two part question using 3.8 VDC batteries (dc to dc converter?)
two part question using 3.8 VDC batteries (dc to dc converter?)
(OP)
Steven here. Mechanical engineer. I have a pretty nice mechanical design here using a 3.8v dc battery supply and a 3.4v 13A LED. I need to use some 5v fans.
So my question is....
how to get the 3.8v down to 3.6V to 3.3V
and....
how to get the 3.8V up to 5V-6V
There are no electrical engineers to fix my problemo here
So my question is....
how to get the 3.8v down to 3.6V to 3.3V
and....
how to get the 3.8V up to 5V-6V
There are no electrical engineers to fix my problemo here





RE: two part question using 3.8 VDC batteries (dc to dc converter?)
Next was that 13A? What size is this battery? 13A is non-trivial.
Keith Cress
kcress - http://www.flaminsystems.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
Did you mean 13 mA on the LED? 13 Amps sounds like quite an LED array. That'd be either one monsterous fan cooled LED or an array of around 500 standard LEDs. If you meant 13 mA, use a resistor. 5V-3.4V/.013 = 120 ohms. 1/4 Watt resistor will be plenty.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
"Next was that 13A? What size is this battery? 13A is non-trivial." 4 D cell 11,000mA
The 3.3v fans spin but I need to overpower them to get the correct 15 CFM. 5.5v would be lovely.
13a is The current draw but might get to about 15a if I run them at 3.8v which is why I need to step it down a bit.
5V-3.4V/.15 = 10 ohms. ? Watt resistor (how do you decide what wattage resistor to us?
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
13A into an LED array? What is it, a searchlight?
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If we learn from our mistakes I'm getting a great education!
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
Sizing your resistor is simply a power funtion I^2 * R or V^2/R. I'm going to use the V^2/R.
First you'll need to determine a value for your resistor:
5V battery - 3.4V LED = 1.6V drop in resistor.
Since we know the LEDs are requiring 13A, we apply V = I*R and get:
R = 1.6/13 = .123 ohms - This is not a normal resistor value, so we'll need to make it from some parallel or seies resistors. I'll go with parallel. If using all the same value the resistors parallel rating will be R/Number resistors. So: 5 X 0.63 ohm resistors in parallel will work. So will 8 X 1 ohm resistors in parallel.
Now for the Wattage requirements:
We know P = V^2/R (The I^2 *R yields same result) and we know V drop on the resistor bank is 1.6V. We also know R is ~.123.
So you'll need a resistor bank rated for at least 21 Watts. Since the power dissipation is divided equally among parallel resistors the wattage value needed is:
Wattage of bank/#parallel resistors.
So if you use 8 X 1 ohm resistors, they'll need to be 3 watts or more. If you use 5 X .63 ohm resistors, they'll need to be 5 Watts or more.
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
http://www.enginyr.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
Keith Cress
kcress - http://www.flaminsystems.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
http://www.enginyr.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
Keith Cress
kcress - http://www.flaminsystems.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
http://www.enginyr.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
I'm skeptcal.
http://peakbeam.com/index.html
Keith Cress
kcress - http://www.flaminsystems.com
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
The picture suggests this might be carried in you pocket. Is this really meant to be carried around? 4 D-cell batteries is enough weight to bring my pants to my ankles.
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: two part question using 3.8 VDC batteries (dc to dc converter?)
http://www.enginyr.com