Inductive kickback problem?

V

v man

Guest
Hi,

I have a small 12V DC off-the-shelf circuit that operates a few 240V AC
relays. The circuit is controlled by a PC via a parallel port.
It works OK with no load, no problem there.

However, when I manually unplug any of the devices connected to the relays
(they are neon and halogen lamps) somehow the circuit board gets all screwed
up and switches on (or off) the relays at random. Even worse, it also
happens when the board itself switches the relays off. When there is no
load connected to the relays everything works 100%.

I suspected that it might be the "inductive kickback" problem, so I
connected 0.1uF caps snubber across each load terminal. It did not help
unfortunately. I also tried powering the circuit board from a power point
in a different room, no change.

Is there anything else I can try? I think maybe the caps are not of the
correct value, but I was not able to find any accurate info on that. The
mains are 50Hz, 240V the load is variable, up to 2A.

Thank you for any kind of help.

Peter
 
I am under the impression you are using relays with 12 volt actuation, and
are using 240 VAC across their contacts.

I would suspect that there is an electrical interference from the device
that is being turned off and on. I would not buy the idea of inductive
kickback.

The drive circuits on the board are probably sensitive to the electrical
interference created by the load. Since you are using neon lamps (I think
you are referring to fluorescent lamps), they tend to give off some
electrical interference. The halogen lamps also pull a lot of current, and
when switched off and on can make some transient interference.

I would be looking at trying to see if I could make the drive circuits to
the relays to be less sensitive to electrical interference.

Just for curiosity, see if turning a fluorescent lamp on and off that is
located near by and is connected to the mains, but not through your control
device, and see if it also makes the relays change state while everything
else is running.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:14lRb.300$KW.16670@news.optus.net.au...
Hi,

I have a small 12V DC off-the-shelf circuit that operates a few 240V AC
relays. The circuit is controlled by a PC via a parallel port.
It works OK with no load, no problem there.

However, when I manually unplug any of the devices connected to the relays
(they are neon and halogen lamps) somehow the circuit board gets all screwed
up and switches on (or off) the relays at random. Even worse, it also
happens when the board itself switches the relays off. When there is no
load connected to the relays everything works 100%.

I suspected that it might be the "inductive kickback" problem, so I
connected 0.1uF caps snubber across each load terminal. It did not help
unfortunately. I also tried powering the circuit board from a power point
in a different room, no change.

Is there anything else I can try? I think maybe the caps are not of the
correct value, but I was not able to find any accurate info on that. The
mains are 50Hz, 240V the load is variable, up to 2A.

Thank you for any kind of help.

Peter
 
Thank you for your reply. I will do the test you suggested.

It will be difficult I think to change the board to deal with the
interference I am afraid. It is because the board is sold as a kit and I am
not sure what would need to change to fix the problem.

How would one go about isolating the interference?

Thank you again.



"Jerry G." <jerryg50@hotmail.com> wrote in message
news:bv4ocf$qit$1@news.eusc.inter.net...
I am under the impression you are using relays with 12 volt actuation, and
are using 240 VAC across their contacts.

I would suspect that there is an electrical interference from the device
that is being turned off and on. I would not buy the idea of inductive
kickback.

The drive circuits on the board are probably sensitive to the electrical
interference created by the load. Since you are using neon lamps (I think
you are referring to fluorescent lamps), they tend to give off some
electrical interference. The halogen lamps also pull a lot of current, and
when switched off and on can make some transient interference.

I would be looking at trying to see if I could make the drive circuits to
the relays to be less sensitive to electrical interference.

Just for curiosity, see if turning a fluorescent lamp on and off that is
located near by and is connected to the mains, but not through your
control
device, and see if it also makes the relays change state while everything
else is running.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:14lRb.300$KW.16670@news.optus.net.au...
Hi,

I have a small 12V DC off-the-shelf circuit that operates a few 240V AC
relays. The circuit is controlled by a PC via a parallel port.
It works OK with no load, no problem there.

