Boost converter or turn series to parallel in an LED work light.

HR19 said:

I'm trying to convert it to use my Milwaukee tool batteries, 21V max, 18V nominal.

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rjenkinsgb said:

Just remember the voltage range of the battery.

At full charge, 5 x 4.2V = 21V
By the time it's discharged, it will be down to roughly 3.5V per cell so 17.5V total

With a simple LED + resistor circuit, that's a change of 3.5V, almost entirely across the resistor, which will give a very significant change in brightness.

That's why some form of converter is normally used, so you get a constant output voltage or constant current, regardless of battery voltage.

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HR19 said:

My plan is to use a rheostat so I can adjust the brightness.

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Nigel Goodwin said:

Bit difficult when you can't even decide what current or power it's taking - you've given two wildly different values (1W and 24W), which is it?.

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HR19 said:

One is a calculated usage, one is a rating from the manufacturer. A rheostat could also easily handle numbers like those, not sure why you think there's a problem.

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Nigel Goodwin said:

I suspect you don't really understand the wattages involved? - and a rating of 24W isn't only going to draw 1W, and wouldn't be terribly bright if it did. 1W from an LED totch is pretty damn bright, but only in a small area - lighting to cover an area is MUCH more spread out and needs much more power.

A rheostat is an antique term (pre-1960's?) and usually refers to a massive huge wirewound device, such as used to be used in ancient theatre lighting (they used to have them where I went to school ) A modern device is a potentiometer, which is only low power, and designed to control electronics.

I think there's a problem because you appear to be hoping to control 24W with a device that may only be able to control milliwatts - there's also the issue that as you get towards the end of the track you get high wattage across only a very small portion of the track, which futher limits their power capacity.

If you're actually using an antique rheostat, then there shouldn't be any problem - other than inefficiency and heat.

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