Yet more E3N dynamo questions

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Yet more E3N dynamo questions

Postby Group Leader » Tue Jun 13, 2017 7:42 pm

Group Leader wrote:1) To power the field coil from the battery, load on the dynamo output, isolated from the field, and run the engine and see whether that will kick it into life


Well that worked :) so the obvious step to follow was to remove the battery from the field, short the field to the dynamo output in the normal manner and see if it would now spring back into life having had a couple of minutes running and hopefully re-magnetising the pole piece.

Sadly no such luck and the bulb remained stubbonly unilluminated. It would appear therefore that either the residual magnetism isn't up to it, for whatever reason, or the field coil is only hanging on by the skin of its teeth (again for whatever reason) and will only work if driven hard.

Still, it's a kind of progress and on the brightside I have to say the beast starts beautifully now - I was just trying to get it gently up to compression before kicking it and it roared into life . Lovely :)

Further ideas and views would still be most welcome.

Alan
1953 AJS 16MS and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

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Re: Yet more E3N dynamo questions

Postby Pharisee » Wed Jun 14, 2017 4:32 pm

Please forgive my ignorance (of most things electrical).... If you connect the dynamo to a battery as a motor... i.e. battery ground to dynamo body (positive in my case) and battery live to both D and F terminals, the dynamo should 'motor'... ok?
Should it motor in the direction that it would normally be driven or the opposite direction?
If necessary, what would I need to do to change the direction?

Thanks
John

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Re: Yet more E3N dynamo questions

Postby aobp11 » Wed Jun 14, 2017 9:23 pm

Further ideas and views would still be most welcome.
Alan, you gave the suggestion yourself in action 2): check motoring is in the correct direction. Alternative: feed F from the battery, run the engine, and check with a multimeter that D has the same polarity (w.r.t. earth) as F. When the motoring direction is not the same as when in use as dynamo then the output will be completely zero.
Note that with D and F connected (self-energising) and loaded with a bulb, you need considerable higher revs to light the bulb (as compared to F fed by the battery). Once lighted you can drop revs substantially before the light goes out. This is because the still cold bulb filament has low resistance and takes away a lot of current.

John, just reread the message by Groily.

Albert

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Re: Yet more E3N dynamo questions

Postby Groily » Thu Jun 15, 2017 8:51 am

Exactly as Albert says.

I usually connect a meter (using a suitable - eg 20 volts - scale) between the bridged F&D wires and earth first; then spin it to see if under (almost) no load it starts to produce. When/if it does start up, I hook a bulb on as well. It will light now more easily than if it had been connected from the beginning for the reason Albert makes clear.
(Maybe worth noting because of how confusing this subject can be, that although it's not relevant in this particular case the bridging of F&D only applies to 'standard' Lucas practice. Where, for example, a JG electronic regulator or other unit requiring the field coil to be wired between F & D instead of F and earth is fitted, the test is different.)

Depending on the wattage of the bulbs available, if you wanted to, you could see from connecting more than one (or a single big one) whether the dynamo is capable of supporting somewhere around its rated load. Around, say, 2500 dynamo rpm it should light loads of up to 40+ watts brightly while showing a voltage on the meter somewhat in excess of 7v (otherwise there would be nothing for the voltage regulator to regulate/maintain the battery were everything connected up as for normal running).

I've edited my previous comment re motoring to make it explicitly clear that the direction in which it motors must be the same as when it is being driven as a generator - as Albert also made clear.

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Re: Yet more E3N dynamo questions

Postby Group Leader » Thu Jun 15, 2017 7:05 pm

We have light! :)

After re-reading Groily's and Albert's advice I was champing at the bit to get home and check the sense of the dynamo output on the bike when the field was energised with the battery. Sure enough it was inverted (i.e. -7 volts ish not + 7 volts ish) when measured with respect to the field voltage. A quick swap of the brush connections (it was easier to do the brushes than the field coil with the dyno on the bike) and another test showed the correct +7 volts this time.

Armed with this success the next test was to connect the bulb. At first there was no luck but then, remembering yet more of those wise words, I gave it some more revs and Hey Presto! there was light, and all without the aid of my nice new field coil - never mind it will keep!

So, many thanks to you all for your input and particularly so to Groily and Albert.

On to the next fettle then which will be to get the electronic voltage reg working and to see that ammeter moving in both directions at last.

Alan
1953 AJS 16MS and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

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Re: Yet more E3N dynamo questions

Postby aobp11 » Thu Jun 15, 2017 8:09 pm

Congratulations Alan!
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Re: Yet more E3N dynamo questions

Postby Groily » Thu Jun 15, 2017 9:42 pm

That is GOOD NEWS.
Also, I reckon it's quite good news not to have had to replace that field coil, as new ones can sometimes be a bit of a so-and-so to fit.
Fingers crossed for the next stage . . . .

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Re: Yet more E3N dynamo questions

Postby Group Leader » Fri Jun 16, 2017 8:16 pm

Well that's that then!

Small Amps.jpg


I've had my first go at sealing the chaincase today (it's still dry on the outside!) so I might take a look at the Jampots next.

Thanks once again gents.

Alan
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1953 AJS 16MS and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

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