The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Tumbleweed on 30.08. 2018 14:48

Title: test dynamo
Post by: Tumbleweed on 30.08. 2018 14:48
hi everybody  .  I am trying to make a good dynamo out of two old ones .  when I spin it with a drill A/Clockwise I only get2-3 volts set on  20 position on my  meter joining F and D together  to  neg   and pos  to + it wont light a bulb just a faint glimmer, but it motors quite fast.        any ideas TW  how fast does it have to turn befor it works with the dynamo off the bike
Title: Re: test dynamo
Post by: bsa-bill on 30.08. 2018 15:39
Quote
oining F and D together  to  neg 


Dynamo body would be neg or pos depending on polarity usually positive earth on these bikes
Title: Re: test dynamo
Post by: Tumbleweed on 30.08. 2018 15:53
 yes Bill its off my a10 and its +earth  , 
Title: Re: test dynamo
Post by: JulianS on 30.08. 2018 18:14
Lots of interesting stuff on electrics on Matchless Clueless site;

https://matchlessclueless.com/
Title: Re: test dynamo
Post by: bsa-bill on 30.08. 2018 18:14
a week or so ago I got similar results before changing polarity back to positive earth (long story)  , turned out I had painted the dynamo not thinking about it's need to earth, had to rub of the paint (under the strap) and put a piece of copper between the strap and the dynamo, magic upto 20 volts at times
Title: Re: test dynamo
Post by: trevinoz on 30.08. 2018 22:33
That is usually indicative of an armature with open circuits.
Title: Re: test dynamo
Post by: Tumbleweed on 31.08. 2018 09:45
thanks for your help chaps ,  the matchless site was useful as well     TW
Title: Re: test dynamo
Post by: Tumbleweed on 03.09. 2018 13:38
hi, everybody ,  I have just run a test with a electric drill and at 2000 rpm    I get  14 v charge from it I am hoping this will do for my a10 ?    TW
Title: Re: test dynamo
Post by: Rex on 03.09. 2018 18:54
a week or so ago I got similar results before changing polarity back to positive earth (long story)  , turned out I had painted the dynamo not thinking about it's need to earth, had to rub of the paint (under the strap) and put a piece of copper between the strap and the dynamo, magic upto 20 volts at times


It should earth just fine through the ally end plate to the engine.
Title: Re: test dynamo
Post by: bsa-bill on 03.09. 2018 19:02
Quote
It should earth just fine through the ally end plate to the engine.


Really , I find on mine the cork gasket makes a good insulator  ;)
Title: Re: test dynamo
Post by: Rex on 03.09. 2018 21:16
Mine must be a different design then, as the cork gasket only touches in the middle section and the outer portion is well and truly butted up to the crankcase.
Title: Re: test dynamo
Post by: bsa-bill on 03.09. 2018 21:20
possible the cork has compressed, if the alloy touches first then the cork is doing nothing.
The reason mine did not earth was I had stupidly painted the body ( a bit too well)
Title: Re: test dynamo
Post by: trevinoz on 03.09. 2018 22:42
TW, if you are getting 14V the generator is fine.
Title: Re: test dynamo
Post by: coater87 on 04.09. 2018 15:29
 After some of the hassle I had with mine after rebuild, I would power up a bulb with it before I buckled it up. 14V is nice, but I would make sure it will run a load first.

 Lee
Title: Re: test dynamo
Post by: Tumbleweed on 11.09. 2018 12:16
hi folks ,   well I fitted  it to the bike and I don't even get 1 volt direct from dynamo    *sad2*  also I  flashed the F terminal for polarity ,  the D terminal flashes as well  is this normal ?   TW
Title: Re: test dynamo
Post by: Tumbleweed on 11.09. 2018 15:24
HI FOLKS ,    I have removed said dynamo and tried it on the drill again ,  a two speed drill  gives 4v  at 900rpm  and 14v at 2400rpm  how fast will the dynamo spin at medium revs on the bike because I get under 1v revving the engine slightly  TW
Title: Re: test dynamo
Post by: trevinoz on 11.09. 2018 22:21
Do you have a good contact between the generator body and the crankcase?
Title: Re: test dynamo
Post by: Tumbleweed on 12.09. 2018 07:50
hi, Trevinoz  I am going to put it back on the bike sometime to day and I will make sure that is so .   thanks  TW
Title: Re: test dynamo
Post by: bsa-bill on 12.09. 2018 10:00
Quote
how fast will the dynamo spin at medium revs on the bike because I get under 1v revving the engine slightly


Belt drives increase the speed of the dynamo, beneficial at low revs
Title: Re: test dynamo
Post by: duTch on 13.09. 2018 11:27

 
Quote
hi folks ,   well I fitted  it to the bike and I don't even get 1 volt direct from dynamo    *sad2*  also I  flashed the F terminal for polarity ,  the D terminal flashes as well  is this normal ?   TW

 I've always been of the notion that 'D' & 'F' have to be connected together from the desired battery terminal to 'flash' for polarity  *conf2*
Title: Re: test dynamo
Post by: bsa-bill on 13.09. 2018 16:22
Quote
I've always been of the notion that 'D' & 'F' have to be connected together from the desired battery terminal to 'flash' for polarity 


need to be connected together to get correct voltage from dynamo, then flash the F field terminal.
Title: Re: test dynamo
Post by: trevinoz on 13.09. 2018 23:23
It'll flash the field either way.
Title: Re: test dynamo
Post by: bsa-bill on 14.09. 2018 10:44
Quote
need to be connected together to get correct voltage from dynamo, then flash the F field terminal.


