Is 12vdc compressor from solar possible

[NotWavingDrowning]

I have a cruising catamaran and want tanks before hookah. I was thinking of using an 80cf tank and filling it to 2000psi. My math says I should be able to do it with around 0.6kWh of power which I can make with solar.

My problem is reality doesn't seem to agree (happens a lot), from what I have told I will need at least double that which I can't make.

Anyone know if it can be done.

 

[clownfishsydney]

No, not enough power to pump the pressures you want. Also, I doubt there is a 12 v dive compressor that pumps anything but very low pressures. On my cat we had to convert my 240 v Bauer to petrol to use. A Bauer uses 2.2 kW but needs well over 5 kW to start.

 

[NotWavingDrowning]

No, not enough power to pump the pressures you want. Also, I doubt there is a 12 v dive compressor that pumps anything but very low pressures. On my cat we had to convert my 240 v Bauer to petrol to use. A Bauer uses 2.2 kW but needs well over 5 kW to start.

I was hoping to overcome the start with a capacitor or maybe even a clutch or worst case a hand crank .

When yours draws 2.2kW is that the maximum draw... i.e. just before shut down @ 3000psi ?
How long does it take to fill an 80cf tank ?


2.2kW is workable if it takes 20min to fill 80cf to 3000psi

My dodgy maths would make this (20min = 1/3hr) roughly 1/3hr x 2.2kW = approx. 0.75kWh

If I only fill to 2000psi that should be 0.75kWh x 0.5 = 0.375kWh or 1 x 300Wh solar panel for 2 hours

 

[Danseur]

Anything is possible, but unless it's Waterworld or a BIG boat, not worth the trouble, IMHO

 

[NAM001]

I was hoping to overcome the start with a capacitor or maybe even a clutch or worst case a hand crank .

When yours draws 2.2kW is that the maximum draw... i.e. just before shut down @ 3000psi ?
How long does it take to fill an 80cf tank ?


2.2kW is workable if it takes 20min to fill 80cf to 3000psi

My dodgy maths would make this (20min = 1/3hr) roughly 1/3hr x 2.2kW = approx. 0.75kWh

If I only fill to 2000psi that should be 0.75kWh x 0.5 = 0.375kWh or 1 x 300Wh solar panel for 2 hours

Your back pressure regulator will determine the min draw. If it is set at 2700 than it makes no difference how full you fill to up to 2700 the draw will be the same. If you lower it to 2000 then you will reduce the electrical load until tank pressure goes above 2000.

 

[JamesBon92007]

Do you have a link to a 12 volt scuba compressor? I'd like to see it.

Regardless of the total amount of kwh it takes you need enough amps to get the compressor started. My math is horribly rusty at the moment but, for example, I have a small 110VAC compressor that will run from a 15 amp outlet. That means you need at least 1800 watts of starting power available. Ordinarily solar panels are used to charge a bank of batteries and then an inverter is used to supply the needed power. You need enough batteries to supply that start up power or the inverter will shut down. I'm guessing, off the top of my head, that you would need 6-8 "golf cart" batteries. I can't recall the battery ratings at the moment but it used to be a standard. You might need only a few hundred watts of panels to charge the batteries enough to run the compressor for 30 minutes or whatever. 1800 watts of panels seems like a lot to put on a small boat. Personally I think, under the circumstances, I'd go with a gasoline-powered generator or, even better, a gas-powered compressor. Gas is only $3/gallon and I've had some good luck with cheap Chinese compressors If you have a 12VDC compressor it might start with the batteries mentioned but might not run long enough to suit your purposes.

 

[hammet]

Do you have a link to a 12 volt scuba compressor? I'd like to see it.

