Dynamo sort of charging... ish

[GoldenFailure]

Just put all the bits of my bike together, now have filtered clean oil, electronic ignition, a DVR2 and a rebuilt dynamo (rebuilt by me though). It started first kick, haven't been for a test ride yet as its dark and I still have no lights, but it seems to run ok, but the dynamo doesn't seem to be up to much.

With a wire connecting F and D terminals on the dynamo, then a multimeter from there to ground I only got 0.16 ish of a volt.

At the battery, everything off it measured 12.49V, then at tickover dropped to 11.89V building to 11.96V with a good handful of revs.

Ammeter shows a slight discharge at tickover and a quarter charge with a handful of revs.

As I'm now running electronic ignition at 12V, I'm dicing with pushing it home if I run out of electricity, so, in the infinite wisdom of this forum, does all that sound right? Because it doesn't to me (but electrics are not my strong point)

All advice appreciated, I wouldn't have gotten this far this quickly if it weren't for the advice from some of you.

[beezermacc]

You are absolutely right to start by testing the dynamo in isolation. With F and D bridged together and nothing else connected to the dynamo you should have about 7v between the bridge and earth (engine casing or frame/bare metal) at a fastish tickover. If you're unsure about your voltmeter you can use a 12v bulb instead. The bulb should glow at tickover and brighten as the revs increase to half throttle, beyond that the bulb might blow as E3L dynamos are quite capable of producing 20+ volts. Occasionally dynamos don't charge on the bike because they've been painted and are not making a sufficiently good contact with the engine casing so try using the dynamo casing itself for the earth  when doing the bridge / voltmeter / bulb test as previously described. If still no charge then your dynamo needs investigating and I'm prepared to bet the armature is duff, assuming the brushes are fitted correctly and everything else is as it should be. Running 12v seems to kill off dynamos more quickly than running 6v (not surprisingly I suppose). If you've dumped your magneto in favour of electronic ignition then you really do need a reliable charging system. There has been a very similar thread http://www.audioworld.net/BSA/forum/index.php/topic,5169.0.html on the forum during the last couple of weeks which you may wish to read in the Electrics category. I'll send you a PM with some more help.

[manormike]

the dynamo doesn't seem to be up to much.

With a wire connecting F and D terminals on the dynamo, then a multimeter from there to ground I only got 0.16 ish of a volt.

It could be that the rebuilt dynamo is wired for the opposite direction. It may be worth reversing the 2 field wires OR the brush connections (not both at once) and looking at the output with D & F connected.

Flashing the field sometimes help with a unit which has not been used for a while.

Cheers
Mike

[GoldenFailure]

Well, Mike was spot on, I'd got the field wires the wrong way round, when I swapped them over the dynamo kicked out 18v with a handfull of throttle. But the out put at the battery remained unchanged, 11.9V ish upto 12V with throttle.

I just spoke to Mike, as the DVR2 was from him last week, and he's kindly offered to check it over if I send it back to him, but I'm loath to take it out if its just me making a silly mistake.

DVR2

Green - Dynamo D
Yellow - Dynamo F
White - insulated
Black - Battery Negative
Brown - 10A fuse to ammeter to ignition toggle switch to 10A fuse to Battery positive

Pazon 12V Electronic ignition

White - Battery Negative
Black - 12 twin ignition coil
Red - Ignition toggle switch to 10A fuse to battery positive
Y/B - Ignition trigger
W/B - Ignition trigger

12V Twin coil

Black - Pazon Black
Yellow - Ignition toggle switch to 10A fuse to Battery positive

2 inline 10A fuses
12V 5amph wet battery
Questionable old ammeter
Battery negative to frame
No lights or horn
Checked continuity with a multimeter from dynamo to frame, its fine

Can anyone suggest where Ive been an idiot before I strip out my neatly soldered DVR2 and waste Mikes time?

[groily]

Without looking further, Green is Field, Yellow is Dynamo unless Mike's changed the design conventions since I bought my most recent DVR before Xmas . . . . Therein may lie your prob methinks!

[GoldenFailure]

Hi Groily, well spotted, but it was my error, typing from memory instead of checking, I win full idiot marks, the bike was correctly wired. Just bypassed the ammeter out of curiosity, because it was the only old component and Im suspicious of them, and now the battery reads 13.5V at half throttle, so all is well I think (although Ive struggled so much I'm finding it quite hard to believe that it may actually be working for once!)

[LJ.]

Isn't it a lovely feeling when you finally get it fixed. 

[groily]

Well done on the single by-pass job - sounds as if you've cracked it. Plenty of comments on here about 'good bad and ugly' ammeters. My favourites are proper Miller 2" ones with white faces which middle-aged long-sighted people can read through blurry goggles on wet days and dark nights - but not everyone wants to take a saw to their nacelle or shell  . . .
However, there be those who think a decent ammeter is the only instrument really worth having, the rest being frippery. I'd be one. (Especially if I had charging/battery-dependent ignition!)