Relay problem

lee_g47 · Oct 5, 2005

I have a small 24v relay on a e stop circuit that is in a panel with other contacts and servo equipment. The problem is that it does not release sometimes when the e-stop is in. It appears to have a possible magnetic field from other equipment holding it in.
The e-stop does open the voltage source. Is there a simple way
to install a bleeder or snubber circuit to stop this from
Happening. Thanks

stasis · Oct 5, 2005

let me get this straight....the relay is in parallel with your E-stop circuit? And when you push in the E-stop button, the relay is still pulled in?

if so, it sounds more like a mechanical problem rather than a field issue.
(stupid question) Have you changed the relay?

leitmotif · Oct 5, 2005

Uhhhhhhhhh
les think about this.
1. You activate the E stop
2. This is supposed to deenergize all components
3. All relays are supposed to drop out

After activating E stop
have you checked the terminals on the relay to ENSURE it is dead?
You are sure it is not a latching relay
You have removed it and tested on bench to recreate the conditions?
AND it still sticks open

IF yes to all then you got a bad relay. Encapsulate in clear plastic and save for desk souvenir and hands on demo.

Dan Bentler

CaseyK · Oct 5, 2005

When I first read this, my first thought was to just put a light light across the relay.

The more I thought about it, I have not witnessed this before, could it be that the relay has a fairly large load, and the contacts are sticking a little due to some arcing?

regards.....casey

panic mode · Oct 5, 2005

are you sure it's contacts are rated properly?

k.dougherty · Oct 6, 2005

Why aren't you using a proper safety relay?

Johnny T · Oct 6, 2005

lee_g47 said:
The problem is that it does not release sometimes when the e-stop is in.....
The e-stop does open the voltage source.

If it works sometimes and not others, and by "e-stop does open the voltage source" you mean that it drops off the 24 on A1 and A2 on the relay contacts then its probably a duff relay.

Never heard of a relay being pulled in by the close proximity of other equipment... but I suppose it's possible...

But as K.Dougherty stated, you should really be using a safety relay that's self monitoring really for this application.

leitmotif · Oct 6, 2005

I am not sure what you mean by term self monitoring safety relay.
Can you give me an explanation and maybe some examples please?

Could this be a "Master Safety Relay" or "Master Control Relay" that controls other relays and PLC power to inputs and outputs

OR do all relays controlled by an E Stop have to be safety relays?
For example E stop turns off relays A, B, C ie "primary relays"
Relay B turns off relays 1, 2, 3 ie "secondary relays"
Do just relays A,B,C have to be safety relays or will this extend down to 1,2,3 also?

Dan Bentler

rdrast · Oct 6, 2005

leitmotif said:
I am not sure what you mean by term self monitoring safety relay.
Can you give me an explanation and maybe some examples please?

Safety relays are designed so that they are both positively force guided (the entire armature is driven, not just pulled at a central point) through a larger distance than normal relays, but they also have 'Proof' contacts which provide feedback that the relay has indeed switched.

This will cause a fault on the safety device if there is for example a welded contact, or even contacts that don't transfer in the design time (as in 'About to Fail').

Technically, for a safety system, all contacts used should be contacts off of a safety slave relay, properly wired into a master safety relay which does the monitoring.

lee_g47 · Oct 6, 2005

Thanks, I quess i did not truley understand what was going on.
The 24vdc relay is slaved with a mcr. And what appeared to happen
was not the case. We was trying to check voltage across the 24v relay coil with a meter then the mcr would open, It seemed that
the relay was keeping the mcr closed. But we removed the control wires off of the mcr and it stayed in for a few min before it released.
It is sized ok and it is opening the main power, so I quess
the contactor is bad. I am going to check on the safety relay's
I am going to brake it down and check the contacts. Thanks for the reply's

Rod · Oct 6, 2005

A quick check would be to lighty tap the relay and see if it releases.
'course that's the way I test things - sometimes a larger hammer is required. KIDDING

It does sound like a bad relay (sticking armature/contact)

Go with a 'safety relay' on an E-Stop circuit. E-Stop does mean EMERGENCY STOP

my $0.01

Rod

Relay problem

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panic mode

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