Topic: Question about instaling headlight relays....

[78CB750CAFE]

Since I have a lot of time right now and very little $$ I am doing a lot of minor refinements upgrades this winter.
We all know the stock headlight set up is weak for night riding especially on unlit roads in the dark winter months, so why not do the relay thingee, right?

My questions for those that have done this are:

1  In all the schematics I have seen (mostly for doing horns) they spec 15 amp fuses.. standard headlight on the CB is 40/55 watts give or take, wouldn't a 5 (low) and 7.5 (high beam) amp fuses suffice? 7.5 and 10 amp would give almost 100% headroom, 15 amps seems like overkill.

2 Low beam... I have installed a switch in my headlight bucket a while ago, should I use that for the switching input for the relay or wire the relay as normally hot? I would like to still have the ability to switch the headlight on and off via the switch for warming up/ idling, so would running the relay normally hot with the switch upstream of the relay be an option?
Is there a way to do this  that would allow me to have a switchable low beam (where low voltage is passed through the switch, extending it's life) but would automatically kill the low beam when I hit the high beam switch, while using as little of or none of the existing harness wiring?

These may all be stupid questions, and I may be confused and talking cross purposes and yes I scoured the FAQs first few pages and searched the site for "headlight relay" , so if any of you electron stream geniuses can help me out, please do. I used to be a professional production electrician and should know these answers but my head is too mucked up by my recent change in employment status to make any sense of anything right now.

thanks in advance to the usual electrical problem solvers (Hondaman, TwoTired...)

I need a beer right now, but point me the way and I will head out to the garage and keep myself warm with the old soldering iron

[Spanner 1]

Regarding your Q.1....the fuses on your bike are matched to the size of the wire in that particular circuit, i.e.the wire to the headlight can carry 15A, hence the fuse of this rating.The fuse as such does not protect anything, only to stop the wire melting if an overload/short on the circuit.. At 12v a15A fuse can carry 180watts ( 12v x 15A = 180w ), give or take a little.
Q.2. is a little too complicated for me to follow !!
One caution tho' , the alternator may get fried trying to keep-up with a bigger headlight load !
I'm not sure what the max. load allowed on the alt. is....anyone know?

[super pasty white guy]

On mine, the handlebar switchgear controls the relay, that way the high - low switchover is automatic.  if you want to be able to switch off the low beams, just wire that in series with the handlebar switch.

Or did I totally miss what you were saying?

sorry to hear about the job.  that freakin' sucks ass.

spwg

[Steve F]

This is the way I have mine wire up.......

[Spanner 1]

Good one SteveF ! That's 2 relays, or a twin relay with 2 coils maybe ?

[Steve F]

2 relays,, like the ones use for fog lights and such.  I mounted them in the triangular area just above the coils with pop rivets.

[bryanj]

You can get a change over relay but its cheaper to fit 2 standard relays feed the power to the dip switch via the already fitted switch in the shell then all the switches only carry low current. split main power into relays and put one fuse in the line OR if you want a bit of safe redundancy feed each seperate with two fuses

[78CB750CAFE]

Regarding your Q.1....the fuses on your bike are matched to the size of the wire in that particular circuit, i.e.the wire to the headlight can carry 15A, hence the fuse of this rating.The fuse as such does not protect anything, only to stop the wire melting if an overload/short on the circuit.. At 12v a15A fuse can carry 180watts ( 12v x 15A = 180w ), give or take a little.
Q.2. is a little too complicated for me to follow !!
One caution tho' , the alternator may get fried trying to keep-up with a bigger headlight load !
I'm not sure what the max. load allowed on the alt. is....anyone know?

OK, I guess I was more frazzled and convoluted in my wording then I thought.

My questions re: fuse amperage were for direct hot lines off the battery to feed relays and then the headlights, so references to the stock fuses and alternator loads is a little off track.

[Spanner 1]

Gotcha, I thought you meant the existing h.l. fuse, why was it not smaller amp, also thought you were wanting a big ole 100w headlight or somethin' !!

