AC Driver Problem

I have this driver
http://dx.com/p/jlnke-hta060240250-waterproof-2-5a-60w-constant-voltage-power-source-led-driver-silver-black-218164

connected to 8 PT-54 (red) in series.

When I turn on the power, I get what could be described as a fast beacon - ie 1 flash from all leds at the same time, about once a second.

I tried removing one of the pt54s so that I would have 7 in series - same behavior.

If I measure output voltage without LEDs connected I get a steady 24V.

any ideas on what might be wrong?

thanks!

The LEDs are probably drawing too much current for the supply to handle.

What is the Vf of the PT54’s? It could also be the Vf of the LED string is out of the range the supply can handle.

sort of what I was thinking - but this is my first (claimed) constant voltage driver

measuring voltage across the output leads with 8 in series jumps around near 12 volts…

Vf is min 2V, typical 2.7V, max 3.5

If is 8.1A

I’m a little worried about trying 6 in series…would suck to ruin the string

I figured with 8 in series a (claimed) 24V, 60W driver would be safe… |(

Those LEDs want to draw like 10 amps each… that’s around 30 watts EACH…

I figured, I guess incorrectly, that it would stay at 24V and give the rated output….

so i guess I save the driver for something else and find one that will drive 7 or 8 of them from AC power.

they’re each on their own original projector heatsink, but I’m not using the stock peltier or external cooling - i guess i could add a fan easily enough

finding a driver has been a PITA

two of these (12V, 3A, constant current and constant voltage)

with emitters in 4S2P should work?

http://dx.com/p/ip65-water-proof-led-driver-silver-black-12v-3a-220856

or, is there (simple) some way to limit the current drawn from the driver I already have?

Constant current drivers should work just fine… they will limit the current that the LEDs are trying to suck… but for full brightness you would want 10 amp ones…

Why do you need all that red light? Opening a bordello?

beats my idea of camera film developing room

i guess i’ll order two of those. I wish there was some way to augment what I’ve got, instead of dumping more money into the project, but that’s the way it goes i guess…

red light therapy. a friend with rosacea pays for sessions (like a tanning bed, but red bulbs).

main concern is the face, so these should be much brighter than the bed, even at 3A

Try a current limiting resistor in series with your constant voltage driver. I’d start with a 1 ohm power resistor (5-10 watts) and see what happens. Might need more or less ohms to get it right…

I will, thanks for your help (yet again) :slight_smile:

two resistors in parallel, each rated ~12W, for total resistance of ~3.5 ohms did the trick.

2.5 ohms would still flash, 5 ohms was noticeably dimmer than 3.5 ohms.

I epoxied them to heatsinks but they heat up the sinks pretty quick. I’ll need to add a fan to get 20 minute run time, but i’ve got plenty of those around.

at least i’m in business until the slow boat brings me a couple 12V constant voltage/constant current power supplies

thanks again