Topic: voltage drop at coil

[Outboardbill]

I was checking voltage at the coils with the key and stop switch on and comparing it to the battery voltage.  I have a 1978 cb750f.  It had 12 volts at the battery, but checking the lead to the coils it had only 10 volts.  Is that normal?  Where have those two volts gone?  Would that cause a weak spark?  I disconnected the key switch connector and ran a jumper through the connector to rule out the switch.  It still had only 10 volts at the coils.  What am I missing?

[TwoTired]

Check the wire diagram and you will find multiple conectors/switches between the battery and the coils.  When the connector age/corrode, they increase resistance and absorb some voltage.  Aged/worn switch contacts can do the same and drop voltage.
If 10 connections/contacts drop .2 V each, you lose 2 Volts upon delivery.

Yes, low voltage at the coils can cause weak spark.

Btw, it is not only the coils drawing power that causes the voltage drop.  The coil power hangs off a circuit that provides power to everything on the bike.  Those other devices drawing power also make those inline resistances eat up voltage, too.  So, basically every connection in the path between battery and the black wires needs cleaning to restore a low resistance connection that can't lose voltage when current is drawn through them.

Cheers,

[Bodi]

There is a lot of wire and connectors and 2 switches in the coil circuit. The wire contributes a bit of voltage drop, this is hard to avoid. Larger wire will reduce the lost voltage but the wire is not the main culprit.
The bullet connectors corrode over the years and their resistance rises, causing more voltage drop. The switch contacts do the same. Exercising the kill switch occasionally will clean its contacts, the ignition switch gets turned a lot and generally stays clean.
The bullet connectors need a good cleaning every decade or so. Just unplugging and replugging helps a lot. Cleaning both male and female ends then using a bit of dielectric grease to seal out water and air is best.
Voltage loss is proportional to resistance and current (good old Ohm's Law), the coil current won't change so reducing the circuit resistance is your only path.
You can add an automotive relay: run a fused (15A) power line from battery + to the relay switch and a wire from the switch to the ignition coils. Power the relay coil from the existing power wire to the coils, retaining the key and kill switch functions. You can use a heavier gauge wire if you wish, too.

[bucky katt]

i soldered the wire from the kill switch to the coil to the harness to get rid of my voltage drop. and that was in a new harness.

[Outboardbill]

Thanks guys.  I'll start on those bullet connectors tomorrow.  If that doesn't work I'll hook up a relay and that way bypass the problems of a 30 year old harness.

[Nikkisixx]

You can add an automotive relay: run a fused (15A) power line from battery + to the relay switch and a wire from the switch to the ignition coils. Power the relay coil from the existing power wire to the coils, retaining the key and kill switch functions. You can use a heavier gauge wire if you wish, too.

I like it - have you done this with good result?

[Tnutz]

easiest and beast way to avoid the above problem is the relay.

[dave500]

if your handy with a soldering iron,replace all the bullet type connectors with spade type,you can buy multi plugs and wire them to suit your needs,unless you want the original aspect kept.,check that voltage with the engine running aswell.

[Outboardbill]

Check out this link for the relay wiring.  http://www.wgcarbs.com/index.php?option=com_content&task=view&id=12&Itemid=26.

[TwoTired]

easiest and beast way to avoid the above problem is the relay.

I disagree.
This leaves all the corroded connectors in poor condition and eating up/wasting power.

If you restore condition to as new, it will work as new everywhere on the bike.

[Nikkisixx]

[/quote]
I disagree.
This leaves all the corroded connectors in poor condition and eating up/wasting power.

If you restore condition to as new, it will work as new everywhere on the bike.
[/quote]

I hear ya Twotired, but IF a frog had wings...
I agree it is not the optimal fix that a clean wire harness would be, but I can see a benefit to the relay setup.  Hypothetically speaking, what could it hurt? 

[Spanner 1]

It could hurt the Planet.! The time and effort/gas used/CO2 produced by sorcing a suitable relay to just fix a bad connection in your ign. circuit...!! You could clean-up every connection on yer bike x2 by the time you would have a relay in your hand...IMO.

[TwoTired]

I hear ya Twotired, but IF a frog had wings...

Then he could fly close to the sun and croak there...?

I agree it is not the optimal fix...

It is not a fix at all, its a bypass of a real problem that still exists.

  Hypothetically speaking, what could it hurt? 

1. Such a modded bike no longer has an accurate wire diagram.  So, you are trading today's problems for tomorrow's (WTF?).  And, the next owner will curse the P.O for turning the bike into a "kludge" with "creative wiring".

