Motorcycle Electrical Issues - Page 1
Forum section: electronics / general

author: mendip_discovery
author_rank: Super Contributor
timestamp: May 08, 2023, 11:34:55 am
content: So as a glutton for punishment, I own a 1961 Matchless G3LS. I broke it a few years ago so it stayed unloved in the shed for a while. During COVID I got around to rebuilding it. Put it back together and then I ran into some issues, the wiring loom was cracked and shorting out all the time. So I have to change a few things.I removed the oldLucasrectifier and fitted a modern full bridge rectifier aKPBC3510which I bought at an autojumble. I also swapped out the battery for aCyclon Battery.I'm getting running issues that make me think it is the electrics. The bike has a feature that allows the bike to be started using Emergency Start which starts the bike without connecting to the battery etc but once started if you give the bike any amount of throttle it starts to pop and bang a lot. The issue I have currently is the bike starts (sometimes) then it will tick over happily but as soon as I go to ride off it stutters and pops and bangs just like it is in emergency mode and after a few attempts to go somewhere it really becomes hard to start.The bike is just 6V electrics which are really really basic. What I am wondering is whether the rectifier is failing as it got hot a few times, not being helped by a battery that charges via a constant voltage type system. There is no regulator for 6V just a magnet spinning around a coil (stator) to generate the single-phase power. I have checked the timing, replaced the condenser and the coil etc. so covered a lot of the basics.Questions for the masses,Can I test the FBR to see if that is the issue?Should I bolt the FBR to the frame to reduce heat as it is currently in the open under the seat?Should I go back to an old-style lead acid battery?Any other thoughts on the cause?I have just bought another battery (gel) and a replacement regulator KBPC5010 & GBPC5010 as one is better designed towards heat dissipation. I will see if I can find a bike shop nearby that can get me a battery as annoyingly the only ones online come without acid. Partly because the postal service doesn't like posting it, the other is because some adults can't be trusted not to use the acid to melt people's faces.

author: jmelson
author_rank: Super Contributor
timestamp: May 09, 2023, 01:20:27 am
content: Well, having a fair bit of experience with lawn mowers, if the engine sputters when the throttle is opened, that could be spark blowout, ie. the spark voltage is not high enough to bridge the gap in the spark plug when cylinder pressure is higher. Is this emergency mode using magneto spark, but normal mode uses battery spark? That sounds pretty wierd, it would require mostly duplicate spark systems.Popping sounds like lean mixture, maybe the main jet is clogged, but the idle jet is fine.Another issue I have seen is a mower that runs fine for several minutes, then gets weak and finally won't run at all. Then, after cooling off, the whole process repeats. This was fixed by replacing the magneto unit.Jon

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2023, 02:37:22 am
content: Can you post the original wiring diagram? Is it a single phase or 3-phase stator?The original Lucas 49072 introduced 1962 silicon replaced older selenium rectifiers like square plate 47132.It looks like the stator has multiple windings to permit different output i.e. powering radios:https://commons.princeton.edu/60-tiger-cub/wp-content/uploads/sites/139/2019/08/LucasServicemanual_noSB519_part3.pdfedit: is this the (attached) schematic?The rectifier should get warm but not hot. Its case is isolated so it can be bolted to anything. Is it wired in properly, to cause the heating.Conversion to a silicon bridge rectifier, it will have much more output than a selenium beast I would say too much so the battery will see well over 7V and overcharge which gel batteries cannot withstand at all. You'd have to add the Lucas zener diode system to add some regulation.The ignition system issues, I don't know the bike but I did once have really weak point spring and they would bounce at any speed much above idle and cause misfiring. It would start and idle fine but it acted like a rev limter. Otherwise, your condenser is suspect or the coil/plug (resistor), wiring.

author: Circlotron
author_rank: Super Contributor
timestamp: May 09, 2023, 03:22:27 am
content: If you can reach it, while the engine is idling, remove the plug wire and see how far the spark will jump while idling. Using that as a gauge, slowly increase the revs and see if the spark fizzes out or begins to fire erratically.

author: Gregg
author_rank: Super Contributor
timestamp: May 09, 2023, 04:18:32 am
content: Do you have the coil polarity correct? Most of those old Lucas systems use positive frame ground. The wiring on the stator could be suspect, the insulation they used back then is far from ideal especially considering it lives in a hot oil bath.I have had a BSA Goldstar, Triumph Cub and currently own a MGA; I feel your pain! I'm glad to be rid of the motorcycles and the MGA has had all of the Lucas stuff except the starter and distributor replaced.Also, Amal carburetors have their own quirks. The mounting bolts distort the body causing vacuum leaks and sometimes causing the slide bore to become out of round.

