A car battery should have enough voltage provided it is fully charged. An easy alternative would be a simple car battery charger. From there you just need a container for the water with two chambers for gas collection. One chamber should be over each electrode as the hydrogen gas will come off one electrode and oxygen from the other. It is possible to add material, such as salt or metals, to help the process. Oh, almost forgot, a neutral plate isn’t necessary.
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1. A car battery/alternator gives about 4-5x the voltage required.
(Extra voltage is wasted as heat.)
The amperage drawn is governed by the plate areas
and conductivity, (salt or acid content), of the water
used.
2. Both plates are important.
3. You will not be making ‘HHO’, but an explosive mixture
of hydrogen and oxygen.(Don’t let any large amount accumulate
or you are likely to regret it.)
4. You might get a small increase in ignition efficiency, (with the
possibility of ‘knocking’), but you will never recover the energy you waste.
Can you spell ‘dumb idea’?
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this is a scam, beyond any question. And dangerous also, as the H2 O2 mixture (not HHO, that is a sales gimmick) is extremely explosive!

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