Electrical problem diagnosis...

[bikemonkey]

Did you do the tests in part C?

The alternator readings aren't that bad, I'd be suspecting the reg/rec.

[magg]

Your battery voltage at idle is normal for an NC35 because lights always ON is a significant electrical load that the charging system cannot support at such low engine rpm. At 5000 rpm, the battery voltage should be 14-15 volts.

A simple test for the true output from the rect/reg is to measure the voltage between the green and red/white wires that come out of the rect/reg. Should get 14-15 volts at 5000 rpm if charging system is ok.

easout

[edgey]

in response to bikemonkey:
Just done part C of that diagram and I believe it fails some tests, I disconnected the plug & left the reg/rec bolted to the bike (I assume thats what it meant by disconnect reg/rec).

1st test I get OL, OL, OL = PASS (all OL)
2nd test I get 0.554V, 0.534V, 0.542V = PASS (all around 0.5V)
3rd test I get OL, OL, 0.001V = FAIL (one reading is lower than 1V)
4th test I get 0.550V, 0.538V, 0.001V = FAIL (one reading lower than 0.2V)

Does this conclude reg/rec is knackered?
The reg/rec on here isn't original, previous seller replaced original, this one is beefier with fins. Should it have failed? or has something else misbehaving caused it to fail? which would cause a replacement to fail etc.

magg:
Bit late to be revving my bike to 5k for neighbours sake, I might do that one tomorrow for good practice.

Cheers all.

[magg]

Just a note regarding battery and rect/reg voltage readings just after start up, they will be low until the battery has acquired some charge after the discharge from starting the engine. It could take a couple on minutes to reach a steady value, particularly if there have been a number of start ups without any running time between.

[speedy231278]

Anyway, between A+B, A+C, B+C (yellow wires), all read:
Idle = just shy of 10v
5k = 43v

These readings are a bit shy of what they should be I believe, what now chaps?

Nah, you're OK. When I had issues with dodgy wiring I was getting similar. Even after I removed several inches of grotty wire from both sides of the alternator plug and fitted a new plug and spades I was only getting something very similar to that. I seem to recall that after doing that and also the same at the reg/rec end, I didn't really gain any volts at all. I did lose about .1 ohm across one or two of the pairs, but as they were all around 0.6 anyway they were well in spec. I'd just make sure that all your wires are in good health, and that you don't have any dirty or corroded connectors. If you decide to replace the plug on the reg/rec then for the sake of a few mins extra work I'd buy some nice heavy multi-strand wire (something like 2.5/3mm area), a 30 amp inline fuse, and connect the reg/rec output directly to the battery. Fuse goes in the positive side. Plenty of threads about it on here. Before I cleaned/replaced/modified I was getting about 12.5 at idle and 13.3 at 5K. I now get closer to 13 and 14 respectively. The former is fine for long trips, but doesn't give you much margin to recharge the battery after starting and/or pottering around town at low revs.

[edgey]

Cheers Speedy,

I found Magg's thread on the matter, will read it in more depth later but seems simple enough, get the right electrical components, rewire +ve & -ve reg/rec outputs to respective battery terminals, tape up ends of old loom +ve & -ve reg/rec output wires.

Currently in work but when I'm home this evening I'll test the output voltage of my reg/rec as Magg suggests (suspect it is low, thus direct wiring would be a good idea), will probably redo those 4 tests on the reg/rec wiring I did last night as I was somewhat knackered which may have affected results.

[edgey]

I have just redone the 4 tests and got similar results (voltages a little lower probably due to using battery for starting ignition without it getting charged). I still get a fail value on 3rd test and a fail value on 4th test as before on the same pins.

I also let the bike run a little and measured more voltages:
Accross battery:
Idle = 11.5V, @5K revs = 12.3V

Across reg/rec output wires:
Idle = 11.84V, @5K revs = 12.4V

My across battery voltages are a little lower than at the start of the thread I assume due to starting bike a few times without any charging time.

Am I right in this concluding that my reg/rec is the first thing I should replace?

Cheers guys.

[speedy231278]

I'd charge the battery fully on a charger, then fire up the bike and measure. If it starts first time on a healthy and fully charged battery, it won't drag it down a huge amount. You are getting a reasonable if not spectacular increase in voltage at the battery with rpm, it's just that both figures are very weak. Also, the best part of 0.4V drop between the reg/rec and battery at idle seems a little high to me. The quickest and most simple thing to replace is the reg/rec, and if it doesn't fix the issue, well they have a habit of dying so a spare is a handy thing to have. However, I would really consider the direct wiring mod too. I would expect to find the voltage readings at the reg rec and battery to be very close, the 5K readings are within a tenth, but .34 at idle suggests you're maybe losing a bit to corrosion. That said, at idle literally a few 10s or 100s of rpm can make a big difference in the output so if your bike isn't idling very, very smoothly it can bounce around a little.

[edgey]

Cheers speedy, I think I'll take the plunge on a new reg/rec then, as you say, if it doesn't help matters a spare can't hurt. I intend to do the direct wire mod too, my commute to work is a relatively short journey so anything to help the charging system can only be a good thing.

[magg]

Should have read your post more closely, the C test results indicate that one of the diodes in the rect/reg has shorted, the 0.001V results. Do not think you will end up with a spare rect/reg. When you fit the new rect/reg make sure to use heat transfer compound between the ret/reg metal mounting surface and the chassis mounting surface. Also check to make sure the chassis mounting surface is flat. Helps keep the rect/reg cool as possible for long life.