I believe there are no mistakes in the schematic, various other people with electronic circuit design skills have looked at it without any criticism to its safety. It has been designed to be safe for leaving a battery connected to it indefinitely, safe electrically, and designed not to stress any of the components.
DISCLAIMER: I designed this cos i wanted a decent charger quickly, I'm sharing it for the purpose of sharing informtation. This info comes without any warranty. Its not a guide, if you build its entirely at your own risk. Seek professional advice etc. Electricity is dangerous, sparks are dangerous, petrol is dangerous.
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This is meant to be a cheap, quick, easy charger for topping the battery up at night and safe for leaving the battery hooked up to it after the battery is fully charged. It can be used on wet or gel cell 12V lead acid batteries.
Unlike some cheap chargers which apparently float batteries at 14.4 or even 15V once they are fully charged. (Very bad for lead acid batteries)
The LM317T is a great chip, its got short circuit protection and thermal protection. Hopefully these features wont ever be "needed" :)
Pointers:
* Its best to keep the AC cable long (as needed) and the DC cable (output of charger) as short as possible (basically reach from the floor to the bike's battery and a bit extra) This is to minimize the wire's resistance which acts to decrease charging voltage and current.
* I power up the charger, connect the negative terminal to the chassis where the battery bolts to it, then blow on the positive terminal as I hook up the positive crocodile clip.
Then give both clips a little wiggle to ensure they are firmly attached and making a good electrical connection. The reason I blow on the positive is to ensure there aren't a bunch of petrol vapours lurking around it. Spark plus petrol = ignition. Its just a precaution. Prevention is better than cure :) Just like keeping your battery charged.
* When batteries are in a state of discharge (Below 100%) they slowly self destruct, the rate depends how dead they are. Lead acid batteries can last many years.
* A charging connector mounted on the bike presents a convenient option which would likely provide a more solid electrical connection with lower resistance.
*The charger is designed to handle a short circuit, and the amount of power it puts out is limited to about 4W.
A big metal frame can dissipate 4W with ease. On the other hand, using a high current battery charger, a lot more heat could be generated by a short circuit.
Enjoy! Lope