[bradweingartner]

The point of the Relay is to cut out the middle man so to speak. You want the relay to be wired directly to the battery with a dedicated wire. And use whatever switch you currently use to switch the relay(s).

Just putting a relay in line with whatever wiring currently exists completely defeats the purpose of the exercise.

Now on these Hondas, the switches ARE in fact pretty anemic, but by far the biggest issue is not the switches but rather the charging system. So relays might help a little but you need to look at a total system approach. Example: If you cut down every filament bulb on the bike from the dash to the blinkers, replace them with LEDs, the savings would be significant.

[78CB750CAFE]

On mine, the handlebar switchgear controls the relay, that way the high - low switchover is automatic.  if you want to be able to switch off the low beams, just wire that in series with the handlebar switch.

Or did I totally miss what you were saying?

sorry to hear about the job.  that freakin' sucks ass.

spwg

Pasty

yeah yeah, that's the ticket right there. I will leave the switch i have downstream the relays and use the stock hot feed to the low beam to feed the relay, and the stock high beam switch to feed the high relay.

yeah, unemployment sux.

holler when you wanna pull that engine, I have the garage, lift and nothing but time.

Drew

[78CB750CAFE]

The point of the Relay is to cut out the middle man so to speak. You want the relay to be wired directly to the battery with a dedicated wire. And use whatever switch you currently use to switch the relay(s).

Just putting a relay in line with whatever wiring currently exists completely defeats the purpose of the exercise.

Now on these Hondas, the switches ARE in fact pretty anemic, but by far the biggest issue is not the switches but rather the charging system. So relays might help a little but you need to look at a total system approach. Example: If you cut down every filament bulb on the bike from the dash to the blinkers, replace them with LEDs, the savings would be significant.

every light aside from the headlight is LED (brake/tail, f/r blinkers, plate, dash idiot lights), I have a brand new AGM battery, solid state reg/rect, new starter solenoid and a stator that meters to spec.

[78CB750CAFE]

This is the way I have mine wire up.......

copy that, just what I needed, thanx

[TwoTired]

About the fuses and fuse ratings.

The stock bike used a 15 amp to protect everything (accept the alternator/ rectifier).  From that fused branch, was a separate branch for the headlight fuse of 7 amps, and a tail light branch with a fuse of 5 A.  This arrangement would keep the bike running if either or both of the headlight circuits and tail light circuits drew excessive currents.

Fuse capacity assignments are not really sized for the wire used.  Rather the wire is sized to minimize losses in the circuit at the expected load without excessive heating that could damage the wire insulation.  The fuse rating is selected for about 2/3 to 75% of the expected load in the circuit.  The stock bike used about 10 amps through the main fuse, or about 2/3 of the 15 amps fuse rating.  The stock headlight drew about 4.3 amps which is about 61% of the 7Afuse rating.  I haven't measured or calculated the tail light current draw, but I'd expect about a 3 amp-ish draw through the tail lamp circuit.

Fuses ARE a safety valve to protect the circuit from over-currents, usually gross ones, like powered wires touching frame components.  When the circuit resistance approaches zero, the current approaches infinity.  Such currents will heat wires to the point of melting their insulation.

If you are putting searchlights on the front of your bike  , you can expect a higher current draw through the circuits.  Divide the wattage rating by 12.8V and you will get the current drawn at that voltage.  Then select the next standard size fuse so that you are drawing about 2/3 through the fuse for that circuit.  If your new headlight is, say, 90 watts, it will draw about 7 amps.  An 11 amp fuse would be appropriate for this lamp and circuit. The fuse should survive normal operation yet break the circuit if gross over-currents are sensed.  A 15 would also work, as the a 15 amp fuse will blow almost as quickly as an 11 amp, with currents approaching infinity, and unless you are using doorbell wire, or high number gauge wire, the fuse will still part before there is insulation damage.  However, any fuses in the path between that fuse and the power source will also need to be resized to account for the higher expected current draw.

