Topic: Voltage loss at Ignition switch

[trebuchetxlt]

I was checking the voltage at my Ignition switch, '75 CB550, and noticed that although the voltage reading at the Red wire into the switch was at 12.8 Volts it was only reading 11.8 Volts at the Black wire coming out of the switch, the reading was taken at the connector on the switch side. I thought it was probably due to resistance in the switch, it was the bikes original, so I tried it with another switch I had, admittedly it is one of the Emco aftermarket deals, but, it's not had much use, and got exactly the same reading.
It seems strange that 2 different switches would give the same results, any thoughts?

[Don R]

Hondaman says that happens, that's why he makes a relay to help with that problem. It's been discussed here before. Try searching voltage drop maybe.

[Deltarider]

I'd say it's not abnormal.

[Bodi]

I don't think that should be considered normal. One volt drop at the switch with 5 amps (a low guess of actual current) means 5W of heat  produced at the switch contact. That is a lot of heat for a small area - look at a 5W resistor, it's pretty big and they still get stinking hot in free air with 5 actual Watts dissipating. It's enough to melt the plastic around an enclosed switch contact.
I would accept a few tenths of a volt but 1V seems definitely high here.

[Deltarider]

With all respect Bodi but I'm afraid you've got it all mixed up. Can't make sense of your Watts. It's about Ohms law that measures in: volts, ampères and Ohms.

[TwoTired]

The switch normally carries about 10 amps through it.  A one volt drop indicates a resistance of 0.1 ohms using ohm's law, or using watt's law 10 watts dissipation (or 10 watts wasted of alternator output.)

Bodi is correct.  A one volt drop through the ignition switch is NOT normal, and in my opinion, unacceptable.  All end devices will operate as starved and crippled receiving less voltage than available, and the voltage regulator will be unable to determine the correct voltage state of the battery.

The stock ignition switch can usually be rebuilt if the internal bits that hold the contacts and springs in proper position aren't melted too badly.
It does take some prowess and care to do without losing essential internal bits.

[Deltarider]

trebuchetxlt,
Please do the test again with a running engine. I bet your voltage drop is gone. That is what it is all about. It's from experience.

[strynboen]

have you testet vith amp meter to thek flow...in my headlight housing i only have 11,5 volt..same at coils..but 12,5 at battery..so some power goes to heating coils and generator magenet..and control panel bulb

[TwoTired]

trebuchetxlt has done the correct test, and measured the loss directly across the switch.  He KNOWS there is a volt lost across it.  He just doesn't know the exact current.

Knowing the current, it is a simple math equation to solve.  Experience has nothing to do with it.  I just posted the simple and basic formulas to solve electrical unknowns.  Anyone with proper training will already know these to be true, internet "experience" notwithstanding.

ALL of the bike's current usage flows through the Key switch.  The stock bike draws right around 10 amps.

If you change the current flowing through the switch, by adding or drop loads on the circuit, the resistance will stay the same.  But, the voltage loss will be different due to ohm's law.  This is really simple math, folks.  If you can make change using money, you really ought to be able to calculate. R= E/I.

A running bike may allow vibration to improve a doggy switch contact.  But, vibration should NOT be a necessary ingredient for a key switch to operate.  In fact, vibration should have no effect on a proper key switch.

Further, a running bike should increase the voltage applied to the switch as well as all he load devices, which will increase the current flow and increase the voltage drop across the switch resistance.

If experience is any teacher, 30yrs in the electronics industry teaches way more than very reliable and basic, ohm's and watts law.

If you have lost a volt between battery and headlight.  You have either connector resistance issues or switch contact issues.  This sort of loss was NOT present when the bike was new.  When new the loss was about .2 volts.  Anything more than a 0.5V loss indicates a connectivity problem developing.

