Dynamo looses polarity over night

[klaus gerhard]

The dynamo of my 1953 VH produces a good charge. Its connected to a electronic regulator of the same type like on my NH supplied by Marco Boelis from NL. (pos earth on both bikes)
The only problem I have found with the VH is that it won't show a charge on the next day. I have to connect - of the battery and D of the Dynamo for a second and it will charge right away.

Any suggestions why this happens?

Thanks
Best Regards Klaus

[Knud.Degnbol]

I had the same problem with my Huntmaster. But it was not a real problem. Every time I gave the engine some revs, it started to charge.

[MARK.WALSH]

I have the same issue on my panther m100.
I have fitted a flick switch that just gives out a charge from the battery for a split second to make it work.
I wonder if it is more of the fact that these electronic regulators need much higher revs to initiate the unit. (Sometimes if I give the bike a handful of revs it will cut in - but I don't like doing that in general)
In addition I wonder if other topics on 'electronic units not working' could be the same thing. (My square 4 wont work on an electronic reg but fine on a mechanical one)

Cheers
Mark

[paul.jameson]

I have a theory that the dynamo on any given bike will have its own opinion as to what its polarity should be. Presumably this is a function of the magnetism from the magneto in particular but also from other parts of the bike. So when I build a bike and start it for the first time I use a multimeter to see whether the dynamo is positive or negative earth. If it happens to be the "wrong" way round I simply reverse the field coil connections. That way, the dynamo has the magnetism the way it likes it to be and the output is the way I like it to be. I only ever "flash" a dynamo as an absolutely last resort because I think the dynamo can revert to its preferred state over time, due to the magnetic influences I mentioned earlier.

[Michael.Brown]

Paul,
Where do you connect your multimeter to the dynamo to check polarity. My battery has never charged on the WNG since I got it. It is fitted with an electronic regulator as per photo. Any tips to get it charging would be very useful. My battery is +ve earth by the way.

Mike

[nevhunter]

Paul's theory has some merit. The magnet in your magneto does exert a field outside its self that may well overcome the small residual magnetism in the Generator This field varies in strength depending on where the Magneto armature is positioned. Ideally one would think it would be advantageous to have the two in synch with each other. Most seem to ignore it BUT?? The elements of the generator basically mild steel which really does not act as a permanent magnet very effectively. Once it's running it's self energizing. Swapping the field coil ends will reverse Field magnet polarity. It might also reverse the Pos earth aspect also. Check that out before you go far or you will be charging the battery backwards and that won't be a good idea.. Use a boy scout's basic compass if you want to check magnetic polarity. They are pretty cheap. Nev

[fpassmore]

Having worked in the power generation industry and DC motors/drives for Stal Laval, ASEA & ABB for 38 years I have seen quite a few permanent magnet and residual magnetism machines. You are correct Nev in that mild steel is pretty poor at retaining magnetism so the actual residual magnetism can be pretty haphazard, has to do with material, homogenous structure, air gaps, etc...
I can say that Paul's method has great merit in that residual magnetism has to do, to a certain extent, with the "memory" of the material and swapping the field around is an easy and effective method of taking advantage of that memory. Use of a meter to double check polarity is needed of course.
I will add here that the magneto magnetism will have a very minor influence on the magnetism in other parts as the distance between magnetized pieces is quite large ( in magnetic field terms).

I have never had one of these Ereg units apart but the design and components in use would generally require that there is enough voltage produced to exceed the minimum break-over voltage which you do not have on the mechanical regulators as there is just a set of points (dead short) initially in the circuit. Therefore the experience of revving the engine to make it start charging is just a product of having to get the resultant voltage from low residual magnetism to overcome the break-over point on an Ereg or even to excite the field coils in some cases on a mechanical reg.

Hope this is of some help. Frank

[paul.jameson]

To check polarity of the dynamo, disconnect the two leads. Then temporarily join F and D on the dynamo together. This joint forms one connection for your meter. Earth on the bike is the other connection for the meter. Start the bike, run for a few seconds and see what the meter shows.

[Michael.Brown]

Thank you Paul. I will give it a go

Mike