2.  If you still have ANY current flowing through remaining corroded, resistive, connectors the resistance wastes unnecessary power in the form of heat.  This is energy that is now unavailable to makes lights brighter, recharge the battery, etc.  Essentially, that power is robbed from your alternator power.  Even if you only lose 10 watts to these connections, that still turns your 40 watt at idle and 150 Watt@ 5000 rpm alternator into a 30 watt/140 watt @ best case alternator.

3.  The assumption is made that the "Kludged" relay addition is installed perfectly, mounted perfectly, connected perfectly.  If the "Kludger" doesn't have adequate skills to clean and re-assemble connectors, what are the odds he can install a relay, mount it correctly, and have reliable connections?  Will he then also make a revised wire diagram for the now unique bike?

4. The corroded connectors will not stop corroding with a bypass in place.  They will continue to corrode further and become increasingly worse at being an electrical connection.  So, a bypass is just shifting the maintenance to the next owner, or yourself in the future, possibly in the middle of a trip.  It's sort of like not changing your spark plugs until they fail completely rather than when they simply become less efficient at sparking.

I found a similar kludge on a cb400 I refurbished.  A PO replaced the stock turn flasher with a home made one.  It worked well for a while and was voltage insensitive. But, it was just a wad of parts and relay, point soldered together, wrapped clumsily in bits of oozing black tape, and left to dangle by the wire connections.  Any surprise it eventually failed altogether, simply from the vibration of the running machine?  It literally fell apart, and with no schematic, it found it's rightful place in the trash heap.  Yes, I could have made it work again for next to nothing.  But, it was embarrassing to see it, or even know that it was hiding behind a side cover waiting to fall to pieces again.

[Fritz]

easiest and beast way to avoid the above problem is the relay.

I disagree.
This leaves all the corroded connectors in poor condition and eating up/wasting power.

If you restore condition to as new, it will work as new everywhere on the bike.

+1:

Adding a relay adds power consumption, plus you add more components that corrode/need to be taken care of in the future. TwoTired is right in saying that a relay is just a workaround for problems that should be taken care of anyway.
I like the KISS principle: Keep it simple, stupid!

Many of my friends think that electrical systems are designed by evil forces from outer space in order to drive them mad. Often enough, I find that these evil forces are called "previous owners" that hacked into the wire harness. 

The following might be a little overdone for the topic of this thread. But if you have a stock wire harness, it might be worth going through it, before you further attack your electrical problems.

To me, taking care of the electrical system wasn't that painfull, after I made a "check list".

This is what I've done: Followed the whole electrical path from the battery through the connectors and switches to the contact breakers, cleaned everything with a brass brush and used contact spray/WD40 and battery grease. Pulled one connector at a time, cleaned it and put it back together. I found that many bullet connectors fit very loose. I used small pliers and gently bent the female connectors to make a tight fit.

My "check list":

1. Battery poles: Clean and grease. Make sure the ground wire running from the "-" pole of the battery has good contact to the frame
2. Magnetic starter switch: Take off all connectors, clean and grease/use contact spray
3. Take off the "electrical plate". From the magnetic starter switch "+" pole, a red wire is running into a multi-pole connector. Clean it, use contact spray
4. The main fuse holder: Clean the muliti-pole connector to it and clean the holders/"blades" itself, use contact spray
5. Clean all other contacts in this area: Connectors to the alternator, rectifier, flasher, regulator. Remount the electrical plate
6. Ignition switch: Clean the connector, use contact spray on the contacts of the switch. I've disassembled the whole switch to do so
7. Open the head light. Clean all connectors and use contact spray
8. Kill switch: Take off the switch assembly and clean all contacts in it. Use contact spray. A black/white wire goes to the coils
9. Coils: Remove tank and clean all connectors to the coils - Black/White, Blue, Yellow, while you are at it, clean all other bullet connectors in this area
10. Clean the yellow and blue connectors to the points. This connector is located at the end of the cable that is running to your points cover
11. Alternator and oil pressure switch connectors. On a 550 they are located under the front sprocket cover. Dunno about a 750
12. Tail light and rear turn lights connectors under the seat
13. Front/Rear break light switch connector
14. Meter the coils to confirm that they are healthy

The hardest parts were the kill and the ignition switch because I disassembled them. Maybe a good shot of WD/40 into a gap or orifice in the switch housing would have been enough.

Going through all above, rewarded me with a healthy spark. All this took between 3 and 4 hours and I am sure that it saved me much more time to figure out various electrical problems in the future.

