Contactor control circuit

[Nick Moore]

Hi guys and gals, I am struggling to figure out how to achieve what seems to be a simple control circuit. I’ve wired a test rig and the system works as expected apart from the lamp not illuminating! What I am trying to achieve is a 13amp socket controlled contactor. Part of the control circuit will be a 230v 15watt warning lamp, once the lamp blows or is removed the contactor will drop thus de-energising the 13amp socket. When tested the lamp glows ever so slightly so obviously there’s an issue with such a high resistance of the contactor coil! Is there a different type of coil available on the market with a lower resistance? Is there another method that I’m not thinking of? Advice would be much appreciated. Thanks in advance.

 

[snowhead]

Why not use an LED indicator, it's far less likely to fail.

 

[Andy-1960]

How are you trying to achieve this at the moment?
A sketch of your circuit would be interesting to see as what you are trying to do is not as easy as it seems.

 

[Nick Moore]

Why not use an LED indicator, it's far less likely to fail.

I totally agree with you. Part of the stipulation was that if the lamp does fail the socket must de-energise. I thought that maybe the LED control gear might keep the circuit closed even if the diode fails?

 

[TJ Anderson]

Hi guys and gals, I am struggling to figure out how to achieve what seems to be a simple control circuit. I’ve wired a test rig and the system works as expected apart from the lamp not illuminating! What I am trying to achieve is a 13amp socket controlled contactor. Part of the control circuit will be a 230v 15watt warning lamp, once the lamp blows or is removed the contactor will drop thus de-energising the 13amp socket. When tested the lamp glows ever so slightly so obviously there’s an issue with such a high resistance of the contactor coil! Is there a different type of coil available on the market with a lower resistance? Is there another method that I’m not thinking of? Advice would be much appreciated. Thanks in advance.

You have lamp and contactor coil in series.....you have a dim lamp......what do you think is happening!

 

[Nick Moore]

You have lamp and contactor coil in series.....you have a dim lamp......what do you think is happening!

I know exactly what’s is happening, I’ve mentioned the very high resistance of the coil/ acting as a resistor. I’m looking for a soloution

 

[SparkyChick]

If the failure of the lamp is that critical, I think you need to be looking at proper safety systems.

What's the overall purpose of this setup?

 

[Nick Moore]

If the failure of the lamp is that critical, I think you need to be looking at proper safety systems.

What's the overall purpose of this setup?

To comply with legislation in regard to portable x-ray equipment

 

[Andy-1960]

I think I would use a current sensing relay to monitor the load taken by the lamp.

Omron do a nice little unit that will sense down to 2mA

 

[buzzlightyear]

To comply with legislation in regard to portable x-ray equipment

are you designing this or think about it ,cause their will be lives a steak hear with radation.

 

[ElectroChem]

@Andy-1960 beat me to the punch, I'd be using a current sensing relay. Have its control contacts cut the contactor if your indicator lamp burns out.

If you need to run a lamp in series with the coil, you'll need to very carefully balance the current & voltage ratings to give reliable operation, a non-trivial challenge without detailed specs.

 

[Nick Moore]

are you designing this or think about it ,cause their will be lives a steak hear with radation.

These machines are used by trained professionals. We’re are simply talking about a power supply, a contactor and a warning light. Once energised these mobile machines have to be activated by competent persons.

 

[Nick Moore]

@Andy-1960 beat me to the punch, I'd be using a current sensing relay. Have its control contacts cut the contactor if your indicator lamp burns out.

If you need to run a lamp in series with the coil, you'll need to very carefully balance the current & voltage ratings to give reliable operation, a non-trivial challenge without detailed specs.

Yes buddy this would be as close as I have got so far.

 

[SparkyChick]

These machines are used by trained professionals. We’re are simply talking about a power supply, a contactor and a warning light. Once energised these mobile machines have to be activated by competent persons.

I think the point we're trying to make is... if this warning light is the only thing standing between a non-competent person getting an unwanted dose of x-rays and them not, then it needs to be pretty bullet proof in terms of reliability.

I'd be thinking multiple lamps, possibly two sense relays and two contactors to provide some level of fail safe setup.

There are special relays I believe that are designed for use in safety solutions that basically prevent operation if a component fails, but machine safety is a specialised area that I'm not familiar with.

 

[Darkwood]

Out of interest, what specific regulation are you trying to comply with here?
Off the bat there would seem to be a few cheap solutions as oppose to building a monitoring circuit, an example been redundancy, why not just have 2 lamps and when one fails it is clearly obvious and maintenance will repair it or the user trained to report it.
That aside the current monitoring option seems the best as previously mentioned but my concern is your reliance on a contactor to isolate a power outlet, if this is for safety then by design it needs to be fail safe and have redundancy in the design thus the contactor needs monitoring as well via a safety control circuit... when you are trying to comply to machine code standards or similar standards then what often seems a simple solution can require a expensive and complex system to ensure safe use and operation.

 

[Nick Moore]

I appreciate everybody’s reply’s and concerns. They’re all valid in their own right. Thank you.

 

[snowhead]

Is this a first installtion of it's type?
I would have thought that hundreds of these machines would be in use and if it's goverened by legislation there would be an approved and tested method of providing the socket supply.

There must be a similar system in Hospitals with the Danger Xray in use sign above the door, presumably if that indicator fails then the equipment must be disabled.

As above somewhere a backup indicator would seem the simplest choice with a warning notice.

 

[Nick Moore]

I appreciate everybody’s reply’s and concerns. They’re all valid in their own right. Thank you.

Out of interest, what specific regulation are you trying to comply with here?
Off the bat there would seem to be a few cheap solutions as oppose to building a monitoring circuit, an example been redundancy, why not just have 2 lamps and when one fails it is clearly obvious and maintenance will repair it or the user trained to report it.
That aside the current monitoring option seems the best as previously mentioned but my concern is your reliance on a contactor to isolate a power outlet, if this is for safety then by design it needs to be fail safe and have redundancy in the design thus the contactor needs monitoring as well via a safety control circuit... when you are trying to comply to machine code standards or similar standards then what often seems a simple solution can require a expensive and complex system to ensure safe use and operation.

New HSE regulations for x-ray machines in vetinary surgery’s.

 

[Nick Moore]

Is this a first installtion of it's type?
I would have thought that hundreds of these machines would be in use and if it's goverened by legislation there would be an approved and tested method of providing the socket supply.

There must be a similar system in Hospitals with the Danger Xray in use sign above the door, presumably if that indicator fails then the equipment must be disabled.

As above somewhere a backup indicator would seem the simplest choice with a warning notice.

It’s an old school surgery that just had a red lamp in a batten holder. The X-ray machine just on a 13amp standard plugtop. Warning notices present.

 

[buzzlightyear]

when designing those systems they have to to bullet proof to make sure that nobody walk in on x ray machine is on . other wise god help them , is ok to stand behind a lead sheild.