The other day I found plans for a $3 battery charger that was just a diode and light bulb in series with the battery, using mains electricity. I poste d a question about modifying it with a dimmer switch here: Everyone there said I was a candidate for a darwin award and that I should come to before I kill myself. Taking their advice to heart, I have not built this darwin battery charger, but I do still have batteries to charge, namely a 7.2v nicd battery pack f or a jigsaw. I found an 8.7vdc 360mA wall wart, and by putting a 12v car he ater/fan in series with the battery, I got the amps low enough to trickle c harge it. However, I suspect the 8.7v isn't enough, and also, as the charge goes on, the current falls. After a few hours, I measured C/24, and overni ght it was C/60. I've read that nicads need at least C/10 to fully charge ( though another source says C/16 will work), so this wall wart seems to be i nsufficient. (Strangely, when the current reached C/24 and C/60, removing t he heater didn't affect the amp rate at all. I wonder why?) My new idea is to take a 24vac wall wart that I have and add a diode to rem ove reverse current, then put it in series with the battery and some curren t-limiting load. This is essentially the same $3 dangerous battery charger except using 24vac instead of 110 mains voltage. Is it still dangerous? Peo ple in the other group said even 25 mA is lethal if it crosses the heart, l ike would happen if you stupidly grabbed both leads of unshielded alligator clips, and it doesn't matter that the current is limited. It's not limited enough, especially when the lightbulb begins cold. Other questions, assuming this circuit isn't dangerous: 1. Could I use 12v appliances or light bulbs as the current limiter or will the 24v burn them out? Since it's attached to a 7.2v battery, the voltage will be lower, right? 2. Would a dimmer switch work to make it finely tuneable? That way I could monitor it and increase it as it falls, keeping...

We purchased a number of cheap cordless drills at work. The chargers that come with them are nothing more than a wall wart, diode and resistor. They work for a while, but eventually the batteries all died, some of them simply would not take a charge, others got hot and melted while in the charger. Save yourself a lot of grief and just purchase a proper charger.

--- And yet you don't, but still you bitch. If I make an error I usually find it and own up to it, knowing that it'll never be found out by the likes of you, but that it still needs to be corrected. As a consequence, you cry "wolf" when you wouldn't have known the wolf was there until someone told you. --- --- I guess you're British, but you sure don't know much about English, since: "Although you're such an ill tempered cuss, most people walk on by hoping not to attract your attention!" Should read: "Because you're such an ill tempered cuss, most people walk on by hoping not to attract your attention!" Can you discern the difference? -- JF

Is this homemade battery charger circuit dangerous?

Jul 17, 2013 41 Replies

Rate this thread:

John Fields 12 years ago

And yet you don't, but still you bitch. If I make an error I usually find it and own up to it, knowing that it'll never be found out by the likes of you, but that it still needs to be corrected. As a consequence, you cry "wolf" when you wouldn't have known the wolf was there until someone told you.

Vote

John Fields 12 years ago

Indeed. In his case, I think he doesn't know how abjectly ignorant he is and, as a consequence, feels forced to display his plumage.

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required