milk frother

Someone who actually knows will be along in a minute but from what I remember of physics at school I think the Back EMF is the key factor here.

When a DC motor is running freely it's not only consuming but also generating electricity and the net power running through the coils is relatively low. Relative to start-up power - or in your case, full load power - that is. I suspect what really matters to the motor is how much maximum current is passing for how long and if you can wire an ammeter in series, you can find this out.

Nick

style foam when the batteries are new. So having returned an espresso make r due to the feebleness of the steam outlet, I went back to the aerolatte f rother, and tried it on 4.5v and 6v in place of the usual 3volts.

on the motor ?

in which case what is the best way to measure the rotation speed ?

If it's rated at eg 3v for 2 minutes, it'll run way less time before frying on 6v.

NT

All depoends on the load. My model planes were running nominal 6v brushed can motors on 11v+ lithiums, and provided I geared them down and let them rev on lowish currents the limiting factor was the cheap and nasty brushes..

I got about double the power and 50% more efficiency than people running then 'on spec'

for a 3v motor try a single li-ion cell at 4.2v fully charged, 3.8v flat..

ino style foam when the batteries are new. So having returned an espresso m aker due to the feebleness of the steam outlet, I went back to the aerolatt e frother, and tried it on 4.5v and 6v in place of the usual 3volts.

ss on the motor ?

lk, in which case what is the best way to measure the rotation speed ?

Are you suggesting that in a highly cost conscious consumer appliance the m otor might be bigger than it needs to be when run on 3v? I would suggest th at if anything it's smaller than it should be.

NT

Its not so much the speed but the current taken to maintain the speed and the torque. Often pulsed dc can maintain a slower speed but with more torque, and as the duty cycle is lower the motor might last longer, assuming it is a standard brushed type not some kind of electronic speed adjustable one, which form you comments about volts, is unlikely.

Its all down to design and build quality. If its a cheap device it may just be that the short life is the price you pay for it working with more volts. Brian

Of course if its over engineered it may be OK as I said in my other reply. My take would be find a wall wart to power it at a reasonable current just a bit up from the nominal you see at 3 v and it will probably give you as long a life. Make sure of course that the wall wart is rated for the start up current first. I have an issue with a shaver control circuit which won't let the motor start even though the battery condition is not too bad. I suspect the motor is wearing out and taking more current to start due to wear on the brushes etc. Brian

Yes, I am suggesting that.

These motors are churned out un vast numbers in far east factories by the likes of mabuchi, sagami etc etc.

The voltage rating is practically irrelevanyt. In reality motors do not have a voltage rating. They have a current rating, a maxium heat dissipation, an RPM per volt rating, and an RPM limit, and a brush and bearing wear limit.

Usually to keep costs down they wont habve a gearbox. that means operaring a bigger motor at lower voltage and RPM.

For example my '6v' motors actually generated best power and effeiciency at aroudn 24v and 50,000 RPM or would if brush bounce wouldnt stop them getting there. So I ran them around 25,000/11v and stuck a 3:1 gearbox on. 75% efficiency

Better than massive current at 6v and say 10k rpm 50% efficiency running VERY hot.

The limiting factor on your frother will be heat. Take te ferriote magnets past about 150C and the curie point and they will lose magnetsim. As the magnetism goes, the motor will speed UP as it isnt generating the back EMF any more, and take even MORE cirrent and the next thing is magic smoke coming out of the things.

So monitor the heat.

ccino style foam when the batteries are new. So having returned an espresso maker due to the feebleness of the steam outlet, I went back to the aerola tte frother, and tried it on 4.5v and 6v in place of the usual 3volts.

ress on the motor ?

milk, in which case what is the best way to measure the rotation speed ?

frying on 6v.

he motor might be bigger than it needs to be when run on 3v? I would sugges t that if anything it's smaller than it should be.

Fan torque goes up rapidly as rpm increases. Current is proportional to tor que. Thus by feeding the thing more volts he's also feeding it more amps. T hus it can run for less time. Typically handheld kitchen appliances already have short duty cycle ratings.

NT

Cube law I think on my model planes. Can't remember, Certainly at least square law.

Correct.

Non reliable sequitur. All depends on how near the limit it is. My whole point is that motors that are muppet proof and can probably be safely stalled on 3V are, provided you understand what you ate doing, probably fine at 24V if you gear them down, and probvably fine at 6V of you don't stall them.

So do model planes :-)

one hour to charge, 5 minutes flying time.