Cheers and happy Christmas to everybody!
Carsten

[eurban]

I have relayed my coils.  I have a high performance motor with a Dyna III electronic ignition and 3 ohm coils.  I want as much voltage to the coils as possible.  I have gone over every single connector on my bike and have installed a new ignition switch (aftermarket) and new oem switchgear.  The voltage drop to the coils was still close to 1 volt.  Adding the relay (it and its wiring and fuse are neatly installed) has reduced this voltage drop to almost nothing.  Is there a noticeable performance increase?  It would probably require a dyno to show it, but coil output is most certainly affected by the voltage you feed it.  Corrosion begats resistance which begats heat which damages connectors and wires and increase resistance and so and so on.  Running less current through the 30 year old harness and switchgear will significantly reduce the potential for damaging heat build up. I would expect a good quality automotive relay to last a good while as long as they are kept from engine heat and the elements.  It is also a simple matter for me to return to the original voltage feed should the relay crap out on the road.   BTW my "cold blooded" 78 750 K starts easily in mid 20F temps.  Found out just yesterday . . . .

[Nikkisixx]

Twotired, eurban, fritz, et. al. - thanks for the thoughtful responses!  Good stuff, great info! 

Happy Holidays all 

[Fritz]

Hi Eurban!

I have relayed my coils.  [..] Running less current through the 30 year old harness and switchgear will significantly reduce the potential for damaging heat build up.

Good point. But still, you need to maintain this 30 year old harness in order to avoid other electrical problems. If you take care of it properly, it will perform like new.
I think what TwoTired pointed out was, that a relay does not save you from addressing the corrosion in your connectors and switches every decade or so. And that every modification to the wire harness may give you and future owners headaches.

Doesn't mean that there is no room for improvements but running 3Ohm coils is a different topic... 

Cheers
Carsten

[Tnutz]

I disagree.
This leaves all the corroded connectors in poor condition and eating up/wasting power.

If you restore condition to as new, it will work as new everywhere on the bike.

well, i was thinking along the lines of my own scratch wired bike.  I have one dedicated cicuit from a relay right to the coils.

Power is not wasted/used if there is nothing else hooked up to the circuit.  But It's actually not a bad mod to do regardless. It's a very popular mod on suzuki TL1000R's.  I Like to know i have uninterrupted 12v right to my coils with no drop along the way.  especially if i make the move to H.O. coils.

[TwoTired]

well, i was thinking along the lines of my own scratch wired bike.  

Ok, when were you going tel the OP to rewire the rest of his bike?

I have one dedicated cicuit from a relay right to the coils. 

That's only half the power path.  You have to get power to the relay as well.

Power is not wasted/used if there is nothing else hooked up to the circuit.  

You missed the point, I think.  If your existing bike is losing power to the coils, it's losing power to other devices, too.  Fixing only the power to the coils doesn't help the other electrical devices on the bike, like headlights, alternator coil, Vreg, etc.  Therefore, those deteriorated connections still waste power.   If you fix the connection for the coils, the entire bike benefits.

But It's actually not a bad mod to do regardless.

You are certainly entitled to your opinion.

It's a very popular mod on suzuki TL1000R's.  

Neither "popular" nor references to Suzis offer any technical merit to the relay mod.
Way back, "Pet Rocks" were popular, as was "snake oil".  Lot's of popular things have latter proven of dubious value.
So, "popular", used as a proof is of very small value, in reality.  IMO

I Like to know i have uninterrupted 12v right to my coils with no drop along the way.  

Stated like that was a requirement not satisfied by millions of Hondas wired via the stock wire harness/equipment. 

especially if i make the move to H.O. coils.

Yes, that is another "popular" mod, often done without relation to actual needs or requirements.  Possibly, because of the "mystique" of electrical device operation, I suppose.
Though, if you have modded the stock engine in a way to require H.O coils, then you do need them.  But, they won't gain you any power in their own wright.
But, this is taking things father off topic, no?

Cheers,

[Tnutz]

Well sorry TT...the j-man electrician knows nothing i guess....

why did my xs650 start so much easier with h.o. coil vs the stock one? i changed nothing else.  i know i didn't gain power...but larger plug gap and easier starting were worth the mod.

That's only half the power path.  You have to get power to the relay as well.

if you want to be douche and argue that the wire is broken where it connects to the relay terminals....okay...THERE IS NOTHING ELSE SHARING THAT CIRCUIT.....there...

   I like the idea that the bike will always run if i need it to regardless of what happens to the other power feed that feeds +12v to everything else.


, you can maintain all the connections all you want....but you have no idea at the state of the #$%*ty high aluminum content wire inside all the tape and loom thats almost 40 years old until your trying to push the thing home.

[TwoTired]

Well sorry TT...the j-man electrician knows nothing i guess....

There is a difference between knowing nothing and knowing the right things.  Electricians and electronic engineers face a wide variety of specialities.

why did my xs650 start so much easier with h.o. coil vs the stock one?

Because you increased the spark current with a lower input voltage.

i changed nothing else.  i know i didn't gain power...but larger plug gap and easier starting were worth the mod.

