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SSR vs Relay
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

SSR vs Relay

by mjpcarbon on Wed Apr 09, 2014 8:31 pm

In this project I wish to rapidly make a connection, I have the sketch working fine but now want to convert the led pulse to a connection.
I am not connecting any power simply interrupting a ground , rapidly
Can I use an SSR or is a conventional relay better like the little white guy supplied in the starter kit ?
Since I am not trying to power something I am unsure how the SSR connections would be made or if it would work at all in this application

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Re: SSR vs Relay

by adafruit_support_bill on Wed Apr 09, 2014 9:00 pm

I am not connecting any power simply interrupting a ground , rapidly

A little more definition would be helpful. What are you interrupting the ground to?
And what do you mean by rapidly? 10Hz, 10KHz, 10MHz?

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Re: SSR vs Relay

by mjpcarbon on Wed Apr 09, 2014 9:27 pm

Ok I was trying to spare the boring details
I built a device that reads exhaust gas temperature and at a given temp(overheat) I wish to sputter the engine.
So I thought I would interrupt the kill switch at 500 millisecond intervals. delay(500); ? There isn't any power just need to open and connect a wire not carrying power.

On a side note if I am also blinking a led on a separate pin how can I keep the two delays isolated, seems like the last delay takes precedence over any previous ones....is this a fact or my imagination

BTW still having a great time with all this !!

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Re: SSR vs Relay

by adafruit_support_bill on Wed Apr 09, 2014 9:44 pm

So I thought I would interrupt the kill switch at 500 millisecond intervals. delay(500); ? There isn't any power just need to open and connect a wire not carrying power.

There must be some voltage and at least a little current flow, or you wouldn't be interrupting anything. A circuit diagram would be helpful.

500 milliseconds is relatively slow. but it would be pretty annoying to listen to a relay clicking that fast.

On a side note if I am also blinking a led on a separate pin how can I keep the two delays isolated, seems like the last delay takes precedence over any previous ones....is this a fact or my imagination

If you are trying to schedule two things at the same time, delay() is your enemy. A call to delay will stop everything in its tracks for the duration. You should look into some of the timing libraries in the Arduino Playground: http://playground.arduino.cc/Code/SimpleTimer

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Re: SSR vs Relay

by mjpcarbon on Wed Apr 09, 2014 10:10 pm

Ahh so I was correct about the delay
I dont have a schematic for the machine, I will have to check that with a meter to see what exactly is going on . I was under the impression it was grounding the ignition coil but again I am unsure

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Re: SSR vs Relay

by mjpcarbon on Thu Apr 10, 2014 7:51 am

Holy cow, I thought I was doing so well in understanding this stuff til I looked in "playground" !!

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Re: SSR vs Relay

by Barry914 on Thu Apr 10, 2014 1:44 pm

What's the kill switch connected to? Does is ground the output of the coil? If it does, you are talking about voltages in excess of 20Kv, so an SSR or a relay has to be able to withstand that voltage.

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Re: SSR vs Relay

by mjpcarbon on Thu Apr 10, 2014 8:53 pm

The system is a NO type and grounds the primary to the coil, No high voltage there.
So will a SSR work or would a coil type relay be better like the one in the starter kit?

Also I visited the playground and dont think I have the grey matter to pull that stuff off so I will ask.
If I wanted the relay(whatever type) to be open for 1000ms and closed for 50ms can I but them in brackets or would the latter still overrule the command and make the delay50ms ?

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Re: SSR vs Relay

by adafruit_support_bill on Fri Apr 11, 2014 5:34 am

If I wanted the relay(whatever type) to be open for 1000ms and closed for 50ms can I but them in brackets or would the latter still overrule the command and make the delay50ms ?

That depends on where the brackets are and how your code is structured. If you post the actual code you are considering we might be able to answer.

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Re: SSR vs Relay

by mjpcarbon on Fri Apr 11, 2014 8:18 am

I will for sure,
Back to the original question if it is a grounding type operation can I use a SSR ? and if so how would I wire it if you can ?
I was also reading on your site about transistors, on the site it sort indicates they act as switches ?
Am I off base on this

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Re: SSR vs Relay

by adafruit_support_bill on Fri Apr 11, 2014 8:26 am

Back to the original question if it is a grounding type operation can I use a SSR ? and if so how would I wire it if you can ?
I was also reading on your site about transistors, on the site it sort indicates they act as switches ?
Am I off base on this

Transistors can act as switches in certain situations. They are not a drop-in replacement for a mechanical switch. You need to understand the nature of what they will be switching. That is why we have been asking for a circuit diagram.

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Re: SSR vs Relay

by Barry914 on Fri Apr 11, 2014 9:45 am

You will still have to contend with fairly high voltages on the primary side of the coil due to the inductive load. A mechanical relay is probably going to be a better choice, especially since you are talking about relatively long on and off times. 50 ms is pushing it for some relays though. A reed relay might be a good choice. They usually have operating times of a few ms or less. They have fairly low driving currents too, and with a shunt diode you can drive some of them directly with a digital output pin.

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Please be positive and constructive with your questions and comments.