What you're after is a simple amplifier. There are lots of ways of doing this, the easiest is by using one transistor and one resistor.
Go to find a graphic of how to do this. Use a transistor with a maximum current rating (Ice) of more than what your electrolyser needs. You may need to amplify the signal from the 555 a bit more than with just one transistor, but this should get you started.
In the diagram, the output from the 555 goes in place of Vbb, and your electrolyser goes in place of RL. The current needed for the base is about 1/50 times the current that your electrolyser draws. So if your electrolyser draws 1 amp, then you need 0.02A base current, or 12/0.02 = 600 Ohms for the base resistor.
Alternatively, you can use a FET, which doesn't require a base resistor, and is more efficient. However FETs are a bit more finicky and can blow up a lot more easily if you're not careful. You need to put a high value resistor between gate and source otherwise the FET will fail. Here's a which shows the basics of using a FET.Statistics: Posted by nebbian — Sat Sep 30, 2006 11:11 pm
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