12 V compressor for mini scuba tanks: refill from the boat or the 4WD

The 12 V / 220 V compressor refills OXSEA tanks with no effort. It is a portable high-pressure compressor with its own filtration, built from components chosen for salt air and spray. Clamp it to a 12 V battery or plug it into mains power, connect the tank, set the pressure and it stops on its own when it gets there.

Fill times

Tank	Volume	Time
OX500	0.5 L	About 12 minutes
OX500Plus	0.5 L	About 12 minutes
OX1000	1 L	About 20 minutes
OX2000	2.3 L	Longer: start it as soon as you are out of the water

Without access to a dive shop fill, it is the only way to refill the OX1000 and the OX2000: the hand pump only fills the half-litre tanks.

Why your tyre compressor will not do

A tyre inflator works at a few bar, a workshop compressor at around ten. A mini scuba tank needs 200 bar, and the air has to be fit to breathe. That takes a high-pressure breathing-air compressor with filters, which is what this is.

Which battery to use

On the boat: the house battery. Never the cranking battery. A cranking battery is designed to deliver a big current for a few seconds, not to be drained and recharged over and over.

In the 4WD: the auxiliary battery of a dual-battery setup, if you have one, rather than the starting battery. Engine off during the fill (see below), then drive to top it back up.

The drain is easy to work out: amps on the rating plate, times the hours it runs. Say the plate reads 30 A. Twelve minutes is a fifth of an hour, so a half-litre fill costs about 6 Ah; a one-litre fill, a third of an hour, about 10 Ah. Now the battery: with lead-acid, plan on using only half of what the label says. A 100 Ah house battery really offers around 50 Ah, and the fridge, the sounder and the lights want their share too. That covers two or three fills over a day, as long as you put the charge back in once you are home. Our article on refilling from a boat battery has the full sums and the cable sizes.

Engine off, clean air

It seems smart to let the outboard or the 4WD idle so the alternator keeps the battery up. It is the one thing not to do: exhaust carries carbon monoxide, and the compressor will happily pack it into the tank you are about to breathe from at the bottom.

• Nothing that burns fuel should run nearby: motor, generator, the neighbour's barbecue.
• Outside, on level ground, out of the sun, with the intake pointing into the breeze.
• At a marina berth, mind the boats running their engines around you.
• Stay beside it for the whole fill, eyes on the gauge.

Looking after it

The filter changes in a few minutes, and the OXSEA School on oxsea.shop has a video for it, as well as one on using the compressor. Watch both before your first fill, not on the day you need it.

Compressor or hand pump?

The compressor, if you have the 1 litre or 2.3 litre tank, dive several times a day, or would rather not pump for 20 minutes. The hand pump, if you only use a half-litre tank, dive now and then, or often find yourself with no power at all.