The stock bike, switches the lighting on via the key switch, using the Black wire distribution.  If you get relay power from the black wires, it is unlikely to get any voltage gains at the headlight.
The stock switches are quite robust when the internal contacts are clean, even with normal wear.  They can be reconditioned to provide a low resistance/ low voltage drop connection.
Adding a relay can help dirty or worn out switches serve their intended function a little longer, if the owner doesn't wish to address switch overhaul.  However, if the switches are maintained properly, they can handle quite a bit more current than the stock bike normally draws, and still deliver full (or very nearly so) voltage to the headlight.

If your relay is to be connected to the battery upstream (nearer to the power source) from the stock main fuse, then your fuse only has to keep the new wires you have installed, from melting its insulation when there is a short circuit.  Most likely a 15 amp will do this job fine, given you have selected a proper size wire gauge for the circuit.

I warn you, none of this may make any sense depending on the beer count while reading. 

Cheers,

[Spanner 1]

While I totally respect TwoTired's knowledgable posts, I would want to hear from someone who had increased the headlight load to know if it had caused the alternator to fail...the stock load may be close to the max. available. If your staying with the regular H.L. wattage then no prob....a relay might help ( don't know why Honda would allow a voltage-drop on the stock wiring tho' ! ).

[TwoTired]

While I totally respect TwoTired's knowledgable posts, I would want to hear from someone who had increased the headlight load to know if it had caused the alternator to fail...the stock load may be close to the max. available. If your staying with the regular H.L. wattage then no prob....a relay might help ( don't know why Honda would allow a voltage-drop on the stock wiring tho' ! ).

Er, doesn't quite work that way.  The bike is actually powered by the battery.  The alternator just recharges the battery whenever the bike's load is less than what the alternator can provide and the battery is below peak voltage.  If you increase the bike's electrical load so that the battery cannot get recharged, it drains, lowers it's voltage until their is not enough to spark the plugs.  Then the bike won't work until you recharge the battery.
The 750 is rated for 210 watts output at 5000 RPM. Its less at idle, probably about 100 watts.  It would be difficult to overload the alternator itself as extra heat generated at the coils would be transferred to the case rapidly.  However, the yellow wires to it or the rectifier and its wires would likely melt and disconnect themselves before damaging the stator coil.

As to Honda design...
Some voltage drop in the system is unavoidable.  You'll get some with a relay setup too, as all materials have some resistance to electrical current.  A new Honda had a bright headlight, with maybe as much as a half volt loss between battery and headlight.  However, these bikes aren't new anymore and if you look at the wire diagram you'll find many elements in the electrical path.  Some/most of these are exposed to atmospheric oxygen, sulfur, humidity (if not water) and other elements that corrode non-noble metals and degrade their electrical conductivity over time.  I don't think Honda gold plated anything in the electrical path so each connection or switch contact is subject to increasing resistance over time.  I recently did a work up of the elemental loss points in the path between battery and voltage regulator supply terminal like this:
• Battery post to to battery terminal
• Battery Cable lug to Solenoid Terminal lug
• Solenoid terminal lug to solenoid post
• Solenoid post to Red wire terminal
• Red wire terminal lug to red wire
• Red wire
• Red wire to red wire terminal in inline plug
• in-line plug terminal male to in-line terminal female
• inline terminal to red wire
• Red wire
• Red wire to red wire terminal in fuse block plug
• fuse block plug terminal male to terminal female
• fuse block terminal to red wire
• Red wire
• red wire to fuse clip terminal
• fuse terminal to fuse end cap
• Fuse
• fuse end cap to fuse terminal
• Fuse terminal to red wire
• red wire
• Red wire to red wire terminal in fuse block plug
• Fuse block plug terminal male to fuse block terminal female
• Red wire (to key switch)
• Red wire to red wire terminal in key switch plug
• key switch plug female contact to male terminals
• key switch terminal to internal contact (Red wire side)
• key switch red wire contact to black wire contact inside switch (Black wire side)
• Black wire switch contact to key switch plug terminal
• key switch plug female contact to male terminals
• key switch plug terminal to black wire
• Black wire
• black wire to black wire terminal.

