Electrical Issue

[courtney]

1936 B2

Hello, I hope someone can help.

I recently got my bike back from being fettled and all is running well, but I developed an issue with the electrics the last time I rode it resulting in me racing home before it got too dark. I've only done a few short rides on the bike since I got it back, no more than 6 miles at a time I would estimate.

I've had a bit of a read online. The bike has had a Motobatt 6v 4AH battery fitted. As I understand it, this battery is too small and it should have had a larger AH battery fitted, at least 8AH preferably 13AH I believe, to prevent overcharging. I understand that a standard lead acid battery is preferable for these old bikes. The dynamo is the standard 3 brush E3MD. Paul Goff sells a Westco 13AH 6v AGM battery that fits in the rubber battery box, so I am considering that. Does anybody here use that battery?

The battery tests at 6v with my voltmeter. The rear light and pilot light illuminate off the 6v battery, though they are quite dim. The horn doesn't sound, even when connected directly to the battery. The main headlight bulb doesn't illuminate off the battery. It isn't blown as I've tested it off the bike quickly on a 12v battery and it illuminates fine. Why might this be the case? Can a battery show 6v but not be able to power something properly? Is it dependent on the wattage of the bulb?

I have removed the dynamo to check inside. It's quite mucky inside, so I will clean it up and have ordered some new brushes. I have read that if the battery overcharges that it can damage the dynamo and throw the solder off the armature; is that correct? I haven't noticed any evidence of this, but I'm not sure where it would come off from exactly.

I am hoping it is simply the battery, but am hoping for some pointers. Many thanks in advance.

[Steve.S]

I assume the Motobatt is a sealed battery. If your dynamo is 3 brush, you should have a half charge resistor in the headlamp switch which should have a 'C' position on it. The possible output of the dynamo would be too high for a sealed battery and would probably damage it.....which is what may have happened to yours.
I am sure you should use an old fashioned wet lead acid battery with your system. I would not recommend using a Westco battery with a 3 brush dynamo.
If you want to use a sealed battery, then you should convert the dynamo to 2 brush and fit an electronic voltage regulator.
A 6V battery showing 6 volts is said to be 100% discharged. So your battery is flat. You could try charging it, but only with a modern charger suitable for AGM batteries.
Yes, a battery can show 6 volts but not be able to light a bulb, it depends on the wattage of the bulb. But this is academic, because the battery is flat. A fully charged battery should show 6.8 volts or thereabouts.
From what you have said, I think you will have to buy a new wet battery.
You should just about get away with a 35/35W headlamp bulb, and when running at speed, with the headlamp on, it will perhaps show roughly 0 to +1/2 Amp charge. On half charge, it may show roughly 2 to 3 Amps.
I wonder what your ammeter is showing?  I would think the solder would only melt if the dynamo was producing a  high amperage for a period of time, which it could easily do if your 3rd brush is not working properly. It would melt where the armature windings are soldered to the commutator.
It is a fairly simple matter to convert to 2 brush, you just remove the 3rd brush and spring, remove the cut out, and fit 1 additional wire.
Let us know how you get on.

[courtney]

Thanks Steve.  What you've said confirms what I was thinking and there's some helpful suggestions.  I asked on a Facebook group and got a load of information but no answers, so you've been very helpful, thank you.

The half charge resistor is that saggy spring in the headlight, isn't it?

With regards to the ammeter, when the switch is turned, with the engine off, the ammeter drops right down. I know on other bikes I have it will drop a little,  but this is different.  I didn't look when running as I wasn't sure how much faith to put into whether it was working or not.

I think converting the dynamo to 2 brush might be a good idea if it is as simple as you say. Do you have any information regarding the extra wire to add?

Many thanks again,  it's hugely appreciated.

[courtney]

Hello again,

I charged the battery and just went to check without engine running. Everything works, so it was a flat battery as Steve suggested.

There is something I noticed though, which I'm not entirely sure about, so I'm hoping for some clarification on. I was looking at the DVR2 regulators so wanted to check if the bike was positive or negative earth. I knew from a wiring diagram it should be negative earth, but my battery had been wired to be positive earth. Out of curiosity, I checked it with the battery leads switched round and the lights and horn work either way.

After I got it back from the menders, he'd fitted a new battery positive earth. When I got the bike originally, I fitted a new battery and am certain I connected it negative earth.

If the wires to the battery were switched, would this affect the dynamo charging it?

