Solid State Relay leakage current problem

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Hello everyone,
I am working on a project that will enable remote control to my rolling shutter.
I have the PCB's printed and soldered with the components, and They are ready to be inserted into the wall.
The control of the rolling shutter is achieved by switching two live wires, as in this schematic:
rolling shutter.png
(More information in this thread)
The SSR is the AQG22105J.
The issue is that the expected behavior from the switches it that only up to one of them should be closed at a time, which means they may be both off (the rolling shutter will stay still), or one of them is open and the other closed (the rolling shutter will go up or down according to which wire is closed).
The state of both switches closed is unknown. The original wiring in the wall (which is drawn in the thread I linked), is based on an SP3T switch and therefore will not allow such state. The SSR's However, are 2 SPST switches, which means this state is possible.
Preventing both SSR's from fully closing can be done in software of course(and it is done), but what about leakage current?
The datasheet says theres a maximum 1.5mA leakage current at 200V@60Hz. My mains voltage is 230V@50Hz, so I guess the leakage will be a little higher. It means that we have around 1.5~2.5mA flowing to both of the "up" and "down" wires which is exactly that unknown state, just with lower current.
My question is, should I worry that this leakage will cause a problem in the motor? The thing is I can't know whether or not the motor will blow up or just don't move until it happens.
Thanks in advance!
 

MaxHeadRoom

Joined Jul 18, 2013
20,084
I would hazard a guess that is a AC PSC (permanent start cap) motor, if so it would mean that there is a small leakage current present at the cap/winding junction, from the opposite (off) Triac.
I would suspect this is not a problem, the motor activation is probably fairly brief, so if the system performs OK and there is no observed detrimental effect on the motor, overheat or slow run etc, I would not be concerned.
Max.
 

ebp

Joined Feb 8, 2018
2,332
The "leakage" is likely due to an RC snubber.

Can you see the motor at all? Some motors for this sort of application are long tubular things with limit switches built in and operated by a finger on a threaded rod. Typically there are little knobs on the end of the motor to adjust the positions of the limit switches, which also are on threaded rods.

There may be problems, depending on the motor(s). If there are actually two separate motors all will likely be OK.

One little detail that the datasheets for some of these motors don't cover is that they behave as transformers because they have two windings - one for each direction. This can result in the voltage from the common wire to the "open" wire being very substantially higher than line voltage, which may make both the snubber and the rest of the SSR output very unhappy. It also means that you cannot directly parallel two motors. It is easy to confirm if this is the case by simply measuring the voltages on the wires while the motor is running.

There may be a single motor and some kind of internal circuitry that switches the connections of motor and a capacitor depending on which power lead is energized. It's hard to say what the leakage might do in this case.
 

MaxHeadRoom

Joined Jul 18, 2013
20,084
I don't see much point using two motors, this is my PSC guess.
I don't see a couple of Ma making all that difference.
In the pic, the run and start winding notation should be reversed for each direction
Max.

upload_2018-6-15_12-23-15.png
 
The motor sounds like a syncronous motor. A capacitor is between the direction inputs and only one is powered at a time. Unloaded motors may appear confused if the capacitor is bad.

https://www.hurst-motors.com/documents/A_AB_Synch_DD.pdf

I've used SSR's to control 10 W versons of synchonous motors.

It basically looks like two coils relative to ground phase shifted by a capacitor.

The leakage current means, you can't use your voltmeter to determine if the SCR is on of off when the motor side is disconnected. It will always appear on.

You can, but I don;t think it;s necessary, use a resistor across the motor leads.

In reality, if you connect only one SSR to the motor and have the SSR off, there should be a large voltage drop across the SSR. Nearly line voltage.

Synchronous motor speed is set by frequency and not by load unless you reach maximum torque.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Thank you both for your help!
Currently the motor is covered by a panel held by some screws.
I will open it and return with info in some minutes
 

ebp

Joined Feb 8, 2018
2,332
What I am concerned with is not the small snubber current but the fact that the DOWN SSR could have 350 V or more applied to it when the UP SSR is on. That voltage does not come from some high impedance.