However, when I manually unplug any of the devices connected to the relays
(they are neon and halogen lamps) somehow the circuit board gets all
screwed
up and switches on (or off) the relays at random. Even worse, it also
happens when the board itself switches the relays off. When there is no
load connected to the relays everything works 100%.

I suspected that it might be the "inductive kickback" problem, so I
connected 0.1uF caps snubber across each load terminal. It did not help
unfortunately. I also tried powering the circuit board from a power point
in a different room, no change.

Is there anything else I can try? I think maybe the caps are not of the
correct value, but I was not able to find any accurate info on that. The
mains are 50Hz, 240V the load is variable, up to 2A.

Thank you for any kind of help.

Peter
Click to expand...
 
Get a digital storage scope and monitor the gate or base of the device that
is driving the relay that is falsely activating. Look for a transient pulse
that is associated to the event. This will tell you something. You would
want to know the characterises of the transient pulse, if it is there, and
the amplitude of it. This would be a start. You may be able to work out
exactly why it is there.

Sometimes a small cap on the device input, going to the reference ground may
do the trick. You would have to work out the value of the cap(s) according
to the device input resistance or impedance, and to the time length of the
transient. This is not an easy thing to work out and answer over an email.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:KymRb.311$KW.16681@news.optus.net.au...
Thank you for your reply. I will do the test you suggested.

It will be difficult I think to change the board to deal with the
interference I am afraid. It is because the board is sold as a kit and I am
not sure what would need to change to fix the problem.

How would one go about isolating the interference?

Thank you again.



"Jerry G." <jerryg50@hotmail.com> wrote in message
news:bv4ocf$qit$1@news.eusc.inter.net...
I am under the impression you are using relays with 12 volt actuation, and
are using 240 VAC across their contacts.

I would suspect that there is an electrical interference from the device
that is being turned off and on. I would not buy the idea of inductive
kickback.

The drive circuits on the board are probably sensitive to the electrical
interference created by the load. Since you are using neon lamps (I think
you are referring to fluorescent lamps), they tend to give off some
electrical interference. The halogen lamps also pull a lot of current, and
when switched off and on can make some transient interference.

I would be looking at trying to see if I could make the drive circuits to
the relays to be less sensitive to electrical interference.

Just for curiosity, see if turning a fluorescent lamp on and off that is
located near by and is connected to the mains, but not through your
control
device, and see if it also makes the relays change state while everything
else is running.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:14lRb.300$KW.16670@news.optus.net.au...
Hi,

I have a small 12V DC off-the-shelf circuit that operates a few 240V AC
relays. The circuit is controlled by a PC via a parallel port.
It works OK with no load, no problem there.

However, when I manually unplug any of the devices connected to the relays
(they are neon and halogen lamps) somehow the circuit board gets all
screwed
up and switches on (or off) the relays at random. Even worse, it also
happens when the board itself switches the relays off. When there is no
load connected to the relays everything works 100%.

I suspected that it might be the "inductive kickback" problem, so I
connected 0.1uF caps snubber across each load terminal. It did not help
unfortunately. I also tried powering the circuit board from a power point
in a different room, no change.

Is there anything else I can try? I think maybe the caps are not of the
correct value, but I was not able to find any accurate info on that. The
mains are 50Hz, 240V the load is variable, up to 2A.

Thank you for any kind of help.

Peter
Click to expand...
 
Yes, that's what I was afraid of. Not an easy fix.

BTW, I did the test you suggested, and you were correct, turning the lamp
on/off in a near by power point shows the same problem.

Thank you for you help. I will try to do what you suggested...

