A standard diy arc welder (transformer type - heavy) produces about 40 volts AC.
I connected this to a bridge rectifier to convert it to DC. These are availabe in most electonics stores or Ebay for about £10 or £5 if you are willing to wait for it to come from China!
Make sure you get one with a heat sink as it will be working hard with 2 or 3 cells running off it.
With the welder on its lowest setting I get 36v DC from my bridge.
Connected across a single cell I got a lot off gas but also some intenal sparking (very bad with HHO gas present) and heat so did not risk using this set up.
Split across the 2 cells and a stainless coil in series provides about 12v to each just as a vehicle battery would.
The 12v per cell seems stable and runs well for long periods with little heat generation.
The construction of my cells, bubbler and 'torch' are mostly from scraps or standard diy materials.
Welder - transformer type - about £60 but most diyers have one lying around
Bridge rectifier - about £15 - had to buy two as I blew the first one which had no heat sink
Double pole switch - £3
Jars - 3 for £5 in a local bargain store
8mm Copper tube - left over from an oil tank installation
Thin stainless tube cut from a ball inflator
KOH - drain cleaner crystals - £1 from a local hardware store
T-pieces / straight connectors & plastic tubing - fish tank fittings from Ebay - about £6
Bubbler - herb jar with a rubber tube siliconed into its neck and an old broken drill chuck set on top
Stainless wire taken from old rigging cables
Stainless mesh plates cut from an insect screen
Already had the welder so reckon the additional parts came to less than £40
Step 1: Building the Wet HHO Cells
To make the cells I used cheap glass jars, stainless wire, stainless mesh, an old plastic starage container, an old chopping board, two spouting bolts, some epoxy glue and a little silicon sealant.
I cut 70mm squares out of an old chopping board (fit in the neck of the jars with a couple of mm clearance each side) and stuck them into the lids using epoxy glue.
While this set I attached the spouting bolts to the stainless wire and coiled it so it will wedge the neutral plates and spacer plates.
Once the glue was cured I drilled three 6mm holes in each lid. Two for the electode connections and one for the gas output fitting.
I then put a smear of silicon gasket sealant round the aquarium push fitting and inserted it into the center hole and also put silicon gasket sealant in the groove between the jar lid and section of chopping board. This will create a gas tight seal when the lid is held down by a cable tie.
For now I am using stainless mesh as my plates - just an old insect screen. It is easily cut with sheet metal cutters. I cut 9 of these 70mm by 120mm for each cell. Two will become active plates wedged against the stainless loops - the rest neutrals.
For spacers I used plastic sheets with holes. The red ones are an old plastic storage basket cut into sections the same size as the SS plates. The white ones in the other cell are just a plastic pipe drilled, cut and flattened.
Before final assembly it is good to put it all together and add the water / KOH. I put the loops / plates and spacer in and filled nearly to the top with just ordinary tap water. Then I applied voltage to the wire loops at each side of the cell.
Not very much will happen till the KOH is added - do this slowly as heat is generated from the caustic soda as it dissolves into the water and also from the electrolysis which should get quite active after a couple of spoonfulls have been added. Be very careful with this liquid as it is very caustic and can burn skin.
If your cell gets hot quickly you will need to reduce the voltage or dilute the electrolyte you have mixed.
To complete the cell I removed and washed the SS loops so I could handle them to bolt them into the lid. Use sealant around the bolts to prevent gas escaping through the threads. Putting the loops back into the jar with the lid attached is tricky enough but you can use a screwdiver to move the plates & spaces to one side then the other as you insert the loops and lower the lid. Secure with cable ties or similar.
Step 2: Bubbler
Not the best looking bubbler but does work.
Carefully drilled top and bottom 6mm holes for the aquarium fittings and drilled out the center of the lid for gas release in the case of a flash back.
I tried using plastic bags as rupture discs in the lid but was nearly defened by the bang each time I had a flashback.
The weight on top of a rubber tube just jumps a few millimeters with a good pop when there is a flashback, much better for your nerves.
Rubber bushing / tube sealed into the lid / top of jar with silicon sealant can be blocked closed with any small weight. In this case I just shoved a smooth headed spouting bolt into an old broken drill chuck. The curved surface makes a good seal pressed against the rubber.
I fill the bubbler with industrial alcohol to stabilise the flame and always keep it as full as practical to reduce the amount of stored HHO.
Step 3: Torch
The torch is very simple. I tried a standard ball inflator first but do not have enough gas production to keep a flame and constantly got flash backs. When this is crimped to a smaller size the gas flow rate is faster (but a smaller flame) and flash backs become rare.
I cut off the tube part of one of the inflators and brazed it into an 8mm copper tube. This feels easier to hold in the hand and absorbs more heat.
Step 4: The Dump Coil
I was getting sparks betweem the SS loops and the active plates when each cell was running at near 20 volts. They were also getting hot - a dangerous combination when generating and gathering hydrogen and oxygen together.
In the longer term with the third cell in series the voltage across each cell should be near 12v which seems stable but in the meantime I coiled some SS wire and put in in series with the 2 cells. The full length coil in the picture dropped over 20 volts leaving nothing happening in the cells. Moving the connection to the mid position - pictured below - reduced this voltage drop to about 14v leaving plenty for the cells. It gives off a good amount of heat when running and even vibrates a little on start up.