Back EMF on solenoid control

[TMcRally]

We use 24Vdc 1.2Amp solenoids. Some of these can have cable lengths of 150m. We use either a bi-directional transorb (limits spike to 33V) for latching solenoids (reversed polarity release) or a diode for non-latching.

We have had no issues from any of the companies that supply and install the control hardware, except for in one state where the company who supply the hardware claim our solenoids create so much back EMF that it is impossible to keep relays from failing. I have spoken to other companies on this and they do not experience a problem. Most fit a diode across the relays at there end as standard practice just because of the capacitance in the long cable runs.

I am quite sure they are over stating the issue to serve some other agenda however...

1. If they are legitimate concerns how do I address the problem. OR
2. If they are playing games, how should I argue my case in a meeting.

TIA

 

[3DDave]

You cannot argue if you have not been to their site to see exactly what they have done.

They may have grossly undersized the relays or are using a far higher duty than is typical or have wired it into something it should not be wired to. The world is full of daft ways to do damage.

I have had more than one mystery claim from a supplier and customer and it often took only a few minutes on site to see the problem.
---
One was a sophisticated control system that had a cursor control on a screen. The customer demanded that the cursor would suddenly take off at random, a large problem for what was being controlled. We put an engineer at the site and they noted that every time this happened it was when the operator shifted position. It turned out they had been bracing their foot on a connector for the joy stick that was under the control desk, a joy stick that used strain gages to sense the applied force; this use of a boot deformed the housing enough to be detected. The customer had recorded dozens of events and never noted what the operator was doing as the operator did not have their hand on the joystick and didn't see the connection.

We ended up making a cage to protect the connector from the boot of the operator.

 

[TMcRally]

You cannot argue if you have not been to their site to see exactly what they have done.

They may have grossly undersized the relays or are using a far higher duty than is typical or have wired it into something it should not be wired to. The world is full of daft ways to do damage.

I have had more than one mystery claim from a supplier and customer and it often took only a few minutes on site to see the problem.
---
One was a sophisticated control system that had a cursor control on a screen. The customer demanded that the cursor would suddenly take off at random, a large problem for what was being controlled. We put an engineer at the site and they noted that every time this happened it was when the operator shifted position. It turned out they had been bracing their foot on a connector for the joy stick that was under the control desk, a joy stick that used strain gages to sense the applied force; this use of a boot deformed the housing enough to be detected. The customer had recorded dozens of events and never noted what the operator was doing as the operator did not have their hand on the joystick and didn't see the connection.

We ended up making a cage to protect the connector from the boot of the operator.

Thanks.

Is there anything more I can do on my end to control it, or are these solenoids something unusual or the methods I'm using to control the EMF not industry standard.

 

[3DDave]

Unless it is your solenoids that are failing there is nothing more to do. They should contact the relay makers to determine the reason the relays are failing.

I did have a production problem where our remote factory said they were unable to mark certain parts. I told them I had an airbrush, a CO2 tank, could get the ink from our stores and have stencils made up and drive to the factory that day; would be ready the next morning to do all the marking.

Their response - they don't actually have the items they were responsible to obtain. They wanted engineering to create a delay by removing the requirement to mark the parts as cover for not having the parts.

 

[waross]

We ended up making a cage to protect the connector from the boot of the operator.

Gives a new perspective to the term;
"Re-Booting"

 

[TMcRally]

The problem I have is, this company has the Government Department believing there is a problem with my product, which means I am not getting sales.

I am arranging a meeting with all concerned and it is my chance to have this settled. I am hoping I can get some information to support my case and address this companies accusations.

I believe...
I am using the best available Industry Standard protection and that these are not problematic solenoids, nothing special or over the top as far as power consumption or higher levels of spike than other solenoids.

 

[3DDave]

Which government and why are they involved?

 

[TMcRally]

Which government and why are they involv

I appreciate the discussion but we are getting off track, sorry to be a bit curt, but this is a serious problem for me.

I'm hoping someone can help by giving me some ammunition to counteract their claim that we are doing something wrong or unusual.

 

[3DDave]

You give zero information about what is being done regardless of who is doing it. It's concerning when a government is involved when they also don't know what it is that is being done.

Post the data sheet for the solenoid.

 

[waross]

Theory states that when a DC potential is applied to a circuit with a combination of resistance and inductance (The solenoid coil), the current rises from zero to a value determined by the resistance and Ohm's law in about 5 time constants.
Theory also states that with a properly applied diode, when the potential is removed, the current and the potential across the solenoid coil will drop to zero in about 5 time constants, without a spike in back EMF.

I am sorry but I spent too much time in the field and less time sheltered behind a desk.
I strongly suspect corruption and kick-backs.
If a person in a company or a department was to attempt to blacklist a component to direct sales to his preferred source it would often look like this.
There may be money or favours changing hands.
or
Someone may prefer a particular brand of solenoid and has blacklisted yours out of personal prejudice.
or
Their standard relays may be incapable of controlling your solenoids and rather than change their design, they make excuses.
You should really obtain and test a sample of the solenoid that they do use and compare it to your solenoids.
If possible, you should also obtain and test a sample of their relays.

That said, there may be a different reason not to use your product, and Back EMF is just an excuse.
It may be personal; Perhaps the purchasing agent just doesn't like your salesman.

