If your lights were designed to run on regulated 12.0 VDC from the noisy supplies, you would be giving them about 24% over-voltage using those transformers, a bridge rectifier and a capacitor. In this case, 24% over-voltage can have damaging consequences.
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PS: I'm guessing the dimmer is Pulse Width Modulation and may throw annoying interference.
With the provided (matched) power supplies, the LED strips operate quite bright--much brighter than I desire. I will use a dimmer, which, as you described, appears to be a pulse width modulator. It is a simple device, weighs almost nothing, and has solid state circuitry within (my curiosity drove me to open one). I expect that the lower output of the LED's will equate to a lower voltage. Am I correct?
It has already been tested in conjunction with the battery charger, and does not create noise, although when operated at the extreme bottom end, one can see pulsing in the light output. That happens at a level far below where I anticipate its use. I am of the opinion that the combination I will use will most likely result in acceptable lifespan of the LED's, but I'd appreciate your expert opinion if I am misguided.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Harold_V wrote:...With the provided (matched) power supplies, the LED strips operate quite bright--much brighter than I desire. I will use a dimmer, which, as you described, appears to be a pulse width modulator. It is a simple device, weighs almost nothing, and has solid state circuitry within (my curiosity drove me to open one). I expect that the lower output of the LED's will equate to a lower voltage. Am I correct? "
Rambling typing as I think:
Pulse Width Modulation will provide variable width pulses of full voltage, resulting in pulses of full current. Are 50 mA pulses of a 40% duty cycle the same as continuous 20 mA? Overall brightness should be the same BUT: Is 250% current for brief blasts a good thing?
Real world analogies can provide helpful understanding: When I get out the push mower, I can push it across the lawn with a force of perhaps 20 pounds, or I could shove the handle with 50 pounds of force 2/5 of the time. Either will propel it across the yard. My guess is that the second option will be much more damaging to the mower and my arms. I'm not going to try it. Similarly, I would expect that LEDs planned to last well on a consistent 20 mA will not last equally well on narrow pulses of 50 mA.
Were this my project, and I wanted to maximize LED life, I would use a linear regulated power supply and adjust it to provide somewhat less than 12 VDC for the desired lower brightness. Alternatively, I'd find a 12VDC switching supply that does not interfere and use the PWM module to dim.
Thanks. That makes sense to me. Now I wish I'd have pursued 6 volt transformers, as the level of light the battery charger puts out on that voltage is quite acceptable, and it would be well within the design voltage of the LED strings, according to what you've said.
Looks like this may not be resolved yet.
By the way, I even tried using a power supply from a computer. Same problem. Noise. I would have expected that it would be well filtered. Apparently not.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
I expect I can route the secondary of the transformer I intend to use through one of them to drop the voltage to an acceptable level. I've even considered running the primary through, although they appear to be rated for only 75 volts.
Comments?
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
oldvan wrote:Hmmm, they were designed for audio at up to 75 Watts. Audio includes 60 Hz.
I'd be tempted to try one and see if it gets hot. If not, Magic.
Thanks. I was thinking exactly along the same lines.
I'd like to drop the voltage to ensure I don't have issues with life of the strings.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
I think these are multi tap transformers, so a.c. in application ??
Or is that the l pad attentIons.
It may be simpler to use a larger wattage resister a look at the app store will show several led calculator s as well as some online
I am sending some 6 v and 5 volt supply as part of the care box
hammermill wrote:I think these are multi tap transformers, so a.c. in application ??
Yes, I figured I'd feed the attenuator, lowering the voltage, then hook the bridge rectifier to the output of the attenuator. The way they are wired, the black wire is common, the red wire is the input and the green wire is the output.
It may be simpler to use a larger wattage resister
That ran through my mind, but I was a bit apprehensive, considering the amount of amperage involved on the secondary side.
What are your thoughts on putting the resistor on the primary? Much lower amperage (although wattage should remain about the same). Am I thinking clearly? In either case, it would be a huge resistor, wouldn't it?
It was this thought that gave me cause to investigate the attenuators, which were purchased years ago, when I built the castle. They were never installed because we sold the structure.
a look at the app store will show several led calculator s as well as some online
The problem with such things is that when I read them, my eye glaze over. I don't know enough to understand what I'm reading.