author: Dundarave
author_rank: Regular Contributor
timestamp: May 09, 2023, 04:41:10 am
content: I had a 1972 Triumph Trident many years ago, and discovered that while it would run without the battery, it needed a decent-sized capacitor (I used a 2200uF electrolytic) in order to smooth out the pulsating DC current.I think what happens as the revs start to rise, the pulses (with no battery to smooth them out) don’t allow the coils to work properly.Try putting a big cap across the battery connections and give it a try.

author: Circlotron
author_rank: Super Contributor
timestamp: May 09, 2023, 05:51:15 am
content: Quote from: Dundarave on May 09, 2023, 04:41:10 amI was thinking similar, but you would expect the rectified pulses from the alternator would always have the same phase relationship to the ignition points, so a pulse would be available while the points are closed and the coil is charging. Unless of course there is a mechanical advance mechanism on the points and as the engine speeds up it moves the points closed position too far away from the alternator DC pulse and so it begins to run badly?

author: Dundarave
author_rank: Regular Contributor
timestamp: May 09, 2023, 04:55:28 pm
content: Quote from: Circlotron on May 09, 2023, 05:51:15 amI believe that this is exactly the problem. The Trident had a mechanical spark advance (a spring-and-weight arrangement on the spinning cam plate), and this seemed to account for why it would idle fine, but not run well. I would imagine the OP’s bike would have a similar Lucas arrangement.

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2023, 05:22:07 pm
content: Anyone know what the "resistance wire" between (+) GND and light green wire on AC is for? It appears to end up across one diode in the bridge. Assuming that wiring matches OP's bike.I had one old car resistance wire (ign coil ballast) broke in a harness as it was brittle hard wire, harder than nichrome. I think vibration broke it.

author: Gregg
author_rank: Super Contributor
timestamp: May 09, 2023, 06:51:09 pm
content: Quote from: floobydust on May 09, 2023, 05:22:07 pmI think the resistance wire is to keep the alternator voltage from going too high when the lights are not providing load. Since the rotor is a permanent magnet, the voltage would become too high when the engine is revved without the resistor load. Or perhaps it is a source of the all too common Lucas magic smokeThe spark ignition without the battery is quite similar to a true magneto in that the ignition winding and magnetic rotor of the alternator are timed; the Triumph Cub I had didn't have a battery and they called the ignition system the energy transfer system.

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2023, 07:19:40 pm
content: It's an extra half-wave load so I suspect this thing is phased, it seems odd. So the new bridge could be wired flipped on the AC terminals?OP has two problems - the ignition system , and the charging system with the new bridge rectifier which seems to run hot.The bike should be able to run entirely off the battery, towards troubleshooting the ignition system issues. I wonder how you set dwell and timing, a timing light could also reveal if the points are working and stable.

author: Dundarave
author_rank: Regular Contributor
timestamp: May 09, 2023, 09:57:00 pm
content: I found this Matchless manual that might help with the repairs:http://archives.jampot.dk/book/Workshop_manuals/1957-1964__=M=_Workshop_Instruction_Manual_all_models_SEARCHABLE.pdfIn the electrical section, it explains how the alternator coils are “doubled up” in the “emergency” ignition mode, the purpose being to charge a dead battery enough to run properly. It warns to only leave it in this position for 10 minutes, just enough to give the battery minimal charge.

