The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: roadrocket on 16.07. 2014 19:24
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A very common heading I'm sure, but everyone's a bit different. I have no charge despite many efforts: I have checked that dynamo works as a motor, which it does quite convincingly, and the same way around, anti clockwise, as when running. The wiring inside the dynamo is correct, with Field connected to earth via one brush, and the other brush directly to Dynamo on the end cover. Ammeter shows discharge when lights are on. I have polarised the dynamo. I have checked belt drive to dynamo. Voltage regulator is spanking new. What can possibly be wrong? Next step is Alton generator!
Otto in Denmark
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The fact that the dynamo motors is not an absolute test. In an ideal world you need a 'growler' to test the armature but checking the output on the bike with a 12v bulb or voltmeter should be good enough. Are you doing the usual test, i.e. disconnect the D and F wires, bridge the terminals, connect the bridge back to the dynamo body via bulb or multimeter, run the bike slightly over tickover and check output?
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Thanks, will try that.
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As Andrew said, motoring is not the ideal test, unless you have a variable voltage available. Usually, if a generator will motor at 3-4V, it is OK.
I have a growler but never use it, I prefer to "voltage drop" the armatures.
In fact, there are people with growlers who don't have a clue how to use them properly and only test for short circuits, completely disregarding open circuits, which is the most common fault.
Then there are earth faults, uncommon, but again, disregarded.
Trev.
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My dynamo passed all tests but would not self generate enough voltage in the field coil eg kIck off charging after a few hundred miles unless I cleaned the armature. I got tired of doing this obviously...... *problem* *pull hair out*
New brushes solved the problem *wink2*. Seems the old ones had gone soft or were the wrong material.
A test for this problem is to apply power to the field with the engine running and see if it starts generating and then keeps generaring when you remove the power to the field coil.
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Read a good article about testing the dynamo; it looks like my field coil is shot. The dynamo yields 0,35 V, and the resistance between field and earth is 0,05 ohm. Have ordered new field coil. Thanks chaps!
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apply power to the field with the engine running and see if it starts generating and then keeps generating when you remove the power to the field coil.
Yes, always try that one, with the engine running at a fast idle.
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So I changed the field coil... Everything nicely assembled, polarised and with big hopes I fired up. No charge! I have changed armature, control unit and field coil. No charge. I will now buy an Alton generator, and never need to worry again.
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Try reversing the brush connections, to reverse the dynamo's direction.
Did you try briefly putting battery live to to dynamo F, with engine at fast idle?
My Alton failed in service. So did the supplied regulator.
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Hi Triton; do I do that with both D and F connected to the regulator? The Dynamo turns the right way around (anti clockwise) when motoring, so I take it the brushes are OK? I have now cleaned the cummutator for good measure, but have not fired up yet, as the neighbours would probably not like it at this hour.
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Try reversing the brush connections, to reverse the dynamo's direction.
Did you try briefly putting battery live to to dynamo F, with engine at fast idle?
My Alton failed in service. So did the supplied regulator.
Also had to reverse the brush connections on my dynamo to get it going after a rebuild so well worth a try. Seemed illogical to me at the time because I was 100% sure I reconnected them as they were before but had 0 output until I (accidently I admit) connected them the other way round...
You can easily test a dynamo outside the bike. I use a 4" length of rubber tube, push it on the shaft, and use an old drill bit in a drill to drive the other end. Connecting D & F together should give at least 10-14V at drill speed.
About the Altons, a bloke from wich I buy spares and who used to sell Altons told me he gave up on them because of to much returned units and an almost none existing manufacturers support.
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Hi Triton; do I do that with both D and F connected to the regulator?
Yes. With engine running fast enough that it should be charging and everything connected normally, get 6 or 12V live onto the F, with some sort of jump lead from the battery live. Just for a second or so. It sometimes wakes the dynamo up.
The Dynamo turns the right way around (anti clockwise) when motoring, so I take it the brushes are OK?
I don't actually know if motoring direction is the same as charging direction, but reversing the brush pigtails has worked for me, with a new (to me) dynamo, in the past.
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Motoring direction is the same as generating.
Trev.
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I have now measured the resistance between the segments on the commutator, and I have nil resistance between any of them. I guess thats bad? The armature has been rubbing on the field coil retainer, but the dynamo has worked since that up to a point. So new armature?
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You may have fitted the field pole shoe wrongly. It's something of a specialised job.
Testing an armature needs special gear too.
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That was from the old fitting made by a specialist, but with an armature fitted by me. The new field coil neeed some persuasion, but is now snug. Funny how it didn't fit when delivered, but had to be bent. I have read that the segments opposite to each other should be of equal resistance, and that there should not be continuity between one segment and the others. Anyhow, the dynamo still doesn't work.
