DC Voltage Drops While Running

[veloduke]

Can you post a diagram of how the bike is wired?
It could be helpful to see where those wires come from.

[blaat!]

test-1.JPG

[mrkprsn]

Moving the white spark coil wire from the + red battery wire to the + gray non battery wire would have all your electrics run off the gray wire and use the red wire ONLY to charge the battery. If you have an LED light this should be fine although I don't think this is the solution to your probem.

In your wiring diagram I think you are missing the second battery that is running the bike.

It looks like you might have a parasitic loss. Time to pull out the multimeter and track it down. With everything hooked up and ignition off, test for amps from the - neg battery post to the - neg battery cable. Then do the same test with the ignition on ONLY (no lights). What are the results?

https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

[MonzaMan]

I agree with Mrkprsn. The fact that the voltage is dropping with the engine running suggests that there is a path to ground (not a full short, but a partial one) from the ignition switch.

I read recently that it is fairly common that the ignition switch is shorted to ground through the headlamp bucket (shell), although I am not sure which switch the problem is related to.

Another thing to check is the primary winding of the ignition coil. It should have a resistance of about 1.5 ohms. If it is considerably less, it could be working but adding load to your system.

With everything off and the engine running, 6 amps seems like a large current to me. We know that no current is actually charging the battery.

Best regards,

David
68 W/C Monza

PS: I meant to add... An easier test of this would be to run your bike and take measurements with the switch removed from the shell, safely supported and positioned so as to avoid the frame and other wires. Might be quicker than tracing everything with your meter.

[blaat!]

In your wiring diagram I think you are missing the second battery that is running the bike

That thing sketched in at the bottom of the diagram is a DC power supply (in place of a battery) and not a multimeter.


For the parasitic loss:
With the key off the bike is drawing 0.0V

With the key on the bike is also drawing 0.0V, except when the points are closed. When the points are closed (not running) the bike is drawing about 4.9A. I think a 6V coil should draw more like 2.5A, no?

I tested the resistance stator coil. Initially it reads 1.4 Ohms, but it slowly drops for the next 13 seconds and stabilizes around 0.8 Ohms. Problem?

While I was at it I tested the current draw of the headlight, brake light, parking light, and horn:

High beam (LED): 0.7A
Low beam (LED): 0.2A
Parking light: 0.3A
Tail light (LED): 0.3A
Horn: 0.8A

Those all seem to be fine

[blaat!]

Update:

The ignition coil I had in the bike was a 6V universal type for any vehicle (cars or motorcycles) so I swapped for a Lucas 6V I got from Lacey which is specified as a replacement for Ducati singles. The current draw for that is lower at 2.7V and I have 6.15V at the battery with the bike running.

[blaat!]

Ugh. Snatched defeat from the jaws of victory.

I tested the battery voltage at 6.39V with the bike off, then went for a 30 minute ride. The bike ran beautifully. When I got back I tested the battery again with the bike off and it read 6.28V which could be just fine since the voltage at the battery while running was about 6.22V. Maybe the trickle is charging my battery to 6.39V but the regulator is charging it a little lower to 6.22V. Both may be okay?

Then... disaster... I started the bike up again to go for another short ride and it started nice and easy. Because I had just been riding I didn't think I needed to break the (sticky) clutch free, but when I popped it in gear it stalled. I put it on the center stand, grabbed the clutch lever, and kicked the kick start and freed the clutch. Then I went to start it again and it wouldn't even try to catch. No backfire, no sputter, no cough, nothing. After a bunch of tries and confirming fuel I figured I would test the battery to be sure it had enough charge to generate spark.

The voltage tested 2.5V!!!

I turned the key off and the voltage was still 2.5V. I wiggled the exposed wires, popped the headlight off to see if anything was wrong in there or if one of the switches was shorting, but everything seemed fine. All that took about 10 minutes and I realized I needed to get the battery out to prevent damage. This wet lead acid battery is only a couple months old.

Once I got the battery out the voltage climbed back up to 3.7V. I looked the battery over and everything is fine. No cracks or leaks, all three cells are slightly below the max liquid level, and nothing ever came out of the overflow. I hooked up the "smart" trickle charger and it just switches to "error" and won't charge. I left the battery for a couple hours and it is still around 3.7V.

IMG_6211.jpg

What could cause that to happen to a battery so quickly? A huge draw on the battery? A power surge to the battery? Is it cooked? I don't want to order a new battery only to have the same thing happen again.

I hooked the power supply up instead of the battery because it tells me the voltage and amp draw. Everything looks normal with the bike just as before.

That $3,000US Honda XR150L is looking more attractive every day.

[themoudie]

Aye blaat,

I decided to go for the electrex full package from Nigel and that has fixed the issue. My old stator is now a paper weight.

As a thought, do you have a good earth ground to the engine from the battery? Something as simple as a corroded or poor earth will prevent the current getting back to the battery?

I'm committed to the 6V at this point and I'm learning a lot... like how stubborn I really am

Yeah, the battery has a nice fat ground wire bolted to the frame with the paint stripped away and some dielectric grease to prevent corrosion.

Maybe Dave354 has had some nice canters under his tyres this summer! Just saying.

Electrex 12v full kit, 12v battery, new wiring loom, refurbish all the switches, LED lights front and rear and then ride it.

Good health and hope that yours doesn't turn into a Tolstoy epic, as mine did.

Bill

[Jordan]

I hooked up the "smart" trickle charger and it just switches to "error" and won't charge.

Try a "dumb" battery charger first to get some charge into the battery, then swap to the smart one (or not).

[blaat!]

Good call Jordan. I hooked the DC power supply up to the battery set to 6.4V and a max of 2A. It drew 0.7A at the start and then slowly dropped to drawing 0.0A. After an hour or so the battery was back up to 6.4V and it’s on the trickle now with the green light and not needing to charge so far. I’m a little concerned it will not have the capacity it had? I may bring it to the parts store for a load test.

I just ordered a fuse holder to put between the battery and the bike. Whatever happened must have drawn a big load on the battery for a short period… right? I’m thinking of putting a 7.5A in there so that doesn’t happen again. Will need to keep a bunch of those in my pocket on rides just in case.