the house battery is full but doesn't deplete with the house battery and if you need it you have MUCH more energy available than trying to generate electricity from compressed air.
As a side story, I have a small diesel motor that I start with compressed air / air motor. The air motor is rated at about 4 hp and sucks down a 60 gallon 125 PSI tank in no time flat. The motor can only handle about 100 PSI but needs a huge amount of air. I use a 1/2" hose to feed it but should really be using a 3/4" hose for best use of the available air. I would think that a big issue would be the regulator freezing up as you try to go from 3000 PSI to 100 PSI - 80 cu ft used up in something like 30 seconds or less.
Ok, looked it up, my Gast motor uses 128 CFM at top speed !!!!
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Old 01-06-2013, 20:27   #15
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Re: SCUBA tank to drive a batt charger motor

Yes, a second battery or maybe a solar panel... You will not get far on turning an alternator with a scuba tank...

... Do you have a dedicated start battery with a switch?
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