Induction motor help. Table saw

i have a small kity saw with an induciton motor. the other day it suddenly struggled to start.
if i spin up the blad eby hand, then press start it gets up to speed find and has normal amount of torque, can still cut fine.

have checked bearings and belt etc. all fine.

other syptom is some of the time it wants to start backwards!

any help where to start diagnosis appreciated. i guess i’ll just need to pull the motor off and give it a clean out with the compressor. but would like to know what’s going on really

thanks

What you suggest sounds like a good start, no pun intended. There are many different types of induction motor, but many rely on a centrifugal switch to engage some extra starting windings. In a dusty environment the switch contacts often get clogged up. Clean and degrease to ensure dust doesn’t stick and then give it another go. Also check the visual condition of any capacitors. Leaks, bulges or burn marks. Remember that capacitors hold a lot of energy. Don’t go near any of the electrical contacts unless you have shorted the capacitor to disapate the energy with an insulated tool of some sort.

Typical capacitor failure symptoms , find and check the details of the hopefully one – start/run capacitor and order one , will be a rating of voltage -and uf (micro farads) should cost about £7 .
They dry out and fail over time, or keep going forever.
Heed the warnings about getting zapped.

As above, sounds like the capacitor has gone or the connections to it. And once again heed the warnings about getting zapped.  I used to work with caps that would hold 10000v and every now and then I would forget 🙁

well that’s all quite positive sounding, thanks everyone.

so do i just short the capacitor(s) out to earth?

and is there a way to test which one it is if there are more than one? i kinda suspect there won’t be given the size etc

Typical capacitor failure symptoms , find and check the details of the hopefully one – start/run capacitor and order one , will be a rating of voltage -and uf (micro farads) should cost about £7 .

Wot ‘e said.

if i spin up the blade by hand,

Maybe the way to go with old hand cranked engines, but you really dont want to be doing that with a table saw 😆

yes

so do i just short the capacitor(s) out to earth?

unplug machine

if the capacitor terminals are next to each other then you can just short them together with an insulated handle screwdriver.  If they are at opposite ends of the capacitor then use a piece of insulated wire with the ends bare and then touch the bare ends to either end of the cap.

In reality the cap should already be shorted out but if you have a dodgy connection then it might not be

nothing to stop you checking with a multimeter to make sure you have done it correctly as well 🙂

Avoid being tempted to try the 9v battery trick with your tongue 😉

thanks but is there a way to test with a multimeter if a capacitor is faulty, as opposed to checking it’s not still charged?
never understood capacitors, tho the explanations are simple…

so where is/are the capacitor s ?

are they likely to be wrapped on that tape?

never mind. found the capacitor
duh
its massive

A special meter is needed to reliably test a capacitor of the size used for that size of motor.
They are usually fixed to the side or end of the motor near the wiring , with the Kitty model number you should be able to lookup a parts list/diagram.
Likely to be large film canister size +

like this:

There is a very remote possibility that you have a motor with a start winding and internal switch , you will need to take the motor apart to fix that – its not hard but you should do some youtube research.

right it was the capacitor, which was totally easy to access and, as crogthomas said at the start, has a big lump on it (= overheating?)

ill try to find one with the same specs. and jobsagoodun, hopefully.

A special meter is needed to reliably test a capacitor of the size used for that size of motor.

Yeah, multimeters have no place checking a motor is dead.

specs question:

it’s a 16µF

it says
AC 400V B
AC450V C

i see one by same manufacturer, and 16µF, which says

AC 400V A
AC 450V B
AC 500V D

will this be fine?

i see plenty others of right specs but not many with the right configuration of spade connectors. sure i could solder some onto some cables, but i’d prefer it to just have the same.

Yep that exceeds the voltage spec you need. Looks good.

ok great thanks

ordered. 12€
happy days

love this forum : )

Asked same question on here a few years ago about a planer thicknesser. Same symptoms. Same answer. About £10 from eBay for replacement capacitor and been great ever since. More recently had same with a Kärcher pressure washer. Also fixed for a few quid.