"Jerry G." <jerryg50@hotmail.com> wrote in message
news:bv5opb$4kl$2@news.eusc.inter.net...
Get a digital storage scope and monitor the gate or base of the device
that
is driving the relay that is falsely activating. Look for a transient
pulse
that is associated to the event. This will tell you something. You would
want to know the characterises of the transient pulse, if it is there, and
the amplitude of it. This would be a start. You may be able to work out
exactly why it is there.

Sometimes a small cap on the device input, going to the reference ground
may
do the trick. You would have to work out the value of the cap(s) according
to the device input resistance or impedance, and to the time length of the
transient. This is not an easy thing to work out and answer over an email.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:KymRb.311$KW.16681@news.optus.net.au...
Thank you for your reply. I will do the test you suggested.

It will be difficult I think to change the board to deal with the
interference I am afraid. It is because the board is sold as a kit and I
am
not sure what would need to change to fix the problem.

How would one go about isolating the interference?

Thank you again.



"Jerry G." <jerryg50@hotmail.com> wrote in message
news:bv4ocf$qit$1@news.eusc.inter.net...
I am under the impression you are using relays with 12 volt actuation,
and
are using 240 VAC across their contacts.

I would suspect that there is an electrical interference from the device
that is being turned off and on. I would not buy the idea of inductive
kickback.

The drive circuits on the board are probably sensitive to the electrical
interference created by the load. Since you are using neon lamps (I
think
you are referring to fluorescent lamps), they tend to give off some
electrical interference. The halogen lamps also pull a lot of current,
and
when switched off and on can make some transient interference.

I would be looking at trying to see if I could make the drive circuits
to
the relays to be less sensitive to electrical interference.

Just for curiosity, see if turning a fluorescent lamp on and off that is
located near by and is connected to the mains, but not through your
control
device, and see if it also makes the relays change state while
everything
else is running.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"v man" <peterv@catuity.com.au.delete> wrote in message
news:14lRb.300$KW.16670@news.optus.net.au...
Hi,

I have a small 12V DC off-the-shelf circuit that operates a few 240V AC
relays. The circuit is controlled by a PC via a parallel port.
It works OK with no load, no problem there.

However, when I manually unplug any of the devices connected to the
relays
(they are neon and halogen lamps) somehow the circuit board gets all
screwed
up and switches on (or off) the relays at random. Even worse, it also
happens when the board itself switches the relays off. When there is no
load connected to the relays everything works 100%.

I suspected that it might be the "inductive kickback" problem, so I
connected 0.1uF caps snubber across each load terminal. It did not help
unfortunately. I also tried powering the circuit board from a power
point
in a different room, no change.

Is there anything else I can try? I think maybe the caps are not of the
correct value, but I was not able to find any accurate info on that. The
mains are 50Hz, 240V the load is variable, up to 2A.

Thank you for any kind of help.

Peter
Click to expand...
 
I did something similar on a device I built. It senses current
through one plug, and switches on another when current is present,
just like the big fancy shop vacs that you can plug a tool into, and
the vac will turn on and off w/ the tool. I used a current
transformer, a few op amps, and a transistor to drive the relay. I
was getting tons of transient jitter on the output of the transistor
when I switched on a device, but this wasn't a big project by any
means, so I just kept strapping on snubbing caps on the transistor
base until it stopped. I know this is incredibly untechnical, but it
worked, which is all I needed (for using a small shop vac and a
dremel).
On Tue, 27 Jan 2004 08:22:09 -0500, "Jerry G." <jerryg50@hotmail.com>
wrote:

Get a digital storage scope and monitor the gate or base of the device that
is driving the relay that is falsely activating. Look for a transient pulse
that is associated to the event. This will tell you something. You would
want to know the characterises of the transient pulse, if it is there, and
the amplitude of it. This would be a start. You may be able to work out
exactly why it is there.

Sometimes a small cap on the device input, going to the reference ground may
do the trick. You would have to work out the value of the cap(s) according
to the device input resistance or impedance, and to the time length of the
transient. This is not an easy thing to work out and answer over an email.
Click to expand...
 
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