This thread jack belongs in other bikes, now.  But, not all SOHC4 have the power to drive low ohm coils and keep the battery charged.  Your xs650 may not have that issue.  Potentially, many other bikes don't either.

That's only half the power path.  You have to get power to the relay as well.

if you want to be douche and argue that the wire is broken where it connects to the relay terminals....okay...THERE IS NOTHING ELSE SHARING THAT CIRCUIT.....there...

OK, if you want to be obtuse, you had to get power to the relay from some where.  If you connect to the black wires, you only get that voltage and no gain, it you connect to Battery POS terminal you then get a potential voltage gain.  I merely stated you only specified half of the power path; from relay to coils.

perhaps there is no reason to do it that way.   I like the idea that the bike will always run if i need it to regardless of what happens to the other power feed that feeds +12v to everything else.  

Hey it's your life, your decision.  Do what you want.  I'm just trying to help people make informed decisions.

[Tnutz]

so the h.o. coil wasn't worthless like you made it sound was it?

thats why you install a ballast resistor if you use a coil with a low primary resistance on points..  yes your spark output voltage is lower because of a lower input voltage....but it is still way higher than the barely adequate stockers that are now almost 40 years old.

i am aware it's off topic...but don't try to tell me the h.o. coils are a worthless mod either.

i am also trying to help people.  My bike may get me home if something happens because i did that coil mod while you sit on the side of the road trying to farmer something together.  it costs almost nothing to do too.

i am not saying don't clean your harness/connections up and fix the low voltage problem.  go through the whole thing front to back....i just think it's great peace of mind.

[bucky katt]

mine runs better without the ho coils, ballast resistor or not. with same input voltages.

[TwoTired]

so the h.o. coil wasn't worthless like you made it sound was it?

For most bikes, it IS worthless (except to the seller of coils, of course).  They certainly are not better than the stock ones, only different.
These bikes had no trouble starting when they were new.  And, if you make the electrical as new, it has no trouble starting.

As for your action of putting in coils and it starting better in your derivitive test case of one, the new coils may simply be compensating for some malady that still exists on that bike.  You didn't prove the new coils were THE answer, or the only answer, just the answer that you chose.  It may still have other issues you didn't identify and the new part is masking.
You think the bike was hard starting when new?  If not, why not?

thats why you install a ballast resistor if you use a coil with a low primary resistance on points..  yes your spark output voltage is lower because of a lower input voltage....but it is still way higher than the barely adequate stockers that are now almost 40 years old.

I don't think you understand how the points system works.
It is the spark gap that determines the firing voltage.  They fire at the same voltage whether driven by H.O. coils or stock coils.

The coils don't deteriorate with age.  They can deteriorate with abuse.  The copper windings don't change properties or their physical relationship, and as long as the outer cover of the coils remains undamaged, the internal wire insulation doesn't change either.  The 40 year old coils are capable of delivering the same voltage as they did when new.  Just feed them the same voltage they had when new.
Further, the stockers were far more than adequate, and they still run and operate bikes today as well as they did 40 years ago.  So, stop making groundless claims.

i am aware it's off topic...but don't try to tell me the h.o. coils are a worthless mod either.

Don't put words in my mouth.  If the engine specifics (i.e. high compression) needs HO coils then it is a necessary mod.  If it doesn't need it, as in a stocker, then it is worthless and unnecessary.

i am also trying to help people.  My bike may get me home if something happens because i did that coil mod while you sit on the side of the road trying to farmer something together.  it costs almost nothing to do too.

That's really a rich speculation/contrivance.  I've been riding SOHC4 since 1975 and have never had a coil or ignition failure the entire time (except for water in the points compartment).  What reality do you live in?
It DOES cost something, both time and non-zero dollars!    Failed relays and hacked up wiring can leave you by the side of the road. So, you are hardly immune.

I'm glad you are trying to help people, btw.  I just wish it to be with factual data rather than speculative or assumptive data.

i am not saying don't clean your harness/connections up and fix the low voltage problem.  go through the whole thing front to back....i just think it's great peace of mind.

I'm glad we finally have agreement on that.  Thanks for changing that position.

Cheers,

[mystic_1]

The coils don't deteriorate with age.  They can deteriorate with abuse.  The copper windings don't change properties or their physical relationship, and as long as the outer cover of the coils remains undamaged, the internal wire insulation doesn't change either. 

Really?  I always figured that chemical breakdown would eventually kill them, no idea how long that actually takes for these materials though.

Also, lots of old coils have developed cracks in the casings, surely this isn't ALWAYS a sign of abuse?  Seen it happen on any number of stock bikes.  My belief is that vibration and heat cycles will cause this.

mystic_1