DC Voltage Drops While Running

[blaat!]

Sorry for another long delay. Fall trail riding in New England is currently the priority! The bike is now in the basement for the winter…unless we get some warm days. Word is that there will be another MotoGiro in the Pocono Mountains of Pennsylvania mid May. If I don’t have a conflict, I’ll be targeting that. Last one was such a blast!!!

mrkprsn - I think the voltage came up as a result of a combination of disconnecting the (OEM) ground in the stator, using the Electrex World reg/rec, and running with a battery (a.k.a. capacitor) which is required for that reg/rec. I’m not sure that I previously had all three in place at the same time during testing or riding. I’m still not convinced all is right, but I’ve never measured that much voltage before so moving in the right direction.

Nigel - thanks for the idea. I’ll test it out depending on how the voltage looks going forward.

Nick - my bike seems to be putting out the right amount of amps from the generator so I think the flywheel magnetism is okay!?! Would love to check it though. Unfortunately a lot of the tools and knowledge is disappearing

Max - I won’t rule out an overfilled battery if it stops leaking before running low on liquid then I will know.

Thanks all. I’ll update more as it comes. Once this is confirmed sorted I’ll try to make a summary post to save everyone from reading this whole thread!

[blaat!]

Just back from the MotoGiro in the Pocono Mountains of Pennsylvania, USA. Around 450 kilometers, 110 bikes, all pre 1969, and under 350cc (or something like that).

Giro.jpg

I fried two more batteries over the weekend. Both read 4.5V now and neither will charge with trickle or straight connected to a DC power supply. Dropped a cell on each?

This is the graveyard of batteries at this point, minus one more wet acid I already recycled. Two different regulators plus one more that MrkPrsn gave me at the Giro (great to meet another Motoscrub in person!) as well as the original regulator.

batts-n-regs.jpg

I had onboard voltmeters all weekend. The one at the battery usually hovered between 7.2V and 7.4V (maybe a touch higher?) and the one at the coil was 6.0V-6.4V

There was one point that I pulled over on the side of the road for something else, and the bike sputtered out when I let the RPMs drop. Both onboard voltmeters read zero with everything connected and on. I disconnected the battery and measured DC voltage with my handheld meter and it was around 5V, but dropped to nearly zero when I put the battery contacts back on. I kicked the starter lever to see if the points open/closed made any difference, but no. Disconnected the battery to prevent more damage and looked for shorted wires. Took the headlight apart, tightend all the small flathead contacts inside, and put it back together. The battery read 5V with everything connected again so I bump-started it downhill in first gear to get the RPMs high enough and it eventually caught so I could finish that leg of the race. Don't know if the headlight contacts made a difference, or if something was overheated and shorting (such as the regulator or coil) and cooled while I was working?

I suspect I have too much juice now and I'm over-charging the battery. Eventually I lose a cell in the battery and bike won't idle/run at low RPMs. Then I can't get it started again if I shut it off. Mid 7Vs seems like a lot during two full days of riding.

Anyway, I think the thing I was missing during most of this thread was that the extra ground on the stator needed to be undone AND the regulator needs the battery in place to function. At many points I was trying to measure DC voltage coming from the regulator and several people have told me that the battery needs to be in place for the regulator to function correctly.

Thoughts?

[blaat!]

Also, BTW, want to get thoughts on using a capacitor instead of a battery, and if it would be more or less reliable. I believe some of the old Triumphs had a capacitor to help at starting, Lacey sells a 12V version as a battery substitute, and 12V cap battery eliminator kits are available on eBay. My thinking is that it acts to buffer the volatile voltage just like a battery?

[Jordan]

Yeah, something's wrong with your wiring.

Regarding going batteryless - what a great idea.
I have done it many times, including on my current single.
Even my Suzuki T500 would start and run, just by replacing the battery with a capacitor.
But to do it properly you should replace the regulator with a high-power type.
A Lucas ZD715 zener diode works well. An alternative is LU49345. They are 12V types.
You could use a positive or negative earth type, as there's no battery anyway.
The capacitor should be at least twice the voltage - 25V or more, and used with a shockproof mounting.
There is one possible problem, with a solution:
Sometimes when at idle, turning on the lights or horn can stop the engine.
Some wiring surgery at the alternator solves that. Ask for details.