Each of these elements has a resistance.  If the wires haven't been subjected to corrosion that reduces it's cross section area, its resistance is the same today as when manufactured.  However, all other elements in the list can and usually do change over time.
BTW, if you use this as a guide, you can make a similar list of circuit elements for the battery to headlight path.  There are over 30 items in the above list.  If 20 of them increase their voltage loss by .05 volts, that's 1 volt less that gets to the systems black wire distribution buss.  The path to the headlight has more elements than listed above, giving more opportunity to lose voltage/power at each element.

Cheers,

[MCRider]

Since I have a lot of time right now and very little $$ I am doing a lot of minor refinements upgrades this winter.
We all know the stock headlight set up is weak for night riding especially on unlit roads in the dark winter months, so why not do the relay thingee, right?

My questions for those that have done this are:

1  In all the schematics I have seen (mostly for doing horns) they spec 15 amp fuses.. standard headlight on the CB is 40/55 watts give or take, wouldn't a 5 (low) and 7.5 (high beam) amp fuses suffice? 7.5 and 10 amp would give almost 100% headroom, 15 amps seems like overkill.

2 Low beam... I have installed a switch in my headlight bucket a while ago, should I use that for the switching input for the relay or wire the relay as normally hot? I would like to still have the ability to switch the headlight on and off via the switch for warming up/ idling, so would running the relay normally hot with the switch upstream of the relay be an option?
Is there a way to do this  that would allow me to have a switchable low beam (where low voltage is passed through the switch, extending it's life) but would automatically kill the low beam when I hit the high beam switch, while using as little of or none of the existing harness wiring?

These may all be stupid questions, and I may be confused and talking cross purposes and yes I scoured the FAQs first few pages and searched the site for "headlight relay" , so if any of you electron stream geniuses can help me out, please do. I used to be a professional production electrician and should know these answers but my head is too mucked up by my recent change in employment status to make any sense of anything right now.

thanks in advance to the usual electrical problem solvers (Hondaman, TwoTired...)

I need a beer right now, but point me the way and I will head out to the garage and keep myself warm with the old soldering iron

I'm not much help to the DIYers in this area. But for my purposes, buying a pre-made harness from http://easternbeaver.com/ and following their directions is my route. They have a harness that will allow the low beam to stay on when the high beam is on, but they warn about excess heat.

I bought a harness from a guy on the HawkGTforum.com for the same reason. On my Hawk it made a huge difference with the stock bulb. A little more watts is just that much more.

For horns and lights I highly recommend it.

To your question in #2, doesn't the low beam go outwhen the high beam comes on with the stock wiring? I think so. Oh I see you want to use as little of the stock harness as possible. Again, I'm not too good in the DIY area with electrics.

[Spanner 1]

Er ,doesn't quite work that way either, TwoTired! Please re-read your first paragraph in your  reply to my last post. the bike is powered by the battery only when the ignition is on but the motor not started. The bike, when running, is powered by the alternator feeding the battery thru' the regulator at all times! Yes ? The varying loads ( turn signals, brakelights, hi/lo beam ) causing the regulator to vary the demand on the alternator to keep the voltage up on the battery. If overloaded the alternator will still try to charge the battery, without letting-up ,until its winding fails due to excess current producing excess heat ( unless a thermal cut-out is installed in the windings ) These bikes don't have that safeguard to tell you to turn-off the 2x 100w headlights !!..

[TwoTired]

Er ,doesn't quite work that way either, TwoTired! Please re-read your first paragraph in your  reply to my last post. the bike is powered by the battery only when the ignition is on but the motor not started. The bike, when running, is powered by the alternator feeding the battery thru' the regulator at all times! Yes ?