author: mendip_discovery
author_rank: Super Contributor
timestamp: May 10, 2023, 08:09:24 pm
content: Today the delivery person brought me some goodies and so I fitted a new battery and a new rectifier.Turns out you are all wrong, and so was I :-)It was the damned fuel taps, they were dribbling like Dave going for a pee. So gave them a quick reverse blow and there was a little more flow. Took it up the road and woop the thing flies again. Thoughts are that when we opened the throttle they were preventing even the fuel in the carb from flowing as there was a blockage at the tank.So I will run the fuel down a bit and then see if I have the confidence to remove the old taps to give the filters a clean and the tank a good flushing. That damned Ethanol.The bike has an emergency mode and it will never happily run on it, it will start and ride but it is not great fun to ride. I was trying to start it in normal mode so it should have been just fine.Quote from: Circlotron on May 09, 2023, 03:22:27 amDo I look that daft! That is a surefire way to get the output of the coil running via you. Next time you see a friend starting a bike, take the plug out, and then put it in the cap, ask them to try and start it and see how long you can hold on. My dad got a V8s worth at the weekend, he is still muttering about it now.Quote from: Circlotron on May 09, 2023, 05:51:15 amThis bike was the epitome of modern tech, gone was the manual advance and retard system that was good for giving you a broken ankle if left in advanced. It has a auto-advance/retard which is just some weights and some springs that as soon as the engine spins they move out. The next advance was electronic ignition but that came after this firm was out of action, which is a shame as the AJS/Matchless brand was the creator of the suspension systems most use today.Quote from: Dundarave on May 09, 2023, 04:41:10 amI might still try this as the battery is ok but I did notice the rectifier isn't perfect and might help a little to have a bit of buffer.Attached below is the wiring diagram I made up when I made the new loom. I upgraded the wire to 2mm² and added an extra positive earth from the headlight to the frame as it's 6V electrics so v-drop is always a worry and the use of the lights after dark is akin to using a candle. I was also a sad person for replacing the wire with the same colour markings as the original loom as I wanted the next owner to be able to read the manuals and make sense of the connections. Nothing worse than a vehicle wired up with just blue wire, how would you know which wire to cut?EDIT: It is a single-phase stator.

author: floobydust
author_rank: Super Contributor
timestamp: May 11, 2023, 04:20:09 am
content: Quote from: mendip_discovery on May 10, 2023, 08:09:24 pmThread is titled "motorcycle electrical issues" and we all believed itThe wiring diagram still looks weird, why are both AC legs (GB & GW) going to the lighting switch? Not that the switch is decipherable lol.

author: mendip_discovery
author_rank: Super Contributor
timestamp: May 11, 2023, 11:43:43 am
content: I thought it was a fuel issue but peer pressure said it was electrical and I had done the carb etc at the weekend so I was left with the magic that is Lucas (the Prince of Darkness) electrics.A headlight bulb doesn't care is its ac or dc so happy for some of the power to head there. I am sure to get the bike to start I had to deviate from this diagram in a few places but that is just the way these bikes were made.

author: Njk
author_rank: Frequent Contributor
timestamp: May 11, 2023, 07:20:13 pm
content: If you want just to fix it, good luck, but the problem is that the permanent magnets are rotating near the winding creating electricity. It's a nice brushless design but the amount of electricity varies with RPM and there is no way to control it. In more recent alternator designs, the magnetism is created by passing DC through the rotor winding so the regulation is done by periodically switching the current on and off. Not in your case. No battery will be happy with that charger. It needs to be improved, not fixed. It was difficult back at that time, but now you can take advantage of the modern semiconductor technology.First, you can break the winding into several sections and switch the sections with transistors. That's the best way, but it's typically difficult job to re-wind a generator, even that of single phase. So the alternative way would be to attach a light permanent RC buffer load to the rectifier output and use a switching regulator to control the voltage in the DC network.Some guys (usually teenagers) used to street drive their motor bikes with powerful loudspeakers attached, generating a huge noise, likely with the purpose to seek the girl's attention. I'm afraid the alternator improved with switching technology will create similar noise in the RF domain. That will make no sense as no girl can hear it. But eliminating that noise seems one more design challenge.

author: Njk
author_rank: Frequent Contributor
timestamp: May 11, 2023, 09:10:47 pm
content: Ihe idea of oversized forks is still a big puzzle for me. Fun for some guys, but is it OK from the road safety perspective?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 12, 2023, 01:39:42 am
content: Quote from: Njk on May 11, 2023, 09:10:47 pmI had lengthened the forks on my bicycles growing up so for me it was comfortable to ride as you just lay back. Road safety perspective? It was under powered compared to my current bike which has lots of skulls to taunt death!***I built a couple others if I need a speed fix.

author: Njk
author_rank: Frequent Contributor
timestamp: May 13, 2023, 03:07:47 am
content: Quote from: joeqsmith on May 12, 2023, 01:39:42 amLooks very nice. Which catalog you're using for assembly parts selection?BTW, what's that console (marked with red in the attached image)? Looks like "Computing across America"

author: joeqsmith
author_rank: Super Contributor
timestamp: May 13, 2023, 03:32:54 pm
content: Quote from: Njk on May 13, 2023, 03:07:47 amI would call the various companies and talk with them directly. Many of the parts I use are custom made here in the USA, including the Dedenbear CC3 which you asked about.***Showing the data logger, wide band sensor and Dedenbear.