DC Actuator problem

[VTI_16V]

Hello. I have a problem with electronics for controlling the actuator... So, this actuator has 2 limit switches, for open and close. Everything works on 12VDC. When you try to open and close actuator when it reaches the limit switches the motor stops momentarily... But somethimes when actuator touches the limit switch it doesn't stop momentarily like it's supposed to, instead it looks like that it is got some kind of inetria left in it, and it proceeds for maybe one or two milimetars. It's is not a big move, it took me some time to notice it in the first place. The problem is that this electronic board is got some kind of protection, so when that happens it goes into error and you can not move the actuator anymore unless you restart it (turn it off and on again)... It doesn't happen often, maybe one or two times per 50, but i want to solve that problem... What can be the reason? Can someone explain to me what is this yellow thing that is connected to COMMON contacts of the relay and what is its purpose?

https://postimg.org/gallery/1iwon2124/

Thanks everyone, looking forward to yours answers!

 

[kellys_eye]

Could be the physical positioning of the limit switch. Could be contact bounce in the limit switch.

Try replacing the limit switch and see what happens.

 

[VTI_16V]

I don't think so... Because when motor hits the switch it dissangages... But it doesn't stop momentarilly like it supposed to that specific time, it looks like he has got some kind of inertia left in it and when he dissangages he proceeds maybe 1 or 2 mm further... Lets say you spin something when you press the push buttom... And when you relase the pushbutton that thing stops momentarilly... But somethimes it doesn't stops momentarilly but proceeds to spin and decelarating for maybe 45 degrees... 99% that the problem is not in the limit switches

 

[kellys_eye]

That is, as you say, just 'inertia' - providing it doesn't carry the movement beyond what's allowed (i.e. it hits some form of physical obstruction) then there's not a lot to be done about it.

I don't really follow when you say:

when you relase the pushbutton that thing stops momentarilly... But somethimes it doesn't stops momentarilly but proceeds to spin

is it MEANT to stop 'momentarily' or is it mean to stop permanently? i.e. until you initialise a reverse movement condition?

 

[VTI_16V]

I mean by stop momentarily to stop at that moment when it reaches limit switch. It shouldn't proceed one milimeter further by some kind of inertia, it should stop at that place (i gave you an example above), not to stop permanently... That inertia that happans sometimes shouldn't happen because when it happens controller goes into error like i've told you before... There must be logical reason why is that happening because that happens maybe 1 of 50 times, the oder 49 times it doesn't proceed further when it reaches the limit switch button... Maybe some kind of self induction or something like that? I heard that there are few ways to stop electromotor from keep spinning when it dissangages but i don't know which ones, and I suspect that the problem is hiding there...

Thanks for trying to help

 

[Minder]

Many linear actuators do not over run due to the mechanical method used, yours sounds as though it evidently has the ability to over run due to inertia.
How is the motor currently driven? By electronic device or relay?
A common, easy method usually used to brake a DC motor is to place a short across the motor terminals after the motor has been disconnected.
Usually done by either the control relay itself or another relay.
With electronic control where the method used is a solid state H-bridge, the bottom two devices are turned on, when the motor is turned off.
M.

 

[VTI_16V]

Motor is driven by 2 relays controlled by electronic device... You can see theese 2 relays and electronics on the pictures above... From my point of view motor is connected (when relays turns off) short between 2 relays on common contacts (you can see that in the picture)... And normally closed contacts are shorted to ground od the PCB... Maybe the problem lies somewhere there? Or in this yellow thing that shortens common of the relays together (you can see that part also on the pictures)? What is that thing by the way?

 

[shrtrnd]

We don't doubt your problem and I can't think of an easy way to 'stop the electromotor' like you've heard of.
I always try simple first.
What kind of lever activates your actuator? Is it worn, bent or out of alignment? Like kellys-eye asked, does it need
to be slightly repositioned?
I heard what you said about the fact that the motor stops 49 out of 50 times, but inertia allows it to continue spinning on rare occasions.
Maybe there's excessive wear associated with the mechanical parts of the motor/ itself?
Is there some other electronic device on the same input power-line that operates intermittently, (I know 'everything' operates at 12VDC, but is ultimate power coming from an AC source?) that is allowing your possible 'self-induction' problem. Something else that might be operating at the moment your limit switch is trying to turn-off your motor? (I've found a lot of times that bleed-over from unintended devices on the same power-line can cause problems).
I know you're frustrated with this, and having to continually restart it.
My first guess is wear on the motor mechanical, but that's just my opinion with what I've read so far.
I'm assuming your solid state relays aren't electrically 'leaking'(?)
If I'm seeing this right, the yellow part next to the SS relays you asked about, looks like a MOV (Metal Oxide Varistor), They're supposed to absorb transient voltage spikes. Somebody here will correct that observation if I got it wrong.
Sure would be nice to see a schematic of the interface between your board and that motor (with the limit switch), if you can post it.

 

[Minder]

Motor is driven by 2 relays controlled by electronic device... You can see these 2 relays and electronics on the pictures above... From my point of view motor is connected (when relays turns off) short between 2 relays on common contacts

From that it sounds like the method I mentioned using shunting the armature at turn off.
Maybe confirm this, if this is already in place and working properly, then one other way is an electro-magnetic brake.
Try and confirm whether it has relay contact braking first that may have poor contacts.
M.

 

[Alec_t]

It's possible there's a bit of wear/play in the mechanism that operates the limit switch.

 

[VTI_16V]

I mannaged to borrow a new electronic board... The problem isn't happenin with the other board... So definitely the problem is with electronics board as I suspected, not with the limit switches or anything mechanical... Fortunately, i don't have a schematic ... I don't know, maybe to try replacing relays?

 

[shrtrnd]

Are you kidding? With all those other components on that board?
Get yourself a oscilloscope and compare readings on the good board with the readings on the bad board to isolate the problem.

 

[kellys_eye]

With the fault being intermittent and the only 'moving' parts are the relay contacts then changing the relays seems to be a logical step.

 

[VTI_16V]

I will try to change the relays.... If that doesn't help, i will have to buy u new board

 

[Minder]

Seems quite a sophisticated board, what does it control?
M.

 

[VTI_16V]

Bow thruster control on the sailboat... It is retractable, the described problem is with the opening and closing... It has a linear actuator that is opening and closing the thruster, you can find it on internet if you are curuios, Quick BTR 185