• Welcome to the Two Wheeled Texans community! Feel free to hang out and lurk as long as you like. However, we would like to encourage you to register so that you can join the community and use the numerous features on the site. After registering, don't forget to post up an introduction!

voltage reduction????

Joined
Mar 21, 2004
Messages
12,142
Reaction score
1,360
Location
Cleburne
First Name
Leon
Last Name
Hogan
I am working on adding front running lights in the turn signals on my SV1K and picked up these dual color changing LED bulbs so that the running lights are white but switch to amber when the turn signals are switched on.

I failed to catch that they are rated for a max of 14.5 volts. the charging system on the SV1K puts out 14.6 volts so the lights cut off when the engine is started and the charging voltage reaches 14.5 volts.

I need to add a resistor in line to reduce the voltage four tenths of a volt to be safe but am not sure what resistor would be best for this aplication?

any electronics experts here?
 
We need the current draw of the bulb(s) to do a proper calculation I think. There's a calculator at the bottom of this page.
 
A diode in series will drop the voltage by 0.7 volt. But again, to size it, you will need to know the current going to the lights.
 
Diodes usually are specified by current rating - either amps or milliamps.
Resistors are usually noted by wattage.
 
20mA per LED is a pretty typical rating, it looks like there are 24 in your arrays (they'll be parallel). Using this calculator -

http://ledz.com/?p=zz.led.resistor.calculator (bottom LEDs in parallel)

It shows a 10 ohm/10 watt resistor for a 2V drop at 14.5V. Since there cheap you might buy a few (5/10/15/20 ohms) and see which one works best.
 
The spec page of the linked LED unit fails to give the draw, so you will have to measure that first.

Or you can take a shot since LEDs are generally pretty low power devices of a half watt or less. A resistor of 15 to 20 ohms and a half watt rating should get your running voltage down around 12 and not let any 'magic smoke' excape components. You will need four of course, one for each lead of each bulb unit.
 
The spec page of the linked LED unit fails to give the draw, so you will have to measure that first.

Or you can take a shot since LEDs are generally pretty low power devices of a half watt or less. A resistor of 15 to 20 ohms and a half watt rating should get your running voltage down around 12 and not let any 'magic smoke' excape components. You will need four of course, one for each lead of each bulb unit.

Yeah you don't want to let out the factory installed smoke. Once you do it's hard to get it back in, and it won't work with out it :lol2:
 
thanks guy's!! what the current draw is on them is the big question.
the clusters they sent me actually have 30 individual white and 30 amber LED's each.
the bulbs I had in them before this used single 3 watt luxeon and the light output is pretty close.

these are smart bulbs and have circuitry and some sort of control and protection, I had tried the calculator and guessed at the current and it recommended a 1 ohm resistor.

gonna hook up my meter to them and see what they draw.
 
thanks guy's!! what the current draw is on them is the big question.
the clusters they sent me actually have 30 individual white and 30 amber LED's each.
the bulbs I had in them before this used single 3 watt luxeon and the light output is pretty close.

these are smart bulbs and have circuitry and some sort of control and protection, I had tried the calculator and guessed at the current and it recommended a 1 ohm resistor.

gonna hook up my meter to them and see what they draw.

if they have smart leds then most are set for any voltage from 6 to 40.

edit most of the current control IC s that I found were 6 to 40 volt DC input.
 
Will the one ohm resistor get you just under the 14.5 cutoff? I suggest picking a target voltage close to the middle of the operating range of the circuit. Most likely has zener diodes in the base to effect the high voltage cutoff and possibly a switching transistor to shut off the white LEDs when the amber circuit powers up.
 
Spec sheet says 11.5-14.5 volts. I would measure running light[white] current draw from idle to max RPM. Then compute resistor value for 13.0 volts[middle of range] to LED light. That means getting rid of 1.5 volts. For example, if your LED light current draw is .6 Amps[600mA],then resistor ohmic value is: R=volt/current; R=1.5/.6;= 2.5 OHMS. Now, you must have a wattage rating for the resistor to "handle" all the power it is going to get rid of. Power=current times current times ohmic value[I squared R]. So, .6 times .6 times 2.5=.9 WATTS. THE CLOSEST IS A 1 WATT POWER RATING. Follow? So, if you have a 2.5 ohm resistor in SERIES with the white led array and your system is running at 14.5 volts the LED array will get 13 volts to run on. I would use a 2 Watt power rating on the resistor. You will need a second resistor for the AMBER array also, so 4 total in your application. Hope this helps, YMMV. Good luck!
 
