Motor mystery: "crank starting" a Kato motor

[mmagliaro]

Max, Any reason to clean the commutators with alcohol instead of something like an electrical contact cleaner?

Contact cleaner should work fine.  I just happen to have alcohol handy and it works.  Actually, "contact cleaner" is a generic term.  Some "contact cleaners" actually are just alcohol.  Some have lubricants in them.  Some have harsher solvents in them than alcohol.  So it all depends on what is actually in whatever you plan on using.  Plain alcohol is perfectly adequate to dissolve the oils and gunk that end up on a commutator, and it evaporates quickly.  Cheap, safe, and effective, just like aspirin... heh.

[Chris333]

I think straight alcohol leaves a residue. If I wipe down my phone with alcohol the screen is all streaked. So the contact cleaner probably has something mixed with it to keep residue to a minimum.

[peteski]

I think straight alcohol leaves a residue. If I wipe down my phone with alcohol the screen is all streaked. So the contact cleaner probably has something mixed with it to keep residue to a minimum.

What are you calling "straight alcohol"?  Rubbing alcohol (70% or 91%) could have (besides water) something mixed in.  But the hardware store 99% Isopropyl alcohol should only leave 1% water after it evaporates, and that 1% of water should also evaporate fairly quickly.

I suspect that even if your alcohol has no additives, what you are seeing is the skin oils, or other crud on your skin that sticks to your phone's surface. The alcohol dissolves it, but not all of the dissolved alcohol-gunk mixture gets absorbed into the towel. Those are the streaks.

Good test for purity would be to take an absolutely clean piece of glass, put a drop of alcohol on it, and let it evaporate. If there is residue, it was in the alcohol.

I also agree with Max that there are multiple versions of contact cleaners. Some include a lubricant which I think is not the best for use on a commutator.  Those work best dry (the brushes usually contain graphite and are self-lubricating).

[Chris333]

Well I have no real argument.   

I just remember a guy who worked with lasers always had to wear safety glasses. They kept getting dirty so they would use alcohol to wipe them off. This left them streaky so they cut it with water (I think) till they found the correct ratio where the streaking went away.

And this is sort of what I saw swiping my phone down.

That and I remember seeing contact cleaner with something like "leaves no residue".

Side note: Contact cleaner doesn't smell like alcohol, but for all I know they add crap to it to make it smell better.

Double edit: Just searched what is in CRC contact cleaner and it is 60-70% naphtha and 20-30% difluoroethane and 1-5% isopropyl alcohol   

http://docs.crcindustries.com/msds/1003218E.pdf

[peteski]

Well I have no real argument.   
. . .
Double edit: Just searched what is in CRC contact cleaner and it is 60-70% naphtha and 20-30% difluoroethane and 1-5% isopropyl alcohol   

Difluoroethane is a propellant, so it appears that the active ingredients are just Naphtha and some IPA.

[Maletrain]

When I asked the question, I was thinking about all those track cleaning threads that ranked various solvents on their protic vs aprotic (polarity) properties.  Contact cleaners varied tremendously on that scale, with CRC being substantially more "protic" (supposedly worse) that WD-40 Contact Cleaner (which is not regular WD-40), so not expected to leave track in as good condition to resist corrosion going forward.

So, I have been using WD-40 contact cleaner for just about everything electrical.  And, it seems to work well for track as well.
 
But, looking at the list of ingredients, it contains the same 3 chemicals that Chris333 posted for the CRC Contact Cleaner.  WTF???  Maybe these products have (or don't have) some "magic sauce" chemicals that they do not list?  Otherwise, how could there be such a big difference in their polarity ratings?  Maybe different percentages of certain chemicals?

Anyway, to be more specific: Is there any reason to not use WD-40 Contact Cleaner to clean motor commutators, etc?

[mmagliaro]

To be, I think we are grossly over-worrying about this.

On a motor commutator, whatever is left on that comm as residue by the cleaner is gone in short order, so it doesn't even matter, unless you are so impatient that you don't give it a minute or so to evaporate.  This isn't like engine wheels rolling over a piece of track.  These are brushes whizzing over that comm surface 5000 - 10000 times per minute.  After a few seconds, I can't believe anything from the cleaner is left on there.  The main point of cleaning the comm is to get the conductive junk out of the slots and to get any oily dirty stuff off the surfaces so that when you start up the motor, that stuff isn't wiped right back into the slots in the first few revolutions.  After that, as long as the comm surface is clean, I doubt it matters at all what it was cleaned with.