knna
Member
The driver is a (24V max) constant current device (500mA I believe). Actually most CC drivers have a CV first stage.
I agree that connecting a high current low voltage driver to several string in parallel is not the most efficient way, but most LED lamps do so. At least those certified, because shock test are way easier to pass that way. When you work with high voltage (anything over 60V), you need a double isolated PS, way thicker dielectrics (worse thermal conductance), earth grounding...nothing of that is required with low voltage.
But connecting several strings in parallel requires an additional way to balancing them, in order to avoid initial difference in brightness and specially, problems if a LED fail. I was talking with EVO's designer about that. There are good solutions to that.
They had diminished the problem of initial difference in brightness by grouping strings by Vf. Likely the copper path is not a problem for a circuit running at 500mA, differential drop in voltage is very low for any standard copper thickness used in PCB. Except if a trace is damaged, of course.I didnt ask for the copper thickness used on the PCB, but standard 1oz often works fine, 2oz or higher is for sure enough to keep voltage drop difference between string completely negligible.
About the sensibility of human eye to difference in brightness, it is not the same looking at reflected light than looking directly to the light sources, and it makes a huge difference if you compare the two light sources one along the other than if not. When you compare them side to side, eye/brain find easily difference in brightness and chromaticity.
Color tone is easier to understand in an example, although eye/brain adaptation mechanism is very similar. Put a lamp of a given CCT,for example a 3000K warm white, turn of and try a 4000K white lamp. It is difficult to notice the difference after a brief period of adaptation. But put turn on them at the time side to side, and you immediately notice the difference in tone.
Anyway, I agree no providing a means to balance current between strings in parallel is a flaw. However the lamp may work perfectly still so. It would be required to know the actual difference in brightness, voltage and current on Habeeb's lamp to have an answer on this, if he can/want to solve it himself or prefer to ask for a change.
Im not involved on any means on the development of this lamp, just I know the people who did it, they are good friends but nothing else. I never would have released a lamp with a circuit like that. But they told me they had tested it and that difference are small and reliability good, with first units working for near 2 years with minimal light loss. I believe them, so probably it is a minor problem, but any one having one should check it for themselves and see if it is so. I dont know if Habeeb's lamp is in good condition or not, or if his lamp is representative or not. Actually, I never had an EVO lamp in my hands.
I just try to help Habeebs on this. If he give me Vf measurements, which dont need anything else than a multimeter and a couple minutes, I could say more accurately and suggest the best to do.
I agree that connecting a high current low voltage driver to several string in parallel is not the most efficient way, but most LED lamps do so. At least those certified, because shock test are way easier to pass that way. When you work with high voltage (anything over 60V), you need a double isolated PS, way thicker dielectrics (worse thermal conductance), earth grounding...nothing of that is required with low voltage.
But connecting several strings in parallel requires an additional way to balancing them, in order to avoid initial difference in brightness and specially, problems if a LED fail. I was talking with EVO's designer about that. There are good solutions to that.
They had diminished the problem of initial difference in brightness by grouping strings by Vf. Likely the copper path is not a problem for a circuit running at 500mA, differential drop in voltage is very low for any standard copper thickness used in PCB. Except if a trace is damaged, of course.I didnt ask for the copper thickness used on the PCB, but standard 1oz often works fine, 2oz or higher is for sure enough to keep voltage drop difference between string completely negligible.
About the sensibility of human eye to difference in brightness, it is not the same looking at reflected light than looking directly to the light sources, and it makes a huge difference if you compare the two light sources one along the other than if not. When you compare them side to side, eye/brain find easily difference in brightness and chromaticity.
Color tone is easier to understand in an example, although eye/brain adaptation mechanism is very similar. Put a lamp of a given CCT,for example a 3000K warm white, turn of and try a 4000K white lamp. It is difficult to notice the difference after a brief period of adaptation. But put turn on them at the time side to side, and you immediately notice the difference in tone.
Anyway, I agree no providing a means to balance current between strings in parallel is a flaw. However the lamp may work perfectly still so. It would be required to know the actual difference in brightness, voltage and current on Habeeb's lamp to have an answer on this, if he can/want to solve it himself or prefer to ask for a change.
Im not involved on any means on the development of this lamp, just I know the people who did it, they are good friends but nothing else. I never would have released a lamp with a circuit like that. But they told me they had tested it and that difference are small and reliability good, with first units working for near 2 years with minimal light loss. I believe them, so probably it is a minor problem, but any one having one should check it for themselves and see if it is so. I dont know if Habeeb's lamp is in good condition or not, or if his lamp is representative or not. Actually, I never had an EVO lamp in my hands.
I just try to help Habeebs on this. If he give me Vf measurements, which dont need anything else than a multimeter and a couple minutes, I could say more accurately and suggest the best to do.