best practice - reconnecting dynamo field solid wire

[Dennis Nicholas]

I have suffered broken solid copper wires to field coils but in slightly larger Riley dynamos.  Vibration - copper work hardens - breaks.  I have used multi strand cable soldered each end onto the connection points.  Multi strand is a bit more flexible and less likely to fracture.  Suspect some of problem has been due to field coils and their wrapping insulation compacting slightly so that the coils were able to move and vibrate slightly.  The coils were also removed an extra wrapping applied.

Dennis

[JonE]

After much mucking around after still not getting charging after sorting all the wiring issues, I've compared another dynamo unit and found they BOTH motor at the same speed. Which brings me back to battery, after checking/swapping out the solid state cutout and still not getting my red light extinguishing or positive amp readings.
The battery presently sitting at 6.24, a few days after being on intelligent charge at 6.7 regulated - and then disconnected and left unconnected. Seems normal when in charge situation.
Two dynamo motorings, and pull of the starter and its now more like 6.14 and then the starter wont turn after another few pulls.

Putting the other dynamo on righted things immediately; all functions restored; charge getting to battery. So I think battery is ok, and was just being starved by duty.

Will now have to investigate reasons for a dynamo motoring as per a working one.... but not returning any charge bar half a volt.

[jansens]

I lost a post here unfortunately but I have just been through all this with a couple of Riley Rotax dynamos. The first, a 4 field 3 brush AT145 would motor slowly but I was never able to get more than 140mV output from it.

One good test is to disconnect the field and power that directly from another source then spin the dynamo to see what you get. I never got anything out of it. I think the issue is the field coils, which were oil soaked are internally shorting and had only half the resistance they should have (3 ohms instead of 6). When connected up as a motor though it would spin which does seem surprising.

I have now stripped and am rebuilding a second later 2 brush AT166 and this one does work. The field coils on that measure 6 ohms and are in much better shape. With the field connected to the output directly I can easily generate 14 or more volts with a drill driving the dynamo even at fairly low speeds.

I don't think the motoring test is a very conclusive one, at least not on the two dynamos I have here.

I found this very helpful for the Riley 4 pole dynamos. Not sure how applicable it will be to the A7 ones though: https://www.rileyregister.co.uk/wp-conte...e-2010.pdf

As I have nothing to lose I am tempted to rewind by hand the field coils on the broken one I have. Someone described doing it for a different dynamo here: https://www.a7a10.net/forum/index.php?topic=13999.0

Simon

[Bob Culver]

hi Simon

I recall a North Shore A7 special builder. whose distinctive name I have forgotten,recounted on here experience of field coil rewinding. Curiously he used ordinary modern varnish .
Adjustable main brushes are supposed to be set for mimimum sparking at normal full output.The 4 pole DEL ones are adj but I have never fiddled with.
It is helpful to know that 2 pole armatures are wound 1 to 2 to 3 etc to 1, but the 4 pole are more involved. 1 to opposite Op,  to (1+1) to (Op +1) etc or somesuch .The 3rd brush position is puzzling . 4 pole motors can have 4 brushes as starters with pairs commoned. The 3rd brush is located realtive the missing virtual brushes, instead of being awkwardky between the real two.
If the field is reversed the generated voltage cancels the residual and wont start to generate, although will motor one way or other.

[JonE]

 I think the issue is the field coils, which were oil soaked are internally shorting and had only half the resistance they should have (3 ohms instead of 6). 

Simon. I'm now realising my internal derusting and cleaning out with diesel (of a really skanky dynamo) wasn't perhaps my best idea... its presently sitting on the top of the woodburner for a few days and I'll do the tests again and see if I can identify fault before sending away. The annoying thing is that it's still easy enough to find another working dynamo rather than embarking on having the expensive work done. I'm nearly at the stage where I'm starting to appreciate just doing the latter so one is equipped for a trouble-free future!

[John Mason]

It is not to difficult to rewind field coils once out of the Dynamo.
1. Fold the coil flat and make a wooden block the same size and thickness of the rectangular hole that will fit inside the windings. Put a hole n the centre of the wooden block.
2. Make two plywood discs with a hole in the centre. Put a bolt through the disks with the wood block in the centre to male what looks like a crude spool. Cut four slots in the spool sides wide enough for the width of a piece of string and cut towards the centre of each face of the spool.
3. Chop through your old windings then count the number of turns that make the coil. Carefully clean 2 or three strands of wire to remove varnish etc. Measure with a mic to establish the gage if wire.
4. Return to your crude winder and put string through each pair of holes ( This is to temporarily hold the coils when made.)
5. Put the wooden spool in a slow electric drill by means of the bolt. Leaving a good amount of spare wire to act as a fly lead start to wind on your new wire counting the turns and keeping it tight until full amount achieved. Tie up the strings to told the windings in place and dismantle the pulley. Remove former block and tape up the windings with cotton tape removing the string as you go on. Shape the coil to an arc shape to fit the iron core.
6. Finally leave in a bath of shellac overnight before baking on a slow heat for about six hours.

I have not done this to an A7 but as an apprentice to many electric motors and dynamos.

John Mason.

[andrew34ruby]

I tried this a few years ago with my seven dynamo and gave up. Wire everywhere, it wouldn't stay where I put it.

[John Mason]

Andrew, That why you need to wind it tight so that the wire bends to shape on the corners and then tie each side tight with the string on all sides of the rectangle shaped coil you have just made before dismantling the spool. Don’t forget to remove the string when wrapping the tape around the coils.


John Mason.