Re: 5v Fan on 3v line

I have 3 in one in my model cupboard. Its OK for quite big motors, but from memory sewing machine oil is better for smaller stuff.

I think the model train and slot car racing people use something lighter than 3 in 1

As do clock and watch repair people.

It seems that 5V fans are typically 300mA or less.

On 3v Id expect them to be around 150mA. That is not a huge amount to load a 3V supply with.

They are also incredibly cheap - $4 or less. Oil to fix a flagging bad one is probably more expensive

They generally use a really nice synthetic oil that's certain not to damage brass.

I've only actually taken measurements a couple of times previously but in my experience BLDC fans work to a first approximation as a constant current sink. E.g. if a fan draws 200mA at 12V it'll draw near as dammit 200mA on 5, 6, or 7V.

Careful though, those cheap fans may work out very expensive especially when the hassle as well as expense of premature further replacement is factored in. It generally pays to get something mid-market (or nearer the premium end of the computer market) with a longer expected service life otherwise you are just replacing junk with junk.

On the other hand, you'd probably find it difficult to justify true premium replacements - e.g. you could easily multiply that budget by ten for certain Papst ranges. Great fans sure, but several tens of dollars each probably isn't a justifed investment.

HTH

Also in the UK.

"3-in-One Oil is a general-purpose lubricating oil sold for household and do-it-yourself use. It was originally formulated in 1894 for use on bicycles, and remains a popular lubricant for their chains. Its name, given by inventor George W. Cole of New Jersey in 1894, reflects the product's triple ability to "clean, lubricate and protect".

The product changed ownership many times throughout the 20th century and was bought by its current owners, the WD-40 Company, in 1995."

That's what I used it for mainly - it kept my bikes running smoothly for a couple of decades.