OOPS that doesn't read as I had intended.

I meant they have to be connected together to get the correct voltage, they don't need to be connected to Flash the dynamo Field
Title: Re: test dynamo
Post by: Tumbleweed on 18.09. 2018 11:21
hi again everybody ,  I cant even get 1v at revving the engine now ive fitted it back on , even ran earth separately still no luck but 2300 revs on the drill I get 14v and lights up a 12v bulb brightly  *sad2*     TW
Title: Re: test dynamo
Post by: groily on 18.09. 2018 17:08
Are you 100% sure you have it set to go the right way? Sounds as if possibly not (or at least, what you are seeing would not be inconsistent with that.) Just a thought. . .
Title: Re: test dynamo
Post by: Tumbleweed on 18.09. 2018 20:25
almost certain Groily,   ive ordered a new set of brushes I will try that , if that don't work I will take it off again and check what you have suggested , although I did run it with the drill anticlockwise when I got the best result . I  wonder what  rpm the dynamo is doing at 30 mph for example.     TW   
Title: Re: test dynamo
Post by: groily on 18.09. 2018 21:50
Hmm  . . . anti-clock is right, certainly, so  . . . dunno!
 
But  . . . if it delivers the voltages you described, and also supports loads when run up on the bench, the darn thing should work on the machine.
What happens if you stuff a meter between the dyn's joined F and D terminals (loom disconnected) and a good earth with the engine running? Loadsa volts? . . . or is that how you obtained the miserable 1v you mention? Loads is good, one measly volt isn't.
If there are loads, what do you then see (loom reconnected) if you stick the meter between the A lead from your regulator (to ammeter, switch etc) and earth, with the engine running? Should see rising volts, settling to steady-ish charging voltage at higher rpm. Or, across the battery terminals with the engine running?

At 30 mph the dynamo will be turning - I'm guessing due to a few variables - in the region of 1700-2200rpm, depending on gearing of the bike and the drive you have on the dynamo. A bit faster than the engine is turning, anyway and well above kick-in speed, but maybe not enough to support serious loads. Mine shows a small charge with lights off at that speed in top on fairly standard gearing (it's minimum snatch-free top gear territory though), but needs a few more revs to balance headlight etc (at 12v).
Title: Re: test dynamo
Post by: Tumbleweed on 19.09. 2018 08:15
the way ive been testing it is F &G joined together on the neg on the multimeter and pos to earth ,    and not connected to the loom and   direct to the dynamo, I will see what happens when the brushes arrive and check  rotation  .         thanks  TW
Title: Re: test dynamo
Post by: bsa-bill on 19.09. 2018 09:48
Quote
F &G joined together 


Typo ?
Title: Re: test dynamo
Post by: Tumbleweed on 19.09. 2018 11:08
F&D  sorry.        *smiley4*
Title: Re: test dynamo
Post by: Peter Gee on 22.09. 2018 20:42
Looking at the dynamo brushes end on, how do you tell D wire from the coil to F? Mine are unmarked and I must rebuild..which one is left  or right?

Cheers
Title: Re: test dynamo
Post by: trevinoz on 22.09. 2018 22:29
When I rebuild I connect the left brush to D, the right brush to earth.
The coil leads are brought out so that the left goes to earth and the right to F.
I motor test and if the direction is wrong I reverse the coil leads by bringing them out of the opposite slot.
Title: Re: test dynamo
Post by: morris on 22.09. 2018 22:34
Looking at the dynamo brushes end on, how do you tell D wire from the coil to F? Mine are unmarked and I must rebuild..which one is left  or right?

Cheers
Trevinoz beat me to to it but I was going to reply in the same sense.
If they are the wrong way round it won't charge so just swap 'em then
Title: Re: test dynamo
Post by: Tumbleweed on 25.09. 2018 16:37
Yes Bill it was as you say running the wrong way I was reading anti clock from the front the dynamo body was the wrong way round the arrow points the other way ,  now its charging well .  thanks everybody   TW  :!
Title: Re: test dynamo
Post by: groily on 25.09. 2018 18:08
It's easily done TW. Happens all the time. All this patting head and scratching belly stuff (the one being a bigger target than the other, don't go there please) makes it dead easy to get things wrong, especially when the arrows mean sod all on most of them 50 years down the line.
The good news is it works and no harm done. Long may it continue  . . .