I have seen a few things with two shaded pole motors and a common geartrain. When a motor is de-energized the armature is pushed by a spring that keeps the gear-cut end of the shaft away from the mating gear. Then the motor is energized the armature is pulled to its normal operating position and the shaft end engages the gear. But I doubt if that is the case in the system in question.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
I opened the panel covering the motor to find no part number at all, only this big cylinder where the rolling shutter is rolled on.
Unfortunately there is no marking except for the number '9'.
This is how it looks like:
Right Side - you can see the wire going in.
20180615_205945_Moment1.jpg
Left side:
20180615_205945_Moment2.jpg
On the very right of the cylinder I saw this interesting part:
20180615_210157.jpg
Hope this helps to find what type of motor is this.
 

MaxHeadRoom

Joined Jul 18, 2013
20,084
Doesn't really show much in the way of motor, I would guess the allen screw adjustments are for the up limit/down limit.
Again I don't see that small a current anything to worry about, do you have a clamp on meter to compare running to not running current?.
Max.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Doesn't really show much in the way of motor, I would guess the allen screw adjustments are for the up limit/down limit.
Again I don't see that small a current anything to worry about, do you have a clamp on meter to compare running to not running current?.
Max.
I don't have that clamp meter.
What I am concerned with is not the small snubber current but the fact that the DOWN SSR could have 350 V or more applied to it when the UP SSR is on. That voltage does not come from some high impedance.
This seems like a serious problem if it actually happens, I will measure the voltage tomorrow.
Thank you all for your help.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Measured it... powering the DOWN line and measuring the UP one gives flipping 400V relative to live voltage, which means 630V to ground.
I am frustrated now... the SSR is rated for 264V so it probably means I can't use it. Is there any way to protect it?
after all of this work... I really hope I can still use these SSR's, because I don't want to again design a PCB, wait for it to be manufactured, wait for parts etc...
 

ArakelTheDragon

Joined Nov 18, 2016
1,327
I also think so. Why are the motor wires shorted on the picture above?
I would hazard a guess that is a AC PSC (permanent start cap) motor, if so it would mean that there is a small leakage current present at the cap/winding junction, from the opposite (off) Triac.
I would suspect this is not a problem, the motor activation is probably fairly brief, so if the system performs OK and there is no observed detrimental effect on the motor, overheat or slow run etc, I would not be concerned.
Max.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
I also think so. Why are the motor wires shorted on the picture above?
Which picture? currently I am not concerned about the leakage current, but about the high voltage (400V) coming back to the SSR from the motor.
Is there a way to protect the SSR from that voltage? the activation time of the motor in a specific direction is up to 45 seconds, which means the protection would need to be active in this time region.
 

MaxHeadRoom

Joined Jul 18, 2013
20,084
currently I am not concerned about the leakage current, but about the high voltage (400V) coming back to the SSR from the motor.
.
How long has it been operating this way?
In all probability the rating of the components is going to be higher than the recommended usage value.
Max.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
How long has it been operating this way?
In all probability the rating of the components is going to be higher than the recommended usage value.
Max.
As I said when connecting the down wire to the live wire(the same as closing SSR-2), the voltage between the up wire to live is 400V.
I don't know "how long" it operates like that. this is what I get when measuring that voltage so probably it was always operating this way.
Can you explain your second sentence?
 

MaxHeadRoom

Joined Jul 18, 2013
20,084
Personally I would have used a higher current than 2a for a motor application, there is a OPTO22 version with practically the same foot print, that is rated for 4A at 380vac working voltage. MP380D4.
My meaning was that the internal component rating is generally higher than the spec sheet usage rating.
Max.
 

olphart

Joined Sep 22, 2012
78
My $.02: I'd have used an SPDT relay for direction, the SSR for power, with a delay btw relay and SSR.
The relay isn't switching power and provides winding isolation (which sure looks necessary).
The delay could be a dual comparator: one side has an RC and a volt divider reference for time,
It's output feeds the other comparator with another volt divider, all fed from the move switch (through one of a pair of diodes).
 
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