Cortland, Mike, Kurt, and All,
If you go back to my post of a few days ago, it sounds as if I may have scored
a direct hit (by dumb accident) on this system; after careful reading of Mike's
information, it does sound like the manufacturer is using a simple, iron core
transformer to go from 120 VAC to 12 VAC. That's the good news.
Now, one thing I have not seen Mike comment on is if the devices inside those
lamp heads are bulbs or LEDs. If they are LEDs, I can tell you that there are
several manufacturers out there making specialized ICs that serve as the
constant current controllers for LEDs. If they are bulbs, then I agree with
Kurt's comments about bulbs not caring if they get AC or DC. Either way, the
picture I am getting is that we have a low voltage, relatively high current
wired distribution system that goes from the step-down transformer to the
individual lamp heads. The problem may well then be what's inside those heads,
particularly if the lighting devices are LEDs.
Since cost is always THE driver these days (sad, but true), I can tell you that
I have been shocked by the number of app notes I have seen from the LED
constant current guys about circuits to use their ships and in which there is
little or even NO suppression of switching noise on the input side of the
device. Some of these chips are meant to run on low voltage AC input, and then
the constant current controiller is a specialized switcher that outputs DC to
the LEDs. So, the bad news is that my "guess" about each lamp head containing a
small switcher might be correct. If it is, wow - what a mess!
-----Original Message-----
>From: Cortland Richmond <ka5s@earthlink.net>
>Sent: Mar 11, 2013 9:21 PM
>To: rfi@contesting.com
>Subject: Re: [RFI] Cree LED Bulbs?
>
>On 3/11/2013 2125, Cortland Richmond wrote:
>> On 3/11/2013 1952, Mike Ryan wrote:
>>> The landscaping lights turn out to be 12 volt AC powered and not 12
>>> volt DC powered. All the suggestions about a car battery and/or an
>>> Astron or other linear power supply now go out the window. -M
>>>
>>
>> But the converter is still very likely a switch-type converter;
>> modern-day efficiency rules often rule out transformers on account of
>> core losses.
>>
>>
>> Cortland Richmond
>> KA5S
>> _______________________________________________
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>>
>
>And even if it does use a linear 12VAC transformer, the LED's themselves
>require a constant current source -- and probably incorporate switching
>regulators at each fixture. Have you contacted the system maker?
>
>
>Cortland
>KA5S
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