Dynamo bearings

Paul Marx

Paul Marx

Hero member
Location
France
As posted, the dynamo on my SF2 is apart because it wasn't producing volts and I found brushes gummed up in their holders by carbon dust. Brushes will be changed though they're far from worn as will be the bearings, one seems a bit rough.
They're 6202 bearings. Is there any point in fitting C3?
Paul
 
No.

Used sealed bearings, they'll see you out...

Why replace the brushes if not worn? Takes about 4 decades for them to wear completely, a change of attitude Paul? ;)

piet
 
sfcpiet said:
No.

Used sealed bearings, they'll see you out...

Why replace the brushes if not worn? Takes about 4 decades for them to wear completely, a change of attitude Paul? ;)

piet
Click to expand...
Thanks. I'll used sealed bearings, they'll keep the grease away from the electrics.
I'm changing the brushes so as to start anew, opening the dynamo is a bit of a pain though simple once you've done it.
Paul
 
Would inspect the commutator segments for cleared grooves, perhaps a light skim also if the frozen brush(es) were arcing for some little time. j
 
I've taken the bearings off.
They're NSK 62028.
I cannot find what the 8 implies compared to a "standard" 6202.
Any one know?
Paul
 
A fifth digit usually denotes a different width from standard. Cannot find a 62028 anywhere in my various catalogues. Sure it's not simply a stain or similar? Give me the dimensions and I'll have another look. Unfortunately, the bearing sizes are not stated in the parts lists, at least not those for the dynamo!

NSK would imply the bearings have been swapped at some stage, only ever found SKF in Bosch products.

piet
 
sfcpiet said:
A fifth digit usually denotes a different width from standard. Cannot find a 62028 anywhere in my various catalogues. Sure it's not simply a stain or similar? Give me the dimensions and I'll have another look. Unfortunately, the bearing sizes are not stated in the parts lists, at least not those for the dynamo!

NSK would imply the bearings have been swapped at some stage, only ever found SKF in Bosch products.

piet
Click to expand...
The dimensions are standard 35x15x11, aka 6202.
I've also asked my bearing supplier who is also mystified.
And yet: 1754321471690.png
 
piranha-bro2 said:
Please explain! Growler ...???
Click to expand...
A growler is basically a transformer, where the growler is the primary windings and the secondary windings are the dynamo armature. If a armature is placed in the growler it will induce a voltage in the armature the same as the dynamo field coil (although the growler is AC and the field coil is DC when you are riding the bike). But there will be no current flow in the armature as there is no current path. If you have a short in one of the windings, you now have a current path and a magnetic field. A piece of metal such as a hacksaw blade will be attracted to the field and will vibrate and "growl". If you have no shorted windings, the hacksaw blade will not see a magnetic field, so no "growling".

The video John posted is only showing how to check for a short in the windings. It does no mention how to use the growler to check for shorts to ground and open windings.

It is a very useful tool if checking for problems with dynamos and electric motors. If you own a bike with a dynamo and do your own work, you need one. Ebay has lots of old ones. And finally never turn the growler on without a armature in it as it will overheat.
 
Last edited:
Indeed Bruce, chose that video as it was "short" ( please no clapping.. puns aplenty here, wince ) more detailed alternate yt videos for the other modes of testing an armature, suffered from ( lack of ) first principles understanding of the operational applications. One video, the operator uses a ferro washer to simulate the operation of a shorted turn by way of the commutator, segments. Plenty of arcing going on. Dependant on the drive of the growler, could actually stress/overvolt the inter-winding insulation. Being a V segment field excitation, testing for output volts, operator did not address why the voltage reading declined as he went around the commutator, moving further away from the point of magnetic excitation in the V form poles.

Perhaps am being harsh, though i did insist my students have first principle(s) understanding and then apply test procedures, being able to predict the outcome of variations to test procedures. Not just see a measurement and then think it was correct. The growlers i see on ebay are at significant money. Where is my degaussing wand... plenty of grunt in that magnetic field.... "whats a degaussing wand...." indeed what.... smile here. j

Slightly off topic, TV show had these service personal all anti static wired up while removing PCBs, including anti stat handling bags and boxes, from an electric train control and drive systems.

All very correct, though did not understand that anti static procedures were for only certain types of silicon fabrication and product ( CMOS for one, bipolar not so much ). Washed the board in a ultrasonic bath ( shudder ) left to rack dry with warm heat, then full blast compressed air across both sides of the board, compressed air has the potential to produce very large static electricity conditions...... at a guess "Electrotechnology" students, ie electricians with electronics training. Oft time first principles are not taught at trade school, unlike the electrical engineering students, whom are versed in first principles and applications. Taught in both departments at TAFE ( College ). Old school is old school... am old.
 
You must log in or register to reply here.
Back
Top