Many thanks

[Y13 Alan G]

Yes it will. there are several articles on the internet on conversion from positive earth to negative earth. You have to decide which you want positive or negative. Generally speaking negative earth is preferable to positive earth. Apart from anything else you may have to swap the ammeter leads and "flash" the dynamo to safely get positive or negative earth.

[courtney]

Many thanks Alan.

I'm not looking to alter it from original.

Just to clarify, if my battery was incorrectly installed (positive and negative the wrong way), would the dynamo charge it?

[Y13 Alan G]

The short answer is NO it won't.

[Steve.S]

As Alan says, the dynamo would not charge if the battery was connected the wrong way round. I would stick with negative earth, as original.
You should repolarise the dynamo for negative earth. To do this on a 2 brush dynamo, Lucas suggest fitting the dynamo to the machine with the wires disconnected. Connect a length of wire to the Positive terminal of the battery and flash the other end on the F terminal of the dynamo. I have a feeling that the method for a 3 brush dynamo might be slightly different. I can't remember. But give it a go.
Yes, the coil that looks like a Slinky toy is the half charge resistor.
As I said before, I would not use a sealed Motobatt battery with a crudely regulated 3 brush dynamo.
So, to convert to 2 brush, pull the brushes out and unscrew the 3 end plate screws. Gently ease the end plate away from the dynamo body. Remove the nut holding the cut out and remove the cutout and it's wires. Remove the 3rd brush post and spring assembly. One end of the Field windings is already connected to the F1 bakelite terminal, and this is left in place. The other end is (I believe, I can't remember) connected to the Positive D brush. (But it might be the earth brush...) Perhaps others can confirm? But try it, and see. Finally, you need to connect a new wire from the Positive D brush to the D bakelite terminal. For neatness, you could fit a stud to the hole left by the cutout stud and connect the wire to that using the existing link plate to connect to the D terminal. You then need to carry out a motoring test to ensure the dynamo is turning in the correct direction. If not, just swap the Field wires over. Phew, I hope that all makes sense?
You might want to take a photo of the existing wiring in case it all goes wrong......
If it all works OK, I would highly recommend a DVR2 regulator. Good luck.

[Steve.S]

As I thought, repolarising a 3 brush dynamo is slightly different. There are 2 ways of doing it.

1. Connect battery earth to dynamo body. Connect F1 to earth. Touch battery live to D terminal

2. Switch headlight on (i.e resistance not in circuit) and press cutout points together.

[courtney]

Thank you both for your help and clarification with all this, it's really appreciated. I'll investigate further and take my time, but I'm sure I'll be back to check and make sure.

I have ordered a DVR2 regulator and will convert to two brush and see how I get on.

Many thanks again.

[courtney]

To update; I  have removed the third brush and cutout, cleaned up  the commutator and replaced the brushes. I've checked the setup with test wires and can get it to motor, albeit fairly slowly.

It seems like there was some friction preventing it turning faster. I  removed a bit of the spring tension from the brushes by holding them back with my fingers, and it spun smoothly and turned faster, but when I let the brushes sit in the holders normally,  it won't spin up. I first tried with the older, worn brushes and it seemed more willing to motor without me holding anything,  presumably because the worn brushes were under less tension from the springs.

What are your thoughts with this, please?

Must I drive the dynamo from a drill to see if it generates any power?

Many thanks

[militaryron]

That would be your best test. The fact that it motors, doesn't prove it will work properly. (motoring will only produce low revs )

If you can spin it either on the bike or in a vice will prove it. Since you've converted it to two brush, you now have effectively an F and D wire. Connect those two wires together and then connect those to a test lamp or bulb (best use 12v in case you blow a 6V) earth the bulb back to the dynamo body. The faster you spin it the brighter the bulb will get.

If you get nothing, then it will probably need a replacement armature.

Ron

[Steve.S]

I think you are worrying unnecessarily about the speed it turns. Just be sure it rotates in the correct direction. Then do the test with a bulb Ron suggests.
It should get brighter with revs, and if you overdo the revs the bulb will go pop. Some people use a short piece of rubber hose and a couple of jubilee clips to provide drive from a drill.

[BEVANC]

An obvious point I guess, but make sure that the DVR2 you have ordered matches whether you decide to have positive or negative earth. All my older bikes are positive earth.
Cheers, Bevan

[courtney]

Thanks again.

I spun it with the drill and connected a bulb and it generates power to light the bulb, so I assume everything is ok. I haven't got round to connecting the regulator and testing it on the bike though.