SSR triac not releasing

[Mark80]

Hi,

I am using a SSR to trigger a coil style relay, however, once triggered, the SSR is not releasing. I think it may be due to high current through the contact side of the SSR. Would a bleeder resistor solve the issue, and if so, what size would I use?

See attached diagram for reference.

thanks

 

[dorke]

Connect a DVM to the input of the SSR.
Measure with the DVM the voltage on the input ,in the "off" and "on" state.
For off you should have less than 1v for on more than 3V,are you actually getting this?

 

[Arouse1973]

Driving a large inductive load with a TRIAC can cause problems. You might find a snubber circuit helpful. Here is a design guide for you to have a look at.

http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00004096.pdf

Thanks
Adam

 

[Mark80]

A snubber circuit is probably what I need. Sadly, that design guide is almost Greek to me!

 

[Minder]

What is the current of the load?
M.

 

[Mark80]

Coil load: 2VA

SSR output characteristics:
Current Rating: 6 A
Switching voltage: 24...140 AC
Switching type: Zero Cross
Max Rate of Rise Off State Voltage (dv/dt): 300 V/us
Min Load current to maintain on: 75 mA
Non-repetitive surge current: 60 A
Max off state leakage current (rms): 6 mA
Typical On State Voltage Drop (rms): 1.6 AC
Minimum Peak Blocking Voltage: 400 AC

 

[Minder]

SSR's of this nature, especially with this light load do not have a problem, especially if the input switching is contact closure, as opposed to solid state?
M.

 

[Mark80]

The input side of the SSR is contact closure. Even when I physically disconnect both + and - on the input side, the load side does not release. Also, I have tested with a small 12vdc resistive load and the SSR works as expected.

 

[BobK]

Um, either I am totally stupid or everyone else is missing something.

The SSR is for AC. You are using with DC. A triac, used with DC acts just like an SCR and stays on until the load is disconnected.

Am I wrong about this?

Bob

 

[hevans1944]

Am I wrong about this?

Yep. Look again at the circuit diagram in post #1. The load, an inductor, is driven from 120 VAC as switched by the Magnacraft SSR. The only thing DC is the control circuit that turns the triac on and off, the problem being it doesn't turn off if the control input leads are disconnected.

I would suggest wiring a small valued resistor across the control inputs to guarantee zero input voltage for the SSR "off" state when the contacts are open. Anything from a hundred ohms up to maybe a thousand ohms should do. Try momentarily shorting the input terminals together, after the contacts are opened, to make sure the SSR turns off. To avoid wasting power when the contacts are closed to command the SSR to turn "on," use the largest shunt resistor that works reliably to turn the SSR "off" when the contacts are opened.

 

[BobK]

Ah, I did not realize that the box was the SSR. Probably because SSRs do not have a coil! Ithought the box was a relay.

Bob

 

[hevans1944]

Ithought the box was a relay.

A natural assumption. I didn't even catch the "coil" inside the SSR, which the OP obviously thought was a functional equivalent to what is really going inside a "zero crossing solid state relay" module. I wish "they" would quit calling these things "relays" when "solid state switch" is more appropriate and descriptive. Most of these should show an optical isolator as the equivalent input circuit, and I believe that is typical of the genre, whether it implements a "zero crossing" turn-on function or not. Not sure why the OP's SSR turns on (or stays turned on) when the input leads are floating, but surely "shorting them out" with a resistor when the control contacts are open will solve the problem. It is supposed to turn off if the input voltage is less than one volt. See @dorke post #2.

I Googled "magnecraft 70s2-04-b-06-n" and found a PDF datasheet. It shows the input circuit represented as a coil and the output circuit represented as a normally-open contact, so the confusion is perpetuated.

 

[Mark80]

Sorry for the misleading diagram. I simply copied what was shown on the actual SSR.

As for the zero crossing. As a simple test, after applying input power to the SSR, I removed both input leads and then jumpered (shorted) across them. Not sure if this would behave the same as a resistor, but it did not release the load side of the SSR.

One thing to note, when I remove a lead from the load side of the SSR, the SSR still doesn't release right away. It lets me reconnect and disconnect about 3 times before it finally releases. It seems like it needs to discharge something? Would the snubber that was referenced earlier solve this issue?

 

[hevans1944]

This is really weird. The SSR should NOT behave the way you describe. Do you have a spare for comparison? Removing and disconnecting the load about three times before the SSR finally releases? Shouldn't happen. Repeat this "test" with the SSR turned "on" but with the control inputs shorted. Can you still interrupt the connection to the load up to three times before the SSR turns off?

 

[Mark80]

I have two and they behave the same way. Even with SSR input shorted, I can still remove and reapply the load about 3 times before it releases.

One thing I now realize could be the issue. On the load side, the coil that I'm energizing is actually a true off time-delay relay. (Macromatic TR-60622). It will time-off once power is released. I wonder if it's somehow feeding something back to the SSR?

 

[Mark80]

It definitely is related to the time-delay relay on the load side of the SSR. When I tested it with a difference load (resistive), the SSR functions correctly and releases when no input voltage. Perhaps it has trouble with inductive loads.

 

[Alec_t]

It definitely is related to the time-delay relay on the load side of the SSR.

Isn't that the whole purpose of an off-time delay relay? Switch off power, wait for time-out, relay switches off load.

 

[Mark80]

Isn't that the whole purpose of an off-time delay relay? Switch off power, wait for time-out, relay switches off load.

Yes - but I need the SSR to switch off power (in order to switch off the off-time delay relay). Keep in mind the time-delay relay is switching a higher current device (not part of the schematic)

 

[Arouse1973]

It definitely is related to the time-delay relay on the load side of the SSR. When I tested it with a difference load (resistive), the SSR functions correctly and releases when no input voltage. Perhaps it has trouble with inductive loads.

What like I said in post 3 If the current through the TRIAC doesn't fall below the holding current then the device will stay on, this might be what is happening.
Adam

 

[Minder]

Not sure such a large one was used in the first place for a 17ma coil?
The specs show a min load of 75-100ma to maintain, but 6ma leakage.
A much small version of one of the Opto22 range would maybe have been alot more suitable.?
M.