How much power does a 1/2hp motor need to start ?

[phill d]

think maybe I better look this up on the net for a lot of detail, maybe a you tube vid etc.
I have taken loads of motors apart, but never come across any weights in them.

so how does this work exactly if its centrifugal ? when mine is switched off and slowing down I do hear a switch like sound in the motor 100%.
if I hear this and then hit the start button while its still spinning a little bit the motor starts straight away. if I let it completely stop it often needs a push on the chuck.
does this sound like a dodgy clutch thing ? or capacitor on the motor ? or ????

phill

 

[brightspark]

here it is https://www.google.co.uk/search?q=c...umberjocks.com%2FCodyC%2Fblog%2F30036;400;246

 

[phill d]

jesus...
looks like a suitcase full of meccano that's been made in the eastern block rammed inside the back of an electric motor.
to me its witchcraft, black magic, voodoo and something nasty with a few springs chucked in for good measure.

what mine does it when i push the on switch is sort of hums then i give it a tiny turn on the chuck and away it goes, does that make any sense ?

if i was to take motor off and open the bottom end would stuff jump out like springs etc, or is it a case of nice and gentle and everything be ok to
have a look at ?

how would i know if its a capacitor on the blink ? and are these easy to get and replace. ?



phill

 

[brightspark]

if a capacitor is fitted take it off and check how many microfarrad it is and get one of eblag .there cheap[ enough and if no better looks like its a stripdown of motor

 

[phill d]

i will take it off tomorrow and have a butchers, when you say cheap. what do you call cheap ?
and i don't know what these do but could i get a sort of bigger one to work better or get the exact same thing ?

 

[eil]

Bigger is not necessary a better thing as a bigger cap would draw more current, try and get a same rating cap or slightly higher rated one

 

[dannyp]

bigger cap will tend to let the magic smoke out of the motor

 

[phill d]

ok so best to get same or near as possible.
ill have a look tomorrow and see what it says, I presume I don't have to destroy anything to have a look at it.

is there any way of testing the capacitor to make sure its bad or good etc ? or is that a specialist thing ?
I realy have no idea about the capacitor things.
but I am learning bit by bit.

phill

 

[dannyp]

dont bother trying to test it. i have a meter with a capactance measureing function and have used it on motor run capacitrs before. quite often a cold capacitor will check out just fine on low voltage. but its actualy knackerd and wont function correctly under working conditions.

they are only a few quid take a punt on one. its ether the cap or the motor is knackerd ( changeing the cap is how you test the motor )

 

[phill d]

well I had a look today at the capacitor and its got some gobblydeegook written on 1 end of it.
I presume this is a 90 to 115 micro wotsits ??? and am I right in thinking this is for 280 to 350 volts !!!!!!
I also took the plate with wires on and had a look inside, it was surprisingly clean to be honest.
I did not spray anything on it to lubricate incase I do something wrong ???
I did run a multi meter across the capacitor and it went straight across and then fell to zero, but I have a sneaky feeling it is this.

here is pic showing capacitor and the wire plate, . I think this is a very old capacitor ?

 

[dannyp]

when replaceing it the replacement needs an equal or higher working voltage ( ever put a volt meter across the run ca on a running motor and you'll see a higher voltage than the motor is supplyed with.

 

[phill d]

ok so on my capacitor it says 280/350. do I need to get say a 350 to 400v capacitor or is it the 280 number that needs to be equal or higher.
also what about the 90 - 112uf ? do I get a number higher than this ?

I realy aint got a clue with this stuff and need as much help as possible, or pointing to a particular item to get.
I go on fleabay and get totally confused with all different numbers and signs.

and what is vrms ? is that just volts ?


phill

 

[brightspark]

350volt root mean squared DONT ASK . TRUE VALUE

 

[the snooper]

350volt root mean squared DONT ASK . TRUE VALUE

I hate rms values, all calculated, not from actual tests

 

[MattF]

It's a damned sight more reliable rating/value than crap like PMPO and such though.

 

[dannyp]

450v capacitor as thats pritty much the std i don't think anyone botheres makeing them with lower rateing anymore

90- 112 uF is basicly the range of accsepatable values for the run capacitor another way of saying the same thing would be 100 uf +/- 10% tolerances are tighter now usally 5%

i would reccomend something like this one, 450v 100uf

http://www.ebay.co.uk/itm/100uF-Mot...al_Components_Supplies_ET&hash=item338125e745

 

[the snooper]

ahh yes but pmpo, that power has been reached for 1 millionth of a second and you have a 1000 watt transistor radio

 

[dannyp]

It's a damned sight more reliable rating than crap like PMPO and such though.

pmpo allways ****** me off and t also ****** me off that idiots fall for it

1000w (pmpo) clamed tv speackers and powerd by a 12w plugtop. same goes for these 10kw car amps. my hifi is a measly 2x100w you can however light up a 100w car bulb on each output channel ( had to test it somehow ) first time i ever used it i reaslised how far off the mark my estimations of actualy power requirements were 2x20w would have been just fine

 

[the snooper]

pmpo allways ****** me off and t also ****** me off that idiots fall for it

1000w (pmpo) clamed tv speackers and powerd by a 12w plugtop. same goes for these 10kw car amps. my hifi is a measly 2x100w you can however light up a 100w car bulb on each output channel ( had to test it somehow ) first time i ever used it i reaslised how far off the mark my estimations of actualy power requirements were 2x20w would have been just fine

but was the impedance of the amps out put matched to the bulbs resistance my guess is the bulb was far lower then the load on the amp should have been

 

[MattF]

pmpo allways ****** me off and t also ****** me off that idiots fall for it

That rating/value has always been one of my pet irks too. It's like they just magically pluck a number from thin air, or, as Snooper suggests, catch the last seen reading before something goes into explosion mode. Those amplifiers where they're rated stupidly high, yet a cats fart would be louder, are prime examples. You could get better output from two cans and a string.