Any EEs Here? School me on Relays?

Started by xsephirot, March 05, 2013, 09:08:33 AM

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xsephirot

So I am trying to make a wiring harness and relay that connects to the bike's standard H4. Basically what I need is this:

1) When I turn the ignition to on and light is 'low beam', the wiring harness will draw constant power but the relay will also be powered to only draw 50% power.

2) When I flip to 'high beam', it still draws constant power but the relay is not powered so the draw would be 100%

I've been reading: http://www.mp3car.com/the-faq-emporium/117895-faq-relays-how-they-work-and-how-to-wire-it-up.html

And I'm pretty much baffled at this point. Can someone who understands this impart some knowledge on me?

JohnEE

What do you hope to accomplish by having the headlight draw %50 power? Better Start? The euro bikes do this automatically if i am not mistaken(headlight off when ignition is on but bike is not started). I think the mod is to swap the left hand controls out for a euro unit. Hopefully someone can verify this....

xsephirot

Quote from: JohnEE on March 05, 2013, 09:35:55 AM
What do you hope to accomplish by having the headlight draw %50 power? Better Start? The euro bikes do this automatically if i am not mistaken(headlight off when ignition is on but bike is not started). I think the mod is to swap the left hand controls out for a euro unit. Hopefully someone can verify this....

Actually I'm thinking of using LED lights. They are obnoxiously bright at 100% so I'm hoping with normal lights on it would be 50% draw and when I flip on high then it would disengage  the 50% dimmer and go 100%...

ducpainter

I'm no EE, but I think you need a device other than a relay to reduce power to the lights.

DM beat me to it.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



Dry Martini

Quote from: xsephirot on March 05, 2013, 09:46:41 AMActually I'm thinking of using LED lights. They are obnoxiously bright at 100% so I'm hoping with normal lights on it would be 50% draw and when I flip on high then it would disengage  the 50% dimmer and go 100%...

You need a dropping resistor to consume part of the 13.8v from the charging system.

The type of relay you would be more involved than the standard N/O or N/C relay, which is what most automotive type relays are. They either open a circuit or close it, once control voltage is applied. You need a relay that switches from one voltage source (low volt) to another (full system voltage).
I feel sorry for people who don't drink. When they wake up in the morning, that's as good as they're going to feel all day. -Frank Sinatra

JohnEE

Quote from: xsephirot on March 05, 2013, 09:46:41 AM
Actually I'm thinking of using LED lights. They are obnoxiously bright at 100% so I'm hoping with normal lights on it would be 50% draw and when I flip on high then it would disengage  the 50% dimmer and go 100%...
One problem right away is that headlight switch probably can't activate the coil of the relay. You'll need a certain voltage and current to be able to flip the "switch" in the relay. You could try adding more resistance with higher resistance power resistors(Most LED kits come with these anyways) to draw more of that current away from the LED to make it less bright.

xsephirot

Quote from: Dry Martini on March 05, 2013, 10:15:11 AM
You need a dropping resistor to consume part of the 13.8v from the charging system.

The type of relay you would be more involved than the standard N/O or N/C relay, which is what most automotive type relays are. They either open a circuit or close it, once control voltage is applied. You need a relay that switches from one voltage source (low volt) to another (full system voltage).


Quote from: JohnEE on March 05, 2013, 10:44:16 AM
One problem right away is that headlight switch probably can't activate the coil of the relay. You'll need a certain voltage and current to be able to flip the "switch" in the relay. You could try adding more resistance with higher resistance power resistors(Most LED kits come with these anyways) to draw more of that current away from the LED to make it less bright.

Thanks for the help guys! After googling alot more I came upon this: http://www.lights.skenedesign.com/IQ_175.shtml

This should work almost like a MOSFET regulator right?

Dry Martini

Quote from: JohnEE on March 05, 2013, 10:44:16 AM
One problem right away is that headlight switch probably can't activate the coil of the relay.

The headlight switch would have no problem supplying ~12v to energize a relay. This was done all the time on BMW bikes,to drive the headlights directly from the battery.
I feel sorry for people who don't drink. When they wake up in the morning, that's as good as they're going to feel all day. -Frank Sinatra

xsephirot

Quote from: Dry Martini on March 05, 2013, 11:07:42 AM
The headlight switch would have no problem supplying ~12v to energize a relay. This was done all the time on BMW bikes,to drive the headlights directly from the battery.

What would you suggest be the minimum gauge to use? Is 18 enough?

On a side note, if you have too thick of a gauge (say 10 gauge) would naything happen?