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Thought there should be continuity (of some measure) between the segments of the two ends of a winding?
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There should be extremely low resistance between each segment.
You need to do the basic test before anything else which is - remove the connections from the generator, join the two terminals with a piece of wire then connect a voltmeter between them and earth.
Run the engine and observe. As you rev the engine, the voltage should rise. Don't overdo it. Also note that the polarity is correct.
Easy?
Trev.
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Easy, and done a while ago, no life whatsoever. It motors fast, but does not put out a single volt.
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The segments shoiuld read very low ohms between each segment. If your meter is not high quality it may say 0 resistance, should be about 0.1ohms.
Short out F and D. Touch earth side of your battery to dynamo body and the live side to the D (shorted to F). the dynamo should motor, this will also polarise the dynamo.
Set your meter to read voltage (DC) with your meter between the D (shorted to F) and dynamo body which should have a good connection back to the earth side of the battery. With the bike running you will get should now get an output. If using a analog meter you may have to reverse the leads if you don't get a reading.
If you do not get a voltage output, reverse the field coil leads and try again.
Check that you have not got the D tag that goes to the armature brush earthed.
Check with a meter with the other brush removed or not touching the armature. You should get open circuit between the D tag and the dynamo body.
With the other brush replaced you should now get a short to earth (well 0.1 ohm.)
If all this checks out you WILL get an output.
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Otto,
If I am reading your reply correctly, you get no output with the terminals bridged.
As it motors in the correct direction, I would say that your armature is faulty.
Your field coil should have a resistance of around 3 ohms, give or take a little.
Trev.
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Yes I think the armature has had it. I have wrapped the whole thing up and will send to Dave Lindsley. The input about Alton generators has put me off wanting one. The Dynamo must be revived, as I'm sure it will be when someone who knows gets his hands on it.
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below is a extract from a article i wrote years ag
hope this help
One trick worth trying first is repolarising the Dynamo simply disconnect the leads and ensure the battery is charged and connected. Now connect a wire to the battery live side (NOT THE LIVE TERMINAL) and quickly flash the “F” terminal. Redo this if you strip the Dynamo.
The first thing although obvious to most is to remove the end cover and kick the bike over. Does the Dynamo turn? If not check your chain on twins or the clutch on the end of the mag on singles. If it dose turn the next step is to connect the “F” and “D” terminal together and lead a wire from it to a 12 volt bulb, take a wire from earth to the other side of the bulb and start the bike if the bulb lights and is bright the problem is in the regulator, If you have a Multimeter you need over 13 volts even on a six volt system. However magdyno’s can suffer from a slipping clutch which means the dynamo is not turning fast enough to check for this remove the Dynamo and try and turn the large fibre wheel in the Magneto case with your fingers if you can turn it your problem is the clutch needs to be tightened. The next step is to remove the Dynamo and carefully strip it down.
Once striped look at the copper/brass part of the armature this is called the commutator very gently clean it with a 600 grade or higher piece of wet and dry. Next step is to clean the gaps between the segments on the commutator with a slim blunt instrument do not press, very carefully scrape out the black carbon, now clean the brushes the next step is to check for circuit as well as lack of it wire a bulb in series with a battery so that you have two wire which when connected together light the bulb, put one wire on the commutator and one in the shaft of the armature if the bulb lights you need a rewind. Now place one wire on a segment of the commutator and touch each segment in turn. The bulb must light on each segment if not rewind once more. THESE MEASURES CAN NOT GURANTEE A GOOD DYNAMO BUT WILL DEFINETLY IDENTIFY A FAULTY ONE. If all is well so far, we will now check the field coils this is the winding inside the dynamo case. Using our bulb connect the wires direct to the battery and note how bright it is, now connect the wire to one side of the field coil and the other to the battery if the bulb is noticeably dimmer the Filed coil is okay if you use your Multimeter you are looking for a resistance of around 2 amps.
A excellent tool for checking a Dynamo can be made from a extension bar off a socket set. If you know someone with a Lathe ask them to turn the end which normally attaches to the wrench enabling it to fit into the chuck of your electric drill (battery drills are not fast enough). Using this tool join the “F” and “D” together and attach to a bulb take a wire from the Dynamo body to the other terminal of the bulb, spin it up ensuring you observe the correct rotation for your Dynamo as “A” & “B” group spin different ways again it should light the bulb or with a Multimeter show over 13 volt’s. If it does not light the bulb try spinning the Dynamo the “wrong way” if it lights simply swap the field coil wire over and try again the correct way it should now work. If you do not have a reversible drill try swapping the Field coil wire and spin again.
Now the bad news if all the above fails you need a rewind.