Need help checking my power calculations

Gerald · 2006-09-01T17:03:54+00:00

Hi,I want to make a battery powered light, powered by a PIC.I have a rechargable 6.6 volt battery, and a 5 watt halogen bulb.The battery is 2.3 amp hours.Am I correct that to estimate the length of burn time this way:5 watts/6.6 volts = current = around 757 milliamps 2.3 amp hours / 757 miliamps = a little over 3 hours.Now, if I use a PIC and pulse the bulb at about 50% to get a dimmeroutput, is it safe to guess that I would get about 6 hours light outof this battery?Also, at that power rating, can anyone suggest a transistor to usethat won't get too hot?Thanks!Gerald

Sep 01, 2006 21 Replies

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kell 19 years ago

Here's a possibility

battery | | halogen light | _| | pwm_____10R_____|| RFP30N06LE |_ | | ground

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The rfp30n06le is a logic level mosfet, so your 5 volts will turn it on. The mosfet won't draw any current from your pic or555. The mosfet has about a twentieth of an ohm resistance, so it won't get hot.

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John Fields 19 years ago

LOL, It wasn\'t _I_ who suggested that a 2.5W lamp will burn brighter than a 5W lamp, was it, dumbass?

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