JohnEE

Quote from: Dry Martini on March 05, 2013, 11:07:42 AM
The headlight switch would have no problem supplying ~12v to energize a relay. This was done all the time on BMW bikes,to drive the headlights directly from the battery.
Thus the probably in my statement, i didn't know for sure. Knowledge is power!

ducpainter

That's the primary purpose of a relay. To allow a circuit not capable of handling high current, like one with a switch with delicate contacts, to trigger a circuit that has high current draw.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



Bill in OKC

#11
EE here, but after 30 years some things might have changed since I was in school.  LEDs do not have much of a high/low brightness variation just from varying the voltage to them.  In the past we designed a circuit that varied the duty cycle ie: turned the voltage on and off quickly at different speeds to dim LEDs.  They will dim a bit from dropping the voltage but as a diode their state is either on or off - they either have enough voltage to turn on or they don't.  Some LEDs come packaged already with a dimmer circuit so maybe your headlight already has this?  If so then you need to control the dimmer circuit.  Another thing to consider is that it is not just the brightness but how the headlight is aimed when switching from low to high beam.  The LED headlights I have seen use different LEDS or combinations of LEDS to create the high and low beams.
A relay is just an on/off switch.  Some older cars/bikes routed the headlight power directly through the on/off switch and the switches just were not rated to handle the current over time.  A relay is used to offload the power from a weak on/off switch to a stronger (and easily replaceable) relay to handle the power better.  YMMV
'07 S4Rs  '02 RSVR  '75 GT550  '13 FXSB  '74 H1E  '71 CB750

xsephirot

Quote from: Bill in OKC on March 05, 2013, 12:03:15 PM
EE here, but after 30 years some things might have changed since I was in school.  LEDs do not have much of a high/low brightness variation just from varying the voltage to them.  In the past we designed a circuit that varied the duty cycle ie: turned the voltage on and off quickly at different speeds to dim LEDs.  They will dim a bit from dropping the voltage but as a diode their state is either on or off - they either have enough voltage to turn on or they don't.  Some LEDs come packaged already with a dimmer circuit so maybe your headlight already has this?  If so then you need to control the dimmer circuit.  Another thing to consider is that it is not just the brightness but how the headlight is aimed when switching from low to high beam.  The LED headlights I have seen use different LEDS or combinations of LEDS to create the high and low beams.
A relay is just an on/off switch.  Some older cars/bikes routed the headlight power directly through the on/off switch and the switches just were not rated to handle the current over time.  A relay is used to offload the power from a weak on/off switch to a stronger (and easily replaceable) relay to handle the power better.  YMMV

Bill, thanks for the info! I will def look into it.

scaramanga

Led's are funny little devices. Each single led has 2 major parameters, forward voltage and max forward current.The forward voltage is fixed and cannot be changed, the current on the other hand can be varied up to the max permissible and thats how the brigthness is controlled. If you have a 10watt led that runs on 10volts we can quickly calculate that in order to emit 10watts of power(most of it being light) we need 1 amp of current. power=voltage*current. therefore you need to limit the current with a resistor to 1 amp or your little led will fry.now if your led drops 10volts and your battery is lets say 12 volts you have 2 volts left over that will be dropped across the resistor you are using to limit the current.(this is a series circuit) To select the proper size resistor you use the formula voltage(volts)=current(amps)*resistance(ohms). to solve for resistance divide 2 volts  by 1 amp= 2ohms. You also need to calculate the power rating of your resistor ( or it too will fry), power = voltage*current, p=2*1= 2watts. resistor needed= 2 ohms 2 watts.
If your led light bulb that you want to install is rated for 12volt use, it shouldn't work when you try to dim it by cutting its voltage by any means.

One way to make an led emit more light than its rated is to send a large current through it but for a very small amount of time. If our previous led has a max current rating of 1 amp (thats continuous) and we decide to send 5 amps through it but for a very short period of time we can get 5 times the power. the problem is that you will only get a quick flash of light. yes you guessed it, why don't we do that alot and really fast. if you pulse that led faster than 30 times per second it will appear as a continuous light source to the human eye. That is how those intelligent controllers work.

in order to decide what size wire to use you need to know how much current it will carry. for a 14 guage wire you can run about 20 amps through a 15 foot length.
 
2008 s2r1000
2011 sf1098

Dry Martini

Quote from: xsephirot on March 05, 2013, 11:26:30 AM
What would you suggest be the minimum gauge to use? Is 18 enough?

On a side note, if you have too thick of a gauge (say 10 gauge) would naything happen?

For the for the wiring used for the control voltage of the relay, 18 gauge is fine. For the actual wiring to the LEDs, 14 gauge would be fine. A larger gauge wire will not have electrical effect, it just makes it harder to run in tight spaces.
I feel sorry for people who don't drink. When they wake up in the morning, that's as good as they're going to feel all day. -Frank Sinatra