Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Gary Thompson wrote: Too many engineers on this list... Hey now, I stayed clear of the whole wheel bearing thing ;-p John '79 300SD
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
If you want certainty, you can only have one engineer or any other professional. If you have 15 you will never be sure, but you do have a better chance of getting things right. BillR. - Original Message - From: John Robbins [EMAIL PROTECTED] To: Mercedes Discussion List mercedes@okiebenz.com Sent: Saturday, March 10, 2007 4:01 PM Subject: Re: [MBZ] Resister to lower voltage to use LEDS as small lights Gary Thompson wrote: Too many engineers on this list... Hey now, I stayed clear of the whole wheel bearing thing ;-p John '79 300SD ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Does that certainty apply to knowing the time? (if you have 3 watches, which one is correct??) Werner - Original Message - From: BillR [EMAIL PROTECTED] To: Mercedes Discussion List mercedes@okiebenz.com Sent: Saturday, March 10, 2007 5:07 PM Subject: Re: [MBZ] Resister to lower voltage to use LEDS as small lights If you want certainty, you can only have one engineer or any other professional. If you have 15 you will never be sure, but you do have a better chance of getting things right. BillR. - Original Message - From: John Robbins [EMAIL PROTECTED] To: Mercedes Discussion List mercedes@okiebenz.com Sent: Saturday, March 10, 2007 4:01 PM Subject: Re: [MBZ] Resister to lower voltage to use LEDS as small lights Gary Thompson wrote: Too many engineers on this list... Hey now, I stayed clear of the whole wheel bearing thing ;-p John '79 300SD
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
They are jarring. But that's part of why they work well. It tends to get people's attention more. There's such a thing as too much attention. A brake light should not require you to yank your eye right to it, I prefer seeing it by peripheral vision, so I can still look out for other things. If more attention-getting was always better, why not have bright Xenon strobe brake lights? LookAtMe-LookAtMe-LookAtMe-LookAtMe... On the front too, even better than DRL's. But I also hate fog lights on clear nights, daytime running lights, and high-mount center brake lights. For much the same reasons. -- Jim
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Right! I have a Radio Shack 12v red LED across the mono valve to tell me when it's open or closed (bad ACC push button panel that I haven't fixed yet). It's been there for a good six months or more - still works. On 3/8/07, Rich Thomas [EMAIL PROTECTED] wrote: I bought a couple of 12V LEDs a the electronic toystore for like $0.99 each. Just go buy a couple, stick them on car power somewhere and see if they work out. If they do, then use them in your application. If they don't then try something else. What we seem to have here is paralysis by analysis. --R (BSLED, Smoke Test School of Engineering) -- OK Don, KD5NRO Norman, OK Even if you're on the right track, you'll get run over if you just sit there. Will Rogers '90 300D, '87 300SDL, '81 240D, '78 450SLC, '97 Ply Grand Voyager
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
OK Don [EMAIL PROTECTED] writes: Right! I have a Radio Shack 12v red LED across the mono valve to tell me when it's open or closed (bad ACC push button panel that I haven't fixed yet). It's been there for a good six months or more - still works. On that topic, are you supposed to be able to hear gurgling in the cabin when the monovalve opens? I can in my car, sounds like bubbles in the heater core. I had the coolant changed last fall, wouldn't any trapped air have been pushed through the system pretty quickly? Allan -- 1983 300D 1966 230
[MBZ] Resister to lower voltage to use LEDS as small lights
ALEX!; if you figure out the resister, (the value ) to use on the LEDS, could you share it with us???; is it used to lower voltage, current or BOTH!?; thanks, Steve
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
ALEX!; if you figure out the resister, (the value ) to use on the LEDS, could you share it with us???; is it used to lower voltage, current or BOTH!?; It lowers both, but its primary purpose is to limit the current. (This being generally true of electrical items. It is the flow of current that ends up performing the useful work, the voltage is just what it takes to induce the electrons to move suitably. That said, measuring the voltage is much easier to do, and is often a perfectly adequate means of seeing what's going on.) -- Jim
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
If you use only a resistor, you will have to seriously under power the LED to prevent killing it. For design purposes, you should plan on seeing 60V spikes in an automotive electrical system. These are caused by suddenly disconnecting a current source from the charging circuit. Resistive lighting can handle the spike just fine, but LEDs can't. You really need a current-limiting control circuit. -Dave Walton On 3/8/07, Stephen D Murrell [EMAIL PROTECTED] wrote: ALEX!; if you figure out the resister, (the value ) to use on the LEDS, could you share it with us???; is it used to lower voltage, current or BOTH!?; thanks, Steve ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
If you use only a resistor, you will have to seriously under power the LED to prevent killing it. For design purposes, you should plan on seeing 60V spikes in an automotive electrical system. These are caused by suddenly disconnecting a current source from the charging circuit. Resistive lighting can handle the spike just fine, but LEDs can't. You really need a current-limiting control circuit. LED's do handle this just fine. The light internal to the window switches in the SDL, for example, are LED's. They'll live for years, much longer than a 'more robust' incandescent will. All they have is a series resistor. LED's are commonly seriously overdriven in multiplexed display operations. Huge current spikes that would fry them if continuous. But they're intermittent, as are the load-dump spikes in an automotive system. For nighttime illumination, the LED is going to be fairly weakly driven anyway. -- Jim
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