Nope.  The stock bike draws about 120 watts whenever the key switch is on.  The alternator only puts out about 100 watts at idle. The bike is still drawing 120watts, and the battery makes up the difference while depleting in the process.  When the R's come up, the alternator makes enough power to restore the battery over the drain the bike makes on the battery.
The regulator is not inline with the alternator output.  It's job is to sense battery state of charge and throttle the alternator output strength, solely to keep the battery from over-charging.  If the battery is low, the Vreg puts full battery voltage on the field coil, so the alternator can be all it can be at whatever RPM the crank is spinning.  The alternator is 210 watts capable.  If you put more resistance on the alternator output directly, the current goes up, but the voltage falls as the stator windings are prevented from reaching peak voltage.  Power is current times voltage.  210 watts can be 7 amps at 30 volts, or 14 amps at 15 V,  or 28 amps at 7.5 V,   The battery is the buffer for this, which is why I say the bike runs on the Battery.  If the alternator is loaded so it can't provide a voltage to the battery higher than its present charge state, the battery simply depletes.  You can't take out of the alternator what isn't there, as that would be excess power generation, of which, it is not capable.  The alternator is an accessory to help keep the battery maintained, in order to power the bike.

The varying loads ( turn signals, brakelights, hi/lo beam ) causing the regulator to vary the demand on the alternator to keep the voltage up on the battery. If overloaded the alternator will still try to charge the battery, without letting-up ,until its winding fails due to excess current producing excess heat ( unless a thermal cut-out is installed in the windings ) These bikes don't have that safeguard to tell you to turn-off the 2x 100w headlights !!..

 From your description, I'm not sure you understand how the vreg actually works on the SOHC4.   

Regardless, the alternator can supply 210 watts of power.  It can't make 300 or 400 watts. It just isn't there.  Higher attempted loads can't be supported because the magnetic field lines of flux in the alternator are limited by the max magnetic field strength created by the the field coil, the number of stator windings present, and the AC frequency created by the spinning electromagnet core.  If your raise the drain on the alternator, the AC voltage peaks diminish from the stator as it is depleted faster than the voltage can rise before the reverse cycle begins.  (Each phase from the stator is a sine wave output spending half the time in the positive and half the time in the negative.)
It won't make more power simply because the demand is higher.  Excess of what the alternator can make (as demanded by the bike loads), is supplied by the battery, until it's voltage falls below the point where the coils can't make the plugs spark.

Does this help?

[Spanner 1]

Yes it helps... thank you,
I still have a couple of Q's tho' ! O.K., low rpm is understood , but within its useful range ( rpm and voltage ) when the battery has reached its fully charged state , the battery is now just a capacitor sitting across the load and the alt. is now coupled to the load directly ( regulated for voltage output at,what, 13 to 14.5v say ) that's what i meant by 'the bike runs-off the alt.' If this were not the case the battery would never charge, right?
Now if the system ( batt./ reg. / alt. ) is overloaded, you are saying the voltage drop in the batt. will automatically reduce the field coil voltage thus reducing the output of the alt. resulting in a nett loss and the battery draining...interesting ! The alt. is protected by the battery from a direct overload !
P.S. I hope you are o.k. with these long discussions !

[78CB750CAFE]

wow... I spurred a deep debate over the charging system. I am happy to sit back and learn.

Back on topic though...

I used a slight variation on SteveF's schematic (BIG thanks!) and it worked fantastic. My variation was just the inclusion of a cut off switch I have mounted atop the headlight bucket.
I do notice that it is a bit harder to actually throw the stock hi/lo switch now, did I possibly screw it up? It feels as if the voltage running through it is making it want to stay in whatever position it is in.

