Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties 1943 WLC charging system

1943 WLC charging system

Moderators: Curt!, Pa

Post Wed Jul 03, 2013 2:35 pm

Posts: 30
Location: Winnipeg,Canada
I noticed yesterday after I started my bike that the tail light and headlight seemed dim. With the bike running and a voltmeter across the battery terminals, I was getting 4.0 volts. I have a new Genuine Harley battery, so I charged it back up to 6.0 volts. When I started the bike again I got the same result, only around 4.0 volts . Is there a way to test the generator and the cut-out relay while still on the bike?

Post Thu Jul 04, 2013 5:59 pm

Posts: 202
Location: Middle England UK
Was everything ok and this fault has just developed?
Why did you replace the battery?
A fully charged quality battery should have a terminal voltage nearer 7 volts than 6.
When you refitted the battery after charging,did you polorise the generator?
Charge the battery up and fit to bike.Put a voltmeter on the terminals and note the reading.Then just switch on the ignition,and note the voltage reading.If you drop much more than 0.75 volts,I think the battery could be suspect.
To test the generator.
Remove the earth cable from the battery -ve terminal and insert an ammeter between the two.
Remove the wires from the "RELAY" terminal of the generator and the +ve battery terminal and isolate them.
Connect a jumper wire between the generator "RELAY" terminal and the battery +ve terminal.
Start the bike and increase the revs to about normal riding revs,you should have a max charge of around 4 amps.
If you get around the above reading,the fault is likely to be the relay,or the wiring between the relay and the battery.
If you get little or no reading,the fault is likely to be the generator.

Post Sat Jul 06, 2013 6:07 am

Posts: 30
Location: Winnipeg,Canada
Hi Dave:
The bike came without a battery so I purchased a new Genuine Harley.
I only have about 90 miles on the battery since I got the bike running.
The headlight and brake light were fine for the first 90 miles, so the problem is new.
No, I did not polarize the generator.

I will flash rhe generator this weekend, hook up the ammeter, and test the charging following your directions.
Thanks for steering me in the right direction.

Post Sat Jul 06, 2013 8:31 am

Posts: 301
Location: Ohio
Are we discussing a three brush generator? If so my limited understand was that they didn’t require the need to be flashed. Something about just turning on the headlamp once before starting the engine set the direction of flow for the current. Anybody heard about this, other than me?

Post Sat Jul 06, 2013 5:15 pm

Posts: 202
Location: Middle England UK
It's the 3 brush.You got me thinking though,we always do it,but I couldn't recall seeing it in a manual.
Strange thing is,I couldn't find it mentioned in any 45 manual,even after rebuilding the generator,which is when you would always do it or when fitting a new one.
I found it mentioned in the 1940-47 Big Twin manual.It says you should flash every time the battery or generator is removed and refitted.I'd take that to be each time the circuit between battery and generator is broken,even if neither is removed from the bike.

Post Sat Jul 06, 2013 5:39 pm

Posts: 30
Location: Winnipeg,Canada
I'm A little baffled here.

Disconnected the neg. battery terminal and put an ammeter in place.
Disconnected the pos. battery terminal and the relay terminal on the generator, and put a jumper between the two.
The bike won't start (the jumper sparks when it's connected to the relay terminal).

Reconnected the pos. battery terminal and the relay terminal, left the ammeter in place. The bike starts now, but the ammeter reads 1.5 amps with the ignition switch in the run position, and 4 amps with the switch in the headlight position.
Any thoughts?

Post Sun Jul 07, 2013 8:46 am

Posts: 745
Location: Pa. , USA
Not an expert with the charging system but seems to me it will demand more amps with the lights on. I'm running a battery eliminator on my K Mod and you can definitly hear the generator working harder with the lights on.
Vintage roadracing, Class C, AHRMA # 335

Post Sun Jul 07, 2013 6:24 pm

Posts: 202
Location: Middle England UK
The field coil is meant to generate 4 amps with the switch in ign position.When the lights are switched on the shunt coil is brought into circuit to increase the charge to balance the load from the lights,so the charge rate is still 4 amps.
I'm trying to work out how it gives 4 amps with the lights on.With a reading of 1.5 amps,I'd have said the field coil was bad,but then I'd have expected much less than 4 amps with the lights on.If it was a problem with the way the field coil was connected,it wouldn't have worked ok for the first 90 miles.

Did you try fitting the charged battery,putting a volt meter accross the terminals,then just switching the ignition on,as sugested above?
If so,what happened to the voltage reading?
I keep looking at the wiring diagram to try and work out if there's a short or backfeed in the ignition position,that goes away in the lights position.
I've never known a low charge from the field coil that returns to normal when the shunt coil is switched in.

Post Mon Jul 08, 2013 6:55 am

Posts: 30
Location: Winnipeg,Canada
I pulled the relay out of the bike yesterday to get a look at it on the bench and it's damaged. The arm for the top set of contacts has a bad downward bend in it, enough that the center contacts cannot move at all. Both sets of points, top and bottom are stuck in the closed position.
I re-bent everything and got them aligned, got the correct gap between the points, and also the air gap at the end of the armature core.
Reinstalled the relay and everything works, 4.0 amps on run and 4.0 amps on headlight position. Also getting 6V-7V at the battery terminals in both ignition positions.
I'm surprised at how well this bike was running, looking at the relay I would have thought it wouldn't run at all.
Thanks to Dave for all your valuable info, and steering me in the right direction.
Everything being said the bottom set of contacts on the points had very little "meat" left on them, they're pretty worn. So I'm going to order a new relay today, this time I'm thinking of going solid state.

Post Mon Jul 08, 2013 7:13 am

Posts: 30
Location: Winnipeg,Canada
Here's a photo of the damaged relay. Hope I attached this photo correctly
You do not have the required permissions to view the files attached to this post.

Post Mon Jul 08, 2013 9:12 am

Posts: 202
Location: Middle England UK
Glad you got it sorted. :D
If you replace the relay,I think electronic is the only option,I don't know of a reliable repop mechanical one.I'd be tempted to see how the original goes for a while.
Beats me how it ran ok for 90 miles,chalk another one up to the twilight zone. :shock:
That would also explain where the 2 volts were going when you refitted the battery.With the points jammed closed,the battery was trying to "motor" the generator.

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