[trebuchetxlt]

Thanks for the input guys, it looks like Lloyd hit the nail on the head. I had a feeling that the problem was due to dirty contacts in the switch and it appears that was correct. I cleaned the switch and I'm now getting 12.5V from the Black lead on the switch side of the connector, so, all good there. I'm still getting a loss on the lighting circuit (Brown) where the reading is 11.5V at idle and rising to 11.8V with RPM above 3000, but, I'm not going to worry too much about that. It was just weird that when I did the initial test with the original Honda Ignition switch and the new(ish) aftermarket switch they both gave the same result. I guess the lesson here is to not trust those aftermarket switches.

[Deltarider]

Glad TT explained you it is simple. I await the results of others 

I guess the lesson here is to not trust those aftermarket switches.

I doubt it. I guess the lesson is the resistance was before the switch and in the connector or wire to the switch. Fiddling with it is sometimes enough.
Here's a tip (from experience again). After a long period of not using your bike you can clean the switchcontacts by vigorously switching the key (preferably with the killswitch off) say ten times. You can do the same with the killswitch (preferably with the ignitionswitch off). I do it every spring and all parts are still original. Didn't need 'simple' schemes or equations to explain that, now did I?

[TwoTired]

You could also try putting fresh entrails of a goat on your dash panel at moonrise to chase away electrical demons.  Lots of folklore to support that one, too.  Works spectacularly well in the Netherlands, I'm told.

[TwoTired]

I guess the lesson here is to not trust those aftermarket switches.

The internal switch contacts are physically smaller than the originals.  Less contact area yields higher resistance.  There have been many postings about early aftermarket switch failure, as the plastic that holds the small contacts in place distorts from resistance heating.  Misaligned contacts garner even more resistance and heating.

[Deltarider]

You could also try putting fresh entrails of a goat on your dash panel at moonrise to chase away electrical demons.  Lots of folklore to support that one, too.  Works spectacularly well in the Netherlands, I'm told.

Ha, ha. Where did you learn that?
We did a lot of vigorously switching in the controlroom of a theatre to clean contacts. Worked wonderful. It was a student job really, wouldn't call it the electronic industry.

[PeWe]

Relays a good idea anyway.
It is very strange that I did not installed relays 30 years ago when I worked with the electrical stuff on my CB750. I replaced all wires from the handle bar switches, soldered them as the crappy OEM solution.
Today it is obvious for me to not trust 5-7A or maybe more thru these connections.

I have so far installed 3 relays.  2 for headlight (HI-LO) and 1 for the ignition coils.
I'll install no:4 for the horn when I have another double horn with option to be replaced by a Stebel Nautilus later on.
This will then be wire no:4 3 direct from battery with a hanging fuse close to battery.

[TwoTired]

Relays a good idea anyway.

I do not agree.  Particularly when they are used as a convenient crutch to circumvent the repair of faulty equipment.  The stock switches handle the stock loads just fine.  But, not forever.  Nothing man makes lasts forever.  Neither do relays which add more complexity to the bike and make the next PO scratch his head when looking at the mess on the bike's wiring that no longer matches published wire diagrams.  Who here that favors relays, have actually made a wire diagram mod or addendum which stays with the bike?

If a switch is installed/replaced that doesn't have the current capacity of the original in good working order, then a relay makes more sense.  But, then the bike has a unique wire diagram, that should follow the bike the rest of it's days in existence.  Yes, even relays will fail, and so will the dodgy switch that you bypassed with relay. 

Switch contact capacity is tightly related to the size of the contact.  All switches have a make/break cycle life expectancy related to the current/power it is expected to control.

Ever read post where the it was asked where to get a whole new wire harness because the PO patched and spliced so many things that they were unable to restore it?

If a cylinder goes out on the engine, do you then add another cylinder to bypass the failed one rather than fixing the one that failed?

For a bike that is revered for it's simplicity, why add the complexity of a relay rather than just fix what wore out?

