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Coverting OEM auto bulbs to LED
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<blockquote data-quote="Geoff1946" data-source="post: 498357" data-attributes="member: 28452"><p>LED lamps take a lot less current to light them than filament lamps. Most vehicles have lamp failure detection systems to tell the driver he has a fault. These detection systems work by monitoring the current flowing to each lamp, and when the current falls below a certain level will trigger the warning. In the case of trafficators it's usually by rapid flashing of the remaining lamps. For brake lights its usually a dashboard warning indicator.</p><p></p><p>The purpose of the resistors is to defeat the warning system by taking approximately the same current as a serviceable lamp. </p><p></p><p>Now some basic figures: The wattage of a lamp is its voltage multiplied by current. e.g. A standard 21 watt indicator lamp on a 12volt supply takes 1.75 amps.</p><p></p><p>So, to use a resistor as a "pretend" lamp you need one which will take that current.</p><p></p><p>Ohms law tells us that Current equals voltage divided by resistance, or the other way resistance equals voltage divided by current. Hence about 6.8 ohms in this case.</p><p></p><p>Note that there is quite a wide tolerance band on these fault detection systems to accommodate several variables. A vehicle 12 volt system actually varies between below 12 to over 14 depending on battery condition and whether charging from the engine. Lamps deteriorate with age, etc Finally the led lamps you are putting in still require some current; I would guess about a tenth of the filament lamp. A bit of trial and error is probably needed.</p><p></p><p>I hope that helps.</p></blockquote><p></p>
[QUOTE="Geoff1946, post: 498357, member: 28452"] LED lamps take a lot less current to light them than filament lamps. Most vehicles have lamp failure detection systems to tell the driver he has a fault. These detection systems work by monitoring the current flowing to each lamp, and when the current falls below a certain level will trigger the warning. In the case of trafficators it's usually by rapid flashing of the remaining lamps. For brake lights its usually a dashboard warning indicator. The purpose of the resistors is to defeat the warning system by taking approximately the same current as a serviceable lamp. Now some basic figures: The wattage of a lamp is its voltage multiplied by current. e.g. A standard 21 watt indicator lamp on a 12volt supply takes 1.75 amps. So, to use a resistor as a "pretend" lamp you need one which will take that current. Ohms law tells us that Current equals voltage divided by resistance, or the other way resistance equals voltage divided by current. Hence about 6.8 ohms in this case. Note that there is quite a wide tolerance band on these fault detection systems to accommodate several variables. A vehicle 12 volt system actually varies between below 12 to over 14 depending on battery condition and whether charging from the engine. Lamps deteriorate with age, etc Finally the led lamps you are putting in still require some current; I would guess about a tenth of the filament lamp. A bit of trial and error is probably needed. I hope that helps. [/QUOTE]
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Coverting OEM auto bulbs to LED
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