The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: raindodger on 05.06. 2013 08:36

Title: Dynamo.
Post by: raindodger on 05.06. 2013 08:36
Gentlemen.
            I have a question for the electrical experts.  On my bike I'm running an E3L through a DVR2.  I'm running the system at 6v and the battery is a pair of Cyclon stacks in parallel.  If the bike is unused for a few days the dynamo does not 'wake up' unless it is given a big fistful of revs, then it works perfectly for the rest of the day.  After a few days rest it does the same again.  My other bike also has E3L/DVR2 and Cyclons at 6v and starts charging instantly.  What is going on, and should I be concerned?
Regards.
Raindodger.

1958 A10
1952 B31
Title: Re: Dynamo.
Post by: a101960 on 05.06. 2013 08:50
Not very helpfull maybe, but I have just fitted a brand new Cyclon battery and I have the same problem. I am guessing that the reason for this behaviour is that the battery is fully charged and therefore the DVR2 is doing what it should do (regulating the charge). Try leaving the headlamp on for a couple of minutes and see what happens then.

John
Title: Re: Dynamo.
Post by: Dynamo Regulators Mike on 05.06. 2013 09:25
Some dynamos seem prone to what appears like loss of the magnetism which starts them up in the first place. I would definitely say that 50 year old dynamos vary more, one to the next, than DVR2's vary. Not sure that the solid battery is significant here.

On the odd occasion the E3L on my test rig has been reluctant to start up initially, but I find that light extra pressure on the brushes gets things kicked off. The same thing is achieved by a wipe clean of the commutator with meths (alcohol) or the like. Any dynamos where the field pole has had any contact in the past with the armature (due to bearing wear) will require a bit more starting as will any with slightly undersized pattern armatures. It may be that the iron used hardens magnetically over the years could also lead to a lazy startup.

It is unfortunate that with electronic regulators such as the DVR2 which use the remanent field (residual magnetism) generation to wake up it will take a few more revs than with a good mechanical regulator, as a little more voltage is required to pass through the semiconductors employed. The alternative is to use voltage from the battery to aid start-up. The serious downside of doing this is non starting without a battery or a low battery charge. This is a characteristic of some units on the market (and leads to the regulator actually taking a discharging current from the battery at low speed). Note that this speed is not the same as up to regulated voltage speed, charge balance speed for which the DVR2 is at least as good as the rest, far better than many well known ones.

Maybe what seems like a lot of revs just after kicking her into life is not so many when on the move when the dynamo will probably come to life in normal riding. In short just as aspect of normal variations no need for concern I would say.

Cheers
Mike
Title: Re: Dynamo.
Post by: KiwiGF on 05.06. 2013 10:17
I had exactly the same problem, in my case it was the brushes, if i cleaned the commutator  then the problem would go away for a while, but it would return because the brushes were soft and quickly making the commutator dirty again.

So new brushes cured the problem, and so far so good.

I used a voltmeter to confirm the issue existed when the commutator was dirty, with F and D joined the voltage was around 0.4 v from memory even when blipping the throttle, and this was obviously not enough to get generating going, after a clean i was getting nearer 0.7volts at tickover and a blip on the throttle would make the volts jump to over 6v and stay there.

Edit: i have a dvr2, and 6v "motoblatt" battery
Title: Re: Dynamo.
Post by: a101960 on 05.06. 2013 14:34
Quote
I had exactly the same problem, in my case it was the brushes, if i cleaned the commutator  then the problem would go away for a while, but it would return because the brushes were soft and quickly making the commutator dirty again.
I shall give that a try, and will report back.

John
Title: Re: Dynamo.
Post by: BSA_54A10 on 06.06. 2013 13:52
The dynamo will only generate when the battery is low.
So if the battery is fully charged you will get a zero reading on the ampmeter.
Title: Re: Dynamo.
Post by: raindodger on 07.06. 2013 13:46
Gentlemen.
              Very many thanks for the comments and advice.  I'll check out the commutator, brushes and spring tension.  Relieved by the opinions that it's unlikely to be terminal/expensive.
Best regards.
Raindodger.
Title: Re: Dynamo.
Post by: a101960 on 07.06. 2013 15:12
My intermittent charging problem turned out to be a slipping belt. I have a "V" belt drive  and it was slipping on the dynamo pulley.

John