Electric Hoist Contactor issue

[Bing]

Hi all.

I am currently working on a Machine that as an Hoist with separate raise lower Contactors. Whilst doing a load test on the Hoist, I noticed that when I manually activated the raise Contactor, on occasion the Hoist would actually lower the load momentarily. This is not a Brake failure, the Motor actually drives in reverse as if 2 of the phases on the Contactor had been swapped. If I wait a second & activate the same Contactor again, the Hoist raises. This isn't just when under excessive load, I have seen it do this without any load on it.
Just to clarify, this as never happened during the machine's automatic running cycle, it as only happened when I have manually operated the Contactor through it's over-ride button on the front of the Contactor.
I have never seen this happen before & am wondering if anyone can offer a technical explanation.
Am I missing something blindingly obvious? Your thoughts please.

Bing.

 

[bernardgreen]

Maually operating a contactor by hand ( pushing in the actuator ) can result in the contacts not operating at the same time as each other. This may be resulting in one phase closing a short time after the other two and the motor may momentarily run in reverse as a result.

 

[Bing]

Thank you for your explanation Bernard. That is what I kind of thought it might be, but just wanted some one else's take on it. That's the beauty of these Forums, you can bounce things around with others!
Thanks.

Bing.

 

[donrkebab]

It is a brake fault. After any up or down operation the brake should automatically and permanently lock the hoist. And it should only release on new up or down movement.

 

[JohnW2]

It is a brake fault. After any up or down operation the brake should automatically and permanently lock the hoist. And it should only release on new up or down movement.

Yes, but if bernard's theory were correct, there would have been "new up or down movement" (to release the brake), albeit momentarily in the unintended direction.

Kind Regards, John

 

[Bing]

Thanks for the replies Donr & Jon.
I did try to write my question as clearly as possible but it seems not clearly enough.
I don't believe it's a brake problem because when the Contactor is released the Hoist stops immediately with 1500Kg load on it. It doesn't creep in the slightest & in fact the Brake was only adjusted 3 Month ago.
This issue only happens when I manually over-ride the raise Contactor, more often than not it will lift rather than lower.
I am quite happy with Bernard's theory but I am open to other views.
Just to reiterate, the Hoist stops the moment the Contactor is released by the Brake, whether it has raised or lowered.

regards.

Steve.

 

[ericmark]

On manual operation is that still electrically activated or are you pushing the contactor with a screwdriver the latter is likely to close only two phases.

Is it a three phase motor or is it single phase using a three phase contactor to energise start and run coils?

 

[Bing]

Hi Ericmark.

The Motor is a 3 phase Motor & yes, I am operating the Contactor over-ride button on the front, with a Screwdriver in the main Control Cabinet.
From your reply & question, I am assuming that Bernard was right with his theory.

Thanks for your input it is appreciated, everyone.

Still learning after all these years!

Best regards.

Bing.