LED light testing

[Larry Singer]

I really appreciate the work and tests you've done. And the fact that you took the time to share your results. It helped me alot.

What do you think of the reply from Thomas G on 2/1/12 recommending the use of a voltage regulator ?

Thanks again,

Larry Singer

[Thomas G.]

..........What do you think of the reply from Thomas G on 2/1/12 recommending the use of a voltage regulator ?...........Larry Singer

.............or you could just ask me why I recommended it.

[Raz]

Originally Posted by Thomas G.

The device has three leg connectors. 12 volt power in connects to the left leg, power out connects to the right leg. The center leg is a common ground.

7805 or 7812 ?

[Thomas G.]

Originally Posted by P. Raz

7805 or 7812 ?

I used a LM2940CT -12 low drop out regulator.

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[Raz]

Originally Posted by Thomas G.

I used a LM2940CT -12 low drop out regulator.

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The reason I asked is because the picture you posted showed a 7805 and both were labeled 5v.

[Thomas G.]

Originally Posted by P. Raz

The reason I asked is because the picture you posted showed a 7805 and both were labeled 5v.

Right. I was answering the question of how to wire the device. This image was handy and I used it for the explanation. You are correct, that the devices shown are 5 volt regulators, but the 12 volt devices are wired identically.

[Spanke]

Originally Posted by Larry Singer

I really appreciate the work and tests you've done. And the fact that you took the time to share your results. It helped me alot.

What do you think of the reply from Thomas G on 2/1/12 recommending the use of a voltage regulator ?

Thanks again,

Larry Singer

Thomas gives good advice. The lights are very sensitive to wanting an even 12volt source. The voltage regulators he recommends are a cheap way to assure you don't over power and fry your new lights. I have purchased and will being installing them when I install my new LED light panels.

Spanke

[Raz]

Originally Posted by Thomas G.

Right. I was answering the question of how to wire the device. This image was handy and I used it for the explanation. You are correct, that the devices shown are 5 volt regulators, but the 12 volt devices are wired identically.

Hi Tom. Not trying to give you a hard time, I just wasn't quite sure if maybe you were using the 5 volt regulators instead. A while back there was a dicussion on using a 7812. Both drop out and oscillation are issues in my mind. Even the 2940 seems marginal to me, but having never bench tested it I'm not sure how low the input can actually go without loosing regulation. Folks seem to be having fun with this so I don't want to get in the way. Take care, Raz

[Thomas G.]

Originally Posted by P. Raz

Hi Tom. Not trying to give you a hard time, I just wasn't quite sure if maybe you were using the 5 volt regulators instead. A while back there was a discussion on using a 7812. Both drop out and oscillation are issues in my mind. Even the 2940 seems marginal to me, but having never bench tested it I'm not sure how low the input can actually go without loosing regulation. Folks seem to be having fun with this so I don't want to get in the way. Take care, Raz

The 2940 was recommended to me because of a low drop out - i.e. it should still provide close to 12 volts with a 12.5 volt input off a wet cell battery. I'd be interested to hear what you find in your own testing.

[ruscal]

Here are photos of how I mounted the 48 SMD panel into the Scamp swivel spots. I cut a piece of thin sheetmetal to fit the outline of the smd panel with a 1/2" x 1/2" tab centered on each end. Then I bent the tabs forward to about 45 degrees. The self stick tape on the back of the panels was used to stick them to the sheetmetal. Then I plugged the electrical in and simply pushed the panel into the bucket until both tabs clicked behind the plastic bucket frame. Before fitting the sheet metal to the SMD I trimmed the SMD around all sides so that it would drop into the bucket farther. I used a belt sander for the trimming. You have to be careful not to cut too much or you could remove a circuit trace and render the panel usless. The double sided tape on the back of the board covers the traces and make it hard to see what you are cutting. I am not using any regulator, since the panels are inexpensive, and I hate electrical noise and light strobing. It would be better if the light panels went into the buckets deeper to prevent glare while looking toward the fixture, but that would require the removal of the internal reflector.
Russ

[ruscal]

Here is another image of the completed spot.
Russ

[Raz]

Originally Posted by Thomas G.

The 2940 was recommended to me because of a low drop out - i.e. it should still provide close to 12 volts with a 12.5 volt input off a wet cell battery. I'd be interested to hear what you find in your own testing.

Half a volt is spec. They have to be doing some clever stuff to make that happen since silicon has a barrier potential of .7v. I can't test a 2940 for you. I don't have one in my junk box. I did check several 7812's I had. With 100mA load they all dropped out at about 13.8 V. which tells me when folks who used one of those switch to battery, the lights won't be quite as bright. Raz

[Rene]

I took Thomas' advice and ordered 2940's. They are not here yet but I won't be installing them for a while yet. I got enough SMD 48 panels and voltage regulators for all the lights in my B1700 for $30. With the money I saved I got a solar charge controller with a system monitor.

[Thomas G.]

Originally Posted by Rene

I took Thomas' advice ...........

Oh great. Now if it doesn't work out it is my fault.....

[Spanke]

Originally Posted by Thomas G.

Oh great. Now if it doesn't work out it is my fault.....

No good deed goes unpunished!

Spanke

[Rene]

I also found that if you google the 2940 part number there are webpages that describe how and why to use the regulator for 12volt circuits. So Thomas can be released from all responsibility here. Very little to go wrong in this case I think.

[Thomas G.]

Originally Posted by Rene

.......... Very little to go wrong in this case I think.

Until Mr. Murphy shows up.

[Rene]

Well I just installed some of the new 48 SMD warm white LED panels from asia. I am very pleased with the quality and output of light. I am not normally a fan of incandescent bulbs or cool white LEDs. These are perfect. Side by side with 1141 bulbs they are whiter than incandescent and yet have no blue tinge to them. Next I will install the voltage regulators. And eventually maybe I can get some pics up in another thread to show the details.

[Rene]

Just had a nasty surprise with these LED panels. The foam tape on the back of the panels has reacted to the heat produced over several hours by shriveling up into a marshmallow like ball. Then the panel drops off the reflector and lays on the lense where it does a lousy job of providing illumination. Much better when fastened to the reflector. Has no one else had this happen? I have to figure out a better method of attachment. The panels do not get as hot as bulbs but it is still uncomfortable to the touch. Any ideas?

[Thomas G.]

Originally Posted by Rene

Just had a nasty surprise with these LED panels. The foam tape on the back of the panels has reacted to the heat produced over several hours by shriveling up into a marshmallow like ball. Then the panel drops off the reflector and lays on the lens where it does a lousy job of providing illumination. Much better when fastened to the reflector. Has no one else had this happen? I have to figure out a better method of attachment. The panels do not get as hot as bulbs but it is still uncomfortable to the touch. Any ideas?

I made a bracket of thin aluminum (like flashing) with tabs that bend over the panel front slightly on 2 sides. The only function of the foam tape is to insulate the back circuitry from the aluminum and hold it in place until I bent the tabs. I pop riveted this bracket to the light fixture.