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What transistor do I need?

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New Member
Hello, everybody!

I have no experience with and very little knowledge of electronics. My school has organized a competition for building the fastest toy car running on solar cells. I want to hide some batteries in my car (for fun, of course - I will reveal the cheat if nobody finds it). The problem is that if somebody covers the solar cells and the wheels keep spinning, it will be obvious that battery power is used. Can I connect the solar cells to the BE pins of a transistor, and the battery-motor circuit to the CE pins, so that the power of the motor depends on the voltage of the solar cells? If yes, what kind of transistor do I need?

Each of the 6 solar cells provides up to 0.5V (tested) and is rated 800mA. Ideally the motor should be supplied with 6V, but I don't know what current it needs. I will be hiding the battery inside another 2.8x2.1cm motor, and the only batteries I found that would fit are 12V car alarm batteries, but they are rated 33mAh, which sounds too low...? The whole event will last more than an hour. Can you think of any better batteries?

Thank you!


Well-Known Member
Most Helpful Member
You do not understand how transistors work so don't connect a transistor the way you described or it will burn out.

The tiny 12V battery is way too small to power a motor for an hour. It is designed to power a low-current electronic circuit for only a moment at a time.
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