How hot should a dynamo get?

[adz25]

Hi,

After replacing an MCR cutout on my 56 g3L with a wassel electronic unit, i have taken her out for a spin. The charge is now immense from it, even a little at tickover.

I happened to reach down and touch the dynamo and it was very hot, not too hot to touch mind. Just wondering if this is normal after a 20 minute ride?

Many thanks

Adam

[clive]

Does not sound right to me. What state is the battery in? Lead acid or gel? If it is gel they dont take well to being fully discharged and will sometimes refuse to take charge again. It does sound as though yours is overcharging though.

[adz25]

Thanks for the prompt reply Clive.

It is a small 4ah sealed battery.

[g80csp11]

Did you fit the unit or was it done by someone else ?

The answer is always check the voltage of the battery
A problem with the battery can cause the dynamo to need to be charging all the time
The regulator only works on voltage
cut in below 4.5 to 5.0 volts and limit to max 7.2V

There are two types of wassell regulator , positive WW10221P and negative WW10221N earth units are not the same , the negative earth one requires the field winding to be reconfigured from what i can see on the instructions supplied with the units . (shown for reference only )

1)Disconnect the field coil wire marked 1 from F and connect it to the D terminal
2)Disconnect field wire marked 2 from earth screw and connect it to F terminal

Positive ones don't require any changes

if you check the voltage of teh battery with engine running lights off and lights on , at idle and increased speed you should be able to determine where the problem is

[adz25]

Thanks for the reply.

It is the positive earth unit and i installed myself as per the instructions that came with it.

Just done a voltage check. 6.1 volts engine off

6.29 volts no lights at idle.

5.99 volts lights on at idle

At half revs 8.65 volts with positive amps indicated on my gauge.

Half revs 6.99 volts lights on with positive amps indicated.

Thanks

Adam

[adz25]

I also should note that after the 20 minute ride, the battery was warm not hot to the touch.

Many thanks

Adam

[g80csp11]

sounds like you could do with a bigger battery , perhaps 2 small ones in parallel . i have seen before problems with a small battery

[clive]

Peter would you expect the voltage to be limited to less than 8.65 volts at half revs? I wonder if a small fully charged Gel mat battery is not giving enough feedback to the regulator. On the way to one of the Germany IJRs I destroyed a gel mat battery with a poorly controlled regulator but that was the old Lucas type. The changes that are suggested for the negative earth unit simply sound like reversing the polarity of the dynamo to me, but I do struggle a bit with the electrics.

[g80csp11]

I don't know Clive , but i've had issues with old gel batteries over charging with high volts , once replaced the voltages were back to normal
even on my 1946 G80 I fit a 6V 14Ah battery

[Groily]

Can't comment on gel mat batteries because I don't have any - but if that 8.6v was a constant, shown on a decent meter, it's too high.
Not sure if the Wassell regulators work with no battery in circuit - but if they do, and you can measure the volts on the A wire off the regulator, it should not go much over 7v max at any speed. (There will probably be spikes though, if using a typical digital multimeter.)
I don't think the dynamo should get hot hot, no, but it's hard to define what hot is!
Battery capacity should be a min of 5 or 6 Amp hours I'd say. More is good, up to a point anyway. 10 is great, and if you're prepared to pay for real quality, you can get 12 or 14Ah too. (You don't want a car-sized battery though, or it could stress a little dynamo trying to charge it up if the batt drops off a bit!)

There is something of 'You get what you pay for' here, in that the Wassell electronic regulators don't compare for performance with some of the better ones out there, such as the DVR2 from Dynamo Regulators Ltd, or the V Reg units from Alan Osborne. Nor with the JG regulators.
There truly are stark differences between makes of regulator in terms of cut-in on rising revs, performance on falling revs as you drop towards cut-out speed, and actual charge rates while in fully-regulated mode.

So it could be that the battery and / or the regulator is / are causing the grief.

The change for negative earth is more than a polarity thing Clive. The neg earth Wassell job regulates on the 'earth' side of things, whereas the pos earth one does it on the 'live' side. Why, the Lord alone knows. Anyway - the difference is that the field coil wires need reconnecting as g80csp says. Often described as the difference between 'shunt' and 'series' wound dynamos in the literature.
Standard Lucas practice was field coil wired between the F terminal and earth, connecting to earth at the same place as the earthed brush usually.
Standard 'foreign' practice, and on many Millers, was to connect the field coil between the F terminal and D.
So the Wassell Neg earth regulator isn't the only one to require this, but it's the only make I know of where their 2 versions require different configurations. JG regulators, as originally designed for use on the Miller systems on bikes beginning with V, and every Bosch or other Europen system I have seen, are F to D too. (This also impacts he standard basic dynamo output test procedure.)
Any dynamo will work on either system, just as it will work with either earth, and will generate in either direction of rotation - but things have to be set up to suit.