Topic: Standard voltage through the system

[Telorand]

Hey all!

I can't seem to find this info anywhere else, so I figured I'd make a new post about it.  I'm working on an LED project, and I know that the voltage of the charging system can fluctuate between 12~14.8v based on the battery charge level.  My question is, therefore:  Does the voltage through the rest of the system get regulated to 12v all the time, or does the regulator just keep it in that 12~14.8v range?  It makes a huge difference, since I will need a heatsink to keep the LEDs from burning out, and I'd rather not build a huge one if I don't need to.  Hopefully that was a little clearer than mud.

[Bodi]

The regulator tries to maintain close to 14.5V to the battery. It actually measures the switched ignition power, so battery voltage will be a bit higher than the black wire voltage assuming everything is working properly - about 1/2V or so, more if your wiring harness connectors are a bit corroded. Anyway, the voltage on the black wires should be around 14.5V in normal operation.

[tlbranth]

Automotive LED's will be OK with 14.5 volts.

[TwoTired]

My understanding is that it is the battery that determines the system voltage.  The voltage regulator attempts to keep it below 14.5 V peak.  However, it is at the mercy of available power from the alternator, which is variable with RPM, and system loads.

Were I you, I would do what is necessary to make the LED's survive when fed 15V, as that will give you a safety margin for the design.  So, if the charging system goes out of spec, your LED's will all survive the indiscretion, and you don't have more to repair than the initial failure.

Cheers,

[burmashave]

For what it's worth, Telorand, there's some info about LED conversions in the Electrics FAQ.

[tlbranth]

I converted my Goldwing to use almost all LED's for lights
 http://www.superbrightleds.com/
The bike is usually running 14.2 - 14.3 volts. No problems.
I also put a LED in the tail/stop socket of my CB750. No problems.
Automotive LED's are designed to work at those voltages.

[grumpy]

Me too.
Everything but the HL on my 750 are LEDS from superbright - even the guages and idiot lights.
(needed to scavenge some wattage for my heated gloves)
No mods needed other than the SS winker relay.

I converted my Goldwing to use almost all LED's for lights
 http://www.superbrightleds.com/
The bike is usually running 14.2 - 14.3 volts. No problems.
I also put a LED in the tail/stop socket of my CB750. No problems.
Automotive LED's are designed to work at those voltages.

[johnrdupree]

Telorand, am I correct in assuming you're not using automotive LEDs but instead are building your project from discreet components?  If that is the case, you'll have to provide a resistor for each LED or each cluster of LEDs.  Different colors have different voltage requirements and you'll have to calculate the resistor needed for a particular location on the bike based on the color of the LED, number of LEDs, how the LEDs are connected in the cluster, and an absolute maximum voltage.  As TwoTired said, 15V would be a safe bet.

More info on your project would be helpful.  If you're just replacing the existing bulbs with LEDs there are plug and play components available, but it sounds like you have something else in mind.

~john

[burmashave]

Mmmmm...mebbe I'm missing something in your setup. I swapped over almost all the lights to LED's using commercially available components, and I wired them directly in to the bike without resistors. I replaced the front and back turn signals, brake license light and the speedo and tach lights.

I encountered only a few minor probs. The brightest LED's I could find at the time wouldn't light up the license, so I installed two extra LED's to light it. The other common problem is that the turn signal relay is not designed for low voltage lights, so it flashes very quickly (as flasher relays are designed to do when a light is out). If you want the normal flash, you can pick up any similar automotive relay that's designed for low voltage. Personally, I think the quick flash is more noticeable, so I left it as is.

There are a bunch of threads about LED's in the forum in addition to info. in the FAQ.

[johnrdupree]

Mmmmm...mebbe I'm missing something in your setup. I swapped over almost all the lights to LED's using commercially available components, and I wired them directly in to the bike without resistors. I replaced the front and back turn signals, brake license light and the speedo and tach lights.

Did you do this with discreet components or ready made automotive bulb replacements from someplace like SuperbightLEDs?

[burmashave]

I did get my LED's from SuperbrightLED's; however, they were generic type of LED's and LED clusters. So that made a difference?

[Telorand]

Thanks for all the advice, everyone.  I am using discreet components for the Headlight build.  This confirms my thoughts on the matter, and I built a circuit that can withstand 14.8v for any period of time.  The last .2v shouldn't be a problem either, because at that point, the main fuse should blow out anyway.

For anyone interested, I'm using a total of 4x 10W LED's, rated at 10v 1A, 700-900 Lumens at normal operating voltage (It's a wide range, because I haven't decided if I want Warm White or Super White).  Two LED's will be on for the low beam, and all four for the high.  According to this calculator, that's something like 135,000 millicandela (per m²?) per LED, giving you a grand total of 1400 Lumens at 135,000mcd for the low beam, and 2800 Lumens at 135,000mcd for the high beam.  According to Wikipedia, "The HID headlamp light sources (bulbs) offer substantially greater luminance and luminous flux than halogen bulbs – about 3000 lumens and 90 mcd/m² versus 1400 lumens and 30 mcd/m²."

