discomikey Posted September 27, 2011 Share Posted September 27, 2011 right so i wasnt sure where to put this so i put it here, feel free to move it if i am wrong. something ive wanted to do for a while now is compliment my amber roof markers on brian with some amber side markers down the sills. now, ive only just really found an ideal set of lights, which come in the form off motorcycle accent lights, but are an ideal size with an ideal light spread. the only problem is they might be a bit bright and i dont want to dazzle other road users with my bling. so am i right in thinking as with non LED bulbs, you can turn down the brightness with a resistor or variable resistor? if so then great, they will be perfect, if not then i may have to rethink. Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted September 27, 2011 Share Posted September 27, 2011 Yes you can, but it's not as easy because they are non-ohmic. Depending on the colour the forward voltage is 0.7v or thereabouts irespective of current, until they fail. Try experimenting, if they are designed to run at 12 volts already you can't damage them, make sure the resistor is more than man enough though as they can get hot. Unlike bulbs, putting 2 in series makes little difference without the associated resistor. Quote Link to comment Share on other sites More sharing options...
Landy-Novice Posted September 27, 2011 Share Posted September 27, 2011 is this helpful? http://ledz.com/?p=zz.led.resistor.calculator Quote Link to comment Share on other sites More sharing options...
discomikey Posted September 27, 2011 Author Share Posted September 27, 2011 thanks, a variable resistor in the form of a turn dial would work wouldnt it, then it would be adjustable for the "show look brightness" or the nice to other cars brightness Quote Link to comment Share on other sites More sharing options...
western Posted September 27, 2011 Share Posted September 27, 2011 vehicle side marker lights http://www.legislati...schedule/9/made there is no light/bulb wattage stated in these regs, colour & visible from 45 degrees as noted below. 7. Colour: Amber or, if within 1 m of the rear of the vehicle it may be red . Angles of visibility– (a) Horizontal: 45° to the left and to the right when viewed in a direction at right angles to the longitudinal axis of the vehicle (b) Vertical: No requirement Quote Link to comment Share on other sites More sharing options...
discomikey Posted September 27, 2011 Author Share Posted September 27, 2011 ralph, whereas there is no actual regulation on side marker wattage, it would be decent not to dazzle other road users too much. as the lights im looking at have a slightly more than 45deg each way angle of visibility it is of more importance not to be too bright. the lights may actually not be too bright anyway, they just look quite bright in the photos, although they are lighting up chromed parts which may make it seem brighter. Quote Link to comment Share on other sites More sharing options...
discomikey Posted September 27, 2011 Author Share Posted September 27, 2011 cheers for the website landy novice, i cant get my head around milliamps to amps though, and at 5 amps (i thinnk 5000 miliamps) it is too high a value for that site. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted September 28, 2011 Share Posted September 28, 2011 If you want proper control over LED brightness, the best way to do it is with PWM (i.e. turning it on and off very fast) Something like this: http://www.ebay.co.uk/itm/DC-12V-24V-3-2-Motor-Speed-Control-PWM-Controller-UK-/180701905840?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item2a12ac43b0 would do the job just fine. You'd need to ensure that your LEDs are 12v, or if not - then you'd need a ballast resistor to drop 12v to 0.7v (unless you connect them all up in series, then it would be 0.7 x as many LEDs as you have) Quote Link to comment Share on other sites More sharing options...
MrKev Posted September 28, 2011 Share Posted September 28, 2011 5A is quite a lot for a LED. What sort of LEDs are you using? @Range Rover Blues, TheRecklessEngineer - you are mistaken, LEDs have a much higher forward voltage than that. 0.7 would be about right for a typical normal diode. An LED can be from around 1.6V through to over 4V, depending on chemistry. PWM is probably over complicating it for this application, and finding the right value resistor would be plenty good enough for marker lamps. Post some more details of your chosen LEDs and we'd be able to help more. Kev Quote Link to comment Share on other sites More sharing options...