I've seen experienced electrical engineers make the same mistake, and I've seen the companies they work for suffer because of having to live with the consequences. If you are just playing around in your backyard then toss in a series resistor. If it dies, you are out a few cents and some time. Not a big deal. If you are designing a product for sale, you might want to learn about the physics involved first. I've been interested in LED lighting for a while and most of the commercially available products ARE NOT engineered correctly. -Dave Walton On 3/8/07, Jim Cathey [EMAIL PROTECTED] wrote: If you use only a resistor, you will have to seriously under power the LED to prevent killing it. For design purposes, you should plan on seeing 60V spikes in an automotive electrical system. These are caused by suddenly disconnecting a current source from the charging circuit. Resistive lighting can handle the spike just fine, but LEDs can't. You really need a current-limiting control circuit. LED's do handle this just fine. The light internal to the window switches in the SDL, for example, are LED's. They'll live for years, much longer than a 'more robust' incandescent will. All they have is a series resistor. LED's are commonly seriously overdriven in multiplexed display operations. Huge current spikes that would fry them if continuous. But they're intermittent, as are the load-dump spikes in an automotive system. For nighttime illumination, the LED is going to be fairly weakly driven anyway. -- Jim ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Jim Cathey wrote: LED's are commonly seriously overdriven in multiplexed display operations. Huge current spikes that would fry them if continuous. But they're intermittent, as are the load-dump spikes in an automotive system. Thats what I think would happen too. If you're lucky enough to have a datasheet for the LEDs there is a continuous and a peak current rating. :) Either way, 60V?!? I don't know if I believe that happening on most vehicles (ie, you had something freaky going on we don't normally see). The reason I say that is one of the projects at my work is to make an engine speed controller so that an HMMV can be at a high enough RPM to generate a 400A 28VDC (yep, 28V) load. We could switch that load on/off and we never saw any monster spikes like that. No doubt it wasn't a clean 28V, but it wasn't quite that insane!! Maybe you were talking about a more local voltage spike and not one across the battery? I'm still new in engineering land so I'm used to being wrong.. ;) As an aside... the current probes measured nearly 800A peak for the stall current on the starter!! John '79 300SD
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
dave walton wrote: I've seen experienced electrical engineers make the same mistake, and I've seen the companies they work for suffer because of having to live with the consequences. If you are just playing around in your backyard then toss in a series resistor. If it dies, you are out a few cents and some time. Not a big deal. If you are designing a product for sale, you might want to learn about the physics involved first. I've been interested in LED lighting for a while and most of the commercially available products ARE NOT engineered correctly. LEDs do have average and peak current ratings... those ratings also have a maximum duration, and maximum frequency the pulse can be repeated at. There are also power dissipation ratings (one would think that the current and power ratings would be the same, but I don't think that ever happens)... I guess its because I've never seen those load-dump spikes (not saying they don't happen, just never seen what they look like), but I seem to think for most of us the LEDs and where we'd be using them in the electrical system should be okay. I'm assuming there aren't any major current consumption devices on the same fused branch as the instrumentation lighting. So if the load dump current comes from elsewhere (the glow plugs say) that 60V spike is going to have to make it across all the inductance of the wire from the battery to the instruments (assuming the battery isn't able to absorb the energy in that spike, and/or hasn't reacted to it yet). Am I following things correctly? I'm not trying to be snotty about this... I'm going to be building a lot of electronics for the car in the near future, and it would be nice to know if I need to account for 60V spike flying around!! John '79 300SD
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Agreed. They have 12v automotive applications for LED's all over. I've bought some LED trailer lights. Guess what? They work. Much better than regular ones too. I'd be willing to bet they'll last a lot longer than regular bulbs... Come to think of it, I seem to recall an old electronics kit I had with variable voltages and light. When I was tired of it and just monkeying around I cranked the voltage all the way up and tried out various things. The regular bulbs blew pretty quick. The LED was the only thing that didn't. (the motor spun really fast for a minute, but that's not related to lights) (: Levi On 3/8/07, Rich Thomas [EMAIL PROTECTED] wrote: I bought a couple of 12V LEDs a the electronic toystore for like $0.99 each. Just go buy a couple, stick them on car power somewhere and see if they work out. If they do, then use them in your application. If they don't then try something else. What we seem to have here is paralysis by analysis. --R (BSLED, Smoke Test School of Engineering) ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Agreed. They have 12v automotive applications for LED's all over. I've bought some LED trailer lights. Guess what? They work. Much better than regular ones too. I hate them. But if they'd just put some soft-start logic in there for the brake light function I'd be happy again. I just hate that bright instantaneous flash when compared to filament thermal lag. I find it jarring. Same with red LED stoplights. -- Jim
Re: [MBZ] Resister to lower voltage to use LEDS as small lights
Levi Smith wrote: They are jarring. But that's part of why they work well. It tends to get people's attention more. I don't have them on my car, But I agree, on a dark night when you're directly behind someone they sometimes seem a little too bright, but they certainly get my attention more than normal ones... But other than brake lights, I don't think I've ever had an application where the instantaneous on was even noticeable, let alone a problem... Yeah, I like the instant on too. Just a preference thing... It would be nice if auto manufacturers would use that same sensor for automatically turning on headlights to slightly dim all the outside indicator lights (like most radio's do when you turn on the headlights). John '79 300SD
