Joined: Aug 2017 Posts: 25 Threads: 6
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Hello all, I’m having trouble getting my (early coil) dynamo to behave. After years of satisfactory service the cut out has become reluctant to cut in and then when it does the charging rate is very erratic. It zoomed up to 15amps and jammed the needle on the ammeter on winter charge, but summer charge seems ok. If I force the cut out to close it will charge so I assume the problem is with the regulation and not the Dynamo itself, although the wire to one of the brushes is loose and just held in by friction which probably isn’t helping.
I have the Dynamo apart on my bench, it has thrown a bit of solder due to the overcharging but looks serviceable. my inclination is to clean it up, fit new brushes and go over to 2 brush and electronic regulator. Any thoughts on what could caUse the symptoms and what I should be checking?
Joined: Oct 2017 Posts: 1,536 Threads: 55
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If it has thrown solder from the commutator connections which are turning in free hot air just imagine what state the armature wires are in in the armature slots, probably hot enough to cook the enamel insulation.
Joined: Aug 2017 Posts: 3,329 Threads: 372
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Why not stay three brush - the most efficient - and put a Magnetoguys smart diode in place of the cut out?
I've bought a few of the chips direct if you want an even cheaper option.
After sussing all the systems, 6V, two brush and electronic regulation didnt seem a very good idea unless you rewind the field coils, ironically taking away the advantage of the field coils and 3 brushes in the first place!
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
Very many Seven dynamos have thrown solder and are cooked looking but soldier on. If it is a 35A or M dynamo comm is wired 1 to 2 to 3 etc and the resistance between adjacent segments can be compared using the very low ohms ability of a digital meter. (The winding for 4 pole is quite different.) Shorts and poor connections show. Might be able to remedy by resoldering poor sections or digging out melted solder. Should be infinite ohms between segments and shaft. If the 3rd brush or its internal wire touches the earth brush or earth the output will increase, altho this would include the summer rate. On the 4 pole dyn the main brushes are at 90 deg which can be confusing.
Changing to a regualtor will not cure an internal problem . It has worked fine. Others on here have recently shown test using an electric drill (note direction of operation!)
If the cutout is not operating or making good connection but dyn working the red light will glow very bright , the ammeter charge reduce. The contacts can be burnished with a finger nail file but must still follow through when operated. The voltage winding about 30 ohms, the other almost none (disconnect battery before fiddling!)
If not familiar electrics, John Cornforths circuit diagram for Ruby will likely prove useful.
