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Old 03-25-2013, 04:40 AM   #1
nisk2007
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Default Are SSRs really necessary?

First off, LOOOONG time lurker, but first post. I am Not an electrician, but have been trying to figure out as much electrical information I can to build a safe, economical brewstand control box. With that said......
I have read multiple threads, searched all over HBT, and other forums, and are still left with a question. Do I really need A SSR for valves? I was originally planning on using a Auber SYL-2362 to actuate a Valves4Projects valve. After reading several threads, and seeing quite a few different diagrams, it seems like a SSR is overkill, and that the PID can easily feed the amps needed for the valves. Ive seen setups that use them, and others that don't. I've also read they are fine switching a March pump without issue.
This would definetly cleanup my control box if I do not need to run SSRs to run said valves. I also Considered using the Auber SYL-2342, But I swear (cannot find now) that I've read that it is slow to switch, and that the internal relay is unreliable. Thoughts?
I really do not have an issue Running SSRs, but I am trying to build a very compact control panel. SSRs would require more space, and it would bring the issue of more heat into the control box. I would just prefer to keep it simple. Thanks!

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Old 03-27-2013, 12:55 AM   #2
AllanMar
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In this case it's not to due with the current. I suspect this is for people PID controlling the valve? (for a propane setup?) People are probably using the PID's because they deal better with rapid switching. They also generate less noise/arcing when switching an AC coil then a relay can.

I guess it depends on how often the valve will be cycling on and off, the practical answer is no, you don't NEED an SSR. You'll be fine with just the relay, but an SSR might be slightly better if your going to be doing rapid switching. You can get small compact (lower current) SSR's if your so inclined.

Heat of an SSR switching this low of a current is not likely to be a significant concern.

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Old 03-27-2013, 01:26 AM   #3
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It comes down to how often you are switching the relay/SSR. SSR are rated for more operations as the relays mechanical limit is usually >10x. SSRs can also switch a lot quicker than relays, which shouldn't be an issue for a propane system as you duty cycle will be a decent time.
I would not say that the internal relay is unreliable but more that if it does go it will be more of a hassle to replace than a SSR driven off a 5V PWM output.
I think from memory most relays have a mechnical life of 100,000 operations, so if used under PID control would last (assuming 2 hours of controlled operation per brewday & 1 brewday per month):
less than 2.5 years @ 2 second duty cycle (typical for a electric setup)
Just over 69 years @ 1 minute duty cycle

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Old 03-27-2013, 03:51 PM   #4
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If the relay can handle the current that the solenoid valve requires then by all means use it. You won't want a cycle period less than 10 seconds anyway. If/when the relay burns out you still have the SSR option.

A flyback diode across the solenoid to deal with the back EMF will increase the life of the relay contacts.

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Old 04-03-2013, 06:58 PM   #5
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I'm having a hard time understanding what you guys mean by "faster switching time". When using a SSR you switch it with the relay on the PID, it doesn't matter if you use a SSR or not the relay on the PID is what ultimately switches the power on/off. The speed of the SSR is dependent on the speed of the PID's relay. The only reason to use SSR's with a PID is if the amps on the device exceed the amp rating of the PID relays. I use SSR's because they switch with low voltage which prolongs the life of the relays on the PID and allows you to run low voltage through the manual switches instead of high voltage.

As long as the amp rating is less on the valve then it is on the PID relays you won't have a problem going without SSR's.

Edit: I looked at the valve you linked and I would not use them. Here are the issues I have.

1- Not food grade
2- 1/4" thread, you need 1/2"
3- Won't work with gravity fed systems so it needs pressure to seal
4- needs 110v for switching, 12vdc is better.

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Old 04-03-2013, 08:09 PM   #6
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Quote:
Originally Posted by Monster Mash View Post
I'm having a hard time understanding what you guys mean by "faster switching time". When using a SSR you switch it with the relay on the PID, it doesn't matter if you use a SSR or not the relay on the PID is what ultimately switches the power on/off. The speed of the SSR is dependent on the speed of the PID's relay. The only reason to use SSR's with a PID is if the amps on the device exceed the amp rating of the PID relays. I use SSR's because they switch with low voltage which prolongs the life of the relays on the PID and allows you to run low voltage through the manual switches instead of high voltage.

As long as the amp rating is less on the valve then it is on the PID relays you won't have a problem going without SSR's.

Edit: I looked at the valve you linked and I would not use them. Here are the issues I have.

1- Not food grade
2- 1/4" thread, you need 1/2"
3- Won't work with gravity fed systems so it needs pressure to seal
4- needs 110v for switching, 12vdc is better.
It is my understanding he planned to use these for his GAS setup, not his liquid.

The voltage is a good point, but you can get 5v relays that can switch higher currents (so this is not unique to SSR's).

The difference is the relay is a mechanical switching, where the SSR is electronic. Therefore it has no mechanical movement to switch on/off, does not arc like a relay can when it switches, and can be cycled many times more then a relay they also don't load the control circuit they are connected to or generate back EMF like a relay does.

Commonly anything that needs to switch on/off often or rapidly uses an SSR for these reasons, its not really about the actual time it takes to switch but rather how it actually switches.

Voltage (as long as within its rating) will not wear the contacts on a relay as much as switching and current will.
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Old 04-03-2013, 09:25 PM   #7
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Quote:
Originally Posted by Monster Mash View Post
I'm having a hard time understanding what you guys mean by "faster switching time". When using a SSR you switch it with the relay on the PID, it doesn't matter if you use a SSR or not the relay on the PID is what ultimately switches the power on/off. The speed of the SSR is dependent on the speed of the PID's relay. The only reason to use SSR's with a PID is if the amps on the device exceed the amp rating of the PID relays. I use SSR's because they switch with low voltage which prolongs the life of the relays on the PID and allows you to run low voltage through the manual switches instead of high voltage.

As long as the amp rating is less on the valve then it is on the PID relays you won't have a problem going without SSR's...
You can get a PID controller with either a relay output or a 5V digital pulse output. The relay output is what you are talking about and yes should be fine in this instance (except for if it does fail it will be more pain to replace that relay). The 5V digital pulse output is what is generally used if faster switching is required. there is no internal mechanical relay for this output.
From Auber's instructions it is mentioned that if using a mechanical relay the duty cycle should be >20s, were the digital pulse/SSR can be down to 2s or less.
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Old 04-03-2013, 09:57 PM   #8
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Quote:
Originally Posted by AllanMar View Post
It is my understanding he planned to use these for his GAS setup, not his liquid.
Okay I will add that to my list. That valve is not made for gas, only liquid.
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Old 04-03-2013, 10:40 PM   #9
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Quote:
Originally Posted by Monster Mash View Post
Okay I will add that to my list. That valve is not made for gas, only liquid.
They are not only for liquid....
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Old 04-07-2013, 05:59 AM   #10
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I have seen multiple build here that use those exact valves for gas, and even some that have used them for liquid. So far, I have not heard of any issues with them.

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