After having the battery suddenly expire on my bike I have replaced it with a Cyclon 8ah version. Normally i'd spend a bit of time making sure things were electrically sound on the bike before venturing out again but today was my car clubs New Years Day Run.

A quick check before I went out showed 6.3vdc across the battery without the engine running. This dropped to 5.7vdc with the engine running with no change as I increased the revs. So, no charge from the dynamo and something dragging the battery voltage down!

I went out anyway, didn't need the lights, and did a very pleasant 50 mile with a good pub lunch stop. Cruising along at 40mph the ammeter showed a positive charge. After lunch the ammeter sat at 12 o'clock, no movement. On returning home I checked the battery again only to find the 8amp inline fuse I'd fitted had blown. I've removed the tank and seat so I can get to work and check the electricals properly.

So, some questions starting with the real basic stuff.

How do I tell if my bike is wired positive or negative earth? The battery is connected positive to ground but maybe this has been done incorrectly by the previous owner. All lights/horn work ok and were not on when the fuse blew.

Could the problem be that the bike is positive earth and the polarity of the dynamo is wrong?

Bike has E3LM dynamo and MCR2 regulator.

The harness is new so I can check connections quite easily against the wiring diagram.

Where do I start?

Stuart

email (option): stu.gibbins@btinternet.com

Hi Stuart

all wiring diagrams of WDM20 show there to be a negative earth on this bike, I had thought it strange at frst as I had thought positive earth had been the norm on British motorcycles until the 1970's.

It seems this positive earth switch took place in the late 40's and into the 50's, so when wiring my bike some time ago, I had found this to be somewhat strange. My 1972 T100R is positive earth

If you want a simple life, maybe best to wire it as negative earth/ground and ensure your dynamo is polarised in the same way - I think there is a dynamo procedure on the technical links section, if not, I'm sure I or someone on line can send it to you. You may not always be the person working on this bike, so if it is wired as standard (negative earth), you or they will have a good basis of understanding

Check all grounds and connectors,switches, (light, horn, brake)

Ensure your fuse is correctly rated and able to cope with front/rear light combined demand and horn if used when on the move. The horn can be a big power consumer, especially if not in good working condition. provide as many hidden earth leads where you can (headlight / tail section), ensure connections are clean and free of corrosion as this increases resistance in the circuit

Henk hss provided the wiring diagram as a download so best to make a cup of tea and study it before jumping in - check wiring at the rear of your main light switch is as indicated

Hope you get it sorted

Best Regards

Jo'b

email (option): jonnyob1@googlrmail.com

Hi Stuart...Start at the dynamo where the power is produced and work on from there in a logical sequence.
These systems can be set up to run either +ve or -ve earth so you just have to choose which, if any, you prefer and set it up to that. As John says -ve earth is standard on these bikes and setting up to that will allow you to follow the standard wiring diagram and test procedures.
So first check that the battery negative is the one that is connected to a good earthing point on the frame when the battery is installed.
Now polarize the dynamo correctly to match this set up. First connect two wires to a charged 6 volt battery. Next disconnect the two wires from the dynamo end cover. The terminals are marked 'D' and 'F' on the bakelite end cover. Hold the negative terminal wire from the battery to the dynamo body and then using the wire from the positive terminal of the battery 'flash' it against the 'F' terminal on the dynamo cover. It will spark on contact and just one 'flash' or contact is sufficient. Use a striking action similar to lighting a match. The dynamo will now be correctly polarised for negative earth operation.
Now you can test the output from the dynamo.
Take two lengths of wire with the insulation stripped back at both ends. Put one end of each wire into the dynamo terminals making sure you have a good connection. You will need to fit a bullet connector or similar to each wire to achieve this.
Now join the two free ends together....
Next, using a multimeter with the scale set to DCV (direct current) on the 0 -50 volt range start up the bike and allow it to idle. Connect the +ve lead of the meter to the joined wires and the -ve lead to the dynamo body.
Gently increase the engine revs and the meter should rapidly rise to 10-15 volts..Excessive revving should not be required.. If you don't get a reading anywhere or a consistantly low reading of 1-4 volts approx. the dynamo itself will require attention...Ian

email (option): ian@wright52.plus.com

Thanks for the guidance John/Ian.

I shall start checking the wiring tonight and make sure it is set up as negative earth. I'm away for a couple of days with work then so will look at the dynamo stage of things at the weekend and report back on my progress.

Cheers,

Stuart

email (option): stu.gibbins@btinternet.com

It is also worth remembering that Cyclon bateries use the case as an electrode ( like a normal dry cell ) so if the case is making electrical contact then it ca be inducing a short circuit.

email (option): wariron@tpg.com.au

Busy weekend so I've only just got in the garage tonight.

Checked all the wiring out and found the live feed wire to the ammeter had been trapped by the switch/ammeter panel when the bike had been apart at some point. It had just about worn through and shorted to ground, hence my blown fuse. Maybe not such a big problem after all.

I've connected the battery to reflect negative earth and have polarised the dynamo to suit. Tomorrow I'll hopefully sort out my dummy fuel tank and run the bike to check dynamo output. Visually it looks like the brushes are quite new and the bits I can see are nice and clean so I'm hoping it's been refurbished not too many years ago.

Stuart

email (option): stu.gibbins@btinternet.com

Hi Stuart, So far it doesn't sound too bad.. ...Ian

email (option): ian@wright52.plus.com

Checking the output from the dynamo on Sunday I found I had next to no voltage on a fast tickover. I pulled the brushes out and cleaned the commutator with some thinners and a piece of cloth. Tried again and then had 0.38v, still nowhere near the 10v I was hoping for.

I've phoned a couple of rebuild people today to get an idea of price and the worst scenario is £160 for a complete overhaul. Less parts/labour and the cost is lower. With this in mind I've stripped the dynamo this evening and checked the field coil, the resistance was 2.9 ohm. The Lucas manual says approx 2.1 ohm so is mine ok?



I've cleaned up the commutator with some scotchbrite cloth and made sure the mica is cut away as described in the manual. The drive end bearing is a little rough so I will replace that with a new one and then rebuild it and try again.



So far so good and It doesn't look too bad laid out as a set of parts. If the field coil is ok and the brushes are good am I right in thinking it can then only be the armature causing the low charge?

Stuart

email (option): stu.gibbins@btinternet.com

Put new bearings in and reassembled the dynamo this evening. Put it back on the bike and hey presto - it works. An easy 10v at a fast tick over. It must have been just a dirty commutator causing the charging trouble.

Rather pleased I had a go at fixing it myself. Plus, if I get trouble while i'm out on the bike I now know how it works and what to check when it doesn't.

Stuart

email (option): stu.gibbins@btinternet.com

Good Man...Glad to hear you got it sorted and that you have 'pierced the gloom' both literally and metaphorically... ....Ian

email (option): ian@wright52.plus.com

Hi Stuart

Good to hear you are sorted

It's a good way of learning and it's great how its gives confidence now that you know how it works

Happy days for you

Jo'b

email (option): Jonnyob1@googlemail.com