I am sending some 6 v and 5 volt supply as part of the care box
You, Sir, are a gentleman. I hope I can repay your kindness someday. I'll cover your shipping costs, and more if you desire. If I find you have a solution overall, do you have enough material that you could sell what I need? At the worst, I need five supplies, but two of them could be combined as one, assuming it produced enough amperage. I expect all of the lights would almost never be operated at the same time, but I should provide for that should the need arise. The power supply I had planned for that circuit is a ten amp. I was going to split it to two supplies, each just over six amps.
I really appreciate the help you guys have provided. I'm clearly out of my element with this project, but I'm determined to solve the riddle.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Don't know if you guys are interested in how this all got resolved, but if you are, here's the deal.
Hammermill sent me a couple (identical) power supplies that worked fine, although they had to be wired completely differently from how they are supposed to be used. The lights in the wet bar were easy---enough 12 volt circuits were readily available, so one of the supplies was installed in place of the original (noisy) power supply. Piece of cake!
For the lights in the record/cd storage cabinets, I needed five 12 volt circuits, or one large capacity one. Suggested factory wiring indicated the units had only two, which, combined, were still too low in amperage, but by using a different negative position, I found five different 12 volt circuits. Why it works as it does, I can not say, but I performed a prolonged test by hooking five reels of LED's, one to each of the five circuits I needed. It worked fine, but got warm, as I was pulling pretty much the entire rated output. I concluded that putting a fan on the unit would be a good idea, so I did. Add to that that the supply isn't likely to see all of the five circuits being used at one time, nor are any of them as long as a full reel, I feel that part of the lighting need was covered adequately. Interestingly, I can still hear a trace of interference when tuned to a very weak radio station, but that's with the cheap radio I've been using while I work. The stereo system is far more resistant to such noise, and preliminary tests indicate it will be silent.
My sincere appreciation for the generosity shown by Hammermill in getting these two systems operational.
Fast forward to the last circuit I needed to install, the lights under the cabinets in my wife's kitchen. For that, I decided to use one of the eight 12 volt 75 watt transformers I got off ebay. After hooking a bridge rectifier to the output, along with an electrolytic capacitor, I was measuring about 16½ volts, which was well beyond acceptable. The light strings I procured are reputed to be acceptable for use in an automobile, so I expect that less than 15 volts would be desirable.
I had on hand several Soundolier attenuators (wire wound autoformers, with taps), which are also rated for 75 watts, but intended for use in controlling volume at the speaker of a sound system. I tried one, and it worked just fine, but the last tap resulted in full voltage, and the second to last tap dropped to about 10 volts, which reduced the light output beyond an acceptable limit.
After thinking on the matter, I decided I'd remove a little of the wire from the secondary winding. All of the transformers have steel covers over the windings, which were welded in place. I cut the welds and removed the caps, and was pleasantly surprised to discover that the primary and secondary winding were wired along side one another, so I had full access to both of them. I removed a small amount of wire to determine the amount of change in voltage, then settled on removing 68". That resulted in 12½ volts, which I considered acceptable. Bolted the end caps back on the transformer (holes were already there), and pronounced the alteration a grand success. I installed the tranformer, capacitor and bridge recitifier, along with a circuit breaker and muffin fan, in a 12" long piece of 4" square wireway, fan on one end, fire screen on the other, and mounted it vertically in the corner of the (corner) Lazy Susan spice cabinet. It just fit, with no room to spare. It is switched on and off by a light switch above the drain board. We now have (totally silent) lights under the overhead kitchen cabinets!
Thanks to you guys, I succeeded in finishing this project. My electrical skills were far too rusty to have solved the problems without your assistance, with a special thanks to oldvan, for his patience in providing me with guidance and encouragement.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Altogether fine. I don't know what amps or much about anything there. There are these little fuse things which can be obtained for different temperature. They would be in series but with 120 or 250 v they break with heat. You can determine max heat temp and they will blow like a fuse. I've looked at them and there are many between 160f and 260f. Not to make it more difficult but something to consider when things get too hot yet don't trip a breaker.
Harold. Now then, when is the party? One last note, did you really call Susan lazy? 