mickeyw Posted September 28, 2011 Share Posted September 28, 2011 5A is quite a lot for a LED. What sort of LEDs are you using? @Range Rover Blues, TheRecklessEngineer - you are mistaken, LEDs have a much higher forward voltage than that. 0.7 would be about right for a typical normal diode. An LED can be from around 1.6V through to over 4V, depending on chemistry. PWM is probably over complicating it for this application, and finding the right value resistor would be plenty good enough for marker lamps. Post some more details of your chosen LEDs and we'd be able to help more. Kev Pretty much of the LEDs we use at work draw around 20mA at 3.3V. This covers all sorts of SMD and through holes types. Based on these figures you'd need 250 LEDs to draw 5A! Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted September 28, 2011 Share Posted September 28, 2011 Pretty much of the LEDs we use at work draw around 20mA at 3.3V. This covers all sorts of SMD and through holes types. Based on these figures you'd need 250 LEDs to draw 5A! That'll be some Christmas Tree! Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted September 28, 2011 Share Posted September 28, 2011 @Range Rover Blues, TheRecklessEngineer - you are mistaken, LEDs have a much higher forward voltage than that. 0.7 would be about right for a typical normal diode. An LED can be from around 1.6V through to over 4V, depending on chemistry. PWM is probably over complicating it for this application, and finding the right value resistor would be plenty good enough for marker lamps. Post some more details of your chosen LEDs and we'd be able to help more. Yup, quite right - wasn't thinking! Quote Link to comment Share on other sites More sharing options...
MrKev Posted September 28, 2011 Share Posted September 28, 2011 I have got some LEDs that run at 1.5A, but they're far too bright to be used as side markers. Kev Quote Link to comment Share on other sites More sharing options...
dave88sw Posted September 28, 2011 Share Posted September 28, 2011 while we are on the subject of led's, i bought some 12v ones to use on my land rover a while back, worked absolutely fine with the engine off cos obviously battery voltage is around 12.5v, however when i fired it up and got the full 14v, they all blew. How would i go about making sure they only receive 12v regardless of whether the engine is running or not because i still have a lot of spares of them. Thanks Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted September 28, 2011 Share Posted September 28, 2011 while we are on the subject of led's, i bought some 12v ones to use on my land rover a while back, worked absolutely fine with the engine off cos obviously battery voltage is around 12.5v, however when i fired it up and got the full 14v, they all blew. How would i go about making sure they only receive 12v regardless of whether the engine is running or not because i still have a lot of spares of them. Thanks Try something like this http://www.ebay.co.uk/itm/170701103535 Obviously you need the 12v one, you could build one yourself cheaper.... Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted September 28, 2011 Share Posted September 28, 2011 Just one of these would do it: http://www.ebay.co.uk/itm/Voltage-Regulator-7812-L7812CV-1-5A-12V-Lot-3-/380089589527?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item587f1adf17 Bolt it to something metal (via a mica washer) as a heat sink and it'll be fine. Quote Link to comment Share on other sites More sharing options...
dave88sw Posted September 28, 2011 Share Posted September 28, 2011 Thanks for the help guys sorry for the slight hijack... Quote Link to comment Share on other sites More sharing options...
discomikey Posted September 30, 2011 Author Share Posted September 30, 2011 5a was just a wild stab in the dark, being as roof markers cant be more than 5a, i had no idea that 5a in LED's would be brighter to be honest. Quote Link to comment Share on other sites More sharing options...
SORNagain Posted September 30, 2011 Share Posted September 30, 2011 while we are on the subject of led's, i bought some 12v ones to use on my land rover a while back, worked absolutely fine with the engine off cos obviously battery voltage is around 12.5v, however when i fired it up and got the full 14v, they all blew. How would i go about making sure they only receive 12v regardless of whether the engine is running or not because i still have a lot of spares of them. Thanks Hi Dave, I have had some experience of this and it can be a tricky problem. I am guessing your LED lights have more than one LED in them? If there are a few LED's in series then most of the battery voltage will appear across the LEDs and only a few volts across the current limiting resistor. Raising the voltage by a couple of volts then leads to a large increase in current which is probably what blew yours. If you can take the lamps apart, the best solution is to separate the the long series string into smaller strings in parallel, each with its own resistor. You can use a 7812 regulator as suggested, but these have a dropout voltage of 2 volts which means they do not regulate until there is 2 volts across the regulator. OK at 14 volts (just), but at 12 your lamps may be dimmer than they were before. No harm in that though if it is acceptable.... Quote Link to comment Share on other sites More sharing options...
MrKev Posted September 30, 2011 Share Posted September 30, 2011 being as roof markers cant be more than 5a Typical markers lamps are 5 Watt bulbs, not 5 Amp. A typical main beam 55W bulb is just about nearly 5A. (Watts equals Volts times Amps). Quote Link to comment Share on other sites More sharing options...
discomikey Posted October 2, 2011 Author Share Posted October 2, 2011 yes silly me, i meant Watts, my roof markers are 5W as per regulations Quote Link to comment Share on other sites More sharing options...
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