 

[TMcRally]

You give zero information about what is being done regardless of who is doing it. It's concerning when a government is involved when they also don't know what it is that is being done.

Post the data sheet for the solenoid.

Sorry Dave, I'm just stressing over this.

 

[TMcRally]

You give zero information about what is being done regardless of who is doing it. It's concerning when a government is involved when they also don't know what it is that is being done.

Post the data sheet for the solenoid.

Sorry Dave, I'm just stressing over this

Theory states that when a DC potential is applied to a circuit with a combination of resistance and inductance (The solenoid coil), the current rises from zero to a value determined by the resistance and Ohm's law in about 5 time constants.
Theory also states that with a properly applied diode, when the potential is removed, the current and the potential across the solenoid coil will drop to zero in about 5 time constants, without a spike in back EMF.

I am sorry but I spent too much time in the field and less time sheltered behind a desk.
I strongly suspect corruption and kick-backs.
If a person in a company or a department was to attempt to blacklist a component to direct sales to his preferred source it would often look like this.
There may be money or favours changing hands.
or
Someone may prefer a particular brand of solenoid and has blacklisted yours out of personal prejudice.
or
Their standard relays may be incapable of controlling your solenoids and rather than change their design, they make excuses.
You should really obtain and test a sample of the solenoid that they do use and compare it to your solenoids.
If possible, you should also obtain and test a sample of their relays.

That said, there may be a different reason not to use your product, and Back EMF is just an excuse.
It may be personal; Perhaps the purchasing agent just doesn't like your salesman.

Thanks waross,

I don't have the inductance of the coil, I will follow up the manufacturer tomorrow and see if I can find it.

I am interested in your comment...
QUOTE:
Theory also states that with a properly applied diode, when the potential is removed, the current and the potential across the solenoid coil will drop to zero in about 5 time constants, without a spike in back EMF.
END QUOTE.

It is at odds to the claim they have been making, they claim that even with a diode across the coil they demonstrated a visible back EMF arc on their relay.

Is it possible?

I have caught them out fabricating evidence previously where they demonstrated with a crow that there was the correct voltage at load at the solenoid. When tested with our equipment it demonstrated that the load pulled the voltage down 30% so I believe they are capable of doing this.

P.S. they have run 24Vdc solenoids with 3.3Amp draw.

 

[waross]

It is at odds to the claim they have been making, they claim that even with a diode across the coil they demonstrated a visible back EMF arc on their relay.

That is the test?
A visible arc?
The relay will be passing 1.2 Amps.
When the relay contacts open, there will be a small arc consistent with 1.2 Amps and 24 Volts.
This is not back EMF.
This is normal.
BUT you have resisted supplying information as to the specs of the solenoid or specs of the relay.
Give us part numbers or model numbers and manufacturers so we can search for the information that you won't supply.
Or;
Go into a meeting quoting free guesses from the internet made by persons with incomplete information.
Or hire a competent local electrical engineer.

 

[3DDave]

The OP doesn't seem to make the solenoids or the relays, doesn't seem to install the solenoids or the relays, doesn't know what solenoids or relays are being installed, and didn't design the installation.

Says "our solenoids".

At this point in 20 Questions:

Is the OP a distributor?

 

[TMcRally]

Attached file on the solenoid we use, it is manufactured for us in Japan specifically to match our load requirements and stroke.

I do not know the inductance.

I do not know what the other companies relays are.

 

[TMcRally]

That is the test?
A visible arc?
The relay will be passing 1.2 Amps.
When the relay contacts open, there will be a small arc consistent with 1.2 Amps and 24 Volts.
This is not back EMF.
This is normal.
BUT you have resisted supplying information as to the specs of the solenoid or specs of the relay.
Give us part numbers or model numbers and manufacturers so we can search for the information that you won't supply.
Or;
Go into a meeting quoting free guesses from the internet made by persons with incomplete information.
Or hire a competent local electrical engineer.

There is no resistance, I was getting frustrated is all.

He argues that he sees a 100V differential across his relay and has to deal with a 100V arc when we use the Zener Diode or Transorb. Description Number - 1.5KE33CA
He says it is so strong it jumps across tracks on his PCB and is destroying his hardware and causing indiscriminate activations. I don't understand how he can see this differential at the same time, I understand he has +24V then drops to 0 then sees a reversed spike as the magnetic field collapses around the coil which is clamped by the Zener Diode to somewhere between 33V and 48V but with little current. If they did occur at the same time the differential would be less I believe ?

Can I explain my understanding of what you have told me and then tell me where I am wrong

A standard Diode will not let any reversed spike passed even for a short while, it will however slow the ramp down when power is dropped. This will maintain 63% of 24Vdc 1.2Amps at the end of the 1st time constant (15Vdc .75Amps) and 9.5Vdc 0.47Amps at the end of the second time constant and so on.... but never a negative.

If this is the case then all he needs to control is the maximum of 24Vdc at 1.2Amps and this is so for all solenoids. Another supplier uses 24Vdc 3.3Amp solenoids which would be significantly worse I expect.

 

[waross]

Possibly the wrong polarity was applied and the diodes are blown open.
I have seen instrument specs on the same projects where some instruments used Colour Code Black for Negative and other instruments used Colour Code Black for Positive.
Alternately the positions of the negative and positive terminals may be reversed to what the tester is familiar with.
Reversed polarity and blown diodes is a real possibility.