I'll be running mine at about 9.5~10v, so I'm guessing the output might be around 500~700 Lumens per each at 100,000mcd.  Hopefully this means it will be unreasonably intense, since the intensity is 1000x that of a HID bulb, and almost as much luminance on High.  Maybe I'll need a  diffusion plate.  I guess we'll see.  I don't have the finances right now to buy everything and build it, but when I do, I'll post pictures and such!

[johnrdupree]

I did get my LED's from SuperbrightLED's; however, they were generic type of LED's and LED clusters. So that made a difference?

Depends on what you bought.  The OP said he'd have to make a heat sink to keep the LEDs from burning out.  I took that to mean resistors, which makes me think he's buying stuff like this

to make his own custom clusters.  You can't hook those to the bike without the proper current limiting resistors.  Well, you can, if you have enough of them in series IIRC.  Then you get into series/parallel combinations where you have to figure voltage and current for each section of the cluster and the math makes my brain hurt.  There are online calculators to figure it all for you.

He didn't provide much detail so maybe I'm misinterpreting what he wants.  Maybe he's using some big-arse 1 watt LEDs like this:

They do need heat sinks, but they also need resistors since the max forward voltage is still only 2 or 3 volts, depending on color.

[johnrdupree]

We must have been typing at the same time.

That sounds like some pretty advanced stuff, Telorand.  Definitely keep us updated.  Do you have a link to the LED you're looking to use?

[TwoTired]

... I built a circuit that can withstand 14.8v for any period of time.  The last .2v shouldn't be a problem either, because at that point, the main fuse should blow out anyway.

Um, better review fuse principles of operation.  Fuses limit current not voltage.  They will happily pass 120V if the current remains below rating.

LED (the element) care about voltage polarity and current.  They have a voltage withstand spec, a voltage blocking spec, and a Max current spec.  And, they can be destroyed by exceeding any one of those specs.  This is where the series resistor comes in, as it will limit current and the voltage that the diode receives.

Do not confuse an LED element with an LED assembly.  An assembly already has current and voltage limiting resistors incorporated into the unit.  It will still have a max voltage applied rating, and if intended for automotive use is likely safe at or slightly above 15V.

If you don't select the limiting resistor size to accommodate system failures that allow high voltages, you'll have to fix more than the charging system after the failure event.  Such a design philosophy is like a house of cards.  It's nice and cozy inside until part of it fails, then the whole thing is reduced to a heap.

Cheers,

[Telorand]

That sounds like some pretty advanced stuff, Telorand.  Definitely keep us updated.  Do you have a link to the LED you're looking to use?

Sure!  It's actually from an eBay seller. Chi Wing LED's  I'm looking at the 10W LED's, but if anyone is interested in anything bigger than a 5W, you'll have to make your own heatsink. They sell heatsinks for the 1W-5W, but after that, the power dissipation makes a lot more heat.  If anyone is interested in trying to make your own (I still haven't tested mine), here's a few of the tools/websites I've been using:

For calculating resistance and necessary resistors.  This is the most helpful and most accurate website of this type I've found.
http://www.ohmslawcalculator.com/ohms_law_calculator.php
For building and testing a circuit. Right click to bring up the component menu.  There's also an option to download the Java applet to your computer.
http://www.falstad.com/circuit/
For calculating heatsink requirements and building a heatsink.
http://www.sm0vpo.com:800/begin/heat-0.htm
For buying sheet metal. (If you plan to build your own heatsink. Aluminum is pretty cheap!)
http://www.fitler.com/basemetal.php] [url]http://www.fitler.com/basemetal.php[/url]
For all other electrical components.
http://www.digikey.com/

... I built a circuit that can withstand 14.8v for any period of time.  The last .2v shouldn't be a problem either, because at that point, the main fuse should blow out anyway.

Um, better review fuse principles of operation.  Fuses limit current not voltage.  They will happily pass 120V if the current remains below rating.

LED (the element) care about voltage polarity and current.  They have a voltage withstand spec, a voltage blocking spec, and a Max current spec.  And, they can be destroyed by exceeding any one of those specs.  This is where the series resistor comes in, as it will limit current and the voltage that the diode receives.

Doh!  You're right.  Brain fart.  I've been crunching numbers and trying to think this through so much for almost two weeks, I think I melted part of my brain.  Maybe I should have built a heatsink for my head...  Anyway, there are series resistors in my build, one for the low beam, and one for the high beam.

[Bodi]

Be careful with dropping resistors. If you have a series string of LEDs the voltage across the dropping resistor is lower but the current change vs voltage change gets more sensitive.
It's best to use a constant current power supply, this is super easy to do with a voltage regulator chip and a couple of resistors: that lets you set the current close to the LED maximum and not worry about dimming when the voltage drops a bit... or burning out the LED when it goes up a bit. Since you're obviously using some expensive LEDs this is a big issue.

[WarwickE36]

For what its worth I have used "superbrightLEDS.com" LEDS for 2 of the Limo's I maintain for work... the quality on both was incredibly poor.  Burned out LEDs, flashing LEDS, and shotty wiring from the get go.  I gave them 2 tries and moved on.  Just my .02... could have been bad luck.