I have two strips of under-cabinet lights in my kitchen. Each strip runs off 3 AA batteries (4.5V total) and has a dozen small led lights. The strips have motion detectors that automatically turn on the lights when they sense motion. The lights have internal timers that turn the lights off after about 30 seconds if they do not detect further movement. They also have light sensors so that they only come on if the room is dark or dimly lit to save battery life.

The lights strips work great and it is convenient to not have to turn a light on or off when getting something out of the kitchen at night. The only drawback is that the lights go through batteries fairly often, so I want to hook them up to a single battery eliminator.

Here's the problem: I tested the lights before running the wiring and when using an eliminator found that when one light goes off, it triggers the other to come on. So at any given time, one of the light strips is on. I isolated the strips visually from each other and made sure there was no movement in the room when testing. I tried them in series with a 4.5V transformer and in parallel using a 9V transformer, but the results are the same either way. I assume the light that is off is being triggered by a voltage change when the other light goes off. (The lights have no effect on each other when battery powered.)

How can I isolate the two strips from each other (other than using two transformers)?

Thanks

Do you have the power comsumption rating for the lights? Also I think your mixing up your terms of series and parallel.


Series would be positive to negative to positive to negative with the power wires hooked at each end and the two middle ones enjoined. (9 volt)

Parallel would be negative to negative and pos to pos with the power wires going to the respected polarity. (4.5 volt)


Depending how bad of a spike your getting you might be able to use a simple capacitor inline to buffer any spikes. If the spikes are bad then it may require what is called a hash filter to stop the actual spike.

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Originally Posted by cdad

Do you have the power comsumption rating for the lights? Also I think your mixing up your terms of series and parallel.


Series would be positive to neg to positive to neg with the power wires hooked at each end and the two middle ones enjoined. (9 volt)

Parallel would be neg to neg and pos to pos with the power wires going to the respected polarity. (4.5 volt)


Depending how bad of a spike your getting you might be able to use a simple capacitor inline to buffer any spikes. If the spikes are bad then it may require what is called a hash filter to stop the actual spike.

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Cdad,

Thanks for the reply.

Yes, I did reverse "series" and "parallel" in my question (but not in my tests).
It would seem logical that the best way to wire them would be parallel, but as I stated, I am getting the same problem wired either way.

As luck would have it I did find this info about the strips:
- When the LEDs are on, the unit consumes between 160mA (when powered by three fresh alkaline AA cells) and 110mA (when powered by three Sanyo eneloop Rechargeable Batteries)
- In standby (AUTO) mode: the unit consumes between 2.2mA (alkaline cells) and 1.7mA (NiMH cells)

How would I determine the capacitor rating I need to put inline and where in the circuit would I place it? (Coming from the transfomer, between the two strips or the negative return?)

I doubt the spikes are very big, just enough to trigger the other light.

Thanks

You would place it between positive and negative. The other problem you might be having is that the unit you bought to power the lights may not be true d/c. Did you check for that at all? You wouldn't need a very big cap as the consumption rating is very low.

How to Install an Electrolytic Capacitor | eHow.com

Quote:

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Originally Posted by cdad

You would place it between positive and neg. The other problem you might be having is that the unit you bought to power the lights may not be true d/c. Did you check for that at all? You wouldnt need a very big cap as the consumption rating is very low.

How to Install an Electrolytic Capacitor | eHow.com

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Yes, definitely DC. I have a bag of various transformers. I save the wal-warts when I replace a broken appliance, electrical gadget, cell phone charger, etc. for projects like this. I have also tested the lights with an actual "battery eliminator" with variable voltages and switchable amperage (100ma or 300ma) and polarity.

Quote:

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Originally Posted by Poergy

Yes, definitely DC. I have a bag of various transformers. I save the wal-warts when I replace a broken appliance, electrical gadget, cell phone charger, etc. for projects like this. I have also tested the lights with an actual "battery eliminator" with variable voltages and switchable amperage (100ma or 300ma) and polarity.

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Give it a try and let us know how it worked out for you.

Not so good. The capacitor didn't correct the problem of one strip affecting the operation of the other, and it destroyed the light/motion sensors in both strips. I used a capacitor with a small uf value as suggested.