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07-23-2011, 05:35 PM #1
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Jacob32123
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Phlatlight Problem

I got my first PT-54 yesterday, and I am having some problems. The spec sheet says that you should be able to drive it at up to 8.1 amps at up to 3.5 volts.

I ordered some LiFePo4 batteries, but while I waited for them to come I decided to hook up the LED to 2 D batteries in series for 3 volts, right in the middle of the voltage range (2 - 3.5 volts). When I hook the LED in series with me ammeter, it only reads in at 2.31 amps max, normally around 1.9 amps.

So I figured that D batteries couldn't handle that kind of load, so I shorted out the 2 batteries with my voltmeter in series and it read in at 15.3 amps.

So now I know that the D's can supply that kind of current, what am I doing wrong?

07-23-2011, 07:03 PM #2
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Cyparagon
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Re: Phlatlight Problem

They don't have enough voltage to push the current through.

The voltage is not a linear function of current (or vice verse) so even if it was in the middle of voltage, it doesn't mean it's in the middle of current.

There's also the internal resistance of your batteries to consider. The voltage sags under load.
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07-23-2011, 07:05 PM #3
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lasersbee
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Re: Phlatlight Problem

An LED is a Current device....
You probably don't have enough voltage to supply
the current required or your battery voltage is drooping
under load reducing the current even more..

EDIT
looks like I was typing while you posted.....

Jerry
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Last edited by lasersbee; 07-23-2011 at 07:06 PM. Reason: Added info

08-15-2011, 08:29 PM #4
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Jacob32123
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Re: Phlatlight Problem

Lasersbee you were right. The voltage drops to around 2 volts with those batteries.

I got a computer power supply and the LED will only take around 5 amps and the voltage dosent drop at all.

With a LiFePo4 18650 it dose the same thing as with the computer power supply.

Any other ideas?

08-15-2011, 08:53 PM #5
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eytyxhs
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Re: Phlatlight Problem

2x Sayno 18650?

08-15-2011, 08:55 PM #6
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Jacob32123
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Re: Phlatlight Problem

Quote:
 Originally Posted by eytyxhs 2x Sayno 18650?
a123 LiFePo4. I tried with as many as 4 in parallel with no luck.

However, I did just get it to take 6 amps from the power supply. Still seems weird, that power supply will put out 19 when hooked up to a proper power resistor.

08-16-2011, 03:49 PM #7
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BShanahan14rulz
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Re: Phlatlight Problem

Using the right wires?

Solder connections?

you got that LED mounted well on a heatsink?

are the batteries in your meter dying?

Assuming your PSU is set to CV mode. What voltage are you putting across the LED? PSU wires dropping any voltage? Have you tried CC mode on your PSU?

http://www.sonic.net/~jayrob/Phlatlight%20Datasheet.pdf

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