Author Topic: Q1 - Charging  (Read 1134 times)

Online cyclobutch

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Q1 - Charging
« on: 11.08. 2010 13:21 »
Or rather - not.

Put the bike back on the road last year after resto - including the dynamo (still running 6v). I'm no sparks but I wired it up myself using a wiring loom from eBay. I bought a solid state voltage regulator (though can't remember which one) rather than reuse the mechanical device. I have an ammeter mounted in the headlamp. That all looked OK until recently when I noticed one evening with the lights on that the ammeter needle was way over on the neg side. I've had a quick peer at my loom but nothing is obviously disconnected or shorting.

Though as noted I'm not up on all of these things I do have a multimeter. I'm thinking I want to work back from the dynamo terminals. What order do I want to check in and what should I look for at each?

Thanks

 
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Online RichardL

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Re: Q1 - Charging
« Reply #1 on: 11.08. 2010 13:46 »
With the lights off and some revs applied do you read positive (reallyn "afirmative") charging?
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Offline a101960

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Re: Q1 - Charging
« Reply #2 on: 11.08. 2010 16:04 »
If the ammeter does not show a charge with the lights switched off check that your dynamo is generating as illustrated below. Use a high wattage lamp as shown below, and do not rev to high. If the lamp does not light then check that the wires are not shorted due to pinching by being trapped by the end cover. Also check brush spring tension and for carbon contamination on the commutator. If all of that is O.K. Its time to get the meter out and check the loom for faults.


John

Online cyclobutch

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Re: Q1 - Charging
« Reply #3 on: 11.08. 2010 16:59 »
Ammeter definitely suggests that I'm not charging, with or without lights. Dynamo has only done 350 miles since recon so I'd presume will be clean inside - but can check of course. Assuming that I can prove the dynamo is OK my next suspicion would lie with that voltage regulator ...
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Offline alanp

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Re: Q1 - Charging
« Reply #4 on: 11.08. 2010 17:20 »
Since you have a multimeter, instead of the bulb you could check the dynamo volts by connecting one side of the meter to the green/yellow junction and the other to earth. When you run the engine without revving it's head off you should get, I recall, around 15volts. You also say that initially it was ok, however, if you didn't notice the ammeter swing initially you may have connected the new voltage regulator up with the opposite polarity. They die quite easily when this happens. Have you done check No 1 which is to put your meter across the battery to see if you're getting charge to the battery? If it is, then you're looking at a wiring problem.
Hope this helps.
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Offline sparx

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Re: Q1 - Charging
« Reply #5 on: 11.08. 2010 19:04 »
Check for voltage on the dynamo "D" terminal at a fast tick-over. It'll probably be less than a volt or so, but if voltage is present (it's called residual voltage) it's a good start.
  No voltage at all suggests a problem with the armature/brushes. Best to repeat the test with the "D" terminal wiring disconnected to eliminate wiring issues.
  This residual voltage should be present at the "F" terminal. If it isn't the problem is with the control box or relevant wiring.
  I'm assuming the bike was charging ok after the rebuild and has failed in service ?
Alan is spot-on about that polarity thing. Not an issue with a mechanical reg providing the field is "flashed" before starting up, but very important with a solid state box.
Dave
Peterborough (UK)

Online bsa-bill

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Re: Q1 - Charging
« Reply #6 on: 11.08. 2010 19:37 »
HI Sparxs - Perhaps you should elaborate the "Flashing" - not unknown for reconed dynos to be polarised the wrong way.
Would explain myself but only ever done it once (couple of weeks back ) don't know if it was needed or not but it was opertune to do it then as most of the bike was not wired up
All the best - Bill
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1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online muskrat

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Re: Q1 - Charging
« Reply #7 on: 11.08. 2010 20:35 »
G'day cyclobutch,
                            one thing not mentioned yet. Is the dynamo turning? The drive sprocket may be slipping on the shaft. That happened to me last weekend after putting a new cork seal behind it. After about 60 miles the cork squashed and sprocket became loose.
 An auto sparks friend advised me that any time work is done on the electrics to flash the dynamo as a precautionary measure.
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Offline sparx

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Re: Q1 - Charging
« Reply #8 on: 11.08. 2010 21:01 »
 "Flashing" Bill?  You need a quiet place and a big overcoat....  ;)
ok. I know it's an old joke.

  The field coil pole piece retains a small magnetic field when the dynamo is at rest just like those nails did when you made electromagnets as a kid. It's called the "residual flux". Depending on if the earth polarity is positive or negative it's either north/south or south/north.
  The dynamo uses this residual magnetic flux to build up the field current when starting from rest. If the flux polarity is wrong the voltage on the "D" lead will be the wrong polarity. The cut-out contacts in the control box will still switch in, but will probably be destroyed by what is more or less a short circuit current flow.
  To prevent that from happening you quite simply disconnect the "F" terminal on the dynamo and feed the field coil(s) directly from the battery for a second or so before starting the machine after changing or reconditioning the dynamo.

  You don't get quite the same problem with a solid state regulator, the diode that isolates the dynamo from the battery when the dynamo output is below battery voltage won't allow the short circuit current to flow, but because the switching circuits are connected to the dynamo output they see a reverse polarity and can get fried.
  I'd best stop there. My eyes are starting to glaze over.....
  
Dave
Peterborough (UK)

Online bsa-bill

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Re: Q1 - Charging
« Reply #9 on: 11.08. 2010 22:11 »
I hear what you say Muskrat, they may well be flashed after being worked on but I know of two that were flashed wrong polarity

I'll read that over a few time sparx  ;)
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco