Would appreciate some help with under cabinet lighting.

[Naturalreef]

Hi everyone,
I purchased 7 led kits from Menards on clearance. Each kit consists of 3 led pucks with a low voltage transformer rated at input 120 /.19 amps max and output of 700ma @ 24vdc max. It says on the package 9 watts of power draw, so I'm assuming 3 watt leds since the manufacturer won't give me any details about the led they use. I purchased 14 gauge low voltage wiring approved for behind wall use with my building department and wired 21 leds in parallel with 3 runs to the basement.
One wire run has 12 leds and the other two are 5 and 4. I took one of the kits transformer and did a test run and all the leds lit up albeit dim because of the small power supply. The reason I hacked the kits up instead of buying everything separately was because these kits were on clearance and it was cheaper than buying what I was looking for online. The kits have a nice silver aluminum finish which matched the kitchen well. I'm sure the leds are of lower quality, but they had a 5 year warranty on the kits before I hacked them

So being proud of my achievement , I go out to search for a bigger power supply at 24vdc. I tried 3 different power supplies 24vdc@ 100 watts and none would light the leds up. The power supply would blink which I believed was protecting itself possibly from the voltage drop. I was confused as to why the small power supply would light them all up evenly and dim and the bigger power supply wouldn't light them up at all? After more research, I realized maybe I need a constant current driver instead of constant voltage.

I would appreciate any advice you could throw my way so I can light these all up and use the power supply that cost me $70 that I can't return now. It's rated at 144 watts /24vdc/ 6 amp max. I can't do any more wire runs or change the configuration of the three runs, because they were a bear to fish through the walls. Can I possibly use dc buckpucks above each cabinet run to give cc 700ma to the leds? I wanted to use my 24vdc pwm rf remote to control the leds if I could. Right now I'm stuck with a lot of labor and money and the wife still has no lighting..... I sincerely appreciate the help.

Nick

 

[DIWdiver]

Do the LEDs still light with the smaller transformer? I'd be a bit surprised if you haven't fried all the LEDs.

They are most likely 2W LEDs, or at least were going to be driven at 2W by the original transformer (most white LEDs are in the range of 2.9-3.3V, and at 700 mA, that's 1.8-2.3W).

Most likely the original strings were in series, not in parallel. If so, and you've cut them all up and wired them all in parallel, that explains a few things. It also means they probably still work. The bad news is that's not the right way to wire them for the supply you have.

To run the LEDs in parallel, at rated power, you'd need 21x0.7 = 14.7A. And the voltage would be a bit over 3 volts.

 

[Naturalreef]

Thank-you for the reply Diw,
The small transformer still lights all the leds at a dim level. If I just light one string of 4 leds with the original transformer, they are full bright as they were out of the package. I'm hoping since they didn't light up with the 150 watt transformer that no damage was done. Could you please explain to me in layman's what type of driver I would need to light these in parallel( all positives to positive and neg to neg). Can I still use the 150 watt 24vdc driver or do I need to grab a cc 700ma driver? I just haven't seen a cc 700 am driver greater than 60 watts. When you say 14.7 amps at 3 volts I'm confused. If you guys could help me get on track to light these leds properly, I would really appreciate it.

 

[DIWdiver]

Do you have a way to measure the voltage across one puck while it's running on the small transformer? I think maybe I don't understand what's in the pucks and how they should be driven.