Last edited:
The most important thing to take into account is the LOWEST VOLTAGE your system will be at. Lets say 12 volts. The in my example, you can only get rid of a half volt since specs on light require 11.5 volts MINIMUM. You can work backwards from what I posted. Can you read your systems low and high voltage values? Then you can "fine tune" the ohms you need.
 
I did some research for you. Off the shelf voltage regulators for 12v output require minimum 14.5 volts input! Thought I could find an "easy" solution[plug 'n play] but I didn't.
 
The most important thing to take into account is the LOWEST VOLTAGE your system will be at. Lets say 12 volts. The in my example, you can only get rid of a half volt since specs on light require 11.5 volts MINIMUM. You can work backwards from what I posted. Can you read your systems low and high voltage values? Then you can "fine tune" the ohms you need.

Thanks Wally!! :thumb:

base line voltage, key off at battery= 12.75 volts
key on engine off, fuel pump on, high-intensity discharge lamp in warm up mode, voltage at battery= 12.25 volts
at engine start voltage rapidly rises (5 seconds) to 14.6 volts at idle and remains rock steady at 14.6 volts all the way to 11K rpm.

the only thing I have found that has the slightest effect on charging system voltage output is a slight momentary drop when the cooling fan starts up.

the regulator on this bike is surprisingly tenacious in its ability to hold 14.6 volts.
 
Remember an ammeter[reads current] is placed in SERIES with the wiring. A digital won't care which way you connect it, you just want the VALUE, i.e. .6Amps[600mA].Whatever that number is, plug it into the formula I posted and get your numbers. There are some really neat aluminum jacketed[with mounting holels] 5 watt resistors that most parts houses can get/order. Might be a buck a shot. If you can't find 'em locally PM me. Good luck! Of course, pictures ARE required. BTW, the formula uses WHOLE numbers, not mA. You may need to convert: 1000mA is 1 Amp so decimals come into play. Or post values and I'll do the math for you.
 
Last edited:
After saying all this remember in wiring NEATNESS COUNTS! You SHOULD, at a minimum, use HEAT SHRINK SLEEVING on all connections. Hope this helps, YMMV
 
Another thought. You will need a stagered bayonett socket for that dual "filament" LED As can be seen from the web sites picture[just like a standard run/brake light blub]
 
Thanks Wally!! :thumb:

base line voltage, key off at battery= 12.75 volts
key on engine off, fuel pump on, high-intensity discharge lamp in warm up mode, voltage at battery= 12.25 volts
at engine start voltage rapidly rises (5 seconds) to 14.6 volts at idle and remains rock steady at 14.6 volts all the way to 11K rpm.

the only thing I have found that has the slightest effect on charging system voltage output is a slight momentary drop when the cooling fan starts up.

the regulator on this bike is surprisingly tenacious in its ability to hold 14.6 volts.

This is of concern if you have a battery which is gonna get cooked to death unless the voltage drops off after say 15 minutes. What do specs say on electrical system?
 
This is of concern if you have a battery which is gonna get cooked to death unless the voltage drops off after say 15 minutes. What do specs say on electrical system?

I know, 14.2 volts is the highest I am normaly comfortable with and like 14 volts even best, I don't know if the higher than normal charging voltage has any thing to do with the bike being designed for a AGM battery stock. I will have to do a extended run voltage test to see if it settles down to a more comfortable voltage.
I do know the factory original battery did last 7 years and even then was still cranking the bike over quite well. I only changed it because I was hooking up a controller for electric heated gear and was nervous with the battery voltage drop while cranking.

I am taking one of the bulbs to work with me tomorrow where I have a more acurate meter, and can set up for the test without having to ballance everything in a headlight bucket or on a fender.

thanks again Wally!!
 
Last edited:
it took some creativity but I did convert the sockets from single to dual.
I am going to take a short video of how the lights work.

I already have integrated the rear turn signals to function as tail and brake lights (in red) that switch to amber for turn signal function. fortunatly the LED's used there are not as touchy about voltage.
 
I gotta rethink voltage regulators for your project. Give me some time on that one.
 
Ok did a preliminary current flow test and with a battery voltage of 12.7 volts the white LED's draw .045 amp
The amber draw .130 amp I have to find a window to run the current test on a running vehicle


Sent from my iPhone using Tapatalk
 
Back
Top