I used a 15 amp (I will prob lower that amperage) fuse straight off the battery, into some nice 10 AWG low oxygen wire and  "Y'ed" it out the 2 relays, from the relays I ran a frame ground to where I grounded the rest of the lights on the bike w/ 16 AWG, ran the "switch" wires to the stock switches with 14 AWG, and the power runs from the relays to the 2 lamps with the same 10 AWG I used for the main power wire. All connections were replaced with new high grade weatherproof 1/4" quick disconnect connectors that were crimped and soldered, and slathered with silicone dielectric grease before mating. I mounted the relays under the tank on the frame just ahead of the coils. when I am positive my mounting location is just right I will probably shorten the length of the main power feed line as I have a few extra inches in there to aid jogging it around a little, and then I will heat shrink the wiring into a neat bundle using some of that godawful expensive waterproof heat shrink tubing.

So all in all I probably spent around $30 bucks and a few hours and my headlight is BLINDING compared to how it was before. When my headlight does burn out, I want to get an Adjure iron cross headlight with an H4 bulb, but that is down the road a bit.

Thanks all for the help, and the general sharing of knowledge.

Drew

PS- Now I am off to the garage to replace the rest of the bullet connectors on the bike with those nice weatherproof quick disco's, and might dive into replacing some of the stock multi-pin connectors with some I have from an Acura wiring harness my local gas station guy gave me. At this rate I should have just built a harness from scratch as I am only using about 1/2 of the original one... oy vey

 

[TwoTired]

Yes it helps... thank you,
I still have a couple of Q's tho' ! O.K., low rpm is understood , but within its useful range ( rpm and voltage ) when the battery has reached its fully charged state , the battery is now just a capacitor sitting across the load and the alt. is now coupled to the load directly ( regulated for voltage output at,what, 13 to 14.5v say ) that's what i meant by 'the bike runs-off the alt.' If this were not the case the battery would never charge, right?

You're pretty close.
The charging circuit is attached to the battery terminal.  The load doesn't care where it gets it's electrons from and it's source is that same battery post. If the load is such that it is within the alternator capacity and the battery is fully charged, then the stock vreg switches the alternator between on, one half, and no power, depending on what it senses on the black wire monitor terminal.  If the battery is full, the vreg switches the alternator to 1/2.  If the bike load is more than this, the battery makes up the difference until it gets below the "full" voltage, whereupon the the vreg turn the alternator back up to full.

Your previous scenario/concern was if the the bike load exceed the alternator capability.  This makes the battery deplete as it has to make of the difference from what the alternator can provide, to what the bike demands.  The vreg would leave the alternator on full, which would only delay the slow depletion of the battery, as it can't make all the power the bike demands.  Eventually, the spark stops, as does the motor.

Now if the system ( batt./ reg. / alt. ) is overloaded, you are saying the voltage drop in the batt. will automatically reduce the field coil voltage thus reducing the output of the alt. resulting in a nett loss and the battery draining...interesting ! The alt. is protected by the battery from a direct overload !
P.S. I hope you are o.k. with these long discussions !

While true, that the reduced voltage to the alternator field coil reduces the output strength of the alternator, there is a little more going on in the alternator to limit its output power.  Even if you maintained the field coil voltage at 12V, simply putting more load on the alternator won't make it produce more power.  The bike (with the exception of the coils) and battery operate in the DC domain, while the alternator operates within the AC domain.  The rules are different for AC devices.  Are you familiar with the differences between DC theory and AC theory?  Impedance calculations, and their interactions with voltage development, are quite different and more complicated than DC resistance calculations.

I don't mind long discussions.   I have some concern about straying far from the original thread topic, though.

Cheers,

[Spanner 1]

While you and I were 'waffling on ' about alternators, the original poster has solved his dim headlight problem... I guess you are right about straying too far off topic !!
O.K. I'm happy with having had some misconceptions straightened-out....until the next time
( just kidding! ). Spanner.

[NitroHunter]

Fantastic stuff - ALL you guys!

[stresssolutions]

TwoTired wrote

The stock switches are quite robust when the internal contacts are clean, even with normal wear.  They can be reconditioned to provide a low resistance/ low voltage drop connection

I appreciate all this information, and would like to read a little more about the above quote.  Do you disassemble the switches, or can you spray some stuff in there to clean them?
thanks