test a capacitor

[JohnW2]

Hi John ... I think it is as you have said

If it is as I said (i.e. resistance increasing from 0.139 M Ω to 1M &#937, then that's probably not far from what one would expect - but, as eric said, that doesn't mean that a fault would not show itself if it were tested at a much higher voltage than a multimeter uses. I therefore fear that you have not moved too far forward.

Kind Regards, John

 

[Harbourwoodwork]

Thanks John
I think my next step is to have a look on other machines and try swapping caps with a known good one.
Cheers Ian

 

[Jackrae]

The Xc for your capacitor is around 9.6ohms at 50Hz so even with a perfect capacitor, if the motor winding in series with it was defective (shortened out), the supply fuse would blow. Your capacitor may be good and you may have a winding defect.

 

[JohnW2]

The Xc for your capacitor is around 9.6ohms at 50Hz so even with a perfect capacitor, if the motor winding in series with it was defective (shortened out), the supply fuse would blow.

FWIW, I actually make it about 10.6Ω - but, even if the winding were totally shorted out, that would only represent a current of about 22A - so I'm not so sure about the supply fuse blowing. What size of supply fuse did you have in mind? Of course, such a current might well kill the capacitor, not to mention the fact that if the winding were totally shorted, the capacitor would be subjected to about double its apparent rated working voltage (said to be 125V).

Your capacitor may be good and you may have a winding defect.

That's certainly a possibility. If the OP's interpretation of the readings is correct, his low voltage (multimeter) tests do not seem to indicate that anything catastrophic has happened to the capacitor - although, as discussed, that doesn't necessarily mean that it will be OK at normal operating voltage.

Kind Regards, John

 

[333rocky333]

Im confused.
what is the problem, is the motor not starting at all
Tripping the rcds when trying to start
Running ok then tripping the Rcd.

im a bit lost how a faulty cap can trip an rcd but well aware a faulty one would hinder starting.

are your other big machines tripping the Rcd.
I have known ice machines tripping rcds in pubs but when tested they were ok, this was due to an earth fault elsewhere on the instalation and due to the high current of the ice machine put on the instalation, was diverting off and tripping the rcd

 

[JohnW2]

Im confused. what is the problem, is the motor not starting at all ... Tripping the rcds when trying to start ... Running ok then tripping the Rcd. ... im a bit lost how a faulty cap can trip an rcd but well aware a faulty one would hinder starting.

Yes, it's very confusing. The other thread seemed to indicate that it was two RCDs that were tripping (even though the OP tends to call them 'fuses'), and therefore that some earth leak was probably the cause. It seems that the manufacturers may be responsible for this diversion down the capacitor tangent (although, like you, I don't see how a faulty capacitor can cause an RCD trip, unless by a leak to an earthed casing) - since, in this thread...

It keeps tripping the main fuse on start up ,I was advised to check the cap by the seller Axminster.

are your other big machines tripping the Rcd.

The OP has said that nothing other than the planer trips anything.

Kind Regards, John

 

[333rocky333]

Thats what i just read, thanks to the link I posted
Maybe if the makers were, by the ops description, assuming its blowing fuses, maybe wrongly diagnosed the cap.

I suppose from there experience a failed cap and moter starting may possibly cause the supply current to increase to a level to blow fuses, is that feasible, but to trip rcds im not convinced

 

[JohnW2]

Thats what i just read, thanks to the link I posted Maybe if the makers were, by the ops description, assuming its blowing fuses, maybe wrongly diagnosed the cap.

Yes, that's possible. Both of these threads here certainly are, in places, pretty confusing about the nature of the device(s) which is/are operating.

I suppose from there experience a failed cap and moter starting may possibly cause the supply current to increase to a level to blow fuses, is that feasible,

I have no idea what the impedance of the winding would be, so really don't know how feasible that would be. However, as I implied in a recent message, I would expect that a current high enough to operate any sort of OPD would probably well and truly 'do for' the capacitor, if it were not already the problem/cause!

...but to trip rcds im not convinced

As I said, same here - other than via the 'leak to/through case' mechanism I mentioned. Having said that, we do sometimes hear these stories of RCDs operating in circumstances which appear not to make any sense - so who knows!

Kind Regards, John

 

[Harbourwoodwork]

Just to try and clarify this

The planer 5A 1HP 240v
Trips the RCCB 80A tripping current mA and also trips RCCB 100A 300mA
Only on start up
BUT It only trips out 50% of the time and when it starts it runs normally
the motor runs smooth and the planer operates as normal
Cheers Ian

 

[JohnW2]

The planer 5A 1HP 240v ... Trips the RCCB 80A tripping current mA and also trips RCCB 100A 300mA ... Only on start up ... BUT It only trips out 50% of the time and when it starts it runs normally, the motor runs smooth and the planer operates as normal

Thanks. As rocky has said, it's hard to understand how anything wrong with the capacitor could/should cause a RCCB to trip. Are you sure that the Axminster folk who pointed a finger at the capacitor understood that it was an RCCB/RCD (and not a fuse or MCB) that was tripping?

Kind Regards, John

 

[333rocky333]

Im quesssing the earth fault is elsewhere in the premises.
The high start load is tipping it over.
What sort of lighting in your workshop, does it dip when you start the planer

 

[Harbourwoodwork]

I cant recall the conversation exactly.
I talk to tec's now and then about tooling and materials and find some really know the subject and other just do questions and answers,I just saw it as a long shot in the hope it could have been a reoccurring fault.
Cheers Ian

 

[Harbourwoodwork]

lighting from tubes
I have not noticed the lights dimming
Cheers Ian

 

[333rocky333]

Regarding the tripping
you say one is 80 a rated the other 100a rated, although the size is irelovant,

Do they trip together or if just one what one, the 80 or 100.
im assuming the 80 is in some sort of mcb/fusebox.

If your a bit flush with money and its your premises and its the 80a tripping it may be worth investing in an all rcbo upgrade

 

[conny]

Can you isolate ALL other electrical appliances including lights etc and just repeatedly try planer.

If it still trips out 50% of the time then there is good chance you do have a problem with it. If it runs every time without tripping then, as suggested, you may have a fault elsewhere and the planer is just tipping the leakage over the limit.