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# fluorescent emergency lamp convert to LED Answered

i have a fluorescent lamp input220v,6.5w, its battery is 6.9v. i want to convert this to led lamp. so pls provide the proper circuit diagram for this. and how many LEDs can handle this battery for 4hours

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## 3 Replies

lemonie (author)2010-12-21

Why?
The thing you have is pretty cool and efficient.

L

seandogue (author)2010-12-21

Well, let's assume 100% conversion.

then you have roughly 1 A (technically 6.5W/6.9V) for whatever time the battery is good for. Let's presume that your "4 hour" comment is in reference to the existing lamp.

So you have a 6.9V 4AHr battery pack. Pitch the 220V drive and associated lamp.

Now, let's assume a current draw of 15mA per LED and a forward voltage on each led of 3V

So, ballpark, you can run 120 LEDs. 60 parallel circuits of series groups of two, with a load resistor on each to compensate for the excess.

Conceivably, you could jut run off the existing 220V source, in which case you could run a very large number of LEDs (perhaps several hundred...220/3 * 3 parallel groups of 220/3 or three strings of 60 running at 10mA each), since it runs at roughly 30mA. A bit more dangerous (in fact, potentially lethal) but doable.

orksecurity (author)2010-12-21

Without seeing the current circuitry, it's hard to answer that.

Essentially, you want to rip away and discard everything between the battery and the current bulb, without disturbing the charging circuit, and replace that with the new switch, current limiting resistors as needed, and LED(s). (I'm sure someone will post a pointer to one of the calculators for picking the right resistor for a given LED and input voltage; I'm feeling lazy.)

How many LEDs you can run for 4 hours depends on how much power the LEDs you've chosen require and on exactly what battery you've got (how many amp-hours it can provide before dropping below a useful voltage). Again, we don't have enough information to tell you much more. For reference: I just got a string of 15 LED xmas tree lights, and the box claims they will run for 120 hours on three AA batteries. Brighter LEDs would draw more power, of course.