[PeWe]

My relay installation is easy to remove and reconnect as it was before. Unplug wires activating the 2 relays for Hi_LO and connect direct to the H4 bulb. Same with ignition relay. Horn relay will be of the same design. OEM cables are not changed.
I did it this way to make it possible to bypass the relay(s) if they get problems. I carefully crimped sockets and pins on correct wires (marked with labels) to  make it possible just plug it together the other way again.

[Bodi]

"With all respect Bodi but I'm afraid you've got it all mixed up. Can't make sense of your Watts."

Well... with all respect you should take another look at Ohm's law.

P=EI so (my guesstimated example) P= 5 x 1 (5 amps and 1 volt drop) = 5W power (as heat).

Or, using Lloyd's 10A current, 1V drop means 10W of heat at the switch contact.

[TwoTired]

Bodi,
Don't you love it when people post "experiences" that defy the laws of physics?

Cheers,

[calj737]

I'm surprised at you, TT. Did you miss the day they taught "New Electrical Math" at school? Tsk, tsk...

[Deltarider]

Don't you love it when people post "experiences" that defy the laws of physics?

Who did that? Read carefully and avoid bias. It's not he first time I have to point you at this but I must admit for some it can be much more difficult than 'simple physics'. 
I maintain talking about Watts here (i.c. voltage drop) is irrelevant. That's what I ment by saying 'Can't make sense of your Watts'. And I had Ohms law in school, thank you. The power consumption in Watts is a consequence and not the cause. So it's no use discussing Watts here. How is trebuchetxlt to measure Watts with his DMM? Please show him that switch position on your DMM.  Show me and I'll buy one instantly for my collection .
Now, if you allow me a question, a question only someone as stupid as I can ask... 30 years of repairing electric fans and hairdryers does that also count as '30yrs in the electronics industry'? Mind you, it's just a question but you, for who so many things are 'simple', seemed the right person to ask.

[grcamna2]

I guess the lesson here is to not trust those aftermarket switches.

The internal switch contacts are physically smaller than the originals.  Less contact area yields higher resistance.  There have been many postings about early aftermarket switch failure, as the plastic that holds the small contacts in place distorts from resistance heating.  Misaligned contacts garner even more resistance and heating.

I've taken apart a few different old OE switches(mains and handlebar) and found a warped contact backing piece which certainly misaligned the contacts and caused higher resistance.I think in a few of those the problem could have stemmed from too much tension on the wires over a few years;correct routing does help too.

[Spanner 1]

There may be a flaw in the OP's test....... If he has 12.8v on the Red terminal at the ign. switch, when he moves the + probe to the Black wire the reading will be 0 volts until he turns the ign ON........ he says 11.8v is then the reading on the Black wire...... but the real test was to put the probe back on the Red terminal and compare it's reading with the ign. ON........ otherwise no test! I don't think he has fixed the problem ( remember changing-out the switch gave the same results)... the actual problem is very likely a crappy main fuse/ holder...... good luck 

[grcamna2]

I was checking the voltage at my Ignition switch, '75 CB550, and noticed that although the voltage reading at the Red wire into the switch was at 12.8 Volts it was only reading 11.8 Volts at the Black wire coming out of the switch, the reading was taken at the connector on the switch side. I thought it was probably due to resistance in the switch, it was the bikes original, so I tried it with another switch I had, admittedly it is one of the Emco aftermarket deals, but, it's not had much use, and got exactly the same reading.
It seems strange that 2 different switches would give the same results, any thoughts?

Who's that guy in your avatar pic ? He looks like a 'scare crow' 

[Spanner 1]

I couldn't help but have a chuckle at TT, Delta and Bodi having a fight over a voltage drop across an ign. switch when it's obvious that the poster NEVER measured the voltage on the Red terminal with the ign On....bet it's 11.8v the same as on the Black wire .....

P.S..... The OP also never said that he tested with the ign. switch plug disconnected, just that he had stuck the probe in the 'switch side' of the connector.....