Regardless of the total amount of kwh it takes you need enough amps to get the compressor started. My math is horribly rusty at the moment but, for example, I have a small 110VAC compressor that will run from a 15 amp outlet. That means you need at least 1800 watts of starting power available. Ordinarily solar panels are used to charge a bank of batteries and then an inverter is used to supply the needed power. You need enough batteries to supply that start up power or the inverter will shut down. I'm guessing, off the top of my head, that you would need 6-8 "golf cart" batteries. I can't recall the battery ratings at the moment but it used to be a standard. You might need only a few hundred watts of panels to charge the batteries enough to run the compressor for 30 minutes or whatever. 1800 watts of panels seems like a lot to put on a small boat. Personally I think, under the circumstances, I'd go with a gasoline-powered generator or, even better, a gas-powered compressor. Gas is only $3/gallon and I've had some good luck with cheap Chinese compressors If you have a 12VDC compressor it might start with the batteries mentioned but might not run long enough to suit your purposes.

+87
Even if you did have an 1800 watt panel, it would have to operate at 100% efficiency...requiring direct sunlight the whole time.

If you had a large battery bank on board, you could run it with an inverter .
At 12 volts, 1800 watts would require 150 Amps. Add another 50 or so for loss using the inverter ... so about 200 amps.
If you had a 400 Amp hour battery bank, a typical size for a cruising sailboat, it would be deplete to half charged in a half hour at that rate. Going below half charge will severely shorten the life of deep cycle batteries.
Now, If you ran your engine with an 100 amp alternator simultaneously, you could get about an hour of air filling time before your batteries were half depleted. In theory.

 

[tbone1004]

alright, so a bit of weird info up there.
You can run any compressor you want on 12vdc. Don't care if it's a 50cfm monstrosity, or a Rix SA3. All you have to do is put a 12vdc motor with appropriate pulley on there and it will go. The problem is finding one big enough to run it at any reasonable speed.
On average, you need 1hp/cfm.
Important notes
1hp=746watts=torque*rpm/5252
Compressors are constant torque applications, so your motor needs sufficient torque capacity to actually turn it, but that's not all that much.
MOST compressors use splash lubrication which means they have a minimum RPM, generally somewhere around 70% of the top speed so you can't slow them down all that much.
Watts=volts*amps, so to get a 1hp/cfm compressor at 12v, you will be continuously drawing 65-70a depending on efficiency losses. You will have to run 2-4awg wire which is thick and expensive. That is why cars went from 6v to 12v systems, and why cars are moving towards higher and higher voltages. Smaller wires are cheaper and lighter. The motors can also be smaller which is ideal.

So. Should you? No, running it on 12vdc is stupid IMO. Use an inverter and run AC. Can you find a compressor that will do it? Not many new ones are small enough to handle it, and none currently in production that I'm aware of that are truly variable speed. You can find an older Rix and put a smaller motor on it which is what I would do if you need to keep it electric, but it sounds like you'll be far better off with either an electric compressor and a generator, or a gas powered compressor.

 

[almostDIR]

would a small booster work for pumping normal air to the required pressures if you generate the low pressure working air using a small 12v compressor so small sized it can be powered from solar panels directly? would be very slow and a tad expensive and you would need to have custom filter assemblies but that would be easily scalable I think.

gas powered proper scuba compressor would be much easier and faster though


something like golf cart electric motor or similar could probably run a normal scuba compressor from low voltage source with proper speed though you would need very large battery bank to run it for the required time

 

[tbone1004]

@almostDIR golf carts are typically 24v as an FYI. Reason being the amp draw is cut in half which makes all of the wiring much easier to manage. Electric golf carts are typically 3-5hp, so the right range for most smaller compressors, but to get that in 12v would be very difficult since you would first have to find a 12v motor that large. It is very uncommon to see a 12v motor larger than 1hp due to the amp draw.
Depending on the voltage of the solar system, it may be possible to wire the panels and battery banks to higher voltage which would allow DC drive in a reasonable range.

@NotWavingDrowning this project is possible if you are truly committed to do it. It is not recommended if you do not have significant experience with high current electrical systems and there is a very real possibility of a fire. Proceed with caution